UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The chemical limnology of two meromictic lakes with emphasis on pyrite formation Perry, Karen Anne 1990

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1991_A1 P47.pdf [ 11.39MB ]
Metadata
JSON: 831-1.0053308.json
JSON-LD: 831-1.0053308-ld.json
RDF/XML (Pretty): 831-1.0053308-rdf.xml
RDF/JSON: 831-1.0053308-rdf.json
Turtle: 831-1.0053308-turtle.txt
N-Triples: 831-1.0053308-rdf-ntriples.txt
Original Record: 831-1.0053308-source.json
Full Text
831-1.0053308-fulltext.txt
Citation
831-1.0053308.ris

Full Text

THE C H E M I C A L L IMNOLOGY O F TWO MEROMICTIC LAKES WITH EMPHASIS O N PYRITE FORMATION b y KAREN A N N E PERRY B.Sc. University of V i c tor ia 1979 B.A.Sc. University of British C o l u m b i a 1983 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES O c e a n o g r a p h y W e a c c e p t this thesis as c o n f o r m i n g t o the requi red s t a nda r d THE UNIVERSITY O F BRITISH C O L U M B I A N o v e m b e r 1990 © Karen A n n e Perry 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date Qn / ^ O DE-6 (2/88) ABSTRACT ii Powel l a n d Sak inaw Lakes a re stably stratified ex-fjords, w h i c h b e c a m e isolated f rom the Strait of G e o r g i a approx imate l y 11000 years a g o by e m e r g e d sills d u e to post-g l a c i a l isostatic r e b o u n d . A l t h o u g h bo th lakes con t a i n highly sulphid ic relict s eawa te r (Powel l 3.0 m M ; Sak inaw 5.5 m M ) , they h a v e distinct c h e m i c a l d i f fe rences , w h i c h m a y b e d u e t o Sak inaw rece i v ing o c c a s i o n a l inputs of s eawa te r ove r the bare l y-emerged sill w h e n strong onshore winds are c o i n c i d e n t with spring tides. Powel l Lake , n o w 50 m a b o v e s e a leve l , has not r e c e i v e d add i t i ona l s eawa te r s ince the sill originally e m e r g e d . Sak inaw has a very sharp c h e m o c l i n e l o c a t e d just b e l o w the o x i c / a n o x i c in te r f ace , whe reas in Powel l , the inter face is sp read out over 200 m of the wa te r c o l u m n . A l though bo th lakes h a v e f r e shened , the ratios of major ion concent ra t ions relative to ch lor ide in the b o t t o m sal ine vyaters a re similar t o those of present-day seawater . There a re some d i f f e r ences , h o w e v e r , a n d these c a n b e e x p l a i n e d , in par t , b y the d i f f e r e n c e in mo lecu l a r diffusivities for e a c h of the ions. The b o t t o m waters of Powel l a n d Sak inaw Lakes are chem i ca l l y similar t o anox i c sed iment porewaters . con t a i n i ng h igh concen t ra t i ons of nutrients, D O C a n d alkalinity. Unlike Sak inaw, howeve r , Powel l Lake has very low concen t r a t i ons of p h o s p h a t e in its b o t t o m waters , in spite of bo th lakes hav ing similar par t i cu la te o rgan i c N:P ratios in their u p p e r ox i c waters . This m a y b e a t t r ibutab le to more recen t a d d i t i o n of su lphate to Sak inaw , a l l ow ing g rea t e r minera l izat ion of phosphorus c o m p a r e d to the relatively oxidant-starved Powel l Lake. High c o n c e n t r a t i o n s of r e d u c e d i ron, h y d r o g e n su lph ide , a n d polysutphides result in fo rmat ion of iron monosu lph ides a n d pyrite in the anox i c wa te r co lumns of bo th lakes. The p r e s e n c e of t hese t w o minera ls co r re l a tes we l l w i th the i r c a l c u l a t e d saturat ion states. Pyrite prec ip i ta tes direct ly with no monosu lph ide precursor at depths where sulphide concen t ra t ions are low; thus monosu lph ide phases a re undersa tura ted . As su lphide levels increase with d e p t h , iron monosu lph ides b e c o m e sa tu ra ted a n d are d e t e c t e d in the wa te r c o l u m n . Pyrite c a n then form v i a the slower reac t ion of e l emen ta l sulphur with monosu lph ide . The large sepa ra t ion of the ox i c /anox i c in te r face a n d the c h e m o c l i n e in Sak inaw (-10 m) a n d espec ia l l y in Powel l Lake (-100 m) relative t o that of sed iment po re waters a l lows exce l lent resolution of these processes. TABLE OF CONTENTS A B S T R A C T ii LIST OF TABLES vi LIST OF FIGURES vii A C K N O W L E D G E M E N T S ix ' 1. INTRODUCTION 1 2. PHYSIOGRAPHY, PHYSICAL A N D CHEMICAL L IMNOLOGY 5 2.1 Int roduct ion 5 Powel l Lake 5 Sak inaw Lake 8 2.2 Mater ia ls a n d Me thods 10 Wa te r C o l l e c t i o n 10 Ana l y t i c a l M e t h o d s Phys ica l Parame.ters 10 Major Ions 10 S o d i u m , m a g n e s i u m , potass ium 10 Strontium 11 C a l c i u m 11 Borate 12 2.3 Results 13 Physical D a t a 13 Major Ions 13 2.4 Discussion 21 3. REDOX CHEMISTRY 26 3.1 Int roduct ion 26 C a r b o n 29 Ni t rogen 32 A m m o n i f i c a t i o n (Deaminat ion ) 33 Ni t rogen Fixation 33 Nitrate Reduc t ion a n d Denitrif ication 35 Nitrification 36 3.2 Mater ia ls a n d Me thods 38 Organ i c C a r b o n a n d Nitrogen 38 Nutrients 39 Ni t rogen 39 Dissolved S i l icon" 39 Alkalinity 40 pH ; '. 40 3.3 Results '. 41 O rgan i c C a r b o n a n d Nitrogen 41 Powel l Lake 41 Sak inaw Lake 41 Nutrients 41 Powel l Lake 41 Sak inaw Lake 42 Alkalinity a n d pH 42 Powel l Lake 42 Sak inaw Lake 42 3.4 Discussion 48 Organ i c C a r b o n . . : 48 DOC ; 48 POC 51 D C O P C C 53 P O O P O N -. 53 Inorganic Ni t rogen 55 Dissolved Si l icon 58 Alkalinity a n d pH 61 4. PHOSPHORUS CHEMISTRY 65 4.1 In t roduct ion 65 The Phosphorus C y c l e 65 Forms of Phosphorus 67 Dissolved Phosphorus 67 Pa r t i cu la te Phosphorus 68 B io log i ca l Impor t ance of Phosphorus 68 Minera l izat ion of Phosphorus 70 4.2 Mater ia ls a n d Me thods 73 Soluble Reac t i v e Phosphorus 73 Total Phosphorus 73 Par t i cu la te Phosphorus 75 4.3 Results 76 Powel l Lake 76 Sak inaw Lake 77 4.4 Discussion 85 Sak inaw Lake 85 Powel l Lake 88 Phosphorus R e m o v a l Due to Adsorp t ion 89 Phosphorus R e m o v a l Due to Direct Prec ipi tat ion 91 B io log i ca l R e m o v a l 94 Why Powel l a n d Sak inaw Lakes Are So Different 98 5. SULPHUR CHEMISTRY 101 5.1 Int roduct ion 101 Sulphur C o m p o u n d s 102 Inorganic Sulphur C o m p o u n d s 102 O r g a n i c Sulphur C o m p o u n d s 105 The Sulphur C y c l e 105 Su lpha te-Reduc ing Bac te r i a 107 Sulphide-Oxidizing Bac te r i a 107 Diagenesis of Sulphur 108 Iron Sulphides 110 Sed imentary Pyrite Format ion 110 Laboratory Studies of Pyrite Format ion 112 5.2 Mater ia ls a n d Me thods 115 Wate r C o l l e c t i o n ' 115 Su lpha te 115 Sulphite, Thiosulphate a n d Polythionates 116 Zerova len t Sulphur 118 Dissolved Su lph ide 119 Par t icu late Su lphide Analysis 119 Iron a n d M a n g a n e s e 122 Spec i a t i on a n d Solubility Ca l cu la t ions 122 5.3 Results i^i Powel l Lake 123 Sak inaw Lake • 124 5.4 Discussion 133 Sulphur Oxyan ions • 133 Su lpha te 133 Thiosulphate , Sulphite a n d Polythionates 135 R e d u c e d Sulphur Spec ies 136 Dissolved Su lph ide 136 Zerova len t Sulphur 137 Iron a n d M a n g a n e s e 144 M e t a l C o m p l e x e s 147 Par t icu la te Sulphides 148 Effect of pH on Pyrite Format ion 152 O r g a n i c Sulphur 153 M a n g a n e s e Sulphides 154 6. S U M M A R Y A N D CONCLUS IONS 155 APPENDIX 1 SOLUBILITY A N D SPECIATION CALCULATIONS 158 APPENDIX 2 DATA TABLES 164 REFERENCES 172 vi LIST OF TABLES Table 2-1 Deviat ions of obse r ved bo t tom wa te r major ion concen t ra t ions f rom those c a l c u l a t e d f rom chlorinity assuming constant relat ive compos i t i on of s eawa te r 25 Table 3-1 Ox ida t ion react ions of o rgan i c matter (from Froelich et a l . 1979)...., 28 Table 3-2 Major classes of react ions invo lved in alkalinity gene ra t i on a n d consumpt ion (from Schiff a n d Anderson 1987) 63 Table 5-1 Inorganic sulphur c o m p o u n d s c o m m o n l y f o u n d in the a q u e o u s env i ronment ICG Table 5-2 React ions at the mercury e l e c t rode (from Luther et a l . 1986a) 117 Table A- l Stability constants used in MINEQL ca lcu la t ions 160 Table A-2 Solubility p roducts used in MINEQL ca lcu la t ions 163 Table A-3 Physical a n d major ion d a t a for Powel l Lake 165 Table A-4 Nutrient, c a r b o n , p H , a n d alkalinity d a t a for Powel l Lake 166 Table A-5 Phosphorus d a t a for stations other t han the South basin in Powel l Lake 167 Table A-6 Sulphur a n d t r a ce me ta l d a t a for Powel l Lake 168 Table A-7. Physical a n d major ion d a t a for Sak inaw Lake 169 Table A-8 Nutrient, c a r b o n , pH a n d alkalinity d a t a for Sakinaw Lake 170 Table A-9 Sulphur a n d t r a ce meta l d a t a for Sak inaw Lake 171 vii LIST OF FIGURES Fig. 2-1 Loca t i on m a p for Powel l a n d Sak inaw Lakes 6 Fig. 2-2.. M a p of Powel l Lake (after Ma thews 1962) 7 Fig. 2-3 M a p of Sakinaw Lake (after Northcote a n d Johnson 1964) 9 Fig. 2-4 Dissolved o x y g e n a n d sulphide concent ra t ions in Powel l Lake. The horizontal line at 150 m represents the ox i c/anox ic inter face 14 Fig. 2-5 Tempera ture , ch lor ide a n d density profiles in Powel l Lake for Apri l 1984 14 Fig. 2-6 Dissolved o x y g e n a n d sulphide concent ra t ions in Sak inaw Lake. The horizontal line at 30 m represents the ox i c/anox ic in ter face 15 Fig. 2-7 Temperature , chlorinity, a n d density profiles in Sak inaw Lake for July 1985 15 Fig. 2-8 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of sod ium in Powel l Lake 16 Fig. 2-9 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of potassium in Powel l Lake 16 Fig. 2-10 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of magnes i um in Powel l Lake 17 Fig. 2-11 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of c a l c i u m in Powel l Lake 17 Fig. 2-12 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of bora te in Powel l Lake 18 Fig. 2-13 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of strontium in Powel l Lake 18 Fig. 2-14 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of sodium in Sak inaw Lake 19 Fig. 2-15 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of potassium in Sak inaw Lake 19 Fig. 2-16 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of magnes ium in Sak inaw Lake 20 Fig. 2-17 O b s e r v e d a n d c a l c u l a t e d concent ra t ions of c a l c i u m in Sak inaw Lake 20 Fig. 3-1 The redox c y c l e of nitrogen (from Brock 1979) 34 Fig. 3-2 Dissolved a n d par t i cu la te o rgan i c c a r b o n in Powel l Lake 43 Fig. 3-3 Dissolved a n d par t i cu la te o rgan i c c a r b o n in Sak inaw Lake 43 Fig. 3-4 Part iculate o rgan i c c a r b o n a n d nitrogen in Powell Lake 44 Fig. 3-5 Part iculate o rgan i c c a r b o n a n d nitrogen in Sak inaw Lake 44 Fig. 3-6 Nitrate a n d a m m o n i a in Powel l Lake (nitrite u n d e t e c t a b l e ) 45 Fig. 3-7 Nitrate, nitrite a n d a m m o n i a in Sakinaw Lake 45 Fig. 3-8 Dissolved si l icon in Powel l Lake 46 Fig. 3-9 Dissolved si l icon in Sak inaw Lake 46 Fig. 3-10 Alkalinity a n d pH in Powel l Lake 47 Fig. 3-11 Alkalinity a n d pH in Sak inaw Lake 47 Fig. 4-1 A simplif ied representat ion of the phosphorus c y c l e in a q u a t i c environments (from Fenche l a n d B lackburn 1979) 66 Fig. 4-2 M a p of Powel l Lake showing six stations s a m p l e d for phosphorus analysis 74 Fig. 4-3 Soluble reac t i ve phosphorus in Powel l Lake. SRP is u n d e t e c t a b l e a b o v e 175 m 78 Fig. 4-4 Soluble reac t i ve phosphorus in Sak inaw Lake. Upper sca le is for the ox ic wa te r c o l u m n ( top 30 m). Bottom sca le is for the anox i c wa te r c o l u m n (be low 30 m) 78 Fig. 4-5 Soluble reac t i ve , par t icu late a n d tota l phosphorus in Powel l Lake 79 Fig. 4-6 Soluble reac t i ve , par t icu la te a n d tota l phosphorus in Sak inaw Lake 79 Fig. 4-7 P e r c e n t a g e of to ta l phosphorus consisting of soluble reac t i ve a n d part icu la te P in Powel l Lake. Total P was u n d e t e c t a b l e a b o v e 140 m 80 Fig. 4-8 P e r c e n t a g e of tota l phosphorus consist ing of soluble reac t i ve a n d par t i cu l a te P in Sak inaw Lake.... 80 Fig. 4-9 Mo la r ratios of part icu late o rgan ic c a r b o n a n d nitrogen to phosphorus in Powel l Lake 81 Fig. 4-10 Mo la r ratios of part icu late o rgan ic c a r b o n a n d nitrogen to phosphorus in Sak inaw Lake 81 Fig. 4-11 Mo la r n i t rogen to phosphorus ratios in Powel l Lake. Soluble reac t i ve phosphorus is u n d e t e c t a b l e in the uppe r 175 m, resulting in infinite dissolved N:P ratios 82 Fig. 4-12 Mo la r n i t rogen to phosphorus ratios in Sak inaw Lake 82 viii Fig. 4-13 Total phosphorus in various basins a n d at the h e a d of Powel l Lake (see Fig. 4-2 for locations). The East basin conta ins relict s eawa te r 83 Fig. 4-14 Part iculate phosphorus in various basins a n d at the h e a d of Powel l Lake (see Fig. 4-2 for locat ions) . The East basin conta ins relict s eawa te r 83 Fig. 4-15 Saturat ion state of phosphorus minerals a n d ca l c i t e in Powel l Lake. . Log (Ksp*IAP) > 0 = supersatura ted . < 0 = undersa tura ted 84 'Fig. 4-16 Saturat ion state of phosphorus minerals a n d ca l c i t e in Sak inaw Lake. Log (Ksp*IAP) > 0 = supersa tura ted , < 0 = undersa tura ted 84 Fig. 5-1 The sulphur c y c l e in a lake, with emphas is on the mic rob io log i ca l processes MS = meta l sulphides, (from Wetze l 1983) 106 Fig. 5-2 G e n e r a l Eh-pH env i ronmenta l limits of: 1) c h e m o s y n t h e t i c (colourless) sulphur-oxidizing b a c t e r i a ; 2) photosynthet ic purple bac t e r i a ; 3) su lphate-reduc ing bac t e r i a ; a n d 4) g r een sulphur b a c t e r i a (from Wetze l 1983) 109 Fig. 5-3 Eh-pS2" d i a g r a m for iron minerals at pH = 7.37, log PCo2= -2.40, T = 25°C. P = 1 a tm . Measurements of natural sulphidic mar ine sediments fall near the d a s h e d line.(from Berner 1971) I l l Fig. 5-4 Possible reac t ion pa thways of pyrite format ion (from Raiswell 1982) 112 Fig. 5-5 Dissolved sulphur spec ies in Powel l Lake 125 Fig. 5-6 Dissolved sulphur spec ies in Sak inaw Lake 125 Fig. 5-7 Rat io of tota l dissolved sulphide (S(-2)) to dissolved zerova lent polysulphide (S(0)) in Powel l Lake 126 Fig. 5-8 Ratio of tota l d issolved sulphide (S(-2)) to dissolved zerova lent polysulphide (S(0)) in Sak inaw Lake 126 Fig. 5-9 Dissolved iron a n d m a n g a n e s e in Powel l Lake 127 Fig. 5-10 Dissolved iron a n d m a n g a n e s e in Sak inaw Lake 127 Fig. 5-11 Pe r cen t ages of free a n d c o m p l e x e d dissolved iron in Powel l Lake. All other c o m p l e x e s we re < 1% of the tota l dissolved iron 128 Fig. 5-12 Pe r c en t ages of free a n d c o m p l e x e d dissolved iron in Sak inaw Lake. All other c o m p l e x e s we re < 1% of the tota l dissolved iron 128 Fig. 5-13 Pe r c en t ages of free a n d c o m p l e x e d dissolved m a n g a n e s e in Powel l Lake. All other c o m p l e x e s we re < 1% of the tota l d issolved m a n g a n e s e 129 Fig. 5-14 Pe r c en t ages of free a n d c o m p l e x e d dissolved m a n g a n e s e in Sak inaw Lake. All other c o m p l e x e s we re < 1% of the tota l d issolved m a n g a n e s e 129 Fig. 5-15 Part iculate sulphur in Powel l Lake 130 Fig. 5-16 Part iculate sulphur in Sak inaw Lake 130 Fig. 5-17 Saturation state of iron sulphides in Powel l Lake Log (Ksp*IAP) > 0 = supersaturated, < 0 = undersa tura ted 131 Fig. 5-18 Saturat ion state of iron sulphides in Sak inaw Lake. Log (Ksp*IAP) > 0 = supersatura ted , < 0 = undersa tura ted 131 Fig. 5-19 Saturat ion state of m a n g a n e s e sulphides in Powel l Lake. Log (Ksp*IAP) > 0 = supersaturated, < 0 = undersa tura ted 132 Fig. 5-20 Saturat ion state of m a n g a n e s e sulphides in Sak inaw Lake. Log flVHAP) > 0 = supersatura ted , < 0 = undersa tura ted 132 ACKNOWLEDGEMENTS This project was primarily f u n d e d by a n NSERC ope ra t i ng grant to my supervisor Tom Pede r sen . A d d i t i o n a l f und ing w a s a lso kindly p r o v i d e d by M a c M i l l a n - B l o e d e l . Powel l River Division a n d by the Bank of Perry (parenta l division). I w o u l d like to thank Tom Pedersen for his input a n d a d v i c e dur ing the writeup of this thesis, no mat ter h o w little I w a n t e d to hea r it. I a lso thank L a w r e n c e Lowe , Bill Barnes a n d G e o r g e Sp i ege lman for ' sitting o n my c o m m i t t e e throughout the e x t e n d e d length of this research , a n d not falling a s l e e p o n c e . I espec ia l l y thank Steve Ca lver t not just for sitting o n my c o m m i t t e e , but also for b e i n g the keepe r of all k n o w l e d g e , a ver i table walking-talking e n c y c l o p e d i a of s c i ence . (Astat ine? A lovely element. . . ) This thesis invo lved a great d e a l of f ie ld work, a n d f ew techn i c i ans m a n a g e d to e s c a p e m y tenure at UBC without hav ing to d o t ime at o n e or bo th lakes. Murray Storm a c c o m p a n i e d m e o n my first trips to Powel l Lake , R am a n d Hugh M a c L e a n h e l p e d me out o n seve ra l f i e ld seasons a n d Heinz Heck l s h a r e d his "wall of f l a m e " c o o k i n g t e c h n i q u e o n various o c ca s i ons dur ing the severa l weeks he spent at bo th lakes. Their i ngenu i t y a n d b ru te s t r eng th ( o o o o h h h t h o s e n i t r o g e n cy l inders ) w a s m u c h a p p r e c i a t e d . Back at the l ab ( and briefly in the field) M a u r e e n Soon was a great he lp to m e with respect to the pilfering of equ ipmen t , sharing of t echn iques a n d gene ra l gossip. Numerous c o l l e a g u e s h a v e h e l p e d m e stay sane dur ing the torture. The other late-nighters - Terri Suther land, D o n W e b b a n d A n n a M e t a x a s - h a v e h e l p e d to k e e p m e a w a k e , a n d more important ly , d is t rac ted from my work. Lastly, I thank my off-world friends, part icular ly Lynn G i r a u d , for provid ing support , m o n e y a n d disbelief for the post mi l len ium. CHAPTER 1 INTRODUCTION E l e m e n t a l c y c l i n g u n d e r s u b o x i c t o a n o x i c c o n d i t i o n s h a s r e c e i v e d cons ide r ab l e a t tent ion in the past f e w years. Examples of a n o x i c env i ronments inc lude hyd ro the rma l systems, s o m e es tuar ine , mar ine a n d lacustr ine sed iments , a n d w a t e r c o l u m n s wi th restr icted c i r cu la t ion . The possibility tha t w i d e s p r e a d a n o x i a m a y h a v e o c c u r r e d in o c e a n s of t h e g e o l o g i c past necess i ta tes a be t t e r unde r s t and ing of g e o c h e m i c a l processes unde r such condi t ions . In a q u e o u s env i ronments , there is a net c o n s u m p t i o n of o x y g e n a t all dep ths b e l o w the c o m p e n s a t i o n d e p t h (the d e p t h a t w h i c h the c a r b o n f ixed by photosynthesis equa l s that respired) d u e to the f ixat ion of c a r b o n (Richards 1965). A n o x i c condi t ions arise w h e n t h e c o n s u m p t i o n of o x y g e n b y m ic rob i a l b r e a k d o w n of o r g a n i c mat ter e x c e e d s the quant i ty of o x y g e n supp l ied by diffusion a n d wa te r c i r cu la t ion , resulting in a r edox d iscont inu i ty b e t w e e n o x y g e n a t e d a n d a n o x i c env i ronments . This r edox d i s con t inu i t y o c c u r s a v a r i a b l e d i s t a n c e b e l o w the s e d i m e n t - w a t e r i n t e r f a c e , d e p e n d i n g o n t h e o x y g e n d e m a n d of t h e d e p o s i t e d o r g a n i c m a t t e r a n d the sed imenta t ion rate. However , the redoxc l ine m a y also b e f o u n d at t he sediment-water i n te r f ace or wi th in t he w a t e r c o l u m n (euxin ic ) , e i ther wi th in or b e l o w t h e z o n e of photosynthet i c act iv i ty. Ma r ine basins b e c o m e a n o x i c d u e t o restr icted c i r cu la t ion w h e r e sha l low sills a n d s t e e p p y c n o c l i n e s a c t as barriers t o restrain hor izontal a n d ver t i ca l c i r cu l a t ion , respect i ve ly (R ichards 1965). This strat i f icat ion m a y b e p e r m a n e n t or intermittent, the latter s tate b e i n g d e p e n d e n t u p o n s e a s o n a l , or a p e r i o d i c f lushing events . Var ious mar ine a n o x i c basins h a v e b e e n s tud ied extensive ly , i nc lud ing t empora l l y stratif ied basins such as S a a n i c h Inlet, a fjord o n the coas t of British C o l u m b i a (Emerson et a l . 1979), or pe rmanen t l y stratified basins s u c h as the B lack S e a (Luther et a l . 1990c) a n d Framvaren Fjord in Norway ( J acobs et a l . 1985). Other pe rmanent l y anox i c mar ine basins that h a v e b e e n e x a m i n e d inc lude Nitinat Lake , a British C o l u m b i a n fjord (Richards et a l . 1965), the C a r i a c o Trench, a n o c e a n i c basin north of V e n e z u e l a ( J acobs et al . 1987), a n d the brine-filled B annock a n d Tyro basins in the Eastern Med i t e r r anean S e a (Luther et a l . 1990b). A n u m b e r of lakes a lso e x p e r i e n c e l imi ted c i r cu l a t i on a n d a re c lassi f ied as m e r o m i c t i c . Examp les of this t y p e of a n o x i c bas in i n c l u d e t h e Solar Lake , Sinai ( Jorgensen a n d C o h e n 1977), M a h o n e y Lake (interior British C o l u m b i a ) (Northcote a n d Hall 1983), Lake V a n d a , A n t a r c t i c a ( G r e e n et a l . 1986), a n d Big S o d a Lake , N e v a d a ( O r e m l a n d et a l . 1988). The t w o lakes e x a m i n e d in this study, Powel l a n d Sak inaw, are fo rmer fjords w h i c h w e r e s e p a r a t e d f rom the o c e a n app rox ima te l y 11000 years a g o , d u e t o e m e r g e n t sills c a u s e d b y post-glac ia l isostatic uplift, w h i c h t r a p p e d now-relict s eawa te r . They a re e x a m p l e s of e c t o g e n i c meromixis , w h e r e externa l events inject e i ther fresh w a t e r into a saline lake , as in this c a s e , or salt wa te r into a f reshwater lake (Wetzel 1983). A n u m b e r of c h e m i c a l processes a n d produc ts are d e p e n d e n t u p o n the redox po ten t i a l . Powe l l a n d S ak i naw Lakes represent c o n v e n i e n t na tura l l abora tor ies for studies of d iagenes is b e c a u s e the wa te r c o l u m n structure of bo th lakes is similar t o that o b s e r v e d in most nearshore mar ine sediments whe re a n ox id ized sur face layer g rades into under l y ing r e d u c i n g depos i ts . Therefore , a c h e m i c a l a n a l o g y c a n b e d r a w n b e t w e e n t h e r e d o x cond i t i ons in t h e w a t e r c o l u m n s of the lakes a n d in c o a s t a l sed iments . A l so , c h e m i c a l g rad ien ts in the w a t e r c o l u m n c a n b e re lat ive ly easi ly s tud ied a n d d e f i n e d by de t a i l ed wa te r samp l ing , a n d the wate r is permanent l y stratified a n d thus stable . The most impor tan t p rocess that o c c u r s in a n o x i c basins is that of su lphate r educ t i on with the resultant p roduc t i on of h y d r o g e n sulphide. Sulphur is a n important , o f t en major const i tuent in organic-r ich sed iments whe re it o c cu r s in bo th o r g a n i c a n d inorgan i c phases , espec ia l l y as sulphide minerals. Pyrite (FeS2) is a c o m m o n auth igen ic m inera l of r e c e n t mar ine a n d lacustr ine sed iments , a n d of sed imen ta r y rocks. The fo rma t i on a n d o c c u r r e n c e of pyrite is of interest t o the c o a l industry (Altschuler et a l . 1983), t o g e o c h e m i s t s s tudy ing t r a c e m e t a l i nco rpora t ion into iron su lph ide minerals (Ra iswel l a n d P lant 1980), t o e n v i r o n m e n t a l scientists e x a m i n i n g h e a v y m e t a l e n r i c h m e n t s in sed iments (Ferguson et a l . 1983) a n d as o n e of seve ra l po ten t i a l indicators of anc i en t euxinic environments (Leventhal 1983). There are t w o p r o p o s e d pa thways of pyrite format ion: 1) the r eac t ion of iron monosu lph ide (FeS) with e l ementa l sulphur (Berner 1967a); a n d 2) t h e d i rec t r e a c t i on of ferrous iron with e l e m e n t a l sulphur or po lysu lph ide ions in the p r e s e n c e of d issolved sulphide spec ies (Howarth 1979). Studies of ear ly d iagenes is in mar ine a n d lacustr ine sediments a re o f ten not conc lus ive as t o w h i c h of the t w o p a t h w a y s is responsib le for the o c c u r r e n c e of pyrite in a n y s p e c i f i c e n v i r o n m e n t . This is d u e t o t h e d i f f icu l ty i n cu r red in s tudy ing c o m p l e x , i n h o m o g e n e o u s sed iments , w h e r e r e d u c i n g m ic roenv i ronments f requent l y o c c u r in ox id i zed horizons. In a d d i t i o n , e l e m e n t a l sulphur, iron monosu lph ides , pyrite, dissolved po lysu lph ides , ferrous iron a n d h y d r o g e n su lph ide spec i e s c a n coex is t in the s a m e sed iment-pore w a t e r systems, t he reby obscur ing the mechan ism(s ) by w h i c h pyrite is p r o d u c e d (Lord a n d C h u r c h 1983). The pr imary ob jec t i ve of this thesis is t o examine pyrite f o rma t i on in a less c o m p l i c a t e d system, such as the a n o x i c b o t t o m waters of Powe l l a n d S ak i naw Lakes. In a n o x i c w a t e r c o l u m n s , d i a g e n e t i c p rocesses w h i c h normal ly t a k e p l a c e over a f ew cent imetres in sediments o c c u r over tens to hundreds of metres. Thus, Powel l a n d Sak inaw Lakes are idea l p l a c e s in w h i c h to study b o t h redox chemistry in gene ra l a n d sulphur chemistry in particular. This thesis consists of essentially four s epa r a t e , but l inked parts, w h i c h deta i l the chemistry of these t w o lakes. The next c h a p t e r descr ibes the lakes in g e n e r a l with a short r ev i ew of their phys i ca l sett ing a n d their strat i f icat ion. The phys i ca l structure (dens i ty , sal in i ty , t e m p e r a t u r e ) is d e s c r i b e d a n d t h e major ion distr ibutions a re e x a m i n e d t o see h o w m u c h this relict s e a w a t e r resembles that of t he present-day. C h a p t e r 3 examines w h a t has h a p p e n e d to the wa te r s ince it has b e e n cut off f rom the s e a , i.e. b i o c h e m i c a l react iv i ty w h i c h has a l t e r ed the chemistry of t he w a t e r c o l u m n . Alkalinity, p H , nutrients (nitrate, nitrite, a m m o n i u m , dissolved si l icon), a n d dissolved a n d pa r t i cu l a t e o r g a n i c c a r b o n a n d n i t rogen are all d i scussed . This c h a p t e r outl ines a n interesting f inding w h i c h is the focus of C h a p t e r 4. The extremely low levels of phospha te o b s e r v e d in the b o t t o m waters of Powel l are i n compa t i b l e with the very h igh amounts of a m m o n i u m present. Var ious phosphorus r emova l processes are r e v i ewed a n d re l a ted t o w h a t m a y b e prevent ing phosphorus bu i ldup in Powel l Lake b o t t o m waters. The final sec t ion ( C h a p t e r 5) descr ibes the sulphur chemistry of bo th lakes, with emphas is o n iron su lph ide f o r m a t i o n , t h e f o c u s of this thesis. D isso lved sulphur s p e c i e s of var ious o x i d a t i o n states ( su lpha te , su lph i te , t h i osu lpha te , p o l y t h i o n a t e , e l e m e n t a l sulphur, po l y su lph ide , h y d r o g e n sulphide) a n d dissolved iron a n d m a n g a n e s e a re e x a m i n e d . 4 The o c c u r r e n c e of iron monosu lph ide a n d pyrite in the w a t e r co lumns of Powel l a n d S a k i n a w a r e t h e n d i s cussed in terms of the t w o p r o p o s e d m e c h a n i s m s of pyrite fo rmat ion a n d c o m p a r e d t o mode l-der i ved solubility ca l cu la t ions . All ana l y t i ca l d a t a discussed in this thesis are listed in A p p e n d i x 2. CHAPTER 2 PHYSIOGRAPHY, PHYSICAL AND CHEMICAL LIMNOLOGY 2.1 Introduction The t w o lakes c h o s e n for this s tudy a re similar in their g e o l o g i c history a n d phys ica l structure. Both c o n t a i n at least o n e basin with anox i c relict s eawa te r at dep th . In this c h a p t e r , the phys ica l a n d c h e m i c a l l imnology of b o t h lakes a re c o m p a r e d a n d con t r a s t ed in s o m e deta i l . Powell Lake Powe l l is a d e e p fjord-lake s i t ua t ed a p p r o x i m a t e l y 110 km northwest of V a n c o u v e r o n the southwest coas t of British C o l u m b i a (Fig. 2-1). It is, o n a v e r a g e , abou t t w o km w i d e a n d 47 km long a n d is d i v i d e d into six d e e p , f l a t-bot tomed basins by a series of sills of differing depths (Fig. 2-2) (Mathews 1962). The lake w a s originally a mar ine fjord; with the mel t ing of the Cord i l l e ran Ice Sheet a t t he e n d of the last i c e a g e a n d c o n s e q u e n t r e b o u n d of the cont inent , the shal low b e d r o c k sill a t the mou th of the fjord rose 46 m a b o v e s e a leve l , isolating the bas in f rom the Strait of G e o r g i a . L o c a l post-g l a c i a l isostatic history suggests that seawa te r was t r a p p e d in the lake b e t w e e n 12,500 a n d 10,500 years a g o (Mathews et al . 1970). A d a m was built o n the sill in 1924, raising the high wa te r mark to 56 m a b o v e m e a n s e a level. Freshwater flows into Powel l Lake , largely v i a Powel l River at the h e a d , at a rate of a b o u t 3 x 10 9 m 3»yr '\ This is the out f low at t he d a m , a v e r a g e d ove r the past 40 years (Sanderson et a l . 1986). A f e w small streams also f low into t he l ake , but their input of f reshwater is smal l . The h e a d w a t e r s of the lake a re under la in b y largely un f rac tu red ho rnb l ende granodior i te (Ma thews 1962). B e cause the sur face of the lake is more t h a n 50 m a b o v e s e a leve l a n d s e p a r a t e d f rom the Strait of G e o r g i a b y b e d r o c k , there c a n n o t b e a n y s e e p a g e of s eawa te r into t he lake. Turbidity currents, w h i c h c o u l d b e c a u s e d by m u d d y streams or b y mudslides from deltas g rowing at the h e a d of the lake , a p p e a r t o b e t r a p p e d in the uppe r bas in , so that in the lower basins there is unlikely to b e invasion of turbid wa te r at d e p t h . O f the six basins in the lake , only the south a n d east (the t w o closest t o the Strait of G e o r g i a ) still c o n t a i n relict s eawa te r a n d are thus meromic t i c , with pe rmanen t l y anox i c monimol imnions . The south bas in is t he d e e p e s t , with a m a x i m u m d e p t h of 358 m. It is Fig. 2-2 Map of Powell Lake (after Mathews 1962) a p p r o x i m a t e l y 15 km long a n d 2 km w i d e , a n d is f l oo red b y sed iments consist ing of organ ic- a n d pyrite-rich gelat inous o o z e (Barnes a n d Barnes 1981). The small a m o u n t of c las t i c detritus present reflects the very low d i rec t runoff into this basin. The south bas in has f r e s h e n e d less t h a n the east a n d w a s there fore c h o s e n for d e t a i l e d study. O n e station (Fig. 2-2) was se l e c t ed in the centre to b e representat ive of the bas in as a who le . Sakinaw Lake Sak inaw Lake also a p p e a r s to h a v e o n c e b e e n a fjord, a n d is n o w s e p a r a t e d f rom the Strait of G e o r g i a b y a n e m e r g e d sill d u e t o post-g lac ia l isostatic r e b o u n d (No r thco te a n d J o h n s o n 1964). It is l o c a t e d n e a r the northern e n d of the Seche l t Peninsula , app rox ima te l y 90 km northwest of V a n c o u v e r (Fig. 2-1), a n d it is a b o u t 9 km long a n d 0.7 km w i d e (Fig. 2-3). It lies in a basin c o m p o s e d primarily of quartz dioritic a n d granodior i t ic rocks, w h i c h are broken a b o u t ha l fway a l ong its length by a narrow b a n d of a l t e r ed v o l c a n i c rocks ( B a c o n 1957, c i t e d in Nor thco te a n d Johnson 1964). The lake consists of t w o basins: o n e relatively sha l low (49 m) a n d whol ly fresh, a n d the other a d e e p (140 m) a n d meromic t i c basin that still conta ins relict seawater . A number of small streams f low into Sak inaw, a l t hough the v o l u m e of the freshwater input, inc lud ing that w h i c h drains nea rby Ruby Lake , is small. S ak i naw Lake lies a p p r o x i m a t e l y 2 m a b o v e m e a n s e a leve l . The smal l river exit ing the lake has b e e n partial ly or c o m p l e t e l y b l o c k e d s ince the ear ly 1900's a n d a p e r m a n e n t d a m a n d f ishway we re installed in 1952. Out f low has b e e n r egu l a t ed s ince that t ime. Prior to the construct ion of the weir, it is possible that incursion of seawa te r from the Strait of G e o r g i a into t he l ake m a y h a v e o c c u r r e d unde r cond i t i ons of strong onshore w inds a n d h igh t ides. V isua l i n spec t i on of t h e out let suggests tha t s u c h incursions m a y a lso h a v e o c c u r r e d s ince the d a m was built. Therefore, the seawa te r in Sak inaw m a y b e of m u c h more recent v i n t age t h a n that in Powel l , w h i c h c a n n o t h a v e r e c e i v e d a n y s e a w a t e r s ince the sill e m e r g e d . A g a i n , o n e stat ion in the cen t r e of the a n o x i c bas in was s e l e c t e d for study (Fig. 2-3). C r e e k | k m Fig. 2-3 M a p of Sakinaw Lake (after Northcote a n d Johnson 1964) 2.2 Materials and Methods Water Collection All w a t e r samples we re c o l l e c t e d f rom a smal l , 5.5 m l a u n c h e q u i p p e d with a g a s - p o w e r e d w i n c h using either 1.8 or 9 L Niskin bott les m o u n t e d o n s t a n da r d iron or stainless steel hydrowire . S amp les w e r e c o l l e c t e d in po l ye thy l ene or po l yp ropy l ene conta iners w h i c h h a d b e e n w a s h e d in 10% HCI a n d rinsed in dist i l led, de i on i zed wa te r (DDW). They we re then stored at 6 °C until analysis. Analytical Methods Physical Parameters Dissolved o x y g e n w a s d e t e r m i n e d by Winkler titration with a d e t e c t i o n limit of 2 p.M a n d a prec is ion of 0 .5% (1 a , rsd). Tempera tu re w a s m e a s u r e d using reversing thermometers (± 0.01°C). Chlorinity was de t e rm ined by s tandard Knudsen titration with a G i lmont mic robure t te , after expos ing the samp le t o air a n d a l lowing a n y H2S present t o either exsolve or oxidize. The d e t e c t i o n limit w a s 0.18 m M with a prec is ion of 0 .5% (1 a , rsd). Density w a s c a l c u l a t e d f rom the t empe ra tu r e a n d chlorinity d a t a . Su lphide was de t e rm ined as des c r i bed in C h a p t e r 5. Major Ions Sodium, Magnesium and Potassium N a + , K + , a n d M g 2 + w e r e d e t e r m i n e d b y f l a m e a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y (AAS). S amp les w e r e a c i d i f i e d wi th H N 0 3 t o a pH < 3 to prevent p r e c i p i t a t i o n of C a C 0 3 , f i l tered t h r o u g h 0.4 N u c l e p o r e m e m b r a n e s a n d t h e n asp i ra ted into the f l ame after appropr i a t e dilution with DDW t o ensure a n a b s o r b a n c e < 0.4. Su lph id i c s a m p l e s w e r e b u b b l e d wi th N 2 prior t o fi ltration to r e m o v e the H 2S. S tandards w e r e p r e p a r e d by diluting IAPSO S tanda rd S eawa te r with DDW. Sod ium a n d potass ium a re part ial ly ion ized in the a i r-acety lene f l a m e , h o w e v e r , t he p r e s e n c e of other alkal i salts lessens this e f fec t . A lso , ionizat ion should h a v e b e e n similar in samples a n d s tandards . B e c a u s e Si a n d A l depress M g absorpt ion in the a i r-acety lene f l a m e , a nitrous ox ide-ace ty l ene f l a m e w a s used for M g 2 + analysis. Al l samples we re a b o v e the d e t e c t i o n limit for these three ions a n d the precis ion was 0 .5% for K + a n d 5% (1 a , rsd) for N a + a n d M g 2 + . Strontium B e c a u s e A A S w a s not suff ic ient ly sensit ive, Sr 2 + w a s m e a s u r e d v i a a t o m i c emission s p e c t r o p h o t o m e t r y (AES). This differs with respec t t o A A S in tha t rather t h a n measur ing t h e rad ia t ion a b s o r b e d dur ing a n e l e c t ron i c transit ion of the e l emen t of interest f rom the g r o u n d state to a n e x c i t e d state, the emission of ene rgy is d e t e c t e d . B e c a u s e there was a salt e f fec t , s tandards we re p r e p a r e d in 0 .5% NaCI . After sulphide r emova l (where necessary ) , samples we re f i l tered through 0.4 u.m N u c l e p o r e filters a n d a n a p p r o p r i a t e a m o u n t of NaCI a d d e d t o bring its tota l c o n c e n t r a t i o n to 0.5%. Several samples fell b e l o w the d e t e c t i o n limit of 0.5 u.M. The precis ion of the analyses w a s 5% (1 a , rsd). Calcium Wate r w a s a c i d i f i e d u p o n c o l l e c t i o n to a pH < 3 t o p revent p rec ip i t a t i on of CaCC>3, a n y H 2S present was dr iven off by bubb l i ng with N 2 a n d then the s a m p l e w a s f i l tered t h rough 0.4 u,m N u c l e p o r e m e m b r a n e s prior t o analysis. Low prec i s ion w a s e n c o u n t e r e d in A A S analysis a n d so the c o n c e n t r a t i o n of C a 2 + was r e m e a s u r e d by c o m p l e x o m e t r i c t i trat ion with 1,2-di(2-aminoethoxy)ethane-A/,/V,N,/S/'-tetra-acetic a c i d (EGTA) (Tsunogai et a l . 1968). This t e c h n i q u e is b a s e d o n the c h e l a t i o n of po lyva lent ca t ions with a m i n o po l yca rboxy l i c a c ids ( comp lexones ) w h i c h h a v e the character is t ic g roup ing - N ( C H 2 C O O H ) 2 . A spec i a l c o m p l e x o n e , EGTA, al lows almost se lect ive titration of c a l c i u m in the p r e s e n c e of h igh amounts of m a g n e s i u m . The e n dpo in t is d e t e c t e d b y t h e f o r m a t i o n of a r e d inner c a l c i u m c o m p l e x w i th t h e Schiff b a s e di-(2-hydroxyphenyl- imino)-ethane (GHA ) , w h i c h is qu i te different in co lou r f rom free G H A a n d less s tab le t h a n the m e t a l - c o m p l e x o n e c o m p l e x . Therefore , w h e n the t itrat ion p r o c e e d s , c a l c i u m ions a re c o m p l e x e d to m u c h stronger EGTA c o m p l e x e s a n d at the s to i ch iomet r i c e n d p o i n t the r ed co l ou r of t he C a - G H A c o m p l e x is r e p l a c e d by the co lou r l e ss f r ee i n d i c a t o r . A n o r g a n i c so l vent (n-butanol ) is a d d e d t o ex t r a c t quant i tat ive ly ( and h e n c e concen t r a t e ) the real C a - G H A c o m p l e x . While stirring, 5 m M EGTA was a d d e d to 1 mL of samp le plus 0.5 mL of 0.04% G H A a n d 0.5 mL bora te buffer. After stirring for 3 minutes, 1 mL n-butanol w a s a d d e d a n d then the s a m p l e was stirred vigorously a n d t i t rated with 5 m M EGTA. S ince the c a l c i u m - G H A c o m p l e x is fairly unstab le . It w a s important t o c o m p l e t e the titration within 15 minutes. I a lso f o u n d that the a m o u n t of EGTA a d d e d to the samp le prior t o the 3 minutes of stirring was cr i t ical . A l t hough Grasshof (1976) r e c o m m e n d s a d d i n g 9 5 % of the EGTA required to r e a c h t h e e n d p o i n t , with m y low salinity samp les , I f o u n d tha t a d d i n g 9 0 % resulted in h igher a c c u r a c y . Al l c o n c e n t r a t i o n s w e r e we l l a b o v e the d e t e c t i o n limit a n d the prec i s ion w a s 0 .5% (1 a , rsd). S t andards w e r e p r e p a r e d by di lut ing IAPSO S t a n d a r d S eawa te r with DDW. Borate Borate w a s d e t e r m i n e d co lour imetr ica l ly after c o m p l e x a t i o n with c u r c u m i n (a subst i tuted B-diketone R C O C H 2 C O R , whe re R is the C 6 H 3 ( O H ) ( C H 3 0 ) C H = G H rad i ca l ) (Uppstrom 1968). Boron forms t w o different c o m p l e x e s with c u r c u m i n : rub rocu rcumin a n d rosocyan in . In this m e t h o d , rosocyan in is f o r m e d in the p r e s e n c e of strong sulphuric a c i d by the r e a c t i o n b e t w e e n bor i c a c i d a n d c u r c u m i n . The e l iminat ion of w a t e r (necessary for c o m p l e x format ion) is e f f e c t e d by p rop ion i c a c i d anhyd r i de c a t a l y s e d w i th oxa l y l c h l o r i d e . The exces s of p r o t o n a t e d c u r c u m i n is d e s t r o y e d wi th a n a m m o n i u m a c e t a t e buffer. To 0.5 mL s a m p l e , 1 mL g l a c i a l a c e t i c a c i d a n d 3 mL p rop ion i c a c i d anhydr ide we re a d d e d a n d the mixture swirled. In a f u m e h o o d , 0.25 mL oxaly l ch lo r ide w a s a d d e d d ropwise , d u e to the v iolent na ture of the r eac t i on . Af ter a l l ow ing the s a m p l e t o sit for 15 to 30 minutes to c o o l t o r o o m t e m p e r a t u r e , 3 mL su lphur i c-ace t i c a c i d r e a g e n t a n d 3 mL c u r c u m i n w e r e a d d e d a n d t h e solut ion thorough ly m ixed . The r eac t i on w a s a l l o w e d to p r o c e e d for a m in imum of 30 minutes a n d t h e n 20 mL of a m m o n i u m a c e t a t e buf fer w a s a d d e d . Af ter c o o l i n g to r o o m t e m p e r a t u r e ( a b o u t 15 m i n u t e s ) , t h e a b s o r b a n c e w a s m e a s u r e d o n a s p e c t r o p h o t o m e t e r at 545 nm in 1 c m cells. As the f inal solution was very sticky, it was important to c l e a n the cells wel l with a c e t o n e b e t w e e n samples. The d e t e c t i o n limit was 1 | iM a n d the prec is ion w a s 3% (1 a , rsd). As there w a s no salt e f f ec t (Uppstrom 1968), s tandards w e r e m a d e in DDW with H 3 B0 3 . 2.3 Results Physical Data The ox i c /anox i c in ter face in Powel l Lake occurs at app rox ima te l y 150 m d e p t h . Su r f ace waters a re we l l o x y g e n a t e d t o 25 m, b e l o w w h i c h the c o n c e n t r a t i o n of 0 2 d e c r e a s e s fairly rapidly until it b e c o m e s u n d e t e c t a b l e at 150 m (Fig. 2-4). Sulphide is first d e t e c t e d a t 150 m, but occurs at low concent ra t ions until a t 275 m its concen t r a t i on rises to a m a x i m u m of 3.1 m M in the b o t t o m water . Ch lo r ide is d e t e c t a b l e in the sur face waters of Powel l Lake (-1 m M ) , a n d gradua l ly increases t o 260 m M in the b o t t o m wa te r (Fig. 2-5), a p p r o x i m a t e l y half t he c o n c e n t r a t i o n of o p e n o c e a n wa te r . The densi ty profile mimics that of the ch lor ide . Temperature initially dec reases with d e p t h , but t hen beg ins t o rise a t t he in ter face such that the b o t t o m w a t e r at 9.4°C is wa rmer t h a n the surface was a t the t ime of sampl ing (April 1984). In Sak inaw Lake , o x y g e n rapidly increases b e t w e e n the sur face (78 u.M) a n d 10 m d e p t h (97 u.M), be fore dec l in ing sharply t o zero va lues at the ox i c/anox ic inter face at 30 m, w h e r e su lph ide is first d e t e c t e d (Fig. 2-6). H 2S increases rapid ly with d e p t h to a m a x i m u m of 5.5 m M in the bo t tom water . The m a x i m u m ch lor ide concen t r a t i on , 170 m M (Fig. 2-7), is s o m e w h a t lower t h a n that in Powel l , app rox ima te l y one-third that of o p e n o c e a n water . A g a i n , the density profile fairly mimics that of the ch lo r ide , e x c e p t in the uppe r 10 m whe re the density was significantly lower at the t ime of sampl ing ( June, 1985). A t that t ime , density var ia t ion re f l ec ted the rap id d r o p in t empera tu re in the t o p 10 m f rom 19°C a t t h e sur face t o app rox ima te l y 5 °C. The t empe ra tu r e t hen increases with d e p t h to a max imum of 9.5°C at the bo t tom of the lake. Major Ions Figs. 2-8 t o 2-13 show the concen t r a t i on profiles of the six major inorgan ic ions in Powel l Lake. The D va lues shown a re the mo lecu la r diffusivities of the ions as d e t e r m i n e d exper imenta l l y b y Li a n d G rego ry (1974) for salt diffusing into distilled wate r , a n d h a v e b e e n ad jus ted to a t empera tu re of 8°C. The o b s e r v e d (Obs.) profiles a re those ac tua l l y m e a s u r e d . The c a l c u l a t e d ( ca lc . ) curves are d e t e r m i n e d using m e a s u r e d CI* va lues a n d a s suming c o n s t a n t re la t ive c o m p o s i t i o n of s e a w a t e r . This a ssumes tha t t he e l e m e n t in ques t i on is c h e m i c a l l y conse rva t i ve a n d lost f rom the l ake v i a u p w a r d diffusion a n d export in the outf low, in the s a m e w a y as CI" (Sanderson et a l . 1986). The Dissolved o x y g e n (piM) Dissolved su lphide (mM) Fig. 2-4 Dissolved oxygen a n d sulphide c o n -centrat ions in Powell Lake. The horizontal line at 150 m represents the ox ic/anox ic interface. Fig. 2-5 Temperature, ch lor ide a n d density profiles in Powell Lake for April 1984 Fig. 2-6 Dissolved oxygen a n d sulphide c o n -centrat ions in Sakinaw Lake. The horizontal line at 30 m represents the ox i c/anox ic in te r face . S igma t Temperature ( °C ) Fig. 2-7 Temperature , chlorinity, a n d density profiles in Sakinaw Lake for July 1985 Fig. 2-8 Obse rved a n d c a l c u l a t e d concentrat ions of sodium in Powell Lake K + (mM) 1 2 3 4 5 QMj i i i i I i i i i I i i i i I i i i i I i i i i 50 100 D K = .045 m2»yr"1 2 -1 D a = .035 m »Y oxic anoxic Powell i i i i i i • i i i Fig. 2-9 Obse r ved a n d c a l c u l a t e d concent ra t ions of potassium in Powel l Lake Fig. 2-10 Obse rved a n d c a l c u l a t e d concentrat ions of magnes ium in Powel l Lake Gci (mM) Fig. 2-11 Obse r ved a n d c a l c u l a t e d concent ra t ions of c a l c i u m in Powel l Lake Borate (|j.M) Fig. 2-12 O b s e r v e d a n d c a l c u l a t e d concentra t ions of bora te in Powel l Lake Sr QxM) Fig. 2-13 Obse r ved a n d c a l c u l a t e d concent ra t ions of strontium in Powel l Lake N a + (mM) Fig. 2-14 Obse r ved a n d c a l c u l a t e d concentrat ions of sodium in Sakinaw Lake K + (mM) Fig. 2-16 Obse r ved a n d c a l c u l a t e d concentrat ions Fig. 2-17 Obse r ved a n d c a l c u l a t e d concent ra t ions of magnes ium in Sak inaw Lake of c a l c i u m in Sak inaw Lake c a l c u l a t e d a n d obse r ved concent ra t ions of sod ium a n d bora te (Figs. 2-8,2-12) are very c lose . Relat ive t o ch lo r ide , m a g n e s i u m , c a l c i u m , a n d strontium concent ra t ions (Figs. 2-10, 2-11, 2-13) a re h igher t h a n e x p e c t e d , whi le potass ium (Fig. 2-9) is lower. Sak inaw shows similar results (Figs. 2-14 t o 2-17), a l though the d i f fe rence b e t w e e n the obse rved a n d c a l c u l a t e d potass ium curves is not as p r o n o u n c e d (Fig. 2-15). 2.4 Discussion Both lakes c o n t a i n w e l l - o x y g e n a t e d sur face wa te r s , a l t h o u g h on ly Sak inaw displays a subsu r f ace o x y g e n m a x i m u m at 10 m (Fig. 2-6); this f ea tu re most likely represents O2 p roduc t i on by b looming phytop lankton at the t ime of sampl ing (July 1985). Light p e n e t r a t i o n in the uppe rmos t met re m a y h a v e b e e n g rea t e n o u g h to c a u s e inhibition of photosynthesis. A similar subsurface m a x i m u m is not seen in the Powel l Lake o x y g e n profi le p r o b a b l y b e c a u s e o x y g e n w a s m e a s u r e d in ear ly Apr i l , dur ing c o l d , rainy wea the r , whereas Sak inaw was s a m p l e d in hot. sunny July. In Powel l , the oxyc l ine is on ly a p p r o x i m a t e l y a s s o c i a t e d wi th t h e t o p of the sal ine d e e p wa te r ; s ign i f i cant ch lo r ide concen t r a t i ons o c c u r at s o m e w h a t sha l lower depths (Figs. 2-4, 2-5). The H2S a n d CI* profiles In Sak inaw mimic one another . A l though the CI" concen t r a t i on a p p e a r s to inc rease m o r e g radua l l y t h a n H 2S ( c o m p a r e Fig. 2-6 a n d Fig. 2-7), this is most likely a n ar te fac t of differing sampl ing intervals, as no CI" measurement was m a d e at 60 m. In b o t h lakes there is a subsurface t empera tu re min imum with the b o t t o m wa te r increas ing to approx imate l y 9.5°C d u e to geo the rma l hea t ing . This va lue in Powel l Lake was shown by Sanderson et a l . (1986) to b e in a p p a r e n t equil ibrium with the geo the rma l hea t flux m e a s u r e d in the south basin by H y n d m a n (1976). The density profile of Powel l c lose ly mimics that of ch lo r ide , ind ica t ing that t empera tu re plays a relatively small role in contro l l ing w a t e r stability. This is a lso true for Sak inaw, a l t h o u g h the densi ty profile dev i a t e s s ignif icantly f rom the ch lor ide in the u p p e r 5 m. This is d u e to the very large inc rease in t e m p e r a t u r e (from 8 to 19°C) o b s e r v e d dur ing the mid-summer samp l ing , w h i c h causes the s i gma t t o fall b e l o w zero. The most distinctive d i f fe rence b e t w e e n the t w o lakes is in the gene r a l shape of all their c o n c e n t r a t i o n versus d e p t h profiles. Powe l l displays very g r a d u a l c o n c a v e -u p w a r d profi les, w h e r e r ap id increases to m a x i m u m concen t r a t i ons of most spec ies o c c u r 125 - 150 m b e l o w the ox i c /anox i c in ter face (eg . Fig. 2-5). Sak inaw has a very sharp in te r face ; the density profile is a lmost s tep-shaped with m a x i m u m concent ra t ions of most spec i e s o c cu r r i ng within 45 m of the in te r face ( eg . Fig. 2-7). To exp la in this d i f f e rence , a brief discussion of the freshening process is required. The rel ict s e a w a t e r in Powe l l Lake has f r e s h e n e d c o n s i d e r a b l y s ince it was t r a p p e d a b o u t 12,000 years a g o . Assuming that the original salinity was approx imate l y tha t of present c o a s t a l w a t e r , or p e r h a p s slightly fresher d u e t o d i lut ion by g l a c i a l mettwater , the bo t tom wa te r salinity has d e c r e a s e d by a f a c to r of a b o u t 1.5. Streamflow f rom Powe l l River is substant ia l a n d w a s p r o b a b l y e v e n h igher immed i a t e l y after sill e m e r g e n c e d u e t o contr ibut ions f rom g l a c i a l melt. W h e n the lake w a s initially f o r m e d , turbulent mixing w o u l d have f lushed out the surface saltwater at the s a m e rate at wh i ch freshwater en t e r ed the system. Eventually, a surface layer of fresh wa te r overlying wate r of increas ing salinity w o u l d b e establ ished. Freshening w o u l d then con t inue more slowly b y loss of salt f rom the lower layer b y ve r t i c a l diffusion. O n c e a su r f a ce layer of essential ly zero salinity ex is ted, f reshwater enter ing Powel l Lake v i a Powel l River w o u l d t e n d t o f low over t o p of the m o r e dense wa te r b e n e a t h . There w o u l d then b e f e w if any processes with w h i c h t o mix the t w o layers of water . Be low the in ter face , a n d particularly at d e p t h , t h e ver t i ca l diffusion is so small as t o b e c o m p a r a b l e to mo lecu l a r diffusivity (Sanderson et a l . 1986). The south basin has r e a c h e d this s tage at the present t ime, with essential ly zero salinity t o a b o u t 180 m a n d a g radua l l y increas ing salt con ten t until a sharp ha loc l i ne is r e a c h e d at 275 m (Fig. 2-5). As salt diffuses into the over ly ing fresh wa te r s , it is f l ushed f rom the l ake . The four nor thernmost basins h a v e f r e s h e n e d c o m p l e t e l y , d u e t o their proximity t o the major f reshwater sou rce . Turbidity currents a s s o c i a t e d w i th s ed imen ta r y d i s c h a r g e m a y a lso h a v e c o n t r i b u t e d to the f lushing process in the basins nearer the h e a d of the lake (Williams et a l . 1961). The f reshening of Sak inaw Lake w o u l d h a v e o c c u r r e d v i a similar processes a n d the lake is currently at the s a m e s tage as Powel l . A l though freshwater input to Sak inaw is m u c h l owe r , t h e l ake has f r e s h e n e d m o r e d u e t o its c o n s i d e r a b l y smal le r size. Therefore, why is there such a large d i f fe rence in the s h a p e of its chlorinity profile ( and in f a c t , all its major ion profiles)? To expla in this, the processes invo lved in ver t ica l diffusion must b e d iscussed further. Ver t i ca l diffusion inc ludes bo th e d d y a n d m o l e c u l a r diffusion. Unlike the latter, e d d y diffusion requires s o m e input of kinetic ene rgy to the system. Most of the ene rgy input t o Powel l Lake w o u l d o c c u r at the surface. As the energy p r o p a g a t e s d o w n w a r d it is part ia l ly d i s s i pa t ed , l e a d i n g t o lower e n e r g y levels a n d less d iss ipat ion a n d e d d y dif fusion a t g r ea t e r dep ths . In the unstrat i f ied f reshwater layer , ve r t i ca l overturning a s s o c i a t e d with c o o l i n g at the sur face dur ing winter p r o b a b l y cont r ibutes to ver t i ca l e d d y diffusivity. Dur ing t h e D e c e m b e r t o February p e r i o d , t he month l y m e a n air t empe ra tu re ( a v e r a g e d ove r 1951 - 1980) a t Powel l River airport (4 km southeast of the lake) w a s b e l o w 4 °C , t he t empera tu re of m a x i m u m density of freshwater. This denser w a t e r will sink, l e a d i n g d i rect ly t o l a rge ve r t i ca l e d d y diffusivities in the unstratif ied sur face layer. Strat i f icat ion at d e p t h prevents this ver t i ca l mixing f rom pene t ra t ing far into the ha loc l i ne . Howeve r , t he overturning c o u l d g e n e r a t e internal w a v e s as sinking parce ls of wa te r b o u n c e against the ha loc l ine (Sanderson et al . 1986), a n d these internal w a v e s c o u l d in turn c a u s e mixing in the stratified region. Nea r the sur face , mixing d u e to sur face gravity w a v e s must o c c u r , but this ene rgy w o u l d d e c a y with d e p t h long be fore the in te r f ace w o u l d b e r e a c h e d . A rough c a l c u l a t i o n g i ven a 15 km f e t c h , a 2 hour durat ion a n d 10 m^s"1 w i n d s p e e d indicates that the w a v e amp l i tude w o u l d d e c a y to < 1 c m b y approx ima te l y 15 m d e p t h . Therefore, in the stratified layer a n y mixing that c o u l d o c c u r will b e re l a ted t o internal w a v e s rather t h a n sur face gravity waves . There is a n add i t i ona l source of turbulent energy assoc i a t ed with the b o t t o m bounda ry , such that a l o c a l inc rease in e d d y diffusion occurs . This thin layer at t he b o t t o m has little e f fec t o n t h e net ra te of salt loss f rom the sal ine layer , w h i c h is con t ro l l ed by t h e diffusivity min imum w h i c h lies wel l a b o v e the bo t tom diffusion layer (Sanderson et a l . 1986). A t d e p t h , t he re fo re , e d d y dif fusion is virtually nonex is tent , a n d t h e ve r t i ca l diffusivity is so smal l tha t it is c o m p a r a b l e t o the m o l e c u l a r diffusivity. S ince different c h e m i c a l s p e c i e s h a v e con t r as t i ng m o l e c u l a r diffusivit ies, t h e y shou ld di f fuse a t different rates a n d thus b e lost f rom the b o t t o m waters t o different degrees . In f a c t , the ratios of t h e major i on i c const i tuents in the b o t t o m w a t e r of b o t h lakes d o differ c o n s i d e r a b l y f rom those f o u n d in m o d e r n s e a w a t e r (Figs. 2-6 t o 2-17). Before the reasons for these distributions are d iscussed , the d i f fe rence b e t w e e n the gene ra l shape of the Powel l a n d Sak inaw ion profiles must b e exp l a ined . The processes w h i c h contr ibute t o vert ica l diffusion in Sak inaw will be the s a m e as those in Powe l l , as b o t h lakes, b e i n g c lose toge the r , a re subject t o essentially the s a m e w i n d reg ime. M o l e c u l a r diffusion is the dominan t process as is cha rac te r i sed by a strong c h e m o c l i n e , w h i c h is s i tuated fairly nea r the ox i c /anox i c in te r face in Sakinaw. The l ack of c o n c e n t r a t i o n g rad ien t th roughout most of the lower a n o x i c wa te r c o l u m n ind i ca tes tha t e d d y diffusion processes a re important in this reg ion. A n y energy input f rom t h e su r f a ce w o u l d t e n d t o mix the c h e m o c l i n e , so the d i s t u r b a n c e must b e g e n e r a t e d at d e p t h . A likely c a u s e of the mixing is f rom input of d e n s e , saline wate r at d e p t h . This w o u l d h a p p e n if s eawa te r f rom the Strait of G e o r g i a w a s to enter Sak inaw ove r the ba re l y e m e r g e d sill. The denser w a t e r w o u l d f low into the bas in , entra in some fresh wa te r f rom the surface layer, sink a n d mix with the bo t tom wate r in the d e e p anoxic bas in . This process w o u l d ef fect ive ly bunt the c h e m o c l i n e (wh ich h a d b e e n establ ished th rough mo l e cu l a r diffusion processes) upwards in the wa te r c o l u m n (B. Sanderson , P.H. LeB lond pers. c o m m . ) , resulting in uni form, m ixed wa te r be l ow the thermoc l ine . The ratios of the major ionic constituents in the b o t t o m wa te r of bo th lakes differ cons i de r ab l y f rom those f o u n d in m o d e r n seawate r . Those ions wi th l a rge m o l e c u l a r diffusivities are lost more rapidly f rom the d e e p wa te r t h a n those with smaller diffusion coef f ic ients . The m o l e c u l a r diffusivities (D) of six major ions in Powel l Lake are shown o n the co r r e spond ing c o n c e n t r a t i o n profiles in Figs. 2-8 to 2-13. As w o u l d b e p r e d i c t e d by their diffusivities, concen t ra t ions of M g 2 + , C a 2 + a n d Sr+ a re en r i ched relative to CI", w h e n c o m p a r e d to m o d e r n s eawa te r (Figs. 2-8. 2-10. 2-11). The diffusivities of these ions are tower than that of CI" a n d therefore they diffuse at a slower rate. K +. converse ly , diffuses, faster than C f a n d is relatively d e p l e t e d in the b o t t o m wa te r (Fig. 2-9). N a + has a diffusion coef f i c ient e q u a l t o that of CI", a n d the o b s e r v e d a n d c a l c u l a t e d profiles a re virtually i den t i c a l . A diffusion coe f f i c i en t c o u l d not b e f o u n d for b o r a t e ; f rom Fig. 2-12 a n d assuming conse rva t i ve behav i ou r , it w o u l d b e p r e d i c t e d t o b e similar t o tha t of CI*. Sak inaw Lake (Figs. 2-14 to 2-17) shows similar behav iour . M o l e c u l a r diffusion m a y not b e the only process o p e r a t i n g , however . No te that M g 2 + a n d C a 2 + h a v e iden t i ca l diffusivities a n d yet C a 2 + is m u c h more e n r i c h e d in the b o t t o m wa te r t h a n M g 2 + . Similar results were o b t a i n e d for Sak inaw (Fig. 2-16). Apparen t l y , s o m e c h e m i c a l p rocess t ha t c a u s e s ex t ra e n r i c h m e n t of C a 2 + (or p e r h a p s under-enr i chment of M g 2 + ) is ope ra t i ng in bo th lakes. A par t i cu la te c a l c i u m m a x i m u m occurs at t he redox in ter face in F ramvaren . a n d is at t r ibuted to bac te r i a l u p t a k e (Anderson et a l . 1987). B a c t e r i a c a n b i n d ca t i ons , inc lud ing c a l c i u m ion , v i a adso rp t i on o n t o the sur face , b ind ing t o proteins, e t c . (Lalou 1957; Mor i ta 1980), a n d d e a d cells c a n take u p as m u c h c a l c i u m as living cel ls (Greenf i e ld 1963). In F r amva ren , c a l c i u m is "released at d e p t h d u e t o d e g r a d a t i o n of t h e b a c t e r i a l ce l ls . This c a u s e s e l e v a t e d c a l c i u m concen t r a t i ons in the b o t t o m wa te r , a n d promotes c a l c i t e p rec ip i ta t ion . Bac te r i a a re p r o b a b l y c o n c e n t r a t e d a t the in ter face in Powel l a n d Sak inaw as we l l , so that similar processes m a y c a u s e the enr i chment of c a l c i u m in the b o t t o m w a t e r of these lakes. C o m p a r i s o n of t he m a x i m u m ion concen t ra t i ons (those in t h e b o t t o m wate r ) , a n d the pe r cen t d i f ferences b e t w e e n the obse r ved a n d the c a l c u l a t e d va lues for C a 2 + , M g 2 + a n d K + (Table 2-1), show that m u c h larger d i f fe rences exist in Powe l l relat ive t o Sak inaw Lake . This is further e v i d e n c e tha t there has b e e n s e a w a t e r input to Sak inaw s ince sill e m e r g e n c e , as the mixing of m o d e r n seawa te r with relict s eawa te r w o u l d t e n d to push the major ion compos i t ion of the d e e p wa te r c loser to that of m o d e r n seawater . Table 2-1 Deviations of observed bottom water major ion concentrations from those calculated from chlorinity assuming constant relative composition of seawater. Ion Powell Lake Sakinaw Lake C a 2 + + 4 6 % + 2 5 % M g 2 + + 9 . 3 % + 7 . 6 % K + - 2 . 2 % - 1 . 9 % In summary , b o t h lakes c o n t a i n relict s e a w a t e r a t d e p t h w h i c h has f r eshened cons ide r ab l y , primarily b y m o l e c u l a r diffusion. The d i f f e rence in the g e n e r a l s h a p e of the major ion profiles b e t w e e n Powel l a n d Sak inaw Lakes is most likely d u e to incursion of s e a w a t e r t o the d e e p waters of Sak inaw s ince it w a s s e p a r a t e d f rom the Strait of G e o r g i a . CHAPTER 3 REDOX CHEMISTRY 3.1 Introduction In pure ly i n o r g a n i c c h e m i c a l systems, ox ida t ion-reduc t ion ( redox) reac t ions p r o c e e d wi th a f l ow of e l ec t rons b e t w e e n the ox id i zed a n d r e d u c e d states until equi l ibr ium is a t t a i n e d . A l t h o u g h there is a t e n d e n c y for the r e d u c e d p h a s e to lose e lec t rons a n d b e t r ans fo rmed t o a n ox id ized state , free e lec t rons usually inhibit this process , such that la rge quantit ies of f ree ion c a n exist t oge the r in b o t h r e d u c e d a n d ox id ized states. True redox equi l ibr ium d o e s not ac tua l l y exist in a n y natura l a q u a t i c sys tem b e c a u s e most r e d o x r e a c t i o n s a r e ex t r eme l y s low in t h e a b s e n c e of a p p r o p r i a t e b i o c h e m i c a l catalysis. On ly a f e w e lements - C , N, O , S, Fe, M n , H - are impor t an t pa r t i c i pan t s in a q u a t i c r edox p rocesses b e c a u s e they exhibi t mul t ip le v a l e n c e states, a n d h e n c e c a n unde rgo ox idat ion a n d reduct ion . As n o t e d in C h a p t e r 2, the l imnology of Powel l a n d Sak inaw Lakes is d o m i n a t e d by pe rmanen t stratif ication w h i c h is a s s o c i a t e d with a p r o n o u n c e d d e c r e a s e in the Eh with d e p t h . In this c h a p t e r , s u c h redox var iat ions will b e r e v i e w e d , a n d their i m p o r t a n c e in lake chemistry will b e d i s c u s s e d . Photosynthesis, b y t r app ing light ene rgy a n d conve r t ing it t o c h e m i c a l energy , p r o d u c e s r e d u c e d states of higher free energy (high-energy c h e m i c a l bonds) a n d thus nonequi l ibr ium concent ra t ions of C . N, a n d S c o m p o u n d s (Stumm a n d M o r g a n 1981). In cont ras t t h e respiratory , f e r m e n t a t i v e , a n d o ther n o n p h o t o s y n t h e t i c p rocesses of o rgan i sms t e n d to restore equ i l ibr ium by ca t a l y t i c a l l y d e c o m p o s i n g the uns tab le p roduc ts of photosynthesis th rough energy-yielding redox reac t ions , t he reby ob ta in ing a sou r ce of e n e r g y for their m e t a b o l i c needs . The organisms use this e n e r g y bo th to synthesize n e w cells a n d to mainta in the o ld cells a l r eady f o r m e d . These organisms are primari ly built u p f rom " redox e lements " , a n d their relat ively c o n s t a n t s to i ch iomet r i c c o m p o s i t i o n (CiooFbttOnoNuP) (Redf ie ld et al.1963) a n d the c y c l i c e x c h a n g e b e t w e e n c h e m i c a l e l e m e n t s of t he w a t e r a n d the res ident o rgan isms a f f e c t s t h e re lat ive c o n c e n t r a t i o n s of t h e e l emen t s in t h e env i ronment . Thus, t h e b i o l o g i c a l l y a c t i v e e lements c i rcu late in a pattern different to that of the wate r itself or t o that of the inact ive , i.e., conse rva t i ve , solutes. Organisms a c t as redox catalysts by med i a t i ng the react ions a n d transfer of e lectrons; the organisms themselves d o not oxidize substrates or r e d u c e c o m p o u n d s (Wetzel 1983). At t h e t e m p e r a t u r e . Eh, a n d pH of natura l wa te rs , a n d a t t h e r m o d y n a m i c equ i l ib r ium, on ly a small n u m b e r of c o m m o n dissolved spec i es m a k e u p almost all of the to ta l c a r b o n , n i t rogen, sulphur, h yd rogen , a n d o x y g e n in a q u e o u s solution. They are Haaq). Oaog), ChUaq), COf , H C C i H2CO3. NH 3 , Nh& N2.NO3", H£lOQ). HS', a n d SO4 (Thorstenson 1970). A l l o t h e r s p e c i e s , s u c h as S2O32* a n d NO2. a r e p resen t a t m u c h l owe r concent ra t ions . In a e r o b i c sur face waters ( P 0 2 > 10"4 a tm) a n d most b o t t o m waters, the pr inc ipa l spec ies in equi l ibr ium with the a tmosphe re at neutral pH should b e HCO3, N 0 3 a n d SO4 The f e w excep t ions inc lude b o t t o m waters of some meromic t i c lakes, a n d of restr icted o c e a n basins, s u c h as the B lack S e a or F ramvaren fjord. The p r e d o m i n a n t d isso lved spec i e s a c tua l l y f o u n d in a e r o b i c waters a re HCO3, SO4, a n d N 2 . Dissolved NO3 is relat ively minor , e v e n t h o u g h , a c c o r d i n g t o t h e r m o d y n a m i c cons idera t ions , it should b e m u c h more a b u n d a n t t h a n N 2 . B i o g e o c h e m i c a l react ions involv ing n i t rogen w o u l d s e e m to result in a steady-state c o n c e n t r a t i o n of dissolved N 2 in a e r o b i c wa te r w h i c h is far higher t han that p r e d i c t e d for t h e r m o d y n a m i c equil ibrium (Wetzel 1983). A n a e r o b i c waters (P02 < 10"4 a tm) are usually only f o u n d in the interstitial s p a c e s of sediments ; a e r o b i c waters a re of ten under la in by a n a e r o b i c sediments. The lack of d isso lved 0 2 in s u c h sed iments is d u e t o the ox ida t ion of o r g a n i c mat te r b y a e r o b i c m ic roorgan i sms w h i c h h a v e a h igh m e t a b o l i c rate a n d h e n c e use u p o x y g e n very quick ly . The a e r o b i c b a c t e r i a live o n or nea r t he sed imen t su r f a ce , a n d by utilizing o x y g e n faster t h a n it c a n diffuse f rom a b o v e , prevent it f rom diffusing into the sediment . This c a n only o c c u r if d e g r a d a b l e o rgan i c mat ter is supp l ied to the sed iment faster t han it c a n b e des t royed by a e r o b i c ox ida t ion , a n d typ ica l ly occu r s in regions of extremely h igh product iv i ty or in low ene rgy environments whe re o r g a n i c mat ter is not cont inual ly r e s u s p e n d e d a n d r e m o v e d b y currents. The b o t t o m waters of m e r o m i c t i c lakes are a n a l o g o u s t o the latter: there is little w a t e r m o v e m e n t a n d so n o a d v e c t i v e o x y g e n r ep l en i shment . In s u c h systems, d e c o m p o s i t i o n of o r g a n i c m a t t e r b y a e r o b e s is restricted to the ox ic port ion of the wate r c o l u m n , through wh i ch o rgan i c matter settles. O n c e d i sso l ved O2 is r e m o v e d , a n y further ox ida t i on of o r g a n i c mat te r b y b a c t e r i a must o c c u r b y the util ization of other oxidants . These i nc lude NO3". SO4 a n d 28 ox id ized o r g a n i c spec ies . A s s o c i a t e d redox reac t ions t e n d to o c c u r in o rde r of their t h e r m o d y n a m i c favourabi l i ty a n d a re listed in Table 3-1. Table 3-1. Oxidation reactions of organic matter (from Froelich et al. 1979) 1. A e r o b i c D e c o m p o s i t i o n (CH2O),06(NH3)i6(H3PO4) +138C-2 -> IO6CO2+ I6HNO3 + H3PO4 +122H20 A 3 . = -3190kJ»mor1 2. M a n g a n e s e reduc t ion (CH2O),06(NH3)i6(H3PO4) + 2 3 6 M n a + 472H + -> 236Mn 2 + + IO6CO2 + 8N2 + HPOA + 366H 2 0 ASo = -3090 Id • mor 1 (birnessite) 4Go = -3050 kJ • mol" 1 (nsutite) &o = -2920 kJ • mol" 1 (pyrolusite) 3. Denitrification a n d nitrate reduct ion (CH2O)i06(NH3)16(H3FO4) + 94.4HN0 3 -> 106CO2 + 55.2N2 + H3FO4 + 177.21^0 =-3030 k > mol" 1 (CH2O)i06(NH3))6(H3PO4) + 84.8HNO3 -> 106CO2 + 42.4N2+I6NH3 + H3PO4 + I48.4H2O 4. Iron reduct ion (CH2O)i06(NH3)i6(H3PO4) + 212Fe203 + 848H + -» 424Fe 2 + + IO6CO2 + I6NH3 + H3PO4 + 530H 2O A S = -1410 kJ • mol" 1 (hematite) A3j = -1330 kj-mol" 1 (limonitic goethite) 5. Su lphate reduc t ion (CH2O),06(NH3),6(H3PO4) + 53S04 -> 106CO2 + I6NH3 + 53S2" + H3PO4 +106H2O /5<Si = -380kJ»mor1 6. Fermentat ion ( C H Z O I M O M H ^ ^ ^ P O A ) - > 530O2 + 53CH4 + I6NH3 + H3PO4 ^ 3 = -350kJ«mor1 Reac t i on 1 occu r s in a e r o b i c environments. 2 - 4 in suboxic zones , a n d react ions 5 a n d 6 u n d e r a n o x i c cond i t i ons . Thus, fo l low ing O2 d e p l e t i o n , t he succes s i on of b a c t e r i a l p rocesses in natura l waters (pH -7) is nitrate a n d m a n g a n e s e r e d u c t i o n , f o l l o w e d b y iron a n d su lpha te r e d u c t i o n plus a m m o n i u m f o r m a t i o n , a n d f inal ly , m e t h a n e f o r m a t i o n . This results in t h e f o l l ow ing fair ly p r e d i c t a b l e s e q u e n c e of coex i s t ing d i sso lved spec i e s : D H C C i + S C M + NO", 2) H C Q 3 + S C M +N2 3) HCO", +HS" +NI-C 4) CH4 + HS" +NHI. Observa t ions of mar ine sed iments show that the compos i t ions of po re waters a re in g e n e r a l a g r e e m e n t wi th these pred ic t ions a l t h o u g h spec i f i c excep t i ons o c c u r (e.g. Froelich et a l . 1979). The o c c u r r e n c e of these react ions in natura l sed iments is not l imited to well-d e f i n e d d e p t h intervals within the sed iment c o l u m n . Ove r l ap is c o m m o n . The reduc t ion of NO3 a n d M n 0 2 , for e x a m p l e , h a p p e n s at a b o u t the s a m e pE levels a n d there fore concurrent ly in the sed iment c o l u m n (Stumm a n d M o r g a n 1981). In add i t ion , b ioturbat ion ( G o l d h a b e r et a l . 1977, Berner a n d Westr ich 1985) a n d dif fusion t e n d to blur the boundar i es of these redox processes within the sed iment c o l u m n . In me romic t i c lakes, this series of redox react ions is sp read throughout the wate r c o l u m n a n d h e n c e c a n b e more easi ly o b s e r v e d t h a n in sed iments , whe re the r eac t ion series shown in Table 3-1 is t yp ica l l y c o m p r e s s e d . In sulphide-rich waters the ch ie f spec ies a n t i c i p a t e d (at pH ~7) are H C O 3 , N H 4 , HS", H2S, C H 4 , a n d N 2 . The chemistry of c a r b o n a n d n i t rogen is c o m p l e x , a n d will b e d e s c r i b e d briefly in the fo l low ing t w o sect ions . Sulphur spec i e s will b e d iscussed in a subsequent chap t e r . Carbon The sources a n d compos i t i on of o rgan i c mat ter in natural waters a n d sediments are diverse a n d poor ly unders tood . Near ly all of the o r g a n i c c a r b o n of natura l waters consists of d isso lved o r g a n i c c a r b o n ( D O C ) a n d d e a d pa r t i cu l a t e o r g a n i c c a r b o n ( P O C ) ; l iving b i o t a m a k e u p a very smal l f r a c t i on of the to ta l P O C , a l t h o u g h their me tabo l i sm results in reversible fluxes b e t w e e n the dissolved a n d par t i cu la te phases of detr i ta l c a r b o n . P roduc t i on of d issolved a n d par t i cu la te o r g a n i c c a r b o n is a result of au to t roph i c a n d hetero t roph ic metabo l i sm. Instantaneous measurements of D O C a n d P O C a re highly b i a s e d t o w a r d refractory c o m p o u n d s that a re relat ively c h e m i c a l l y s t ab le , of low solubility, a n d resistant to r ap id (days t o weeks ) m ic rob ia l d e g r a d a t i o n . These ref ractory c o m p o n e n t s of detr i tal o r g a n i c c a r b o n persist for l onger per iods of t ime t h a n the m o r e labi le o r g a n i c c o m p o u n d s . Howeve r , the readi ly uti l izable labi le c o m p o n e n t s c y c l e rap id ly at low equi l ibr ium c o n c e n t r a t i o n s , a n d represent major c a r b o n p a t h w a y s a n d e n e r g y fluxes. Lake waters a re relat ively stat ic c o m p a r e d to most o c e a n i c env i ronments , a n d thus s ed imen ta t i on transfers a g r ea t e r por t ion of c a r b o n a n d its a s soc i a t ed metabo l i sm to the sediments (Val lentyne 1962, Wetze l et a l . 1972). A l l o c h t h o n o u s sources of o r g a n i c mat te r t o a q u a t i c systems a re primarily of terrestrial p lant origin a n d the D O M of surface runoff is c o m p o s e d of relatively refractory o rgan i c c o m p o u n d s resistant to rap id mic rob ia l d e g r a d a t i o n . Most c a r b o n of natura l waters occu r s as equi l ibr ium produc ts of c a r b o n i c a c i d (H2CO3). Ox id ized c a r b o n , i.e. tota l C 0 2 ( I C 0 2 = C 0 2 + H C 0 3 + CO3"). is a d d e d to natural waters by a t m o s p h e r i c e x c h a n g e , l e a c h i n g of c a r b o n a t e f rom soils or rocks, a n d by the b io l og i ca l d e c o m p o s i t i o n of o rgan i c matter. It c a n b e r e m o v e d v i a photosynthesis a n d mineral prec ip i ta t ion. A t m o s p h e r i c C 0 2 dissolves in w a t e r a n d unde rgoes hydrolysis t o form c a r b o n i c a c i d (at pH < 8.5): CO2 (air) <-> C 0 2 (dissolved) + H 2 0 <-» H 2 C 0 3 . H 2 C 0 3 is a w e a k a c i d (pK= 16.30) (More l 1983). a n d rap id ly part ia l ly d issoc ia tes to b i c a r b o n a t e a n d c a r b o n a t e ions: hfeCQs <-» H + + H C 0 3 «-> H + + C O ! . At equ i l ib r ium, hydroxyl ions (OH") a re f o r m e d by the hydrolysis of b i c a r b o n a t e a n d c a r b o n a t e ions: HCO3 + H2O <-> HzCQj + OH" CO?+ H2O <-> HCO3+OH" hbCQj <-> HzO + COz. C a r b o n a t e s a re so lub i l i zed as c a r b o n i c a c i d p e r c o l a t e s t h r o u g h soils a n d rocks , releasing dissolved C a 2 + a n d HCO3. Slightly greater concent ra t ions of OH" ion t han H + ion result f rom the dissociat ion of H C O 3 . C O 3 . a n d H2CO3 a n d h e n c e m a n y fresh waters a re weak l y a lkal ine (Wetzel 1983). The ox ida t ion of o rgan i c c a r b o n by the respiration of b o t h b a c t e r i a a n d higher organisms a d d s C 0 2 t o a e r o b i c waters: e.g.GHsCfc +6a-*6CCb +6H2O AGo = -3190kJ»mol"1. B e c a u s e CO2 forms a w e a k a c i d , H 2 C 0 3 , the e f f e c t of a e r o b i c d e c o m p o s i t i o n is to c a u s e a l owe r i ng of pH . In a n a e r o b i c env i ronments in w h i c h n i t ra te , iron a n d m a n g a n e s e ox ides a n d su lphate a re d e p l e t e d , o r g a n i c c a r b o n c a n n o t b e oxid ized with O2 a n d is instead d e c o m p o s e d by the oxygen c o n t a i n e d within the o rgan i c matter itself by m i c rob io l og i c a l fe rmentat ion : e.g. C6HcO6^3C02+3CH4 *Gi = -35Q\dTno\'\ The grea te r ene rgy y ie ld for a e r o b i c ox ida t ion results in more eff ic ient me tabo l i sm , a n d thus faster o rgan i c matter de compos i t i on relative t o that of fermentat ion. The a m b i e n t pH a s s o c i a t e d with a n a e r o b i c f e rmen ta t i on d e p e n d s u p o n the a m o u n t s of CO2 ( a n d o r g a n i c ac ids ) f o r m e d relat ive t o the amounts of n i t rogenous bases r e l e a sed . The t o p f e w cen t imet res of a n a e r o b i c sed iments genera l l y h a v e a lower pH t h a n over ly ing a e r o b i c waters , ind i ca t ing that f e rmenta t i on react ions (plus su lphate reduct ion) result in net a c i d p roduc t ion (Berner 1971). Very low va lues of pH (< 5) h a v e b e e n f o u n d in s w a m p s a n d bogs d u e t o fe rmenta t ion of o r g a n i c c o m p o u n d s tha t a re low in n i t rogen (e .g . , l ignin a n d ca rbohyd ra t e s ) . In these env i ronments , no C a C 0 3 or o ther b a s i c minerals a r e present t o buffer the pH a n d neutral ize excess c a r b o n i c a n d other ac ids . Bes ides f e r m e n t a t i o n , m e t h a n e m a y a lso fo rm by the r e d u c t i o n of c a r b o n d i o x i d e using e i ther H2 or a w i d e var ie ty of o r g a n i c h y d r o g e n donors as r e d u c i n g a g e n t s : e.g. C O 2 + 4 H 2 - > C l - U + 2 H 2 O . The source of C 0 2 is usually a n earlier fe rmentat ion reac t ion (Brock 1979). Bacter ia l su lphate reduct ion results in the net format ion of b i c a r b o n a t e ion rather t h a n CO2, b e c a u s e a d iva lent ion , SOt. is c o n v e r t e d t o the m o n o v a l e n t ion HS" or a neut ra l d i sso l ved s p e c i e s , H 2S, a n d the c h a r g e b a l a n c e must b e m a i n t a i n e d . The b a c t e r i a (e .g . Desulfovibrio spp,) utilize o r g a n i c c a r b o n as a r e d u c i n g a g e n t a n d the resulting CO2 supplies the required negat i ve c h a r g e in the form of HCO3 ion: 2CH2O + S0 2 " -> 2HCa + H2S or 2CH2O + SO4 -» HCO3+ HS" + CO2 + H2O. W h e r e a s in waters b e l o w the pho t i c z o n e there is a net p r o d u c t i o n of C 0 2 , resulting in a lower p H , in sur face waters CO2 c a n b e c o n s u m e d v i a photosynthesis by phy top l ank ton : 6CO2 +6H2O <-> C6H 1 2a +6O2. This process c a n of ten l e a d to d r ama t i c increases in pH (Wetzel 1983). Both sulphate reduct ion a n d photosynthesis c a n foster CaCG-3 prec ip i ta t ion. If the solution of c a l c i u m b i ca rbona te in equilibrium with C O 2 . H2CO3. a n d C O f loses a port ion of the C O 2 r equ i r ed t o m a i n t a i n the equ i l i b r ium, s u c h as b y p h o t o s y n t h e t i c u p t a k e e x c e e d i n g r e p l a c e m e n t of C 0 2 , or b y H C O 3 f o rma t i on in su lpha te r e d u c t i o n , t he relatively insoluble c a l c i u m c a r b o n a t e will p rec ip i ta te : CcKHCC^? «-* C a C O s + H ^ + C C ^ , until the equi l ibr ium is reestab l ished by the fo rmat ion of sufficient C 0 2 (Kelts a n d Hsu 1978). As CaCC>3 forms a n d p rec ip i t a t e s , i no rgan i c (e .g . , P C M ) ions a n d o r g a n i c c o m p o u n d s c a n adso rb to or cop re c i p i t a t e with the C a C 0 3 a n d are ca r r i ed out of the t r o p h o g e n i c z o n e of l akes , w h i c h m a y result in r e d u c e d m e t a b o l i c ac t i v i t y . M a i n t e n a n c e of supersaturat ion without prec ip i ta t ion , howeve r , m a y o c c u r d u e to the inhibiting e f fec t u p o n crystallization of dissolved o rgan i c matter (Suess 1970). Losses of C 0 2 b y pho tosyn the t i c uti l ization or add i t i ons of C 0 2 f rom b io t i c respirat ion t e n d t o c h a n g e the pH of the wate r . The buffer ing a c t i o n of t he wa te r , howeve r , t ends t o resist c h a n g e s in pH as long as the equi l ibr ia of the C 0 2 system are ope ra t i ona l . A d d i t i o n of H + ions is neutra l ized b y OH" ions f o r m e d b y the hydrolysis of H C 0 3 a n d C 0 3 . The pH remains essential ly t he s a m e as b e f o r e , unless t he supply of H C 0 3 a n d C 0 3 is e x h a u s t e d . Similarly, a d d e d O H " ions r e a c t with HCO ' 3 ions t o fo rm c a r b o n a t e : HCO3 +OH" ^ C O t +H20. Nitrogen The e l e m e n t n i t rogen , a key const i tuent of p r o t o p l a s m , exists in a n u m b e r of ox ida t ion states, r ang ing f rom -3 (organ ic N (R-NH2), N H 3 a n d NHl ) t o 0 (N^ , +1 (N 20),+3 (NO2), a n d + 5 (N0 3 ) . In the porewate rs of fully a n o x i c mar ine sed iments , t he pr inc ipa l spec ies are N 2 a n d N H l (Thorstenson 1970; Rit tenberg et a l . 1955). The lack of nitrate a n d nitrite is d u e to rap id bac te r i a l r educ t ion of these spec ies to N 2 a n d N H 4 . Fig. 3-1 shows the redox c y c l e for n i t rogen. Most of the key redox react ions of ni trogen a re car r ied out in nature a lmost exclusively b y microorganisms. N i t rogen m a y enter a lake as dissolved N 2 . nitric a c i d , N H 4 . N O 3 . a s NH4 a d s o r b e d to inorganic part icu late matter , a n d as o rgan i c c o m p o u n d s , w h i c h c a n o c c u r in either dissolved or par t i cu la te phases (Wetzel 1983). T h e r m o d y n a m i c a l l y , N 2 is t h e most s tab le form of n i t rogen, a n d it is t o this form that n i t rogen will revert under equi l ibr ium condit ions. H e n c e the major reservoir for ni trogen o n ear th is the a tmosphere . The dissolved o rgan i c n i t rogen (DON) of fresh waters o f ten constitutes over 5 0 % of t he to ta l soluble n i t rogen (Wetzel 1983). G e o g r a p h i c var ia t ion is g rea t , howeve r , in relat ion to inputs of inorgan ic ni t rogen from natural a n d artificial sources. Ove r one-half of the D O N is in the form of a m i n o nitrogen c o m p o u n d s , of wh i ch abou t two-thirds is in the fo rm of p o l y p e p t i d e s a n d c o m p l e x o r g a n i c c o m p o u n d s , a n d less t h a n one-third occu r s as free a m i n o ni trogen (Wetzel 1983). Ammonification (Deamination) A m m o n i u m is g e n e r a t e d primarily by hetero t roph ic b a c t e r i a as a pr imary e n d p roduc t of d e c o m p o s i t i o n of o rgan i c matter , e i ther direct ly f rom proteins or f rom other n i t rogenous o r g a n i c c o m p o u n d s . Intermediate n i t rogen c o m p o u n d s a re f o r m e d in the progress i ve d e g r a d a t i o n of o r g a n i c m a t e r i a l , but rarely a c c u m u l a t e , b e c a u s e d e a m i n a t i o n b y b a c t e r i a p r o c e e d s rapidly. A l t hough a m m o n i u m is a major excretory p roduc t of a q u a t i c an imals , this n i t rogen source is quant i tat ively minor in compa r i son to that g e n e r a t e d b y bac te r i a l d e c o m p o s i t i o n (Wetzel 1983). S ince NO3" must b e r e d u c e d to NI-£ be fo re it c a n b e assimi lated by plants, a m m o n i u m is a n energy-eff ic ient source of n i t rogen for plants. Therefore, very low concen t ra t ions of N H l are genera l l y f o u n d in su r f a ce o x y g e n a t e d wate rs , as the ion is preferent ia l ly t a k e n u p by p h y t o p l a n k t o n . W h e n a p p r e c i a b l e amoun t s of sed iment ing o r g a n i c mat ter r e a c h the hypo l imn ion of stratified lakes, NH4 c a n a c c u m u l a t e . Under a n a e r o b i c cond i t ions , bac te r i a l nitrification of NH4 to N02" a n d N O 3 c e a s e s . Nitrogen Fixation A smal l n u m b e r of organisms (primarily t he photosynthet i c c y a n o b a c t e r i a ) a re a b l e t o f ix' n i t rogen a n d r e d u c e it t o a m m o n i u m . Howeve r , a m m o n i u m f o r m e d in this Fig. 3-1 The redox c y c l e of n i t rogen (from Brock 1979) m a n n e r w o u l d b e far less a b u n d a n t t han that f o rmed by the d e c o m p o s i t i o n of originally-d e p o s i t e d o r g a n i c n i t rogen c o m p o u n d s . O r g a n i c n i t rogen in a n a e r o b i c sediments is genera l l y ove r a t h o u s a n d t imes more a b u n d a n t t h a n d issolved N 2 ( a n d N03~) (Berner 1971). Nitrate Reduction and Denrtrification As ni trate is ass imi l a ted b y a l g a e a n d larger h yd rophy t e s , it is r e d u c e d to a m m o n i u m . As m u c h as 6 0 % of the p h o t o a s s i m i l a t e d NO3" c a n b e e x c r e t e d as dissolved o r g a n i c n i t rogen c o m p o u n d s , s o m e of w h i c h are s imple a m i n o a c i d s readi ly util ized b y b a c t e r i a ( C h a n a n d C a m p b e l l 1978). In lakes a n d o c e a n s , nitrate assimilation c a n great ly e x c e e d sources of i n c o m e a n d regenera t ion , in some cases t o the point of reduc ing NO3 t o b e l o w d e t e c t a b l e concentra t ions . In sed iments , t w o major p a t h w a y s of NO3" dissimilatory r e d u c t i o n h a v e b e e n ident i f ied: deni t r i f i cat ion a n d "nitrate ammon i f i c a t i on " (NO3" r e d u c t i o n t o NH4). Whi le some of the contro l l ing factors h a v e b e e n ident i f ied for the t w o processes , a d e t a i l e d unde r s t and ing of the b a c t e r i a l g roups involved- their mutua l in teract ions , a n d their e c o l o g i c a l s i gn i f i c ance in natura l sed iments is still l a ck i ng (S0rensen 1987). "Nitrate a m m o n i f i c a t i o n " , w h i c h has b e e n r e c o g n i z e d rather r ecen t l y , s eems t o b e most important in organic-r ich a n d relatively r e d u c e d sediments. The first e v i d e n c e for s ignif icant NO3" dissimilation t o N H l w a s o b t a i n e d in a n organic-r ich a n d relatively r e d u c e d sed iment (Koike a n d Hattori 1978; S0rensen 1978). The "nitrate ammon i f i c a t i on " pa thway : NO3 -* NO2 -> NH4 w a s original ly o b s e r v e d in fe rment ing b a c t e r i a (Hasan a n d Hall 1975). These c o u l d use NO3 or NO2 as "e lec t ron sinks" t o reoxidize N A D H , but wi thout a d i rec t c o u p l i n g to ATP p r o d u c t i o n (as in t rue ' deni t r i f i cat ion) (Cole a n d Brown 1980). The reduc t ion step from NC^ to NH4 was later f o u n d to o c c u r in a large number of b a c t e r i a wh i ch c a n respire with NCb, but d o not denitrify (Herbert et a l . 1980; M a c F a r l a n e a n d Herbert 1982). Several strains of Desulfovibrio a p p e a r t o switch to nitrate reduc t ion w h e n su lphate is d e p l e t e d . The dissimilatory r educ t ion of nitrate t o a m m o n i u m is not a lways a respiratory process , s ince t h e nitrate m a y a lso f unc t i on as a n e l e c t r o n sink in b a c t e r i a l f e rmenta t ions ( J0rgensen a n d S0rensen 1985). Denitrificcrtion b y b a c t e r i a is the b i o c h e m i c a l r educ t ion of t he ox id ized ni trogen an ions , NO3 a n d NO2, w i th c o n c o m i t a n t o x i d a t i o n of o r g a n i c mat ter . The g e n e r a l s e q u e n c e of this process is: NO3' - * NO2 - * N2O -* Nb, w h i c h results in a signif icant r educ t i on of c o m b i n e d n i t rogen that c a n , in part , b e lost f r o m t h e sys tem if it is not re f ixed . M a n y f a c u l t a t i v e a n a e r o b i c b a c t e r i a , e .g . Pseudomonas spp . , c a n utilize NO3* as a n e x o g e n o u s t e rmina l H a c c e p t o r in the o x i d a t i o n of o r g a n i c substrates ( A l e x a n d e r 1965). A n e x e m p l a r y r e a c t i o n of the ox idat ion of g lucose a n d c o n c o m i t a n t reduct ion of nitrate is: C i H u A + I2NO3" <-> I2NO2 + 6 C Q 2 + 6 H 2 O A & = -1926kj .mol" ' , a n d for the reduct ion of nitrite to molecu la r nitrogen: C s H i i a +8NO2" «-* 4N2+CO2 + 4 C O t +6H2O AG)=-3014kJ.mor 1 . A p p r o x i m a t e l y as m u c h free ene rgy results as in the a e r o b i c ox ida t ion of g l u cose by d i sso l ved 0 2 (AGo =-3190 kJ^mol" 1 ) . The deni t r i f i cat ion reac t ions o c c u r intensely in a n a e r o b i c env i ronments , such as in the hypo l imn ia of eu t roph i c lakes a n d in a n o x i c sed iments , w h e r e ox id izab le o rgan i c substrates a re relatively a b u n d a n t . A b i o l o g i c a l N 0 3 r educ t ion m a y also o c c u r whe re possible reductants c o u l d b e r e d u c e d iron c o m p o u n d s w h i c h a c c u m u l a t e at the lower e d g e of the N G v c o n t a i n i n g sur face layer (the "redoxcl ine") . Nitrite seems more reac t i ve t h a n N 0 3 " towards Fe 2 + , but genera l l y very little is known a b o u t reac t ion kinetics (rates a n d products ) a n d ca ta l y t i c ef fects of surfaces, e t c . (Sorensen 1987). Nitrification Nitrification m a y b e broad ly de f i ned as the b io log i ca l convers ion of o rgan i c a n d i no rgan i c n i t rogenous c o m p o u n d s f rom a r e d u c e d state t o a more ox id ized state (A l exander 1965). The overal l r eac t ion c a n b e represented as: NH l+ I . 5 O 2 <-» 2H + + NG2"+H2O AG)=-276kJ .mof\ w h i c h p r o c e e d s b y a series of ox ida t ion s tages th rough hydroxy l amine a n d pyruv ic ox ime to nitrous a c i d : Nhtf -» NhbOH-* H2N2O2 -» HNO2. The nitrifying b a c t e r i a c a p a b l e of the ox ida t ion of NH4 -> NO2" a re largely c o n f i n e d to Nifrosomonas spp. Ox ida t ion of NO2" p r o c e e d s further to NO3 : NO" +O.5Q2 <-> N O i AG J=-75kJ»mol'\ Nitrobacter is t h e pr imary b a c t e r i a l genus i n vo l v ed in this o x i d a t i o n . The overa l l nitrification r eac t i on , NHj + 2 O 2 <-»NOs" +HzO + 2 H + requires t w o moles of 0 2 for the oxidat ion of e a c h mole of N H l . A l though condi t ions must b e a e r o b i c in o rde r for ni t r i f icat ion t o o c c u r , t hese p rocesses will c o n t i n u e until concen t ra t ions of dissolved O 2 dec l i ne to a b o u t 10 \iM (Devol 1975, c i t e d in Murray et a l . 1978). This r eac t ion is e x c e e d i n g l y s low at room tempera tu re a n d thus, nitrifying b a c t e r i a a c t as ca ta lys ts for the r e a c t i o n . B e c a u s e a m m o n i u m is rap id ly ox id i zed in natura l a e r o b i c wa te r s , it d o e s not a c c u m u l a t e in s u c h env i ronments in suff ic ient ly h igh concent ra t ions to alter the pH. 3.2 Materials and Methods Organic Carbon and Nitrogen W a t e r for pa r t i cu l a t e a n d d isso lved o r g a n i c c a r b o n ( P O C a n d D O C ) a n d par t i cu la te o r g a n i c ni t rogen (PON) analyses was run directly f rom 1.8 L Niskin bottles into we l l- r insed g lass c o n t a i n e r s t h a t h a d p rev ious l y b e e n u s e d on l y for s tor ing c o n c e n t r a t e d HCI a n d h e n c e should h a v e b e e n carbon-free . The samples we re kept o n i ce until they c o u l d b e fi ltered later in the lab . P O C a n d P O N samples we re c o l l e c t e d o n p re-combusted (4 hours at 450°C) glass fibre (GF/C) filters with a nomina l pore size of 1 u.m. The filters w e r e t h e n p l a c e d in p re-combus ted a lumin ium foil p o u c h e s a n d frozen. The filtrate w a s c o l l e c t e d for D O C analysis in 125 mL a c i d - c l e a n e d pyrex bottles. All samples we re f rozen immed ia te l y after filtering. P O C a n d P O N we re de t e rm ined v i a combus t ion in a Perkin-Elmer C H N Analyzer. Filters we re t h a w e d a n d dr ied for 24 - 48 hours in a n o v e n at 60°C. The filters were then ac id i f i ed by expos ing t h e m to HCI fumes for 24 hours to r emove a n y c a r b o n a t e - c a r b o n present. Filters w e r e c o m b u s t e d at 750°C a n d filter blanks we re s u b t r a c t e d from the samples . S tandards cons is ted of careful ly w e i g h e d amounts of a c e t a n a l i d e (71.09% C a n d 10.36% N). All samples we re wel l over the d e t e c t i o n limit a n d the prec is ion was 5% (1 a , rsd). D O C w a s ana l y sed using a n O c e a n o g r a p h y International Total C a r b o n System. After t haw ing the samp le , 5 mL was p l a c e d in a n a m p o u l e conta in ing approx imate l y 0.2 g potass ium persu lphate . Then 200 u.L of 8% H3PO4 was a d d e d a n d the solution p u r g e d with pur i f ied o x y g e n for 6 minutes to r e m o v e a n y c a r b o n a t e ions. The a m p o u l e was s e a l e d a n d the o r g a n i c c a r b o n ox id ized to c a r b o n d iox ide by the persu lphate in a n a u t o c l a v e (1 hr a n d 20 min. at 20 - 30 psi). All g lassware a n d tools used in the ampou l i ng p rocess w e r e c o m b u s t e d a t 500°C for 4 hours prior t o use. The a m p o u l e w a s t hen t a p p e d , a n d the CO2 present ca r r i ed th rough a non-dispersive infra red (IR) analyzer . O r g a n i c c a r b o n Is thus r e a d out d i rect ly as a f unc t i on of CO2 c o n c e n t r a t i o n . The d e t e c t i o n limit was 0.2 mg^L" 1 a n d the precis ion was 5% (1 a , rsd) for samples < 2 mg»L _ 1 a n d 1% (1 a , rsd) for m o r e c o n c e n t r a t e d samp les . S t anda rds w e r e p r e p a r e d f rom dext rose solutions in freshly d e i o n i z e d "Milli Q" w a t e r a n d we re run with the samp les th rough the s a m e p r o c e d u r e . The Milli Q wa te r w a s c h e c k e d for c a r b o n content a n d was f o u n d to h a v e a zero blank at the sensitivity used. Nutrients W a t e r s a m p l e s w e r e c o l l e c t e d in 10%-HC I-washed p o l y e t h y l e n e or p o l y p r o p y l e n e bott les a n d w a s f i l tered th rough 0 .4 u.m p o l y c a r b o n a t e N u c l e p o r e m e m b r a n e s . A n y su lphide present w a s r e m o v e d be fore analysis either b y prec ip i ta t ion w i th ZnAc2 or pu rg ing wi th N 2 . A l l nutrient s amp le s d i scussed in this c h a p t e r we re a n a l y z e d immed ia te l y after co l l ec t ion . Nitrogen Nitrate a n d nitrite we re m e a s u r e d co lour imetr ica l ly a c c o r d i n g to the s tandard p r o c e d u r e of Str ickland a n d Parsons (1972). Nitrate is r e d u c e d to nitrite by running it t h rough a c o l u m n c o n t a i n i n g c a d m i u m filings c o a t e d with meta l l i c c o p p e r . Nitrite d iazot izes with su lphan i l am ide a n d c o u p l e s with naph thy l e thy l ened i am ine to form a highly c o l o u r e d a z o dye . The d e t e c t i o n limit for the two nutrients was 0.5 u.M a n d the precis ion 1% (1 a , rsd ) . A m m o n i u m w a s d e t e r m i n e d a c c o r d i n g to the co lour imetr ic m e t h o d of Koroleff (1976). In a slightly a lka l ine so lut ion , a m m o n i u m reac t s wi th hypoch lo r i t e fo rming m o n o c h l o r a m i n e . w h i c h , in the p r e s e n c e of p h e n o l , nitroprusside ions a n d a n excess of hypoch lor i te , gives i n d o p h e n o l b lue. Interference with M g 2 + a n d C a 2 + ions in seawa te r is e l im ina t ed b y c o m p l e x i n g t h e m with c i t rate . I f o u n d that it w a s necessa ry t o di lute samples with DDW to < 50 u.M before reagen t add i t ion or full co lour d e v e l o p m e n t d i d not occu r . The d e t e c t i o n limit was 1 u M a n d the precis ion 1% (1 a , rsd). Dissolved Silicon Dissolved si l icon w a s measu red b y the m e t h o d of Str ickland a n d Parsons (1972). Samp les r e a c t wi th m o l y b d a t e unde r cond i t ions w h i c h result in the fo rmat ion of the s i l i c o m o l y b d a t e , p h o s p h o m o l y b d a t e a n d a r s e n o m o l y b d a t e c o m p l e x e s . A r e d u c i n g so lu t i on , c o n t a i n i n g m e t o l a n d o x a l i c a c i d , is t h e n a d d e d w h i c h r e d u c e s t h e s i l i c omo l ybda t e c o m p l e x t o g ive a b lue co lou r a n d s imultaneously d e c o m p o s e s any p h o s p h o m o l y b d a t e or a r s e n o m o l y b d a t e , so tha t in te r fe rence f rom p h o s p h a t e a n d arsenate is e l iminated . I f o u n d that samples must b e d i luted to < 100 u.M with DDW before r eagen t a d d i t i o n to a v o i d underest imat ing concent ra t ions . The d e t e c t i o n limit was 0.5 u M a n d the precis ion was 1% (1 a , rsd). Alkalinity Alkalinity was d e t e r m i n e d by the potent iometr i c titration m e t h o d of Gieskes a n d Rogers (1973), w h i c h measures the number of equivalents of a c i d necessary t o titrate 1 L of s e a w a t e r a t 25°C t o the b i c a r b o n a t e endpo in t . S amp les w e r e c o l l e c t e d in pre-w e i g h e d conta iners so that titrations c o u l d b e ca r r i ed out in t h e or iginal conta iners t o ensure that a n y CaCG*3 w h i c h might h a v e p rec ip i t a t ed dur ing s torage w a s i n c l u d e d in the analysis. Samp les w e r e rapid ly t i t ra ted t o a pH of app rox ima te l y 3.5 with a c i d of k n o w n c o n c e n t r a t i o n (0.10042 N for l ow alkal inity s amp le s a n d 0.5454 N for more c o n c e n t r a t e d samp les ) , wh i le stirring v igorously . The s a m p l e w a s t h e n a l l o w e d to stabilize be fore cont inu ing the titration in small increments, record ing the vo l ume a d d e d a n d its co r respond ing EMF b e t w e e n pH 3.5 a n d 2.5. At least 12 points w e r e r e c o r d e d for the G r a n plot (Dyrssen 1965) w h i c h is used to determine the b i c a r b o n a t e endpo in t of the titration b y ext rapo la t ing the linear port ion of a G r a n funct ion . The prec is ion was 0 .3% (1 a , rsd). P H B e c a u s e the re w a s no p o w e r supp ly o n the b o a t , pH w a s m e a s u r e d using colorpHasf® pH p a p e r (Merck) by running wate r direct ly out of the Niskin bott le onto the p a p e r . N o d i f fe rence w a s f o u n d w h e n the pH was measu red in a g love b a g where the s amp l e w a s not e x p o s e d to air. Precision w a s approx imate l y 0.1 pH unit. 3.3 Results Organic Carbon and Nitrogen Powell Lake From a sur face c o n c e n t r a t i o n of 5.6 mg»L"\ d isso lved o r g a n i c c a r b o n ( D O C ) d e c r e a s e s to 1.6 mg«L"' in the u p p e r low salinity layer of Powel l Lake. In the anox i c layer, D O C increases rapidly to nearly 50 mg«L'' at 290 m (Fig. 3-2). Thereafter D O C decreases in t h e b o t t o m 15 m t o 23 mg«L"\ Pa r t i cu la te o r g a n i c c a r b o n ( P O C ) shows a similar distribution to that of D O C , increasing at d e p t h t o a max imum of 280 u.g»L'' at 330 m a n d subsequen t l y d e c r e a s i n g t o 211 u.g«L0 a t t he b o t t o m . D O C : P O C ratios va ry f rom app rox ima te l y 30 in the ox i c part of the wa te r c o l u m n t o a high of 186 in the b o t t o m water . The par t i cu la te o rgan i c ni t rogen (PON) profile is similar, a l though not ident i ca l , to that of P O C (Fig. 3-4). Concent ra t ions range from 4 to 18 ng»L"'. The C :N we ight ratio (all C : N rat ios in this c h a p t e r a r e b a s e d o n we igh t ) of t h e p a r t i c u l a t e f r a c t i o n is approx imate l y 10 in the upper , oxic waters a n d gradual ly increases to 20 at the bo t tom. Sakinaw Lake Dissolved o rgan i c c a r b o n ( D O C ) remains constant throughout the ox ic port ion of the w a t e r c o l u m n at approx imate l y 3 mg«L"' (Fig. 3-3). It then starts to increase a b o u t 10 m b e l o w t h e o x i c / a n o x i c in te r face t o a m a x i m u m of 16 mg«L*\ Pa r t i cu la te o r g a n i c c a r b o n ( P O C ) shows t w o large m a x i m a , a t 10 m a n d at the in te r face , a n d t h e n is fairly constant in the anox i c waters , at a b o u t 240 u.g»L"\ The D O C : P O C ratio ranges from 7 at the in te r face t o 70 in the b o t t o m water . The par t i cu la te o r g a n i c n i t rogen (PON) profile mimics that of P O C (Fig. 3-5), rang ing from a b o u t 22 to 80 u.g»L"'. Thus the C :N profile is reasonably constant with d e p t h at 5.5 to 6.5. Nutrients Powell Lake Nitrate concent ra t ions increase from a sur face va lue of 2.9 u M t o almost 9 u M at 50 m (Fig. 3-6). It t h e n d e c r e a s e s g radua l l y t o zero c o n c e n t r a t i o n at t he inter face . No nitrite is d e t e c t a b l e a n y w h e r e in the w a t e r c o l u m n . A m m o n i u m is not d e t e c t a b l e until just a b o v e the in ter face at 150 m; thereafter it increases t o almost 4 m M in the b o t t o m water . Concen t r a t i ons of dissolved sil icon are a r o u n d 43 n M in the u p p e r ox ic layer, a n d gradua l l y increase t o 300 nM a t the bo t tom (Fig. 3-8). Sakinaw Lake Nitrite a n d nitrate a re bo th low in surface waters, increasing rapidly just a b o v e the in ter face a n d d e c r e a s i n g just as quickly b e l o w it (Fig. 3-7). The m a x i m u m concen t r a t i on of nitrite obse r ved is 0.24 \iM. whi le that of nitrate is 7 jxM. Be low the in te r face , a m m o n i u m rapidly increases t o nearly 8 m M in the bo t tom wa te r (Fig. 3-7). There is a slight d e c r e a s e in t h e b o t t o m water . Dissolved s i l icon o c c u r s at h igh concen t r a t i ons th roughout the wa te r c o l u m n , rising quickly to a b o u t 1000 n M in the bo t tom wate r (Fig. 3-9). In the surface waters it is app rox ima te l y 40 | i M , similar t o the concen t r a t i on in the u p p e r 150 m of the Powel l Lake w a t e r c o l u m n . Alkalinity and pH Powell Lake Alkalinity is very low in sur face waters , increasing gradua l l y b e l o w the oxycl ine to a m a x i m u m of 31 mequiv-L" 1 (Fig. 3-10). The pH was s teady at 5.7 d o w n to 175 m (Fig. 3-10). It then increases gradual ly to a max imum of 6.7 in the bo t tom 90 m. Sakinaw Lake Alkalinity is very low in sur face waters a n d gradua l l y increases wi th d e p t h t o a m a x i m u m of 27 mequiv«L'' (Fig. 3-11). The pH is cons tant in the uppe r 37.5 m at 5.7 a n d increases sharply a t 40 m to 6.5, t h e n c e remain ing cons tant t o the b o t t o m of the lake (Fig. 3-11). Fig. 3-2 Dissolved a n d part iculate o rgan ic c a r b o n in Powel l Lake 0 103 200 300 400 500 P O C C u g . L " 1 ) D O C / P O C Fig. 3-3 Dissolved a n d par t icu la te o rgan i c c a r b o n in Sakinaw Lake 0 5 10 15 20 25 P O N ( j ig .L" 1 ) P O C / P O N (wt. ratio) Fig. 3-4 Particulate o rgan ic c a r b o n a n d nitrogen in Powel l Lake 0 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 P O N ^ g . L * 1 ) P O C / P O N (wt. ratio) Fig. 3-5 Part iculate o rgan ic c a r b o n a n d nitrogen in Sakinaw Lake Fig. 3-6 Nitrate a n d a m m o n i u m in Powell Lake (nitrite unde tec t ab l e ) Fig. 3-7 Nitrate, nitrite a n d a m m o n i u m in Sakinaw Lake Fig. 3-8 Dissolved silicon in Powell Lake Fig. 3-10 Alkalinity a n d pH in Powell Lake Fig. 3-11 Alkalinity a n d pH in Sakinaw Lake 3.4 Discussion Organic Carbon B e c a u s e most lakes a re smal l , with a high propor t ion of their sur face a r e a as littoral z o n e , m u c h of the detrital c a r b o n is of a l lochthonous terrestrial origin. However , in l a rge , s t e e p w a l l e d fjord-lakes such as Powel l a n d Sak inaw , the littoral zone is small c o m p a r e d t o the l a rge su r f ace a r e a , a n d the bulk of t h e c a r b o n is d e r i v e d f rom a u t o c h t h o n o u s sources. This is espec ia l l y true where there is little freshwater input t o the lake as in Sak inaw, or whe re the lake basin is far r e m o v e d from the freshwater source , as in Powel l . Au toch thonous sources of c a r b o n in lakes inc lude : 1) l i ttoral (shorel ine) w h e r e P O M a n d D O M are p r o d u c e d by a c t i v e sec re t i on (extracel lular release) a n d autolysis of the mac rophy tes a n d a t t a c h e d microf lora ; 2) p r imary p r o d u c e r s i n c l u d i n g a l g a l p h y t o p l a n k t o n , a n d p h o t o s y n t h e t i c a n d c h e m o s y n t h e t i c b a c t e r i a . B e c a u s e of t h e l a rge a n o x i c z o n e in b o t h lakes , c h e m o s y n t h e t i c b a c t e r i a m a y con t r i bu te c o n s i d e r a b l y t o the c a r b o n p o o l ; h o w e v e r , the major c a r b o n sou r ce is p r o b a b l y tha t g e n e r a t e d photosyn the t i ca l l y b y a l g a e in the e u p h o t i c z o n e . R a p i d t rans format ions b e t w e e n P O C a n d D O C b y he t e ro t roph i c m i c r o b e s progress ive ly d e g r a d e o r g a n i c mat te r t o CO2 a n d heat . In shal low, small v o l u m e lakes, the bulk of he te ro t roph i c d e c o m p o s i t i o n o c c u r s in the sediments . Howeve r , as the d e p t h a n d v o l u m e i n c r e a s e , t h e o p e n w a t e r b e c o m e s t h e d o m i n a n t site of he t e ro t r oph i c m e t a b o l i s m , w h i c h is a lmost c o m p l e t e l y m i c rob i a l . The a m o u n t of o r g a n i c c a r b o n utilized a n d t rans formed by an imals is quant i tat ively a small port ion of that of the who le s y s t e m . DOC The D O C p o o l consists primari ly of c a r b o n c o m p o u n d s w h i c h a re relat ively resistant t o bac te r i a l decompos i t i on . The major sources t o the D O C p o o l are: 1) pho tosyn the t i c inputs of the littoral a n d p e l a g i c f lora a d d e d t o the p o o l th rough secret ions a n d autolysis of cel lular contents ; 2) a l l o ch thonous D O C , c o m p o s e d largely of terrestrial humic subs tances refractory to rap id bac te r i a l d e g r a d a t i o n ; 3) excret ions of zoop l ank ton a n d higher animals; a n d 4 ) bac te r i a l chemosynthes is of o rgan i c matter with subsequent re lease of D O C . Phy top l ank ton i c product iv i ty a n d a l l och thonous sources f rom the d r a i n a g e bas in are the pr imary sources of the D O C p o o l of o l igotrophic waters such as Powel l a n d Sakinaw. In lakes of this size, phy top l ank ton i c photosynthesis a l o n e c a n d o m i n a t e inputs to the D O C p o o l ; howeve r , bac t e r i a l p roduc t i on m a y a lso b e very impor tant in Powel l a n d Sak inaw, g i ven the un ique character ist ics of these lakes. The D O C profiles in bo th Powel l a n d Sak inaw Lakes are similar in s h a p e to those of the major ions ( c o m p a r e Figs. 3-2 a n d 3-3 wi th Figs. 2-7 t o 2-17). In b o t h lakes, D O C increases in the anox i c port ion of the wa te r c o l u m n , with the increase be ing m u c h more r ap id in Sak inaw. This is a lso similar t o the distribution of D O C in po re waters in most a n o x i c mar ine sed iments , whe re a large increase in the D O C c o n c e n t r a t i o n across the s ed imen t /wa t e r i n te r f ace is t yp i ca l l y s e e n (e .g . N i s senbaum et a l . 1972; Krom a n d Sholkovitz 1977; O r e m et a l . 1986). This is most p robab l y d u e to i n comp l e t e mineral izat ion of s ed imen ta r y o r g a n i c mat te r b y a n a e r o b i c b a c t e r i a in the sed iments (Otsuki a n d H a n y a 1972a,b). The concen t r a t i ons of D O C f o u n d in Powel l a n d Sak inaw Lakes a re t y p i c a l of those f o u n d in a n o x i c pore waters in sediments. For e x a m p l e , Emerson (1976) f o u n d 20 m g . L " 1 D O C in Gre i fensee sed iment pore waters. Krom a n d Sholkovitz (1977) m e a s u r e d D O C in Loch D u i c h , a fjord-type estuary hav ing a solid-phase o rgan ic c a r b o n con ten t of a b o u t 5%. They f o u n d that the D O C inc reased regularly with d e p t h in anox i c porewaters f rom a surface va lue of a b o u t 15 mg-L" 1 to a max imum of 70 mg»L'' in the m e t h a n o g e n i c zone . In ox ic co res , the po re wa te r D O C also i nc reased f rom sur face va lues of abou t 6 m g . L ' 1 t o 16 mg«L'\ showing that there must h a v e b e e n a n au toch thonous p roduc t i on a n d a c c u m u l a t i o n of D O C e v e n wi th in ox i c co res w h e r e the re is n o m e a s u r e d a c c u m u l a t i o n of alkal inity or p h o s p h a t e . In M a n g r o v e Lake , a sha l low sal ine lake in Be rmuda , O r e m et a l . (1986) f o u n d concentra t ions of D O C ranging from less t han 4 mg«L _ 1 in the overly ing wa te r t o greater t han 40 mg«L"' in the pore wate r at a d e p t h of abou t 200 c m . This l ake is m u c h m o r e p r o d u c t i v e t h a n e i ther Powe l l or S ak i naw Lakes , with sed iments con ta in ing 20 to 2 5 % o rgan i c c a r b o n (sediments in the south bas in of Powel l Lake c o n t a i n a b o u t 15% o rgan i c c a r b o n (Barnes a n d Barnes 1981)). A l though M a n g r o v e L ake is m u c h smal le r t h a n b o t h Powe l l a n d Sak i naw , t he o r g a n i c m a t t e r is a lso p redominan t l y a l ga l in origin (Hatcher et a l . 1983) a n d h e n c e should b e equa l l y labi le. Lyons a n d G a u d e t t e (1979) h a v e shown that the nature of the o rgan i c matter in mar ine sed iments has a d o m i n a n t e f f ec t o n the rates of su lphate r educ t ion . O r g a n i c mat ter d e r i v e d f rom a l g a l remains is more readi ly d e g r a d e d by sed imen ta r y b a c t e r i a t h a n o r g a n i c ma t t e r d e r i v e d f rom vascu l a r plants. The rate of d e g r a d a t i o n d e c r e a s e s as o r g a n i c ma t t e r is progressively m e t a b o l i z e d : b a s e d o n a c o m p i l a t i o n of a w i d e range of d a t a . Emerson a n d H e d g e s (1988) f o u n d a near ly one-to-one inverse relationship b e t w e e n d e g r a d a t i o n rate a n d the a g e of the o rgan i c mat te r ove r m a n y orders of m a g n i t u d e . In a study of ove r 500 Wisconsin lakes. Wetzel (1983) f o u n d a r ange of dissolved o rgan i c c a r b o n contents of the waters of 1 to 30 mg-L" 1 with a n a v e r a g e of 15 mg»L'\ The concent ra t ions of D O C found in Sakinaw fall within this range. However , higher D O C levels o c c u r in t h e b o t t o m wa te r s of Powe l l L a k e , in spite of t h e p r e s e n c e of lower c o n c e n t r a t i o n s of reminera l ized nutrients c o m p a r e d with Sak inaw ( c o m p a r e Fig. 3-7 a n d 3-6). The h igher nutrient va lues i nd i ca t e that Sak inaw is a more p roduc t i v e lake , s ince h igher concen t r a t i ons of nutrients in the d e e p waters ref lect a larger supply of nutrients a n d a large c o n c o m i t a n t remineral izat ion of o rgan i c matter. Genera l l y , h igher concen t r a t i ons of D O C w o u l d a lso b e e x p e c t e d t o ref lect higher product iv i ty , as the p r ima r y o r ig in of this m a t e r i a l is r e l e a se b y p h y t o p l a n k t o n a n d i n c o m p l e t e mineral izat ion. Therefore, g i ven a higher settling flux of phy top lankton seston, more D O C might b e e x p e c t e d in the hypo l imn ion . The pr imary r emova l m e c h a n i s m for D O C is heterot rophic up t ake by b a c t e r i a , either in the wate r c o l u m n or at the sediment surface. Sak inaw Lake w o u l d a p p e a r to h a v e h igher levels of b a c t e r i a l act iv i ty in its b o t t o m waters , as su lph ide concen t r a t i ons a re t w i c e as h igh as those in Powe l l Lake. Higher sulphide levels in Sak inaw Lake c o u l d b e d u e t o lower concen t ra t ions of F e 2 + resulting in less p rec ip i t a t i on of FeS 2 (d iscussed in C h a p t e r 5) a n d thus w o u l d not ref lect g rea te r bac t e r i a l act ivity. However , b e c a u s e a m m o n i u m concen t ra t i ons a re a lso m u c h higher in Sak inaw, it is more likely that the the add i t i ona l su lphide reflects a g rea te r supply of s u l p h a t e d u e t o o c c a s i o n a l intrusions of s e a w a t e r into S ak i naw Lake result ing in i n c r eased bac t e r i a l act ivity. M e t h a n e levels a re p r o b a b l y a lso m u c h higher in Sak inaw as b o t t o m w a t e r s a m p l e s d e g a s s e d m u c h m o r e v igorous ly w h e n b r o u g h t t o the surface. This behav iou r persists throughout the wa te r c o l u m n in Sak inaw Lake (from 40 m d o w n ) , w h e r e a s in Powel l it w a s only o b s e r v e d in the d e e p e s t waters. Therefore, e v e n t h o u g h photosyn the t i c product iv i ty is p r o b a b l y h igher in Sak inaw Lake . D O C m a y b e lower d u e t o consumpt i on by grea ter numbers of heterotrophic bac t e r i a . A l a rge d e c r e a s e in D O C c o n c e n t r a t i o n is s een in Powel l Lake just a b o v e the sediment-water inter face (Fig. 3-2). Bacter ia are usually f o u n d in m u c h higher numbers in this r eg i on , e v e n in lakes with anox i c b o t t o m waters. It is possible that h igher bac te r i a l activit ies c o u l d result in the dep le t i on of D O C , dynamica l l y mainta in ing the lower values in b o t t o m wate r . Howeve r , h igher numbers of b a c t e r i a shou ld b e r e f l e c t ed with a n inc rease in P O C . S ince P O C a lso d e c r e a s e s marked l y just a b o v e the sediment-water inter face (Fig. 3-2), this is a n unlikely exp lanat ion . It m a y b e that this is just a n ar te fac t as it is b a s e d o n only o n e measurement . POC As n o t e d earlier, au toch thonous primary p roduc t ion by the phy top lank ton i c a n d littoral f lora is t he major contr ibutor (> 90%) t o the P O C of natura l lake systems. In large lakes like Powel l a n d Sak inaw, phy top l ank ton a n d b a c t e r i a m a k e up the bulk of P O C (Wetzel 1983). A l l o c h t h o n o u s P O C is very sma l l , e spec i a l l y w h e n there is very little f reshwater input. Both lakes h a v e t w o P O C m a x i m a (Figs. 3-2 a n d 3-3). The uppermost max imum in e a c h lake reflects the phy top lank ton s tand ing stock a t the t ime of sampl ing . In Sak inaw Lake , this occu r s b e l o w the surface perhaps d u e to photoinhibi t ion within the uppermost metre. Phy top l ank ton , a n d h e n c e P O C , t h e n dec r ea ses with d e p t h as light b e c o m e s limiting for photosynthesis . P O C beg ins t o inc rease in b o t h lakes at the ox i c /anox i c in ter face . In Powel l Lake , the s e c o n d P O C m a x i m u m occurs at t he p y c n o c l i n e (300 m) (Fig. 3-2), w h e r e the sharp inc rease in densi ty c a n a c t as a barrier t o the sinking of part ic les. The bu i ldup of part ic les, c o m b i n e d with the large increase in salt, m a y i n d u c e f l o c c u l a t i o n , f o l l o w e d by more rap id part ic le sinking, such as is s een w h e n river waters a re m ixed with s e a wa te r (Sholkovitz 1976). Several authors (C loern et a l . 1983; Hamner et a l . 1982; Cu lve r a n d Brunskill 1969) h a v e f o u n d that the c h e m o c l i n e and/or pycnoc l i ne in me rom i c t i c lakes m a y b e the site of l oca l i zed a c c u m u l a t i o n of seston, ind ica t ing that it retards the sinking of b i o g e n i c particles. In Sak inaw Lake , a large P O C m a x i m u m is seen a t the ox i c/anox ic in ter face (Fig. 3-3). This is ind icat ive of a large concen t r a t i on of bac t e r i a . In Powel l Lake the inter face is s p r e a d ove r 150 m a n d so the b a c t e r i a a re not as spatial ly c o n c e n t r a t e d as in Sak inaw, where the in ter face is sharp. The very h igh levels of P O C f o u n d a t the Sak inaw inter face (> 400u.g»L"1), a r e most likely at t r ibutable t o the p r e sence of large numbers of sulphate-r e d u c i n g a n d sulphide-oxidizing b a c t e r i a , w h i c h me tabo l i z e sulphur c o m p o u n d s that diffuse across the in te r face , as wel l as denitrifiers, w h i c h r e d u c e nitrate a n d nitrite a n d nitrifiers w h i c h oxidize a m m o n i u m (Fig. 3-7). This d e p t h is b e l o w the eupho t i c zone , so no photosynthet i c sulphur b a c t e r i a w o u l d b e e x p e c t e d . By b e i n g a c t i v e sites of nutrient r egene ra t i on a n d d e c o m p o s i t i o n for o rgan i c mat te r p r o d u c e d in the t r o p h o g e n i c z o n e , c h e m o c l i n e s c a n a c t as eff ic ient "filters" for sinking o rgan i c matter (Culver a n d Brunskill 1969). If the c h e m o c l i n e is a n inefficient filter, t h e n the mon imo l imn ion c a n b e a sink for nutrients a n d o r g a n i c matter ; o n the other h a n d , if the c h e m o c l i n e is a n eff ic ient filter, then nutrient c y c l i ng in the mixol imnion (the u p p e r m ixed layer) is similar t o tha t in ho lomic t i c lakes (lakes in w h i c h the entire wa te r c o l u m n pe r i od i c a l l y c i rcu la tes ) . C h e m o s y n t h e t i c a n d pho tosyn the t i c b a c t e r i a c a n a c c o u n t for 8 5 % of the to ta l primary p roduc t i on at t imes a n d these organisms sink very slowly, whe reas phy top l ank ton sink m u c h faster (C loern et a l . 1987). B e c a u s e nutrients a n d o rgan i c matter r e a c h very h igh concent ra t ions in the bo t tom waters of Sak inaw a n d Powel l , it w o u l d a p p e a r that in bo th lakes the c h e m o c l i n e opera tes as a n inefficient filter. A gene ra l l y similar distr ibution o c c u r s in Big S o d a Lake , a n a lka l i ne , sal ine lake in N e v a d a , w h e r e a l a rge , l o c a l i z e d p o p u l a t i o n of b a c t e r i a exists a t t he c h e m o c l i n e ( O r e m l a n d et a l . 1988; Zehr et a l . 1987; C loe rn et a l . 1987). This suggests that the density discontinuity might b e a n important site of o rgan i c matter mineral izat ion. However , most P O C (-70%) r e a c h i n g the c h e m o c l i n e passes th rough it. so only a b o u t 3 - 5% of dai ly p roduc t i v i t y a c c u m u l a t e s the re . In a d d i t i o n , v e r t i c a l f luxes of ses ton b e l o w t h e c h e m o c l i n e a re a b o u t 9 0 % of those m e a s u r e d a b o v e it, thus the c h e m o c l i n e of this lake ac ts as a n inefficient filter for sinking part icu late matter. It appea r s , therefore, that a n ex t reme density discontinuity resulting from a salinity c h a n g e of 4%o over <1 m d o e s not grea t l y inhibit t he sinking of bulk par t i cu la te o r g a n i c mat te r or p e l a g i c d ia toms. The c h e m o c l i n e in Big S o d a Lake d o e s inhibit m o r e strongly t h e sinking of b a c t e r i a , howeve r , as e v i n c e d by the a c c u m u l a t i o n of bac te r i a l cel ls at that horizon. However , o b s e r v e d non-e leva ted ATP a n d prote in concen t ra t ions (O rem land et a l . 1988) a n d low thymid ine assimilation rates (Zehr et a l . 1987) i nd i ca te that these b a c t e r i a p l ay a minor role in lake me tabo l i sm a n d nutrient regenera t ion (C loern et a l . 1987). Zehr et a l . (1987) s p e c u l a t e t h a t f e r m e n t a t i o n p r o c e s s e s a r e t h e p r e d o m i n a n t m e c h a n i s m of d e c o m p o s i t i o n of the a n a e r o b i c mixol imnion in Big S o d a Lake . Similar cons idera t ions w o u l d a p p e a r to b e a p p l i c a b l e to Sak inaw, a n d p robab l y to Powel l Lake. DOC:POC Powel l a n d Sak inaw Lakes, rang ing from 23 to 190 in the former a n d 7 to 70 in the latter (Figs. 3-2 a n d 3-3); these d a t a ind ica te that bo th lakes are largely o l i go t roph i a as t h e rat io of D O C t o P O C is rather cons t an t at a b o u t 10:1 in most unp roduc t i v e to m o d e r a t e l y p r o d u c t i v e lakes (Wetzel 1983). As lakes b e c o m e m o r e e u t r o p h i c , the D O C : P O C ratio dec r ea ses a n d f luctuates great ly with season a n d d e p t h ; the ratio c a n d e c r e a s e to <1 (Wetzel 1983). The lower D O C . P O C ratio a t t he in te r face in Sak inaw reflects the large c o n c e n t r a t i o n of b a c t e r i a a n d h e n c e par t i cu la te c a r b o n . The higher ratio in Powel l relative to Sak inaw Lake c a n b e exp la ined in t w o ways. First, d e e p wate r in Powel l Lake has b e e n iso lated for a longer per iod t han that of Sak inaw, a n d h e n c e has h a d more t ime for d issolved o r g a n i c mat te r t o a c c u m u l a t e . S e c o n d , Sak inaw a lmost cer ta in ly has h igher concen t r a t i ons of b a c t e r i a in the w a t e r c o l u m n t h a n Powe l l , a n d thus more c a r b o n w o u l d b e e x p e c t e d in the par t i cu la te f ract ion. The contrast b e t w e e n the t w o lakes m a y a lso ref lect h igher product iv i ty in Sak inaw, with h igher numbers of p h y t o p l a n k t o n sinking out a n d cont r ibut ing to the P O C p o o l . The D O C : P O C ratios in Sak inaw a re m o r e t y p i c a l of those f o u n d in mode ra t e l y p roduc t i v e lakes a n d suggest that Sak inaw is in f a c t more product i ve t han Powel l . POCrPON P O N concen t ra t ions are m u c h higher in Sak inaw t h a n in Powel l Lake , consistent wi th the h igher P O C levels in the former bas in (Figs. 3-4 a n d 3-5). There a re major d i f ferences in the C :N ratios b e t w e e n the two lakes, however . The par t icu la te C :N we ight rat io in Powel l var ies f rom a low of 5 n e a r the redoxc l ine t o a m a x i m u m of 21 in the b o t t o m waters . In Sak inaw Lake , t he C : N rat io remains at 5.7 th roughou t the w a t e r c o l u m n , similar t o that f o u n d for phy top l ank ton under condi t ions of n i t rogen saturat ion (Sakshaug et a l . 1983). High C :N ratios such as those seen in Powel l Lake are o f ten used as a n ind ica t ion tha t o r g a n i c mat te r is of a l l och thonous origin. O r g a n i c mat te r of terrestrial a n d marsh a reas initially has g rea te r C :N ratios d u e t o the h igher ce l lu lose a n d lignin con t en t a n d a lso u n d e r g o e s va ry ing d e g r e e s of d e c o m p o s i t i o n prior to a n d dur ing transport t o a l a ke , dur ing w h i c h m u c h of the o r g a n i c n i t rogen m a y h a v e b e e n uti l ized. Therefore, a l l o ch thonous o r g a n i c mat te r conta ins roughly 6 % prote in a n d o f ten has a C :N we ight ratio of app rox ima te l y 45 to 50 (Hutchinson 1957). Forest humus a n d terrestrial plants a n d w o o d debris con ta in ing lignin particularly contr ibute t o such high C : N ratios (Pockl ington a n d L e o n a r d 1979). In con t r a s t , a u t o c h t h o n o u s o r g a n i c m a t t e r p r o d u c e d by d e c o m p o s i t i o n of p lankton within the lake conta ins a b o u t 2 4 % c r u d e protein a n d has a C :N we igh t ratio of a r o u n d 12 (Wetzel 1983). High C :N ratios c o u l d also b e der i ved from b e n t h i c m a c r o p h y t e s , h o w e v e r , Powe l l Lake is t o o d e e p for m a c r o p h y t e growth . B e c a u s e there is no d i rect f reshwater input t o the south bas in of Powe l l , t he high C :N ratios f o u n d most likely d o not reflect a l lochthonous input of o rgan i c matter. Instead, the high C :N ratios ind ica te that mineral ization is p r o c e e d i n g in the wa te r c o l u m n as p lankton settle. The c a r b o n con ten t is genera l l y at least a n order of m a g n i t u d e grea te r t h a n that of n i t rogen con t en t of o r g a n i c matter. As the c o m p l e x o rgan i c matter within the wa te r c o l u m n is minera l ized to inorgan ic c a r b o n (primarily as CO2) a n d inorgan ic n i t rogen, the proteo ly t i c me tabo l i sm of fungi a n d b a c t e r i a removes propor t ionate ly m o r e n i t rogen t h a n c a r b o n . Rates of d e c o m p o s i t i o n slow as the residual o r g a n i c mat te r b e c o m e s increasingly refractory, but the select ive remova l of n i t rogen by m ic robes results in a net increase in C : N ratios. In F r a m v a r e n , a n a n o x i c N o r w e g i a n fjord c h e m i c a l l y similar t o Powe l l a n d Sak inaw Lakes, C : N we igh t ratios of settling mater ia l c a p t u r e d v i a sed iment traps are app rox ima te l y 8 throughout the wa te r c o l u m n (Naes et a l . 1988). C o m p a r i s o n with the usual C : N va lues of living phy top l ank ton (6 - 10) r epo r t ed by Sakshaug et a l . (1983) ind ica tes tha t the o r g a n i c mater ia l is mostly settling phy top l ank ton . Naes et a l . (1988) c o n c l u d e d tha t minera l izat ion in the w a t e r c o l u m n of F ramvaren is restr icted to the u p p e r 20 m whe re o x y g e n is present. Grad ients in alkalinity a n d H 2S a n d a d e c r e a s e in c a r b o n con ten t in the sediments of this fjord c o m p a r e d with the mater ia l c o l l e c t e d in the 160 m t rap ind ica te that the ma in organ ic mineralization in the fjord m a y t ake p l a c e in the sed iments . Extensive d e g r a d a t i o n of o r g a n i c ma t t e r o c c u r s in B lack S e a sed iments (Ca lver t a n d Karlin 1990), however , Ross a n d Degens (1974) f o u n d that o rgan i c matter is a lso minera l ized in the wa te r c o l u m n . The res idence t ime of o rgan i c matter in the wa te r c o l u m n is m u c h greater t h a n in F ramvaren , howeve r , as part ic les h a v e t o settle th rough 2000 m c o m p a r e d t o 180 m in the fjord; thus, d e g r a d a t i o n dur ing settl ing w o u l d b e e x p e c t e d t o b e more p ro found in the Black Sea . As in F ramvaren , in Sak inaw Lake , w h i c h is only 140 m d e e p , there a lso a p p e a r s t o b e little d e c o m p o s i t i o n th roughout t he w a t e r c o l u m n : t he C : N ratio remains nearly cons tan t with d e p t h a n d the P O C a n d P O N profiles almost ove r l ap (Fig. 3-5). It should b e n o t e d tha t t he c o n s t a n c y of t he C : N ratio m a y a lso i nd i ca te that C a n d N are b e i n g minera l ized a t the s a m e ra te , howeve r , preferent ia l minera l izat ion of n i t rogen usually occurs . Powel l is a lmost 200 m d e e p e r t han Sak inaw, a n d the u p p e r 150 m is ox ic where a e r o b i c d e c o m p o s i t i o n processes are m u c h faster t h a n those unde r su lphate-dep le te a n a e r o b i c cond i t ions . The d e c r e a s e in the C : N ratio a t the ox i c /anox i c in te r face in Powel l Lake m a y ref lect t he p r e s e n c e of microorgan isms. Bac te r i a c o n t a i n a h igher propor t ion of n i t rogen t h a n phy top l ank ton (C :N -4.5) ( Fenche l a n d B lackburn 1979); h e n c e , if they form a n a p p r e c i a b l e f ract ion of the par t icu la te o rgan i c inventory they will c a u s e a lower C :N ratio in the bulk P O M fract ion t h a n if the o rgan i c matter was de r i ved entirely f rom p h y t o p l a n k t o n . In Sak inaw Lake , the C : N ratio similarly is slightly lower a r o u n d t h e i n t e r f a c e , w h i c h is cons is tent w i th t h e hypothes is tha t b a c t e r i a a r e c o n c e n t r a t e d there (Fig. 3-5). Be low the interface in Powel l , the C :N ratio a g a i n increases with d e p t h whe re b a c t e r i a populat ions are e x p e c t e d to b e lower, a n d where ni trogen is preferent ia l ly reminera l ized . The C : N we igh t ratio of t he sed iments in Powe l l Lake is approx ima te l y 18 (Barnes a n d Barnes 1981) a n d remains fairly cons tant with d e p t h . This ratio is very similar t o that f o u n d in P O M in the overly ing wa te r c o l u m n , ind ica t ing that most of the c a r b o n mineral izat ion is occur r ing prior to depos i t ion on the lake floor. Inorganic Nitrogen A m m o n i u m is present in very h igh concen t ra t ions in the b o t t o m waters of bo th lakes, r e a c h i n g concen t ra t i ons of a lmost 4 m M in Powel l a n d near ly 8 m M in Sak inaw (Figs. 3-6 a n d 3-7). A l t hough a m m o n i u m c a n b e g e n e r a t e d v i a several mechan i sms , the pr imary p rocess o p e r a t i n g in b o t h lakes is p r o b a b l y the d e c o m p o s i t i o n of o r g a n i c m a t t e r b y he t e ro t roph i c b a c t e r i a . O the r a m m o n i u m - g e n e r a t i n g processes i n c l u d e n i t rogen f ixat ion, w h i c h c a n b e ca r r i ed out photosynthet i ca l l y b y c y a n o b a c t e r i a a n d var ious o ther b a c t e r i a , a n d non-photosynthet ica l ly b y numerous a n a e r o b i c bac t e r i a l g e n e r a . N i t rogen f ixation usually does not o c c u r to any grea t extent in lakes where there is cons i de r ab l e n i t rogen ava i l ab l e in other, more easily ass imi lated forms, as is the c a s e In Powe l l a n d Sak inaw Lakes a n d h e n c e w o u l d not con t r ibu te m u c h , if any , t o the a m m o n i u m p o o l . Dissimilatory nitrate r e d u c t i o n b y var ious b a c t e r i a a lso results in a m m o n i u m format ion . As nitrate is not a va i l ab l e in the d e e p wa te r , this process c a n n o t y ie ld t h e h igh concen t r a t i ons of a m m o n i u m o b s e r v e d there. Therefore, the bulk of the a m m o n i u m f o u n d in bo th lakes must b e g e n e r a t e d by heterot rophic remineral ization of o r g a n i c matter . There a re normal ly t w o mechan i sms for ex t rac t ing the reminera l ized dissolved n i t rogen f rom b o t t o m waters . O n e is bac t e r i a l u p t a k e at d e p t h . Howeve r , the lower growth yields of a n a e r o b i c (relative t o ae rob i c ) metabo l i sm m e a n that a n a e r o b e s must assimilate larger amounts of o rgan i c c a r b o n a n d h e n c e , its a s s o c i a t e d n i t rogen ( a n d phospho rus ) , result ing in minera l i za t ion of g r ea t e r quant i t ies of a m m o n i u m ( a n d p h o s p h a t e ) . There fore , it is unlikely tha t a n a e r o b i c b a c t e r i a will t a k e up i no rgan i c n i t rogen unless their o r g a n i c c a r b o n source is n i t rogen-deplete . The other m e c h a n i s m for r emova l is t o m o v e the nutrient-enriched b o t t o m wa te r u p in the w a t e r c o l u m n by s o m e phys i c a l p rocess s u c h as overturn a n d d i s p l a c e m e n t or upwe l l i ng . H o w e v e r , b e c a u s e Powel l a n d Sak inaw Lakes are so stably stratif ied, such a d v e c t i v e processes d o not o c c u r ( Sanderson et a l . 1986); virtually no mixing c a n o c c u r o ther t h a n by m o l e c u l a r d i f fus ion , e x c e p t in S a k i n a w , w h e r e o c c a s i o n a l s e a w a t e r incurs ions contr ibute e d d y diffusion. Therefore the basins serve as nutrient traps. As the a m m o n i u m diffuses u p into t h e ox i c por t ion of the w a t e r c o l u m n , howeve r , it is ass imi lated or b e c o m e s ox id ized , either by nitrifying b a c t e r i a (very fast) or b y c h e m i c a l (very slow) processes. The nitrite a n d nitrate g e n e r a t e d m a y b e used by denitrifying b a c t e r i a as a l te rnate e l ec t ron a c c e p t o r s in low-oxygen environments. The o x y g e n concen t ra t i ons b e l o w w h i c h the facul tat ive ly a n a e r o b i c denitrifiers switch to a nitrate-respiratory m o d e is not known with great a c c u r a c y . Ozret ich (1976, c i t ed in Morris et a l . 1985), in a series of c h e m o s t a t studies, f o u n d this cr i t i ca l o x y g e n leve l t o vary b e t w e e n 0.5 -19.7 u.M. Morris et a l . (1985) obse r ved that nitrate d i sappears a n d counts of denitrifiers increase a t a n o x y g e n concen t r a t i on of 18.8 u.M in the C a r i a c o Trench. Note t ha t uncer ta in t ies in the Winkler de t e rm ina t i on of o x y g e n a t r e d u c e d O2 tens ions ( B roenkaw 1969; C l i ne 1973; bo th c i t e d in Morris et a l . 1985) suggest that the a c t u a l c o n c e n t r a t i o n of dissolved o x y g e n at the point where N O i - r e d u c t i o n c o m m e n c e s m a y b e 20 - 4 0 % lower than 19 p M In Powel l Lake , nitrate begins to d e c r e a s e b e t w e e n 50 a n d 75 m d e p t h (Fig. 3-6), w h e r e d i s so l v ed o x y g e n c o n c e n t r a t i o n s r e m a i n h igh (-625 j iM) . The re fo re , t h e d e c r e a s e in nitrate concen t r a t i on b e l o w 50 m c a n n o t b e d u e to r emova l b y denitrifying b a c t e r i a , as denitr i f icat ion Is unlikely to o c c u r a b o v e 140 m. The nitrate max imum at 50 m most l ikely represents m ine ra l i za t ion of sett l ing o r g a n i c m a t t e r w i th s u b s e q u e n t nitrification of the a m m o n i u m g e n e r a t e d . This is suppor t ed by the d e c r e a s e in dissolved 0 2 b e l o w 25 m (Fig. 2-3). N e a r the inter face nitrate is c o n s u m e d by denitrifying bac t e r i a . The lower concen t ra t ions of nitrate in the uppe r 25 m is primarily d u e to photosynthet ic u p t a k e by p h y t o p l a n k t o n . The P O C corre la tes inversely wi th the ni t rate, show ing a m a x i m u m at the sur face (Fig. 3-4), whe re nitrate is at a min imum (Fig. 3-6). Due to little a l l och thonous input, the P O C at the sur face consists a lmost entirely of phy top l ank ton . The f a c t that the nitrate levels remain h igh, e v e n in the phot i c zone , ind icates that it is not the limiting nutrient for p lankton growth. The t w o lakes differ s o m e w h a t in their nitrate distributions. In Powel l Lake , nitrate r e a c h e s a m a x i m u m v a l u e at 50 m d e p t h , a g o o d 100 m a b o v e the o x i c / a n o x i c in ter face , a n d then gradua l ly dec l ines to zero at the interface (Fig. 3-6). In Sak inaw Lake, howeve r , nitrate increases to a m a x i m u m va lue of 8 | i M , 2 m a b o v e the in ter face a n d then rapidly falls t o zero immedia te l y b e l o w (Fig. 3-7). Nitrite shows a strong m a x i m u m 2 m a b o v e the in te r face in Sak inaw, but is u n d e t e c t a b l e in Powel l Lake. Nitrate is not entirely d e p l e t e d in the sur face , ox ic waters in Sak inaw Lake , a l though it d o e s d e c r e a s e quite substantially t o fairly low levels (0.16 \iM) a t 10 m d e p t h . This is most likely the d e p t h whe re phy top l ank ton are c o n c e n t r a t e d , as i n d i c a t e d by the large p e a k in P O C at that hor izon (Fig. 3-5). A b o v e this d e p t h , t he a v a i l a b l e light m a y b e suff ic ient t o inhibit photosynthesis. In the b o t t o m waters of Sak inaw Lake , a m m o n i u m r eaches m a x i m u m c o n c e n t r a t i o n s of 7.8 m M . U p w a r d diffusion a n d ox ida t ion of a m m o n i u m across the in ter face must support the nitrite a n d high nitrate concen t ra t ions obse r ved immedia te l y a b o v e the oxyc l ine . The sharpness of t he nitrite a n d nitrate peaks is m a i n t a i n e d by p r o d u c t i o n b y nitrifiers in t h e p r e s e n c e of o x y g e n , a n d r e d u c t i o n b y denitrif iers immed ia te l y be low . The large increase in P O C at the s a m e d e p t h in the wa te r c o l u m n , w h i c h is a t t r i bu t ed t o b a c t e r i a (Fig. 3-5), supports this ( a l t h o u g h sulphur-oxidizing b a c t e r i a w o u l d a lso cont r ibu te t o the h igher P O C ) . Nitrite is t he m o r e ene rge t i ca l l y f a vou r ab l e e l ec t ron a c c e p t o r a n d h e n c e is used u p first, f o l l owed by nitrate. No te that Sak inaw Lake has app rox ima te l y t w i c e the a m m o n i u m c o n c e n t r a t i o n of Powel l in its b o t t o m wa te r , yet the concen t r a t i on of nitrate in bo th lakes is the same . This m a y a g a i n i n d i c a t e h igher pr imary p r o d u c t i o n in Sak inaw; as nitrate is p r o d u c e d it is qu i ck l y c o n s u m e d . Higher a m m o n i u m levels in the b o t t o m w a t e r a lso i nd i c a t e h igher primary p r o d u c t i o n ; tha t is, g rea te r avai labi l i ty of d e g r a d a b l e o r g a n i c mat te r in d e e p w a t e r suppor ts a h i ghe r inventory of d i s so l ved NH4. H o w e v e r , t h e h ighe r a m m o n i u m c o n c e n t r a t i o n s in Sak inaw Lake m a y a lso b e d u e to a larger supp ly of ox idan t for o r g a n i c mat ter d e c o m p o s i t i o n . Powel l Lake has not r e c e i v e d any s eawa te r input s ince it was s e p a r a t e d f rom G e o r g i a Strait app rox ima te l y 11000 years a g o , a n d therefore , it has b e e n ox idant-dep le te for a m u c h longer t ime than Sak inaw Lake. This w o u l d result in less o r g a n i c mat te r d e c o m p o s i t i o n , a n d h e n c e less minera l izat ion of a m m o n i u m . O n the other h a n d , Sak inaw Lake has likely h a d per iod ic incursions of s e a w a t e r con ta in ing var ious ox idan ts , w h i c h w o u l d a l l ow g rea te r o r g a n i c mat te r b r e a k d o w n a n d h e n c e more a m m o n i u m re lease . Dissolved Silicon The sil icon c y c l e is the simplest of the three major nutrient (P, N a n d Si) c yc l es , as it has only o n e inorgan ic dissolved fo rm, orthosilicic a c i d (H 4Si04), with a n ox idat ion state of Si of +4 a n d no known o rgan i c forms of b io log i ca l impor t ance (Wetzel 1983). The ma in c y c l i n g p a t h w a y is f rom dissolved inorgan ic t o par t i cu la te a n d b a c k to inorgan ic form. In bo th Powel l a n d Sak inaw Lakes, large concent ra t ions of dissolved sil icon are f o u n d at d e p t h (up to 300 \iM in the former a n d 1000 u.M in the latter) (Figs. 3-8 a n d 3-9). There are f ive pr inc ipa l s i l icon-containing mineral groups that c a n a c t as sources of si l icon in lake wa te rs : 1) det r i ta l qua r tz , 2) det r i ta l a luminos i l i ca tes . pr imari ly c l a y minera ls a n d fe ldspars, 3) opa l i ne sil ica in the form of d i a t o m a n d s p o n g e skeletal debris, 4) v o l c a n i c glass in var ious s tages of hydra t ion a n d dev i t r i f i cat ion, a n d 5) au th i gen i c quar tz a n d a luminos i l i cates s u c h as fe ldspars , montmori l ioni te a n d philiipsite (Berner 1975). Quar tz d o e s no t no rma l l y p l a y a role in t h e e n v i r o n m e n t a l g e o c h e m i s t r y of Si a t l ow t empera tu res (Drever 1982), a n d the small a m o u n t of f reshwater input a n d the large d i s t a n c e of b o t h t h e Powe l l a n d S a k i n a w a n o x i c basins f rom f reshwate r sources i nd i ca tes tha t little si l ica input is likely t o c o m e f rom w e a t h e r i n g of quar tz a n d c l a y minerals. A l so , there is a l a ck of c lays in source rocks of t h e d r a i n a g e bas in of Powel l a n d Sak inaw Lakes (B. Barnes pers. c o m m . ) . Therefore, t h e most p r o b a b l e source of d isso lved si l icon in Powel l a n d Sak inaw Lakes is f rom the dissolution of d i a t o m frustules. A t a pH of - 7 . opa l ine si l ica reacts m u c h more rapidly with wate r t han b o t h c l a y minerals a n d quar tz , a n d in most lakes, the sed imenta t ion of d ia toms constitutes the major sil icon sink (Wetzel 1983). In d e e p lakes, frustules typ ica l l y u n d e r g o par t ia l dissolution be fore r e a c h i n g the sediments . It is s u g g e s t e d , therefore , that b e c a u s e dissolution of d ia toms must b e the pr imary contr ibutor of dissolved silicon t o the d e e p waters of bo th lakes, the h igher dissolved sil icon concen t ra t ions f o u n d a t d e p t h in Sak inaw support the previous indicat ions that primary p roduc t ion is higher in this lake t han in Powel l . In Powe l l L ake , t h e s h a p e of the d isso lved si l icon profi le differs f rom tha t of a m m o n i u m (Fig. 3-6). A m m o n i u m is g e n e r a t e d w h e n organisms a re minera l i zed , i.e. w h e n b a c t e r i a f e e d o n these cel ls a n d re lease the inorgan i c const i tuents. A l t h o u g h minera l izat ion a p p e a r s to o c c u r in the Powel l Lake wa te r c o l u m n , phy top l ank ton cells sink fairly rapidly ( C l o e m et a l . 1987) a n d bac te r i a l act iv i ty is greatest nea r the b o t t o m , d u e t o the p r e sence of more substrate a n d e l e v a t e d t empera tu re . Thus, the bulk of the mineral izat ion occu r s a t d e p t h a n d the re l eased c o m p o u n d s diffuse u p into the wa te r c o l u m n into reg ions of lower c o n c e n t r a t i o n . H o w e v e r , in cont ras t t o n i t rogen a n d phosphorus reminera l i za t ion , d isso lved s i l icon is r e l e a sed by the dissolut ion of s i l ica frustules, a strictly inorgan ic hydrolyt ic process w h i c h c a n o c c u r th roughout the wa te r c o l u m n . Thus, t h e s h a p e of t h e d i sso l ved s i l icon prof i le m a y b e a t least part ia l ly g e n e r a t e d b y dissolution of d i a t o m frustules as they settle th rough the w a t e r c o l u m n . Most of the b i o g e n i c o p a l f o r m e d in o p e n o c e a n sur face s eawa te r dissolves be fore it is i n c o r p o r a t e d into the sed iment (Broecker 1971). The rate of solution of a single test is a func t ion of solution t empera tu re , d e g r e e of saturation of solution, s p e e d of wa te r f lowing pas t t h e test , a n d the a v a i l a b l e sur face a r e a of t he test (Hurd 1972). The d o m i n a n t d i a t o m in p l ank ton tows in mid-summer Powel l Lake is a th in-wal led , f ragi le d i a t o m Rhizosolenia sp. (Styan 1976). It is very a b u n d a n t a n d is virtually the only d i a t o m present, a l t hough 19 other g e n e r a of d ia toms h a v e b e e n identi f ied in the lake. S ince Rhizosolenia is not f o u n d in the sed iments of Powel l Lake (B. Barnes, pers. c o m m . ) , these frustules must dissolve as they settle through the wa te r c o l u m n . The d ia toms f o u n d in Powel l Lake sediments consist of more robust spec ies . The majority of the frustules in compara t i v e l y sha l low Sak inaw Lake p robab l y sink without a p p r e c i a b l e dissolution. S o m e researchers h a v e f o u n d anox i c lake waters t o b e part icular ly corrosive to d i a t o m frustules. Mer i ld inen (1969) f o u n d a pauc i t y of shells in the d e e p w a t e r sediments of Lake Skjennungen (Finland), w h i c h he attr ibuted to p o o r preservat ion of the frustules in the mon imo l imn ion , a f a c t w h i c h w a s a p p a r e n t f rom the strong corros ion of the tests. K jensmo (1988) has s u g g e s t e d tha t the p o o r preservat ion of d i a t o m frustules in the m o n i m o l i m n e t i c sed imen ts of Lake Sk jennungen m a k e s the c h a n g i n g c o n t e n t of a m o r p h o u s si l ica in the sediments a n important p a r a m e t e r for the interpretat ion of the onset-time of meromixis in the lake. However , Meri ld inen (1969) f o u n d that in some other me romic t i c lakes there a p p e a r s t o b e no corrosion of frustules a t all . Silicon-rich wa te r shou ld b e less aggress ive t o w a r d si l iceous skeletons t h a n w a t e r poo re r in s i l i con, all o ther fac tors b e i n g e q u a l . Thus a n overa l l d e c r e a s e in dissolution rate with d e p t h is usually s e e n , d u e to the inc rease in the si l icon c o n c e n t r a t i o n a n d the d e c r e a s e in t empe ra tu r e with d e p t h . In Powel l a n d Sak inaw Lakes, howeve r , t empe ra tu re ac tua l l y increases in the b o t t o m waters. G r a z i n g c a n h a v e b o t h adve r se a n d bene f i c i a l e f fec ts o n test preservat ion . Crush ing of tests a n d b r e a k d o w n of ce l l p ro top l asm dur ing d igest ion c rea tes g rea te r spec i f i c su r face a reas a n d partial ly r emoves protec t i ve o rgan i c coa t ings f rom the test (Hurd 1972); b o t h fac tors t e n d t o inc rease the rate of solut ion of the test. Howeve r , incorpora t ion in f a e c a l pellets m a y r emove the test f rom a n a r e a of more ac t i ve to less a c t i v e solution a n d m a y also s p e e d settling of seston. A lso , graz ing c a n only o c c u r in the a e r o b i c waters of bo th lakes. Live d i a t o m cells that are Si-limited t ake up silicon while sett l ing t h r o u g h t h e m e t a l i m n i o n a n d h y p o l i m n i o n , thus a c t i n g t o p r e ven t the a c c u m u l a t i o n of dissolved sil icon in the hypol imnion fo l lowing its re lease (by dissolution) at t he sediment-water in ter face (Stauffer 1986). Tessenow (1966, c i t e d in Stauffer 1986) n o t e d that Si-limited d i a t o m cells ac t i ve ly a b s o r b e d the nutrient in the dark , e .g. b e l o w the t r o p h o g e n i c zone . This process c a n o c c u r as the ce l l is sinking as wel l as after the cel ls h a v e set t led out . H o w e v e r , d u e t o the h igh c o n c e n t r a t i o n s of d isso lved si l icon present th roughout the w a t e r c o l u m n (never < 30 | iM) in Powe l l a n d Sak inaw Lakes, d i a toms are unlikely t o b e Si-limited. A lso , sulphide is toxic to most organisms a n d w o u l d p r o b a b l y halt all metabo l i sm in the anox i c waters. A n o t h e r poss ib le re lease m e c h a n i s m for d i s so l ved s i l i con is r edox r e l a t e d . Mort imer (1941, 1942) f o u n d that the dissolved sil icon con ten t of the w a t e r overlying the b o t t o m sed imen t s in L ak e W i n d e r m e r e i n c r e a s e d t o on ly 620 j i M u n d e r a e r o b i c condi t ions but unde r a n a e r o b i c condi t ions it i nc reased great ly t o a b o u t 980 jxM, c lose to the solubility of a m o r p h o u s si l ica (Siever 1962). Ka to (1969) a lso f o u n d that as a n o x i a p rog ressed in Lake Kizaki, a seasona l l y a n o x i c J a p a n e s e l ake , tha t d isso lved si l icon concen t r a t i ons i n c r eased at d e p t h . He s h o w e d exper imenta l ly that h y d r a t e d oxides of iron a n d m a n g a n e s e co-prec ip i t a te a cons ide r ab l e a m o u n t of d isso lved si l icon. Such c o p r e c i p i t a t i o n of so lub l e p h o s p h a t e a n d s i l i con b y iron o x y h y d r o x i d e s is we l l e s t ab l i shed , a n d has b e e n p o s t u l a t e d as the m e c h a n i s m cont ro l l ing t h e d isso lved c o n c e n t r a t i o n of p h o s p h a t e a n d s i l icon in m a n y sub-tidal sed iments (S tumm a n d Leckie 1970). Loder et a l . (1978) f o u n d that 8 n M F e 3 + c o p r e c i p i t a t e d approx imate l y 1 \JM disso lved s i l icon a n d 0.7 \iM of p h o s p h a t e in a n o x i c mar ine po rewa te r s . B e c a u s e p h o s p h a t e is virtually non-existent in the ox ic port ion of the wa te r c o l u m n in bo th Powel l a n d Sak inaw Lakes ( C h a p t e r 4), larger amounts of dissolved si l icon m a y b e s c a v e n g e d b y iron a n d m a n g a n e s e oxides. Howeve r , unde r a n a e r o b i c cond i t ions or at low pH va l ues , t he h y d r a t e d ox ides a re c o m p l e t e l y d isso lved a n d c o - p r e c i p i t a t e d si l icon is so lubi l ized. Therefore , a n y s i l icon c o p r e c i p i t a t e d wi th iron or m a n g a n e s e ox ides in Powel l a n d Sak inaw Lakes w o u l d b e re leased at the ox ic/anox ic in ter face . In Sak inaw Lake , the concen t r a t i on of dissolved silicon m a y also b e cont ro l led to some extent b y its solubility. The solubility of amorphous sil ica at neutral pH values varies f rom a b o u t 1000 ^M«kg _ 1 a t 5 °C to 2000 j i M - k g ' 1 a t 27°C (Siever 1962). Dissolved silicon concen t r a t i ons in Sak inaw Lake a p p r o a c h these va lues (-980 \iM max imum) . Thus, the d e c r e a s e in c o n c e n t r a t i o n just a b o v e the b o t t o m m a y b e d u e to p rec ip i t a t i on of a m o r p h o u s sil ica. Solubility ca l cu la t ions using MINEQL ( A p p e n d i x 1) i nd i ca te that S i 0 2 is very near saturat ion b e l o w 40 m d e p t h . Alkalinity and pH C a r b o n a t e alkalinity in natura l waters is d e f i n e d as the tota l concen t r a t i on of all d i s s o l v e d b i c a r b o n a t e s p e c i e s ( f ree ions a n d ion pairs) plus t w i c e t h e t o t a l c o n c e n t r a t i o n of al l d i sso l ved c a r b o n a t e s p e c i e s , a n d is a sensit ive i nd i c a to r of d i a g e n e t i c p rocesses (Presley a n d K a p l a n 1968). The ma jo r c lasses of r eac t i ons p r o d u c i n g or consum ing alkalinity in sediments or w a t e r co lumns a re listed in Table 3-2. C a r b o n a t e alkalinity is p r o d u c e d by the react ion of C 0 2 with bases ( C a C 0 3 , N H 3 , S2") a n d c o n s u m e d by the reac t ion of H C 0 3 o r C C i with a c i d s ( C a 2 + . cat ion-free " a c id i c " c lay) . ( C a 2 + is here classif ied as a n a c i d in that it neutralizes alkalinity). In the anox i c waters of b o t h Powe l l a n d S a k i n a w Lakes m e t h a n o g e n e s i s , su lpha te r e d u c t i o n , a m m o n i u m p ro tona t i on , a n d iron a n d m a n g a n e s e ox ide reduc t ion all o c cu r . The primary process c a u s i n g t h e l a rge inc rease in alkal inity in the a n o x i c w a t e r c o l u m n of b o t h lakes is p r o b a b l y bac t e r i a l su lphate reduc t ion a c c o m p a n i e d by a m m o n i u m fo rmat ion (Figs. 3-10 a n d 3-11). Dur ing su lpha te r e d u c t i o n , for every equ i va l en t of SO 2 " r e d u c e d , t w o equiva lents of alkalinity a re a d d e d . S ince N H 3 is the c o n j u g a t e b a s e of the w e a k a c i d NH4 (pK = 9.3), e a c h equ i va l en t of N H 3 l i be ra t ed f rom o r g a n i c n i t rogen c o m p o u n d s should increase the titration alkalinity b y one equiva lent . At po rewa te r pH va lues most of the N H 3 is p ro tona t ed a c c o r d i n g to : NHs + CO2 + H T O <-> NHJ + HCCb. This p r o t o n transfer r e a c t i o n d o e s not d e c r e a s e the t i t rat ion alkal in i ty s ince e a c h equ iva lent of N H 3 p ro tona t ed results in the p roduc t ion of o n e equ iva lent of b i c a rbona t e . It is interesting that a l though Powel l Lake has approx imate ly half the sulphide a n d a m m o n i u m of Sak inaw Lake , alkalinity concent ra t ions are higher in Powel l bo t tom water . B a s e d o n the a m m o n i u m a n d su lph ide , a n d assuming all o ther fac tors t o b e e q u a l , Sak inaw Lake alkalinity should b e approx imate l y 6 meq»L"' g rea ter t han that of Powel l . Instead, t he alkalinity in Powel l Lake in a b o u t 3.5 meq^L" 1 h igher, ind ica t ing that either the re is s o m e a d d i t i o n a l sou rce of alkalinity t o the b o t t o m waters of Powe l l , or that alkalinity is c o n s u m e d in Sakinaw. As shown in Table 3-2, processes other t h a n su lphate r educ t ion a n d a m m o n i u m p roduc t i on c a n contr ibute to alkalinity. However , these c a n all b e ruled out as likely mechan i sms for alkalinity gene ra t i on a t d e p t h in Powel l Lake. First o f a l l , m e t h a n o g e n e s i s a d d s alkal in i ty only v i a the p r o t o n a t i o n of a m m o n i a . Denitr i f icat ion react ions o c c u r only a b o v e the inter face . M a n g a n e s e a n d iron reduc t ion o c c u r nea r the in ter face in bo th lakes (Figs. 5-9 a n d 5-10), howeve r , the concen t ra t ions of F e 2 + a n d M n 2 + a re low relative to the titration alkalinity (Fe 2 + max. 170 u.M, M n 2 + 30 u M in PL; bo th F e 2 + a n d M n 2 + ~7 u.M in SL) a n d thus these spec ies d o not contr ibute a significant a m o u n t of alkalinity. Minera l wea the r ing will not g e n e r a t e alkalinity at d e p t h in the lake , Table 3-2 Major classes of reactions involved in alkalinity generation and consumption (from Schiff a n d Anderson 1987) 1) Aerobic Respiration - including nitrification OrVT + 13802 + I8HCO3 -* 124C02 + I6NO3 + HPO4" + I4OH2O AAlk/Aoxidant -18/138 2) Denitrification a ) With ox idat ion of o rgan ic nitrogen O M + 94.4NG-3 -> 92.4HC03+13.6Ca + 55.2N2 + HPO4" + 84.8H 20 b) Without ox idat ion of o rgan i c nitrogen O M + 84.8N03" -> 98.8HC03+7.2C02 + 42.4Ns + 16NhC + HPO4 + 49.6H2O c ) A m m o n i a p roduc t ion OM+53NO3 +14C02 + 67H2O -* 12OHCO3+ 69NH4 + HPO4 + 53HzO +92.4/94.4 +98.8/84.8 +120/53 3) Mn(IV) Reduc t i on O M + 212MnC>2 + 332C02 + 12CHO ^ 4 3 8 H C 0 3 + 212Mn 2 + + I6NH4 + HPO4" +438/424 4) Fe(lll) Reduc t i on OM+424FeOOH + 756C02 + I2OH2O -»862HC03 + 424Fe 2 + + I6NH4 + HPO4" +862/848 5) SulDhate Reduc t i on O M + 53SO-4 -^67HCCb+ 53HS" +396C02 + I6NH4 + HPG4" + 39H 2 0 +120/106 6) M e t h a n e Fermentat ion O M + 14H+ -» 53CH4 + 53C02 + 16NI-C + HPO 2 ; +14/53 7) C a t i o n Exchange X-M n + + n H + -» X-n(H+) + M n + Where X=mineral or o rgan i c substrate; M = C a 2 + , M g 2 + , K+, N H l , e t c . e .g . C a r b o n a t e dissolution/precipitat ion C0OO3 + 2H + -» 2HCO3+ C a 2 + e.g . A m m o n i u m adsorpt ion (cation-clay) + NHj -* (NHl-clay) + c a t i o n + 1/1 8) Organic Acid Protonat ion R-COO" + H +-»R-COOH 9) M inera l Wea the r ing e.g. CaAfeStAi + H20 +2H+ -> C a 2 + + Al2Si205(OH)4 + 1/1 * O M refers to o rgan ic matter with the compos i t ion (CH2O)i06(NH3)i6(H3PO4) (Redfield et al . 1963) a n d c l a y-ca t i on e x c h a n g e reac t ions a re not impor tant d u e t o the smal l amounts of c l a y present in the o r g a n i c o o z e sed iment . C a C O s dissolution genera tes alkalinity, a n d ca l c i t e prec ip i ta t ion in surface waters d u e t o the rise in pH a c c o m p a n y i n g photosynthet ic utilization of C 0 2 is wel l known in marl lakes (Otsuki a n d Wetze l 1972). As this mater ia l settles the c a r b o n a t e m a y solubil ize, inc reas ing alkalinity. Extremely h igh product iv i ty w o u l d b e requ i red t o raise the pH of Powel l sur face waters (5.7) sufficiently for C a C 0 3 p rec ip i ta t ion to o c c u r (~9); as Powel l Lake is o l igot roph ic this is unlikely to occu r . The high c a r b o n a t e concen t ra t ions in Powel l a n d Sak inaw b o t t o m wate rs are more likely t o c a u s e C a C 0 3 p r e c ip i t a t i on . C a l c i t e p r e c i p i t a t i o n c o u l d c o n s u m e alkal in i ty in S ak i naw Lake b o t t o m waters . Howeve r , solubility ca l cu l a t i ons ( C h a p t e r 4) show that C a C 0 3 is unde rsa tu ra t ed at all dep ths in Sak inaw Lake a n d bare ly sa tura ted in the bo t tom wate r of Powel l Lake. It is unlikely that C a C Q j prec ip i tat ion occurs in Powell Lake, as C a C 0 3 nuc lea t ion is p r o b a b l y inhibited by high levels of D O M a n d lack of s e e d crystals (Suess 1970). The p ro tona t ion of o rgan i c a c i d s has b e e n f o u n d to cont r ibute as m u c h as 2 0 % of the alkalinity in soft wa te r Ontar io Lakes (Herczeg a n d Hesslein 1984). However , these lakes differ f rom Powel l as the concen t r a t i on of D O C is substantially h igher t h a n that of D iC . In Powel l Lake , D O C reaches concent ra t ions of 50 mg«L'\ Assuming 6 c a r b o n a toms per mo l e cu l e , this w o u l d only gene ra t e 0.7 meq-L" 1 alkalinity. All of the mechan i sms for genera t ing alkalinity listed in Table 3-2 c a n b e ruled out for Powe l l Lake . There a lso d o not a p p e a r t o b e a n y m e a n s of s igni f icant alkalinity c o n s u m p t i o n in Sak inaw. Therefore, I c a n n o t exp la in why Powel l Lake b o t t o m waters h a v e so m u c h more alkalinity t h a n Sakinaw. The la rge inc rease in pH in the b o t t o m waters of b o t h lakes is primarily d u e to pro ton c o n s u m p t i o n v i a su lphate reduct ion a n d a m m o n i u m format ion (Figs. 3-10 a n d 3-11). The pH in Sak inaw Lake is slightly lower t h a n tha t of Powe l l , as e x p e c t e d s ince alkalinity is also s o m e w h a t lower. CHAPTER 4 PHOSPHORUS CHEMISTRY 4.1 Introduction In the previous c h a p t e r the alkalinity-, o rgan i c ca rbon- , ammon ium- , a n d silicon-rich b o t t o m waters of Powel l a n d Sak inaw Lakes we re d iscussed in terms of their redox chemistry. In g e n e r a l , similarities exist a m o n g the distributions of all of these parameters in b o t h basins. Howeve r , t he t w o lakes differ cons ide rab l y with respec t t o phosphorus chemistry . Extremely low p h o s p h a t e concen t r a t i ons , re lat ive t o a m m o n i u m , o c c u r in the b o t t o m waters of Powel l Lake; this contrast warrants spec i a l a t tent ion. H e n c e , in this c h a p t e r t he distribution of phosphorus in b o t h lakes will b e d iscussed in de ta i l , in a n a t t empt t o exp la in why Powel l differs so dramat i ca l l y f rom Sak inaw in this respect . The Phosphorus Cycle Phosphorus exists in na tu re a lmos t exc lus ive ly as p h o s p h a t e in w h i c h the ox ida t ion state of P is +5. Of the key e lements of a lga l p ro top lasm (C , N, a n d P), only phosphorus d o e s not c h a n g e v a l e n c e states in na tu ra l , b i o l o g i c a l , or a b i o l o g i c a l c h e m i c a l transformations (Fenche l a n d Blackburn 1979); phospha t e c a n b e r e d u c e d to p h o s p h i t e , h y p o p h o s p h i t e , a n d p h o s p h i n e , but the redox po t en t i a l of p h o s p h a t e r educ t ion is so low that r educ t ion rarely, if ever , o ccu r s in natural env i ronments (Brock 1979). Phosphorus is usually f o u n d in high-energy p h o s p h a t e bonds a n d occurs in m u c h lower concen t ra t i ons in cells t han the other t w o nutrients (C a n d N). The most significant form of inorgan i c phosphorus is o r thophosphate . The phosphorus c y c l e (Fig. 4-1) has a t t r a c t ed a grea t d e a l of at tent ion b e c a u s e this e l emen t has universal s ign i f i cance in a lga l physio logy, a n d is most o f ten b io log ica l l y "limiting" in natura l lakes u n a f f e c t e d by a n t h r o p o g e n i c eu t roph i ca t i on (Schindler 1977). The phosphorus c y c l e , w h i c h is s low, differs f rom those of c a r b o n , h y d r o g e n , o x y g e n a n d n i t rogen , in w h i c h the e lements a re c y c l e d m u c h more quickly . B e c a u s e it takes millions of years t o c o m p l e t e the phosphorus c y c l e , the distribution of the e l emen t c a n b e v i e w e d as a one-way trip f rom rock wea the r ing to the wa te r a n d sediments (Holtan et a l . 1988). In add i t i on to mic rob ia l mineral izat ion activit ies, the c y c l i ng of phosphorus is r e g u l a t e d t o a l a rge d e g r e e b y phys i c a l - chem i ca l reac t ions in sed iments (Forsberg Fig. 4-1 A simplif ied representat ion of the phosphorus c y c l e In a q u a t i c environments (from Fenche l a n d B lackburn 1979). 1989). In this contex t , the sediment-water interface m a y a c t either as a pe rmanen t sink or as a transient source for phosphorus. Forms of Phosphorus In most lakes, a large majority of the tota l phosphorus is in a n o r g a n i c phase , of w h i c h a b o u t 7 0 % or more is within the par t i cu la te (sestonic) o r g a n i c mater ia l , a n d the r e m a i n d e r is present as d isso lved or co l l o i da l o r g a n i c phosphorus (Wetzel 1983). A signif icant quant i ty of the soluble o rgan ic phosphorus is in a co l lo ida l state. Dissolved Phosphorus The i n o r g a n i c forms of d i s so l ved phosphorus i n c l u d e o r t h o p h o s p h a t e a n d p y r o p h o s p h a t e , as wel l as their c y c l i c polymers (metaphospha tes ) a n d l inear polymers ( po l yphospha tes ) . O r g a n i c phosphorus c o m p o u n d s a re t yp i ca l l y p h o s p h a t e esters, such as po lyo l or sugar phospha tes , phosphory l a t ed hydroxyamines a n d a m i n o a c id s , nuc leo t ides a n d phosphol ip ids ( C e m b e l l a et a l . 1986). A n add i t i ona l g r o u p of o rgan i c phosphorus c o m p o u n d s a re the p h o s p h o n a t e s , in w h i c h the c a r b o n of t he o r g a n i c moiety is b o u n d direct ly to phosphorus rather than through a n ester b o n d (Kittredge a n d Roberts 1969). Typ ica l l y , t h e t o t a l p o o l of d i s so l ved phospho rus of na tu ra l wa te r s var ies b e t w e e n 0.1 a n d 35 | iM (Fenchel a n d Blackburn 1979). Only a portion of this p o o l , primarily t he o r t h o p h o s p h a t e f r a c t i o n , is read i l y t a k e n u p by organ isms. Inorgan ic so lub le phosphorus is consistently very low, constitut ing only a f ew pe r cen t of tota l phosphorus, a n d is c y c l e d very rap id ly in the zones of uti l ization. The rat io of i no rgan i c so luble phosphorus to other forms of phosphorus has b e e n f o u n d to b e approx imate l y 1:20 in a large var iety of lakes within the t e m p e r a t e z o n e (Wetzel 1983). The p e r c e n t a g e of tota l phosphorus occur r ing as truly ionic P O f . howeve r , is p robab l y cons ide rab l y less t h a n 5% in most natura l waters. O r t h o p h o s p h a t e is d e r i v e d f r om t h e na tu ra l w e a t h e r i n g a n d e ros ion of p h o s p h a t e minera l s , t h e so lub i l iza t ion of p r e c i p i t a t e d m e t a l l i c p h o s p h a t e s a n d a d s o r b e d p h o s p h a t e , a n d the excre t ion of b a c t e r i a a n d other organisms (Fenche l a n d B lackburn 1979). In recent t imes, soil fertilizers a n d industrial a n d domes t i c was te waters h a v e also b e c o m e important sources of o r thophospha te . Po l yphospha tes (i.e. linearly c o n d e n s e d o r t h o p h o s p h a t e ) of va ry ing m o l e c u l a r we igh t a re synthes ized by living organ isms. They a re uns tab le in w a t e r , w h e r e t h e y a r e s lowly hyd ro l y sed t o the o r t h o p h o s p h a t e form (A l exande r 1978). Phospha te , p y r o p h o s p h a t e , t r iphosphate , a n d h igher p o l y p h o s p h a t e an ions fo rm c o m p l e x e s , c h e l a t e s , a n d insoluble salts wi th a n u m b e r of me ta l ions, the extent of wh i ch d e p e n d s u p o n the relative concent ra t ions of the phospha tes a n d the meta l ions, the p H , a n d the p resence of other l igands (sulphate, c a r b o n a t e , f luor ide , a n d o rgan i c spec ies ) (Stumm a n d M o r g a n 1981). A b o u t 15 to 6 0 % of d issolved ( a n d in part co l lo ida l ) phosphorus consists of the o rgan i c p h o s p h a t e esters w h i c h a re c h e m i c a l l y poor ly de f i ned . These c o m p o u n d s are de r i v ed f rom the exc r e t a or l e a cha t e s of living organisms a n d f rom the autolysis of d e a d organisms (Fenche l a n d Blackburn 1979). Particulate Phosphorus Pa r t i cu l a t e phospho rus c a n b e c o m p o s e d of m a n y minera l s , a m o r p h o u s p rec ip i t a tes , a n d s o r b e d r eac t i on products . A large propor t ion of t he phosphorus in fresh w a t e r (o f ten g r ea t e r t h a n 90% ) , o c c u r s as o r g a n i c p h o s p h a t e s a n d ce l lu la r constituents in the b io t a a d s o r b e d to inorganic a n d d e a d par t i cu la te o rgan i c materials inc lud ing (Wetzel 1983): 1) phosphorus in organisms, as: a) relatively stable nuc l e i c a c i d s , D N A , RNA, a n d phosphoprote ins (not invo lved in rap id c y c l i ng of phosphorus) ; b) low-molecular-weight esters of enzymes , v i tamins, e tc . ; a n d c ) nuc l eo t i de phospha tes , such as adenos ine d iphospha te (ADP) a n d a d e n o s i n e 5-triphosphate (ATP) used in b i o c h e m i c a l pa thways of respiration a n d CO2 assimilation; 2) minera l phases of rock a n d soil , s u c h as hyd roxyapa t i t e , in w h i c h phosphorus is present as d isc re te minera l part ic les or is a d s o r b e d on to ino rgan i c part ic les such as c lays , c a r b o n a t e s , a n d ferric hydroxides; a n d 3) phosphorus a d s o r b e d o n t o d e a d pa r t i cu l a te o r g a n i c ma t t e r or in m a c r o o r g a n i c a g g r e g a t i o n s . Biological Importance of Phosphorus Phosphorus p lays a major role in b i o l og i c a l me tabo l i sm . Phospha t e is essential for the transfer of ene rgy a n d phosphorylat ions, a n d for the synthesis of nuc l e i c a c ids in all living cells. In the ce l l , o r thophospha te is c o u p l e d t o A D P t o form ATP. In c o m p a r i s o n to other macronutr ients required by freshwater b i o t a , phosphorus is least a b u n d a n t a n d c o m m o n l y is t he first e l emen t to limit b io log i ca l product iv i ty . Phosphorus is biolimiting in t e m p e r a t e z o n e lakes (Schindler 1977), a n d its concen t r a t i on c a n b e used to pred ic t the to ta l b iomass of phy top lank ton that will d e v e l o p in such wa te r bod ies (Dillon a n d Rigler 1974). O r thophospha t e is the most easily utilized form of soluble inorgan ic phosphorus by a l g a e , h igher plants a n d b a c t e r i a , a n d the high reactivity of this ion results in its c o m m o n dep l e t i on . Phospha t e interacts with m a n y ca t ions (e.g. Fe a n d C a ) in solution to fo rm, espec i a l l y unde r oxidizing cond i t ions , relatively insoluble prec ip i ta tes . S o m e organ isms c a n t a k e u p o r g a n i c p h o s p h a t e s d i rect ly , whi le others first h y d r o l y z e t h e m us ing e x t r a c e l l u l a r a l k a l i n e p h o s p h a t a s e s . H o w e v e r , o r g a n i c phosphorus in t h e w a t e r c o l u m n c a n b e very resistant to hydrolysis a n d not readi ly a v a i l a b l e t o m i c r o o r g a n i s m s . B a c t e r i a ( a n d s o m e o the r o rgan i sms ) m a y store phosphorus in vo lut in g ranu les w h e n they a re l imited by s o m e o ther nutrient (e .g. su lphate ) . This s tored phosphorus p o o l m a y m a k e u p a l a rge f r a c t i on of the to ta l phosphorus c o n c e n t r a t i o n in the ce l l ( Fenche l a n d B lackburn 1979), a n d is c o m p r i s e d of l inear p o l y p h o s p h a t e s of var ious lengths. W h e n the cel ls b e g i n t o g r o w a g a i n , the phospha tes are rapidly mobi l ized for D N A synthesis (Barsdate et a l . 1974). In na tura l waters , t he a m o u n t of phosphorus c o n t a i n e d in living organisms is usually m u c h greater t h a n the a m o u n t of o r thophospha te dissolved in the wa te r a n d the e x c h a n g e rate b e t w e e n these t w o pools is m u c h g rea te r t h a n the net depos i t i on of undisso lved phosphorus . W h e n there is h igh b io l og i ca l act iv i ty (a lga l b l ooms , bac te r i a l g r o w t h o n eas i l y d e c o m p o s e d o r g a n i c m a t e r i a l , e t c . ) , t h e t u rnove r t ime of o r t h o p h o s p h a t e m a y b e very short (i.e. less t h a n 2 min) , w h e r e a s under cond i t ions of l ow b i o l o g i c a l act iv i ty or unusually h igh o r t h o p h o s p h a t e c o n c e n t r a t i o n , the turnover t ime m a y e x c e e d 100 hours (Fenchel a n d B lackburn 1979). Phosphorus-starved a l g a e possess e n h a n c e d u p t a k e rates for POt (Blum 1966), a n d the extent t o w h i c h the m a x i m u m cel lular up take rates is e n h a n c e d is in f luenced by the d e g r e e of phosphorus l imitation. Highest u p t a k e rates a re most o f t en a s s o c i a t e d with either the greatest nutrient l imitation (e.g. Fuhs et a l . 1972; Rhee 1973; Epp ley a n d Renge r 1974) or with a n in te rmed ia te d e g r e e of l imitation (e.g. Terry 1983; Suttle a n d Harrison 1986). Uptake rates for P O ^ a re typ ica l l y great ly e n h a n c e d in P-deficient cells with respec t t o those that a re P-sufficient ( M c C a r t h y 1981). Bac te r i a m a y o u t c o m p e t e p h y t o p l a n k t o n in the u p t a k e of o r t h o p h o s p h a t e , e spec i a l l y a t l ow o r t h o p h o s p h a t e concent ra t ions (Levine a n d Schindler 1980; Lean 1984; Currie a n d Kalff 1984). In situ studies suggest tha t t he b a c t e r i o p l a n k t o n d o m i n a t e p e l a g i c phosphorus c y c l i n g (Rigler 1956; Burnison 1975; Currie a n d Kalff 1984); Currie et a l . (1986) f o u n d that bac te r iop lank ton are respons ib l e for > 9 5 % of t h e o r t h o p h o s p h a t e u p t a k e , e x c e p t in lakes tha t a r e phosphorus- rep le te . Mineralization of Phosphorus Minera l izat ion of phosphorus involves its transfer f rom detritus t o living b iomass a n d somet imes to f ree ino rgan i c p h o s p h a t e . The net result d e p e n d s o n the t y p e of o r g a n i c m a t t e r d e g r a d e d a n d t h e t y p e of respirat ion u sed in t h e d e c o m p o s i t i o n p r o c e s s . The ac t i v i t y of m i c r o b e s c a n a l so c a u s e c h a n g e s in t h e c h e m i c a l env i ronment that a f f e c t mobi l izat ion of phosphorus. Extracel lular p roduc t s of mic robes s u c h as e n z y m e s a n d c h e l a t i n g a g e n t s (e .g . o r g a n i c a c ids ) m a y a l so mob i l i ze phosphorus f rom o r g a n i c phosphate-esters a n d inorgan ic salts. Ne t minera l i za t ion results in phosphorus f rom the b iodet r i ta l p o o l ( m i c r o b e b i omass a n d d e a d o r g a n i c mat ter ) b e i n g t r ans fo rmed into mob i l i z ed phosphorus (o r thophosphate ) . The extent of transfer b e t w e e n these three phosphorus pools dur ing mineral izat ion d e p e n d s u p o n (Fenche l a n d B lackburn 1979): 1) t he phosphorus con ten t of the o rgan i c matter be ing d e g r a d e d ; a n d 2) the growth y ie ld of the mineralizing bac te r i a . (The growth y ie ld is e q u a l t o the a m o u n t of c a r b o n in o n e ce l l d i v i ded by the a m o u n t of c a r b o n ass imi la ted, i.e. the e f f i c i ency of o rgan i c mat ter decompos i t i on ) . In the mineral izat ion of phosphorus-deplete o rgan i c matter , there is a net immobi l izat ion of nutrients; al l p h o s p h a t e is kept in the bac te r i a l ce l l resulting in no PO4 re lease to the w a t e r c o l u m n (at least dur ing the initial phases of deg rada t i on ) . If sufficient phosphorus for g r o w t h is u n a v a i l a b l e f rom t h e o r g a n i c m a t t e r b e i n g d e c o m p o s e d , b a c t e r i a ass imi late i no rgan i c phosphorus f rom the env i ronment . M a n y a q u a t i c b a c t e r i a c a n g r o w at t he e x p e n s e of o rgan i c mat te r hav ing little or no phosphorus and/o r n i t rogen, whi le ge t t ing their nutrients f rom dissolved inorgan i c sources (Ostroff a n d Henry 1939; M a c L e o d et a l . 1954; M a c L e o d a n d Onofrey 1956; Bick 1958; Skerman 1963). In a e r o b i c b a c t e r i a , g r o w t h y ie lds a r e t yp i ca l l y in the r a n g e of 20 - 8 0 % , w h e r e a s a n a e r o b e s genera l l y h a v e g rowth yields of 5 - 3 0 % (Bostr&m et a l . 1988). W h e n growth yields are low, as dur ing a n a e r o b i c respiration a n d f e rmenta t ion , avai labi l i ty ( a n d thus potent ia l mobi l i ty ) of minera l i zed nutrients relat ive t o the o r g a n i c substrate is higher. The gross phospho rus t ransport in a n d out of b a c t e r i a l cel ls is o f t en m u c h g rea t e r t h a n the m e a s u r e d net transfers. As a n e x a m p l e , Barsdate et a l . (1974) f o u n d that in one w e e k i n cuba t i ons of Carex litter, t he net minera l izat ion of phosphorus w a s 0.027 j iM»h'\ H o w e v e r , t he a c t u a l u p t a k e a n d re lease rates of phosphorus by b a c t e r i a we re 4.84 The propor t ion of phosphorus tha t remains refractory af ter long-term bac te r i a l d e c o m p o s i t i o n of a l g a e and/o r m i x e d p l ank ton i c commun i t i e s ranges f rom 0 - 100% (Lee et a l . 1980). There a re n o c l e a r d i f f e rences b e t w e e n a e r o b i c a n d a n a e r o b i c d e c o m p o s i t i o n . G o l t e r m a n (1975) f o u n d app rox ima te l y 8 0 % of a l g a l phosphorus was c o n v e r t e d t o P C M w i th in t h r ee days a f te r i n d u c e d autolysis. A l a rge a m o u n t of phosphorus r e l eased by ce l l d e a t h m a y r e c y c l e r e p e a t e d l y within the b iomass a n d detrital pools be fore net regenera t ion occurs with, of course , some loss to the refractory p o o l e a c h c y c l e . The ne t i m p a c t of m ine ra l i za t ion o n phospho rus so lub i l i za t ion in s u r f a c e sediments d e p e n d s o n (Bostr&m et a l . 1988): 1) t he d e g r e e of d e c o m p o s i t i o n of set t led o r g a n i c mat te r a n d the d o m i n a n t t y p e of mineral izat ion (i.e. a e r o b i c or a n a e r o b i c ) ; 2) the initial phosphorus con ten t of settling o rgan i c matter ; 3) the avai labi l i ty of phosphorus in surrounding m e d i a ; 4) w h e t h e r sett l ing of o r g a n i c m a t t e r is m o r e or less c o n t i n u o u s or if it o c c u r s ep i sod i ca l l y ; a n d 5) t he t e m p e r a t u r e , r edox p o t e n t i a l , a n d o ther e n v i r o n m e n t a l f a c to r s tha t a f f e c t mineral izat ion a n d c h e m i c a l equi l ibria of s ign i f i cance t o phosphorus mobility. Severa l t ypes of m i c robes c a n t a k e u p phosphorus unde r a e r o b i c cond i t ions , a n d t h e n re lease it w h e n the env i ronment b e c o m e s a n a e r o b i c (Shapiro 1967; Osborn a n d Nicholls 1978; Mara is et a l . 1983; Fleischer 1986). Rap id up t ake of p h o s p h a t e under a e r o b i c c o n d i t i o n s is t h o u g h t t o b e c o u p l e d w i th s t o r a g e of p h o s p h o r u s in p o l y p h o s p h a t e granules (Marais et a l . 1983; Florentz et a l . 1984). This c a p a c i t y for luxury c o n s u m p t i o n of phosphorus m a y result in up t ake of POf" e v e n w h e n b a c t e r i a g row o n o r g a n i c mat te r with low C:P ratios (Levin a n d Shapiro 1965). This r ap id up t ake of POA is thought to involve the fol lowing t w o steps (Wetzel et a l . 1986): 1) utilization of o r thophospha te in po l yphospha te cha ins for ATP format ion ; a n d 2) util ization of ATP for synthesis a n d storage of poly-3-hydroxybutyrate (PHB). These reac t ions c a u s e a c c u m u l a t i o n of o r t hophospha t e in c y t o p l a s m . Therefore, the osmot i c pressure inside the ce l l increases a n d net diffusion of p h o s p h a t e out of the ce l l o c cu r s . PHB is a n ene rgy source used w h e n a e r o b i c cond i t ions recur. Po l yphospha te s t o r age u n d e r a e r o b i c cond i t i ons , f o l l o w e d by p o l y p h o s p h a t e uti l ization a n d PHB s torage in a n a e r o b i c waters c o u l d b e a compe t i t i v e a d v a n t a g e for mic robes that live w h e r e there a re cons tan t shifts b e t w e e n a e r o b i c a n d a n a e r o b i c cond i t ions . Severa l a l g a l , c y a n o b a c t e r i a l a n d bac t e r i a l spec ies in sur face lake sed iment h a v e b e e n f o u n d to p r a c t i c e p o l y p h o s p h a t e s torage (Rodhe 1948; J ensen 1968; C m i e c h 1981), a n d PHB granules h a v e b e e n f o u n d in c y a n o b a c t e r i a l cells in surface sediments ( C m i e c h 1981). Facu l ta t i ve a n a e r o b e s ( and some euca ryo tes such as yeasts) c a n rapidly t ake u p a n d re lease excess phosphorus under b o t h a e r o b i c a n d a n a e r o b i c condi t ions . In a series of 3 3 P t r a ce r exper iments Fleischer (1983, 1985, 1986) f o u n d that pure a n d m i x e d cultures of f acu l ta t i ve a n a e r o b e s c o l l e c t e d f rom lake sed iments a n d a c t i v a t e d s ludge c o u l d t ake u p phosphorus f rom newly p r e c ip i t a t ed Fe(lll) ge l under a e r o b i c condi t ions. This m ic rob ia l phosphorus up t ake c o i n c i d e d with solubil ization of Fe(lll) ge l . Pept izat ion or fo rmat ion of c o m p l e x e s we re thought to b e the pr inc ipa l processes invo lved . Under a n a e r o b i c cond i t i ons , t he b a c t e r i a r e l e a sed phosphorus , most of w h i c h h a d b e e n t a k e n u p b e f o r e t h e y c a m e in c o n t a c t with the ge l . These exper iments c a n b e s u m m a r i z e d as: A e r o b i c cond i t ions : Fe(lll)-Pi + M i c r o b i a l s -> Soluble Fe(lll) + M i c r o b i a l - ^ + P£ A n a e r o b i c cond i t ions : Soluble Fe(lll) + Microbial-(P t + Pj) -> Soluble Fe(ll) + Soluble P 2 + Microbial-Pi The phospho rus r e l e a sed is p r o b a b l y f rom s tored p o l y p h o s p h a t e s (Fleischer 1986). There fore , phospho rus mob i l i za t ion f rom living cel ls m a y con t r i bu t e t o phosphorus re lease f rom a n a e r o b i c sed imen t . The quan t i t a t i ve s i g n i f i c a n c e of this p rocess is, howeve r , unknown. 4.2 Materials and Methods B e c a u s e of t he u n e x p e c t e d l y low dissolved phosphorus concen t r a t i ons initially e n c o u n t e r e d in Powel l Lake , a more extensive study of phosphorus w a s d o n e t h a n for the other nutrients: samples we re c o l l e c t e d f rom five add i t i ona l stations as shown in Fig. 4-2. D i sso l ved r e a c t i v e phospho rus ( P O f ) , t o t a l ( o rgan i c ) p h o s p h o r u s , a n d to t a l p a r t i c u l a t e phosphorus w e r e d e t e r m i n e d . W a t e r w a s c o l l e c t e d in n e w , 10%-HCI-w a s h e d p o l y e t h y l e n e or p o l y p r o p y l e n e bott les tha t h a d neve r b e e n e x p o s e d to de te rgent . Samples we re pressure fi ltered with n i t rogen through 0.4 urn p o l y c a r b o n a t e N u c l e p o r e m e m b r a n e filters in the f ie ld using Niskin bottles with a d d e d pressure fittings. Bo th w a t e r s a m p l e s a n d filters c o n t a i n i n g pa r t i cu l a t e s w e r e f rozen o n dry i c e immed ia te l y af ter co l l e c t i on . Soluble Reactive Phosphorus Soluble reac t i ve phosphorus (SRP) w a s m e a s u r e d by the co lour imetr ic m e t h o d of M u r p h y a n d Riley (1962). Af ter fi ltration a n d r emova l of su lph ide b y purg ing with n i t rogen, a c o m p o s i t e r eagen t of m o l y b d i c a c i d , a s co rb i c a c i d a n d trivalent an t imony w a s a d d e d t o the samp le . The resulting c o m p l e x he te ropo ly a c i d is r e d u c e d in situ t o p r o d u c e a b lue c o m p l e x . Samples we re d i lu ted with DDW to < 2.5 j iM be fo re r eagen t add i t ion . Using 10 c m cel ls, the d e t e c t i o n limit was 0.02 j iM with a prec is ion of 0 .5% ( l a , rsd). This f r a c t i on is large ly c o m p o s e d of o r t h o p h o s p h a t e , a l t h o u g h it a lso inc ludes s o m e d isso lved o r g a n i c phosphorus as wel l . The a b s o r b a n c e w a s m e a s u r e d 10 min. af ter r e agen t add i t i on to minimize the contr ibut ion of o rgan i c phosphorus. Phospha te , SRP, a n d DIP (d isso lved i no rgan i c p h o s p h a t e ) will b e used i n t e r c h a n g e a b l y in this c h a p t e r . Total Phosphorus Total phosphorus (£P ) w a s d e t e r m i n e d a f ter o x i d a t i o n of al l P present by m a g n e s i u m nitrate t o p h o s p h a t e ( C e m b e l l a et a l . 1986). Two mL of 2 0 % m a g n e s i u m nitrate (in e thano l ) we re a d d e d to 40 mL samples in Pyrex er lenmeyer flasks con ta in ing w a s h e d boi l ing chips. Samples we re t hen bo i l ed vigorously until app rox ima te l y 8 0 % of the v o l u m e h a d e v a p o r a t e d . Glass slides w e r e p l a c e d over t he flasks to a l low vent ing a n d the hea t w a s r e d u c e d until spatter ing c e a s e d (when the samples we re almost dry). Hea t w a s then inc reased to m a x i m u m a n d ma in t a ined until evolut ion of b rown fumes of Fig. 4-2 M a p of Powel l Lake showing six stations (•) s a m p l e d for phosphorus analysis. N 0 2 w a s c o m p l e t e d . After c o o l i n g , the samples w e r e b rought b a c k t o their or ig inal vo lume with 0.1 N HCI, s e a l ed with paraf i lm, a n d then a l l owed to sit approx imate l y 24 h to a l l o w t h e salts t o redissolve. The s a m p l e s w e r e t h e n a n a l y s e d for p h o s p h a t e as d e s c r i b e d a b o v e . This d iges t i on t e c h n i q u e gives 93 - 100% r e c o v e r y for i no rgan i c p h o s p h o r u s , p h o s p h a t e esters, a n d p h o s p h o n a t e s , a n d a l so re leases phosphorus b o u n d to iron a n d a d s o r b e d to CaCG-3. Howeve r , it d o e s not re lease all phosphorus i n c o r p o r a t e d into apat i tes . The d e t e c t i o n limit is 0.05 [iM a n d the prec is ion is 5% (1 a , rsd). Particulate Phosphorus Par t i cu la te phosphorus (PP) w a s d e t e r m i n e d v i a thin film X-ray f l u o r e s c e n c e spec t romet r y (XRF). Filters w e r e f rozen immed i a t e l y af ter s a m p l e c o l l e c t i o n a n d the v o l u m e f i l tered w a s r e c o r d e d . S amp le s t a k e n f rom t h e sal ine por t ion of the wa te r c o l u m n w e r e r insed with D D W t o r e m o v e salt be fo re t hey w e r e f rozen. Filters we re t h a w e d a n d d r i ed in a d e s i c c a n t c h a m b e r . Filters we re t h e n m o u n t e d in nylon filter holders a n d c o u n t e d in a Philips PW1400 X-ray f l uo re s cence s p e c t r o m e t e r e q u i p p e d wi th a Rh t a rge t X-ray t ube . Fresh s tandards we re p r e p a r e d e a c h d a y by carefu l ly dr ipp ing lOO j i Lo f dilute K H 2 P 0 4 ( a n d N a ^ C M f o r S analysis) solutions so as t o c o v e r the N u c l e p o r e m e m b r a n e fairly even ly with drops of the s t anda rd . All s amp les c o n t a i n e d « 3 m g of part iculates; under such condi t ions , XRF signal response is a l inear func t ion of s amp le mass (Holmes 1981). All samples we re wel l a b o v e the d e t e c t i o n limit w h i c h was 0.97 nmo l . N o t e tha t b e c a u s e the m e t h o d used for pa r t i cu l a t e phosphorus w a s so sensitive, o f ten PP was d e t e c t a b l e where tota l phosphorus was not. The P O C : P P a n d PON:PP ratios r epo r t ed in this c h a p t e r are not c o m p l e t e l y a c c u r a t e , as the samples we re c o l l e c t e d with different equ ipment . P O C a n d P O N were c o l l e c t e d o n G F / C filters wi th a nomina l po re size b e t w e e n 1 a n d 2 n m . Par t i cu la te phosphorus samples w e r e c o l l e c t e d o n p o l y c a r b o n a t e N u c l e p o r e filters with a nomina l po r e size of 0.4 n m . Therefore , phosphorus m a y b e slightly o v e r e s t i m a t e d relat ive to c a r b o n a n d n i t rogen, i.e. the C:P a n d N:P ratios repor ted are p robab l y s o m e w h a t lower t h a n they are in situ. A l so , P O C a n d P O N measurements we re not m a d e o n the s a m e s a m p l e s as t h e PP s a m p l e s as the latter w e r e c o l l e c t e d o n d i f ferent d a y s , a n d somet imes , at different depths . To c a l c u l a t e the C:P a n d N:P ratios, s ome va lues h a v e b e e n in terpo la ted f rom the P O C , P O N , a n d PP curves (Figs. 4-9 a n d 4-10). 4.3 Results Powell Lake Soluble reac t i ve phosphorus is u n d e t e c t a b l e in the South basin a b o v e 175 m a n d r eaches a m a x i m u m of -0.7 u M in the bo t tom waters (Fig. 4-3). Total phosphorus is also u n d e t e c t a b l e in the ox ic part of t he South bas in w a t e r c o l u m n , but in the underly ing a n o x i c wa te rs , concen t r a t i ons r e a c h 3.7 p M (Fig. 4-5). Par t i cu la te phosphorus ranges f rom 0.005 - 0.013 \LM in the uppe r 225 m a n d increases to 0.14 \iM a t 345 m (Fig. 4-5). The bulk of t he to ta l phosphorus in the b o t t o m waters consists of SRP (-40 - 60%) (Fig. 4-7), whereas PP makes u p a b o u t 2 0 % of I P near the in ter face , d e c r e a s i n g to 5 - 10% in the u p p e r waters . The rema in ing phosphorus p o o l p r o b a b l y consists of d issolved o rgan i c phosphorus. B e c a u s e I P is u n d e t e c t a b l e a b o v e 140 m, the contr ibut ion of the various phosphorus f ract ions t o the I P p o o l c a n n o t b e c a l c u l a t e d in the u p p e r ox ic w a t e r c o l u m n . Both the par t i cu la te o rgan i c C:P (POC:PP) a n d N:P (PON:PP) mo la r ratios show large m a x i m a at the surface (1700 a n d 140 respectively) (Fig. 4-9). The POC : PP ratio then rapid ly d e c r e a s e s d o w n to 50 m, b e l o w w h i c h it is relat ively cons tan t (-300) t o the o x i c / a n o x i c in te r face . Be low the in te r f ace , t he P O C : P P ratio increases slightly, a n d remains fairly cons tan t until the b o t t o m 25 m, where it d e c r e a s e s sharply. The PON:PP mola r ratio profile is similar in shape to that of POC :PP , a l though the increase in PON:PP b e l o w t h e in t e r f a ce is m u c h m o r e p r o n o u n c e d (Fig. 4-9). A l so , PON :PP d e c r e a s e s ma rked l y b e l o w 200 m f rom a b o u t 80 to 8 at 340 m d e p t h . Dissolved inorgan i c N:P (DIN:DIP) molar ratios a re p lo t ted with PON:PP in Fig. 4-11. Because there is no d e t e c t a b l e p h o s p h a t e a b o v e 175 m, the DIN:DIP ratios are infinite in the u p p e r ox ic port ion of the w a t e r c o l u m n . This ratio is lowest at 175 m (-1100) a n d then increases t o approx imate l y 7300 in the bo t tom waters. In the other f ive sites s a m p l e d in Powel l Lake, SRP is u n d e t e c t a b l e at all dep ths at all stations. All stations a lso show very low levels of I P , with most concen t ra t ions b e i n g < 0.2 u M (Fig. 4-13). I P increases in the bo t tom anox i c waters of the East basin to 0.7 u M . PP concen t ra t i ons are also very low, with most samples con ta in ing < 0.02 u M PP (Fig. 4-14). The a n o x i c East bas in c o n t a i n s t h e most PP, w i th m a x i m u m c o n c e n t r a t i o n s of approx ima te l y 0.063 \iM. Sakinaw Lake S a k i n a w con t a i n s m u c h h igher levels of SRP t h a n Powe l l , w i th a m a x i m u m c o n c e n t r a t i o n of near ly 300 \iM in the b o t t o m waters (Fig. 4-4). Phospha te is d e t e c t a b l e a t all dep ths in the w a t e r c o l u m n , a l t hough in the uppe r ox ic waters it is present at very l ow c o n c e n t r a t i o n s of a b o u t 0.07 n M . Be low the o x i c / a n o x i c i n t e r f a ce , SRP rapid ly increases with d e p t h . X P is also present in low quantit ies in the oxic port ion of the wate r c o l u m n a n d then increases b e l o w the interface t o > 400 \iM in the b o t t o m waters (Fig. 4-6). PP displays t w o m a x i m a , at 20 m a n d a t the in te r f ace , w h e r e near ly 0.15 \M are present . Be low the in te r face PP rapid ly dec l i nes t o c o n c e n t r a t i o n s of a p p r o x i m a t e l y 0.005 n M . A g a i n the bulk of the I P p o o l consists of SRP; howeve r , in Sak inaw dissolved p h o s p h a t e m a k e s u p app rox ima te l y 8 0 % of the I P in the b o t t o m waters (Fig. 4-8). The p e r c e n t a g e of I P a t t r ibutab le t o SRP is m u c h less in the ox i c waters , a l t h o u g h right b e l o w the sur face SRP makes up a b o u t 5 0 % of the I P . PP contr ibutes a b o u t 2 0 % of the I P p o o l in the u p p e r ox i c wa te rs , but b e l o w the in te r f ace , a minor a m o u n t of the phosphorus is present in the par t icu la te phase . Both POC : PP a n d PON:PP va lues are extremely high at the sur face of Sak inaw, at nearly 5000 a n d 600 respect ively (Fig. 4-10). These ratios d e c r e a s e rapidly in the uppe r 10 m to app rox ima te l y 400 a n d 50. Be low the inter face bo th ratios increase with d e p t h to m a x i m a of 6300 (POC:PP) a n d 900 (PON:PP). The DIN:DIP ratios also display t w o m a x i m a , a l t h o u g h a t different a reas of the w a t e r c o l u m n (Fig. 4-12). DIN:DIP is greatest at the sur face a n d just a b o v e the inter face. Be low the inter face this ratio is relatively constant at about 27. Fig. 4-3 Soluble react ive phosphorus in Powell Lake. SRP is unde tec t ab l e a b o v e 175 m. Soluble reac t i ve phosphorus (uM) upper 30 m 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 20 40 E 60 a Q 80 100 120 • I Sakinaw OXIC anoxic 140' 1 • 1 1 1 1 • 1 i i t i i i i i i • i i . i i 0 50 100 150 200 250 300 Soluble reac t i ve phosphorus (jaM) d e e p e r than 30 m Fig. 4-4 Soluble react ive phosphorus in Sakinaw Lake. Upper sca le is for the ox ic wa te r co lumn (top 30 m). Bottom sca le is for the anox ic water co lumn (be low 30 m). Fig. 4-5 Soluble react ive , part iculate a n d tota l phosphorus in Powell Lake Soluble Reac t i v e Phosphorus (\LM) Total Phosphorus (jiM) Fig. 4-6 Soluble reac t i ve , part icu late a n d total phosphorus in Sak inaw Lake Fig. 4-7 P e r c e n t a g e of total phosphorus c o n -sisting of soluble react ive a n d part icu late P in Powel l Lake. Total P was u n d e t e c t a b l e a b o v e 140 m. % Total Phosphorus Fig. 4-8 P e r c e n t a g e of tota l phosphorus c o n -sisting of soluble reac t i ve a n d part icu late P in Sakinaw Lake. Fig. 4-9 Molar ratios of part iculate o rgan ic c a r b o n a n d nitrogen to part iculate phosphorus in Powel l Lake POC/PP 0 1000 2000 3000 4000 5000 6000 0 200 400 600 800 1000 PON/PP Fig. 4-10 Mo la r ratios of part icu late o rgan ic c a r b o n a n d nitrogen to part icu late phosphorus in Sak inaw Lake PON/PP 0 20 43 60 80 100 120 140 0 I i i i | i i i | i i i | i i i | i i i | i i j ,|. j -i-50 -103 £ 150 Q. <D Q 200 -250 303 -350 OXIC anoxic partic. Powell 2000 4000 6000 8030 DIN/DIP Fig. 4-11 Molar nitrogen to phosphorus ratios in Powel l Lake. Soluble reac t i ve phosphorus is unde tec t ab l e in the upper 175 m, resulting in infinite dissolved inorganic N:P (DIN/DIP) ratios. PON/PP 0 203 400 600 800 1003 0|— i— i— i—|— i— i— i—|— r—i— i—| i i i—|—i i i— 1^ I i i i t I i i i i I i t i i I i i i i I i i i i I i i i i 0 20 40 60 80 100 120 DIN/DIP Fig. 4-12 Molar nitrogen to phosphorus ratios in Sakinaw Lake Total Phosphorus (nM) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Fig. 4-13 Total phosphorus in various basins a n d at the h e a d of Powell Lake (see Fig. 4-2 for locations). The East basin conta ins relict seawater . Part iculate Phosphorus (^M) 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Fig. 4-14 Part iculate phosphorus in various basins a n d at the h e a d of Powel l Lake (see Fig. 4- 2 for locations). The East bas in conta ins relict seawate r . Log (K s p * IAP) 3 D -- B - C o C Q j - - • - C a s O H C P O O s - • o- • C a H P 0 4 —e-Ca 4 H(P04 ) j — 0 ~ C a 2 F e ( P O « ) * — F e 3 ( P 0 4 ) 2 - l - - M n 3 ( P O ) 2 — a — MgHPO-4 M g N H 4 P 0 4 — X — M g 3 ( P 0 4 ) 2 Fig. 4-15 Saturation state of phosphorus minerals a n d ca l c i t e in Powel l Lake. Log (K *IAP) > 0 = 5 p supersaturated, < 0 = undersaturated. Fig. 4-16 Saturation state of phosphorus minerals a n d ca l c i t e in Sak inaw Lake. Log (K *IAP) > 0 = sp supersaturated, < 0 = undersaturated. g 4.4 Discussion The most striking d i f f e rence b e t w e e n Powel l a n d Sak inaw Lakes is s een in the distribution of phosphorus . In Sak inaw Lake , p h o s p h a t e is r e l eased a t d e p t h (Fig. 4-4), similar t o a m m o n i u m a n d dissolved sil icon ( C h a p t e r 3). Interstitial waters of organic-r ich, a n o x i c sed iments a re o f ten highly e n r i c h e d in p h o s p h a t e , a m m o n i u m a n d dissolved si l icon c o m p a r e d with the overly ing wa te r (e.g. Rit tenberg et a l . 1955; N i ssenbaum et a l . 1972; Har tmann et a l 1973; Sholkovitz 1973; Har tmann et al 1976; Price 1976; Martens et a l . 1978; Morse a n d C o o k 1978), w h i c h supports a n a p p r e c i a b l e u p w a r d flux of these nutrients f rom the sed imen t sur face (e .g. S ch ippe l et a l . 1973; Suess 1976; Aller 1980; Elderfield et a l . 1981). B e cause d e e p waters in Sak inaw Lake are also e n r i c h e d in these three nutrients, as well as H2S, D O C , a n d alkalinity, the anox ic port ion of the wate r c o l u m n c a n b e c o n s i d e r e d to b e a n a n a l o g u e for the interstitial w a t e r of r e d u c i n g c o a s t a l sediments. Unlike Sak inaw Lake , Powel l Lake has very low concen t ra t ions of p h o s p h a t e at d e p t h (Fig. 4-3). Soluble reac t i ve phosphorus (SRP) is very low in the b o t t o m water , with a m a x i m u m c o n c e n t r a t i o n of 0.7 |xM, c o m p a r e d to 300 p.M in Sak inaw (Fig. 4-4). In most other aspec t s the compos i t i on of the b o t t o m waters of Powel l a n d Sak inaw Lakes is very similar: Powel l a lso conta ins h igh levels of H2S, NH4, Si(OH)4, D O C , a n d alkalinity at d e p t h . It is therefore surprising that the phosphorus levels are so different. It is espec ia l l y unusua l for phosphorus t o b e so low , w h e n a m m o n i u m c o n c e n t r a t i o n s a r e so high (almost 4 mM) . Sakinaw Lake Dissolved phosphorus increases t o very h igh c o n c e n t r a t i o n s in Sak inaw Lake b o t t o m wate rs pr imari ly d u e t o minera l i za t ion a n d u p w a r d di f fusion of i no rgan i c p h o s p h a t e (Fig. 4-4). Due to the d e c r e a s e d growth e f f i c i ency of a n a e r o b i c (relative to a e r o b i c ) m e t a b o l i s m , a n a e r o b e s must assimilate larger quant i t ies of c a r b o n , t he reby a l s o ass im i l a t i ng m o r e a s s o c i a t e d p h o s p h o r u s , resul t ing in r e l e a se of e x c e s s phosphorus not requ i red for nutrition ( Fenche l a n d B lackburn 1979). In the previous c h a p t e r I c o n c l u d e d , b a s e d o n the cons t ancy of the C :N ratios in Sak inaw Lake (Fig. 3-5), tha t o r g a n i c ma t t e r w a s b e i n g d e g r a d e d in the sed iments rather t h a n in the wa te r c o l u m n as it sett led. However , the part icu late C:P a n d N:P ratios d o increase with d e p t h in t h e a n o x i c por t ion of the wa te r c o l u m n (C:P increases -25 x f rom in te r face to near b o t t o m , N:P -23 x (Fig. 4-10)). Therefore, s ome d e g r a d a t i o n d o e s o c c u r in the wa te r c o l u m n , with phosphorus b e i n g re l eased preferential ly relative to c a r b o n a n d ni trogen as the par t i c les sink. The re lease of P O f c a n n o t b e d e t e c t e d in the DIN:DIP ratios, howeve r . Be low the oxyc l ine , t h e DIN-.DIP rat io is r easonab l y cons tan t with d e p t h , i.e. b o t h a m m o n i u m a n d p h o s p h a t e are re leased at d e p t h , but in app rox ima te l y the s a m e propor t ion . A l t h o u g h the PON:PP profiles i nd i c a t e some d e c o m p o s i t i o n o c c u r s in the w a t e r c o l u m n , t h e bulk of it o c c u r s in the sed iments a n d thus the smal l a m o u n t of phosphorus tha t is r e m o v e d f rom the PP f rac t ion in the w a t e r c o l u m n (PP d e c r e a s e s from -0.01 | iM to 0.003 J I M ) is s w a m p e d by the high concent ra t ions of P O ? r e l ea sed f rom the sed iments . In Sak inaw Lake the PP max imum at the interface (Fig. 4-6) co inc ides with the P O C a n d P O N m a x i m a (Fig. 3-5), w h i c h is consistent with the interpretat ion a d v a n c e d earlier that the p e a k represents ba c t e r i a . There is a lso a PP m a x i m u m at 20 m, most likely d u e to p h y t o p l a n k t o n , tha t d o e s not c o i n c i d e with the P O C m a x i m u m at 10 m. This m a y ref lect m o v e m e n t of the phy top l ank ton b l o o m , as samples we re not c o l l e c t e d o n the s a m e d a y for b o t h P O C a n d PP. In the DIN:DIP profile (Fig. 4-12), there are a lso t w o m a x i m a , nea r the sur face a n d just a b o v e the in ter face , wh i ch corre la te wel l with the PP m a x i m a . These DIN:DIP m a x i m a i nd i c a t e regions of a c t i v e . g r o w t h ( a n d c o n s e q u e n t p ropor t iona te l y h igher phosphorus up take ) of p h y t o p l a n k t o n (surface) a n d b a c t e r i a ( in ter face ) . The ve ry l ow DIN:DIP v a l u e at 35 m m a y , in par t , ref lect r emova l of i norgan i c n i t rogen v i a reduc t ion of NO3 to N 2 by denitr ifying b a c t e r i a (Fig. 3-7). Howeve r , it m a y also b e d u e to desorpt ion of p h o s p h a t e from iron oxides just b e l o w the in ter face , as the low DIN:DIP v a l ue corre lates with the dissolved iron m a x i m u m (Fig. 5-10). iron oxides very e f f e c t i v e l y s c a v e n g e p h o s p h a t e f rom w a t e r a n d t h e p r e c i p i t a t i o n of i n o r g a n i c p h o s p h a t e b y iron ox ides is b e l i e v e d to limit t h e ava i l ab i l i t y of phospho rus in t r o p h o g e n i c wa te r , t he r eby r e d u c i n g pr imary product iv i ty (Mort imer 1941). W h e n the iron oxides a re r e d u c e d b e l o w the ox i c/anox i c in ter face (d iscussed in C h a p t e r 5), any a d s o r b e d p h o s p h a t e is re l eased . In estuaries, the o b s e r v e d c o n c e n t r a t i o n of dissolved p h o s p h a t e m a y b e entirely con t ro l l ed by processes of adso rp t ion a n d desorp t ion o n iron ( a n d other) par t ic les ( Pomeroy et a l . 1965; Butler a n d Tibbitts 1972; Stirling a n d W o r m a l d 1977). As we l l , adso rp t i on of so lub le p h o s p h a t e b y iron oxyhydrox ides has b e e n pos tu l a ted as the m e c h a n i s m control l ing the phosphorus distribution in m a n y sub-t ida l sediments (Stumm a n d Leckie 1970) a n d lake sediments (Williams et a l . 1970; Shukla et a l . 1971; Li et a l . 1972; Lijklema 1980). At pH < 8.5, amorphous hyd ra ted ferric oxide c a n r e m o v e as m u c h as 5% of its o w n we igh t of phosphorus as o r t h o p h o s p h a t e f rom solution (S tamm a n d Kohlschutter 1965). Extraordinarily h igh C:N:P ratios are f o u n d in the surface wa te r part iculates of both S ak i naw a n d Powe l l Lakes (C:N;P (molar) -4800:580:1 a n d -1700:180:1 respect ive ly ) , a l t hough the P O C : P P ratios d e c r e a s e to -400 throughout the rest of the ox ic port ion of b o t h w a t e r co lumns (Figs. 4-9 a n d 4-10). These ratios a re cons ide rab l y higher t han the a v e r a g e C:N:P of phy top lankton (106:16:1) (Redfield et a l . 1963). However , the wel l known Redf ie ld ratio is a cons tan t sto ichiometr ic relation w h i c h d o e s not a lways exist in nature (Takahashi et a l . 1985); different a lga l groups a c c u m u l a t e fat , c a rbohyd ra t es a n d other s to r age p r o d u c t s in va r y ing proport ions a n d h e n c e c o n t a i n var ious proport ions of c a r b o n , n i t rogen , a n d phosphorus . This var ia t ion c a n e v e n b e f o u n d within spec i e s , d e p e n d i n g o n various env i ronmenta l factors (Lewin 1962), a n d the sestonic C:P ratio c a n vary da i ly ( K a g a w a et a l . 1988). The C:N:P ratios of phy top lank ton c a n also vary wide ly a c c o r d i n g to the nutrit ional status of the phy top l ank ton , with h igh C:P a n d N:P ratios ind ica t ing phosphorus de f i c i ency (e.g. Epp ley a n d Renger 1974; Perry 1976; Rhee 1978; G o l d m a n et a l . 1979; Hea l ey a n d Hendze l 1975, 1979, 1980; G a c h t e r a n d B loesch 1985; Tezuka 1985; Harris 1976; Uehl inger 1981). G a c h t e r a n d B loesch (1985) f o u n d that the b iomass C:P ratio of a g r e e n a l g a , Chlamydomonas, increases dur ing summer , w h e n phosphorus is growth-limiting; during sufficient or excess P supply , the Chlamydomonas C:P mo la r rat io was o b s e r v e d to b e less t h a n 106, whe reas a d e c r e a s e in SRP supply p r o m o t e d a n increase in the C:P ratio to m a x i m u m va lues in the range 300 - 500. The C:P m o l a r rat io of hea l thy a l g a e in phosphorus-l imited con t i nuous cultures increases to more t han 900 (Uehlinger 1981; G a c h t e r a n d Bloesch 1985), a n d rap id P l each ing of d e a d a l g a e furthers this i nc rease in the C :P ratio of detritus u p t o 1470 ( G o l t e r m a n 1964; Uehl inger 1986). H e a l e y a n d Hendze l (1980) f o u n d C:P mo la r ratios as h igh as 1840 in several C a n a d i a n lakes. C:P a n d N:P ratios c a n also d r o p to very low levels w h e n a l g a e assimilate m o r e nutrients t h a n they n e e d , the so-ca l led "luxury* up t ake . This has b e e n seen in a study of 15 lakes hav ing different t rophic levels, whe re N:P ratios in s u s p e n d e d solids va r i ed b e t w e e n 4-13 (Forsberg et al . 1978). Thus, nutrient supp ly a p p e a r s t o r egu l a t e t he s to i ch iomet r i c c o m p o s i t i o n of b i o m a s s . C : P rat ios c l o s e t o t h e R e d f i e l d v a l u e e v i d e n t l y o c c u r on l y w h e n phy top l ank ton growth is not l imited by phosphorus , a situation not t yp i ca l of t e m p e r a t e f reshwater l akes , s u c h as Powe l l a n d Sak inaw dur ing summer . In phosphorus-l imited env i ronments , this nutrient is m u c h more eff ic ient ly used b y a l g a e for biosynthesis of o r g a n i c mat ter , a l l ow ing the phy top l ank ton to assimilate m u c h more t h a n 106 mo l of c a r b o n per mo l of phosphorus. High C:P ratios of seston c a n also ref lect a n a l loch thonous origin. Cons ide r ab l e proport ions of s u s p e n d e d P O C m a y b e detr ital a n d not a l g a l , d e p e n d i n g o n loca t ion . However , detr i tal input should b e minimal in bo th Powel l a n d Sak inaw Lakes, particularly in the former w h e r e there is no di rect freshwater input t o the south basin. For the s a m e r e a s o n . PIP shou ld b e min ima l a n d h e n c e the PP concen t r a t i ons m e a s u r e d in bo th Powel l a n d Sak inaw should represent primarily POP. Powell Lake Phospha t e is first d e t e c t a b l e in Powel l Lake at 175 m (Fig. 4-3), w h i c h is w h e r e N H l starts t o i n c r ease (Fig. 3-6). Therefore it w o u l d a p p e a r tha t t he P O * is b e i n g g e n e r a t e d f rom mineral izat ion of o rgan i c matter as in Sak inaw Lake. However , the N H l c o n c e n t r a t i o n cont inues t o increase fairly rapidly whi le the c o n c e n t r a t i o n of P O * stays fairly cons tan t t o 250 - 275 m; b e l o w this level , the PO4 c o n t e n t a lso beg ins t o inc rease rapidly. This is readi ly seen b y examin ing the DIN:DIP ratio, w h i c h is "infinite" d o w n to 175 m (Fig. 4-11). Pe rhaps phosphorus is r e l ea sed at this d e p t h v i a deso rp t ion f rom iron oxides. Par t i cu la te iron w a s not m e a s u r e d in this study, but d issolved iron (Fe 2 + ) rapidly inc reases t o h igh c o n c e n t r a t i o n s (-170 t iM) b e t w e e n 150 m a n d 200 m (Fig. 5-9), i nd i ca t i ng tha t a s ignif icant a m o u n t of par t i cu la te iron must b e present a t sha l lower dep ths . Be low 175 m, more NH4 t h a n PO4 a p p e a r s t o b e r e l e a s e d , or PO4 is b e i n g preferent ia l ly c o n s u m e d . Be low 250 m, whe re the PO4 c o n c e n t r a t i o n inc reases , the DIN:DIP rat io b e c o m e s fairly cons tan t ( ignoring the 325 m d a t u m ) . The PON:PP ratio a c tua l l y d e c r e a s e s with d e p t h , whe reas P O O P O N increases (Fig. 3-4), i nd i ca t ing that ni t rogen is b e i n g re l eased a n d phosphorus is b e i n g preferential ly i n c o r p o r a t e d into the par t i cu la te phase . The par t i cu la te phosphorus c o n c e n t r a t i o n remains very low in Powel l Lake until nea r the b o t t o m . There is no dec l i ne in PP in the b o t t o m wa te r c o m m e n s u r a t e with the P O C a n d P O N d e c r e a s e s d e s c r i b e d earl ier (Fig. 3-4). Thus, there is a large d e c r e a s e in the C:P a n d N:P ratios b e l o w -300 m (Fig. 4-9). In C h a p t e r 3,1 suggested that the P O C a n d P O N d e c r e a s e s w e r e d u e t o f l o c c u l a t i o n a n d subsequen t r a p i d sinking of la rger part ic les ; but a t first g l a n c e , the h igh PP va lues i nd i ca te tha t this m a y not b e the c a s e . However , the higher concen t ra t ions of PP m a y reflect the p r e sence of grea ter numbers of b a c t e r i a nea r t he sed iment-water in te r face where there is more substrate a n d the PO4 c o n c e n t r a t i o n is relatively h igh. In support of this, note that the d e c r e a s e in P O C is larger t h a n tha t of P O N nea r the b o t t o m , resulting in a d e c r e a s e in the par t i cu la te C :N ratio. As n o t e d in C h a p t e r 3, b a c t e r i a a re known to h a v e bo th lower C :N a n d C:P ratios t h a n phy top lank ton . The low c o n c e n t r a t i o n of PO4 in t h e b o t t o m w a t e r of Powel l Lake is unusual as PO4 is usually m ine ra l i zed in a n o x i c env i ronments as is s e e n in Sak inaw Lake . Three exp lanat ions for the low phosphorus concent ra t ions in Powel l Lake are as follows: 1) t he ana l y t i ca l t e c h n i q u e used d i d not d e t e c t the phosphorus present; 2) t h e phosphorus is b e i n g r e m o v e d inorgan ica l l y f rom the w a t e r c o l u m n v i a minera l prec ip i ta t ion or by adsorpt ion on to part ic les be fore they fall rapidly t o the b o t t o m ; a n d 3) t he c o n c e n t r a t i o n of phosphorus in the lake is naturally very low so that very little c a n b e t a k e n u p by organisms. The first m e c h a n i s m c a n b e ruled out direct ly , as s t a n da r d add i t ions of KH2PO4 we re m a d e t o samp les with subsequen t no rma l co l ou r d e v e l o p m e n t . A l so , t he t e c h n i q u e w o r k e d wel l in the chemical ly-similar Sak inaw Lake water . B e c a u s e various phosphorus minera ls a r e k n o w n t o fo rm in a q u a t i c env i ronments , t he s e c o n d o p t i o n warrants d e t a i l e d at tent ion a n d will b e discussed in t he fol lowing sect ion. Phosphorus Removal Due to Adsorption Phospha te is readi ly a d s o r b e d on to c lays , iron oxyhydroxides a n d C a C 0 3 . O n c e s o r b e d , the ion is not so readi ly d e s o r b e d , a n d the process m a y b e irreversible (Barrow 1983). As t ime a n d dissolved phosphorus concen t ra t ions inc rease , so d o e s the quqnt i ty of phosphorus t a k e n up . Gene ra l l y , sorpt ion inc reases as t h e ion ic s t rength of the b a c k g r o u n d so lut ion inc reases . The south bas in of Powe l l L ake is fa r f rom major terr igenous sed iment a n d there is a l a ck of detrital c lays in source rocks of the d r a i nage bas in (B. Barnes pers. c o m m . ) ; therefore there is little external input of detrital c l ay . As m e n t i o n e d earlier, a n y PO4 a d s o r b e d to iron oxyhydroxides in the u p p e r waters will b e r e l eased in the anox i c waters w h e n the iron is r e d u c e d . C a l c i u m p lays a n impo r t an t role in p h o s p h o r u s r e m o v a l in m a n y lakes. Phospha te has b e e n shown to adso rb strongly o n c a l c i u m c a r b o n a t e (Co l e et a l . 1953; d e Kane l a n d Morse 1978; Otsuki a n d Wetzel 1972; K i tano et a l . 1978) a n d this has b e e n used to exp la in w h y c a l c i u m ca rbona te-r i ch sediments c o n t a i n low concen t ra t i ons of d issolved p h o s p h a t e in their po re waters (Berner 1973; Morse a n d C o o k 1978). Freshly precipitat ing C a C 0 3 absorbs p h o s p h a t e very ef fect ive ly , wi th t yp i c a l P : C a C 0 3 ratios of 1:100at high PO4 concentrat ions or 1:1000 at low P O f concent ra t ions (Lijklema et a l . 1983). The p r e s e n c e of e v e n a smal l a m o u n t of p h o s p h a t e ions in a pa ren t solut ion favours c a l c i t e f o r m a t i o n , a l t h o u g h p h o s p h a t e ions a re c o p r e c i p i t a t e d m o r e eas i ly wi th a ragon i te t han with ca l c i t e (Krtano et a l . 1978). C a C 0 3 p rec ip i t a t i on is f a v o u r e d by h igh t e m p e r a t u r e ( de c r ea s i ng solubility of b o t h C a C 0 3 a n d CO2) a n d h igh pH (Otsuki a n d Wetze l 1972). The c o p r e c i p i t a t i o n of p h o s p h a t e with c a l c i t e d u e t o the rise in phi a c c o m p a n y i n g photosynthet ic utilization of CO2 is we l l k n o w n in mar l lakes (Otsuki a n d Wetze l 1972). Ishaq a n d Kaul (1988) f o u n d photosynthet i ca l l y- induced coprec ip i t a t i on in a H ima l ayan lake where the ca lc ium-r ich sed imen t a c t s as a n exce l l en t phosphorus t rap. The phosphorus u p t a k e was sufficient t o coun te r a 4 0 % increase in the phosphorus input to the lake during the per iod 1971 -1981: no signif icant increase in phosphorus concen t r a t i on o c c u r r e d in lake waters during that t ime ( Ishaq .1985). A similar p h e n o m e n o n has a lso b e e n o b s e r v e d in B lack Lake ( C a n a d a ) w h e r e so luble reac t i ve phosphorus (SRP) concen t r a t i ons e x c e e d i n g 2.5 | iM (Murphy et a l . 1983) fall t o zero in the pho t i c z o n e during b looms of c y a n o b a c t e r i a a n d a s s o c i a t e d i n d u c e d C a C 0 3 prec ip i ta t ion . In b looms where no C a C 0 3 p r e c i p i t a t e d , the SRP d e c r e a s e w a s smal l . The saturat ion state of C a C 0 3 was c a l c u l a t e d using a c o m p u t e r m o d e l (MINEQL), as d e s c r i b e d in A p p e n d i x 1. The results show that C a C 0 3 is undersa tu ra ted at all depths in Powe l l L a k e , e x c e p t a t 300 m a n d b e l o w , w h e r e t h e a lka l in i ty a n d c a l c i u m c o n c e n t r a t i o n s a r e ve ry h igh (Fig. 4-15). As suming tha t t h e M INEQL results a re representa t i ve for these waters it is c l e a r that C a C 0 3 c a n n o t r e m o v e p h o s p h a t e at depths a b o v e 300 m. In add i t i on , it is unlikely that ca l c i t e is prec ip i ta t ing at > 300 m either, g i v en tha t c a l c i t e is only ba re l y sa tu ra ted a t this leve l . The p r e s e n c e of M g 2 + strongly i m p e d e s the g rowth rate of C a C 0 3 crystals a n d thus a h igh supersaturat ion is usually r equ i r ed t o e f f e c t p rec ip i t a t i on (S tumm a n d M o r g a n 1981). C a C 0 3 f o r m a t i o n a lso requires s e e d crystals for nuc l ea t i on for w h i c h there is no detrital source in Powel l Lake. A l so , lacustr ine p l ank ton w h i c h p r o d u c e c a l c a r e o u s shells a re ext remely rare; no such organisms w e r e seen in mid-July p lank ton tows c o l l e c t e d in Powel l Lake (Styan 1976; B. Barnes pers. c o m m . ) . Therefore, g i ven the compara t i v e l y low pH (5.7-6.8) (Fig. 3-10), relatively low yea r round sur face t empera tu res (usually < 10°C), h igh concen t ra t ions of M g 2 \ a n d lack of s e e d crystals, it is unlikely that inorganic C a C 0 3 p rec ip i ta t ion is a very important process in Powel l Lake a n d h e n c e phosphorus c a n n o t b e r e m o v e d v i a this process. No te that C a C 0 3 is s a t u r a t e d in the d e e p wate rs of in Sak inaw Lake (Fig. 4-16). H o w e v e r , prec ip i ta t ion in Sak inaw Lake is unlikely for the s a m e reasons as in Powel l . Phosphorus Removal via Direct Precipitation A n u m b e r of p h o s p h a t e minerals a re k n o w n to form au th igen i ca l l y in natura l waters or sed iments , i n c lud ing ch lo r apa t i t e (Ca5(P04) 3 CI) , f l uo rapa t i t e (Ca 5 (PCM) 3 F) , h y d r o x y l a p a t i t e (Ca 5 ( PC>4 ) 3 OH) , strengite ( F e P 0 4 « 2 H 2 0 ) , v iv iani te ( F e 3 ( P 0 4 ) 2 » H 2 0 ) , r edd ing i t e (Mn 3 (PC>4) 2 ) . struvite (MgNH 4 P04«6H 2 0) , a n d newbery i t e (MgHP04«3H 2 0) . Environments sui table for au th igen i c p h o s p h a t e minera l fo rmat ion a re mostly f o u n d in highly r e d u c e d sed imen t s , w h e r e minera l iza t ion a n d r e d u c t i o n t yp i ca l l y a d d h igh c o n c e n t r a t i o n s of i ron, p h o s p h a t e a n d other ions to interstitial solut ion. Howeve r , in Powel l Lake , p h o s p h a t e remains in low c o n c e n t r a t i o n until very nea r the b o t t o m , never e x c e e d i n g 0.7 yM (Fig. 4-3). The saturat ion state of var ious phosphorus minerals was c a l c u l a t e d v i a MINEQL for b o t h Powe l l a n d Sak inaw Lakes (Figs. 4-15 a n d 4-16). Al l minerals w e r e f o u n d t o b e undersa tu ra ted in Powel l Lake ; most of t h e m extremely so. Hyd roxyapa t i t e is t h e on ly phosphorus minera l tha t a p p r o a c h e s saturat ion in Powel l L ake , a n d then only a t 325 m d e p t h . Therefore, phosphorus r emova l in Powel l Lake v i a minera l fo rmat ion is unlikely t o o c c u r in Powel l Lake. Unlike Powel l Lake , severa l phosphorus minerals a re sa tu ra ted in Sak inaw Lake. H y d r o x y a p a t i t e is supe r sa tu r a t ed th roughou t most of t he a n o x i c w a t e r c o l u m n in Sak inaw (Fig. 4-16). Apa t i t e is t he rmodynamica l l y the least soluble p h o s p h a t e mineral in natura l waters , wi th c a l c i u m hydroxyapa t i t e (Ca 5 ( P04 )30H) a n d c a l c i u m f luorapat i te (Ca 5 ( P04 )3F ) b e i n g the least soluble forms (Emerson 1976). Apa t i t e s c a n b e d i rect ly p r e c i p i t a t e d o n sur faces of b i o g e n i c s i l ica a n d / o r i no rgan i c phases s u c h as c a l c i t e (Burnett 1977; S t u m m a n d Leck ie 1970) or it c a n r e p l a c e C a C 0 3 ( D A n g l e j a n 1968; M a n h e i m et a l . 1975). Wel l crystall ized au th igen i c apa t i t e a n d c a r b o n a t e apa t i t e h a v e b e e n ident i f ied in mar ine sediments (Gu lb randsen 1969; Al tschuler 1973). The p resence of poor ly crystall ine part ic les in lacustrine sediments has a lso b e e n sugges ted (Emerson a n d Widmer 1978), but the prec ip i tat ion kinetics of apa t i t e in such environments seem to b e sluggish (Frevert 1979). A p a t i t e p rec ip i t a t ion occu r s under similar condi t ions to that of CaCC>3. e x c e p t that reasonab ly high concent ra t ions of P 0 4 are requ i red , as the r eac t i on rate is strongly r e d u c e d at h igh C O f / P O j ratios (Stumm a n d Leck ie 1970). Supersaturat ion has b e e n f o u n d for apa t i t e in m a n y sediments (Burnett 1977; D 'Angle jan 1968; G a u d e t t e a n d Lyons 1980; Krom a n d Berner 1980; M a n h e i m 1974; C a r i g n a n 1984; Emerson 1976; Holdren a n d Armstrong 1986; Lofgren a n d Ryding 1985a,b; Norvel l 1974) a n d results f rom nuc l ea t i on barriers: the necessa ry s e e d crystals m a y b e absen t (de Boer 1977), or M g 2 + (Martens a n d Harriss 1970; H a n d s c h u h a n d Orge l 1973), or o rgan i c c o m p o u n d s (Stumm 1973) m a y a c t as sur face inhibitors for nuc lea t ion . Where the M g 2 + c oncen t r a t i on is h igh relative to C a 2 + as in Sak inaw Lake ( a n d Powel l ) , supersaturat ion m a y r e a c h such a d e g r e e that m a g n e s i a n c a l c i t e or a ragon i t e m a y prec ip i ta te metas tab ly (e.g. Berner 1975). O r g a n i c a d s o r b a t e s a lso inhibit t h e crysta l l izat ion r eac t i ons , e spec i a l l y at lower pH va lues . S t umm (1973) f o u n d tha t a t y p i c a l n o n i o n i c o r g a n i c su r f ac tan t , Triton X-100, a t a c o n c e n t r a t i o n of 5 x 10"5 M c a u s e d a d e c r e a s e of a b o u t 5 0 % in the crystall ization rate at pH 6.8; n o signif icant in ter ference o c c u r r e d at pH va lues a b o v e 7.4. He sugges ted that this rate r educ t ion was d u e to adsorpt ion of the surface-act ive m o l e c u l e at the crystal-growth sites. At h igher pH the growth of the crystall ine latt ice m a y b e rap id e n o u g h to s imply c o v e r o v e r the a d s o r b e d m o l e c u l e (Stumm a n d Leck ie 1970). Dissolved PO4 d o e s d e c r e a s e in t h e b o t t o m 20 m of Sak inaw Lake , h o w e v e r , a p a t i t e is unlikely to prec ip i t a t e in Sak inaw Lake d u e t o t h e l a ck of s e e d crystals, h igh c o n c e n t r a t i o n s of M g 2 * , a n d D O C . Severa l other minerals a re sa tura ted in Sak inaw Lake b o t t o m waters. Mg 3 (P04)2 is sa tu ra ted a t 75 m a n d d e e p e r . However , a l though this mineral is very insoluble, struvite (MgNH4P04»6H 20) a n d newbery i te (MgHP0 4 »3H 2 0 ) a lways prec ip i ta te preferential ly t o M g 3 ( P 0 4 ) 2 ( A b b o n a et a l . 1982). Both mar ine a n d fresh porewaters h a v e b e e n repor ted to b e sa tura ted or supersaturated with respect t o struvite (Elderfield et a l . 1981; Martens et a l . 1978; M c C a f f r e y et a l . 1980). Handschuh a n d Orge l (1973) f o u n d that struvite instead of apa t i t e p r e c i p i t a t ed w h e n o r thophospha te was a d d e d to s e a w a t e r con ta in ing .NHl c o n c e n t r a t i o n s similar t o those f o u n d in nearshore mar ine interstitial waters . Struvite f o r m a t i o n has a l so b e e n o b s e r v e d dur ing d e c o m p o s i t i o n of n i t rogen-r ich o r g a n i c materials in laboratory exper iments (Ma lone a n d Towe 1970) a n d in cultures of sulphate-r e d u c i n g b a c t e r i a , u n d e r c o n d i t i o n s c l o se l y a p p r o x i m a t i n g t h e a n o x i c ma r i ne sed imentary env i ronment (Hal lberg 1972). Newbery i te is a lways a s s o c i a t e d with struvite a n d it m a y form by d i rec t p rec ip i ta t ion or by d e c o m p o s i t i o n of struvite (Boistelle a n d A b b o n a 1981). Howeve r , newbery i te prec ip i ta tes only in a def ini te d o m a i n of pH a n d concen t ra t ion i.e. pH < 5.8 a n d PO4 concent ra t ions > 0.03 M (Boistelle a n d A b b o n a 1981). Ou t s i de this d o m a i n , struvite depos i t s , or n o p r e c i p i t a t i o n o c c u r s a t a l l . Struvite prec ip i ta tes whe re pH is < 6.8 a n d p h o s p h a t e concen t ra t ions are > 10 m M ( A b b o n a et al . 1982) a n d is metas tab le a t low NH4 act iv i ty, transforming into newbery i te w h e n (NH 4) < 15 n M . Thus, the prec ip i ta t ion of newbery i te a n d struvite requires h igh m a g n e s i u m a n d p h o s p h a t e concen t r a t i ons ( a n d a m m o n i u m for struvite) t o p rec ip i t a te , all of w h i c h are present in Sak inaw Lake d e e p water . PO4. NH4 a n d M g 2 + c oncen t r a t i ons d o d e c r e a s e nea r the b o t t o m in Sak inaw Lake (Figs. 2-15,3-7,4-6), howeve r , bo th these minerals are undersa tu ra ted in Sak inaw a n d thus are unlikely t o form. S ince struvite a n d newbery i te a re unde r sa tu r a t ed in Sak inaw Lake , it is a lso unlikely tha t M g 3 ( P 0 4 ) 2 p rec ip i t a tes in Sak inaw Lake , e v e n t h o u g h this mineral a p p e a r s t o b e saturated. A n a p a i t e was also f o u n d to b e sa tura ted in Sak inaw Lake. Nr iagu a n d Dell (1974) s u g g e s t e d that a n a p a i t e (Ca 2 Fe (P04) 2 »4H 2 0) c o u l d o c c u r t oge the r with v iv ianite a n d redding i te a n d that a t the pH va lues , a n d c a l c i u m a n d phosphorus concent ra t ions likely t o b e e n c o u n t e r e d in m a n y f r e s h w a t e r s e d i m e n t s , a n a p a i t e , r a t he r t h a n h y d r o x y a p a t i t e , w o u l d b e the s t ab l e , C a - b e a r i n g p h o s p h a t e minera l . H o w e v e r , this mineral has never b e e n ident i f ied in mar ine or lacustrine sediments t o m y k n o w l e d g e . V iv ian i te (Fe 3(P04)2) is the s tab le p h o s p h a t e minera l in r e d u c i n g env i ronments (Nr iagu 1972) a n d yet it is highly undersa tura ted in bo th lakes. It is easily r e cogn i zab l e in the f ie ld as it o c cu r s c o n c e n t r a t e d as c l e a r whi te spots in sed iments w h i c h turn bright b lue u p o n exposure t o air d u e to ox idat ion of part of the Fe(ll) within the vivianite crystal l a t t i c e , f o r m i n g a m i x e d iron (11,111) p h a s e of i n d e t e r m i n a t e c o m p o s i t i o n , t e r m e d ker tschen i te (Faye et a l . 1968). High ferrous iron act iv i t ies a re requ i red to stabil ize v iv iani te in most c h e m i c a l systems (Nr iagu 1972), a n d , there fore , it is the F e 2 + act iv i ty , rather t h a n t h e p h o s p h a t e c o n c e n t r a t i o n , tha t a c tua l l y de te rmines w h e t h e r or not sa tura t ion for v iv ian i te is a t t a i n e d ( Pos tma 1982). As a n e x a m p l e , C o r n w e l l (1987) o b s e r v e d au th igen i c v iv ianite fo rmat ion in Toolik Lake , A l a s k a , a non-ca l ca reous , non-s u l p h i d i c , p h o s p h o r u s - p o o r u l t r ao l i go t roph i c l ake . V i v i an i t e in l ake s ed imen t s is gene ra l l y f o u n d in e u t r o p h i c systems a n d its unusua l o c c u r r e n c e in Toolik Lake is a t t r i b u t e d t o t h e Fe r educ t i on-d i f fus ion-ox ida t i on c y c l e w h i c h results in h igh concen t ra t ions of po rewa te r F e 2 + that also leads to the release of a d s o r b e d phosphorus (Cornwel l 1987). Thus, desp i te low phosphorus inputs, vivianite prec ip i ta t ion occurs . The a b s e n c e of h igh rates of su lphate r educ t i on , e i ther b e c a u s e of low inputs of o rgan i c mat ter or low concen t ra t ions of su lphate , is necessary to prevent s c a v e n g i n g of F e 2 + by sulphides. The most f a vou r ab l e cond i t ions for viv ianite fo rmat ion therefore , a re anox i c f reshwater env i ronments a n d , in f a c t , vivianite has never b e e n conc lus ive ly ident i f ied in ma r i ne sed iments ( Pos tma 1982). To illustrate this, Ellis-Evans & L e m o n (1989) f o u n d vivianite prec ip i ta t ion in Sombre Lake, a freshwater, marit ime lake in the Anta rc t i c wh i ch con ta ins ve ry low levels of su lph ide (4 j iM) in the a n o x i c b o t t o m water . A m o s Lake , a n o t h e r A n t a r c t i c l a ke , h a d m u c h higher levels of su lph ide (25 u M max.) a n d to ta l phosphorus (-250 ^M) , a n d no p h o s p h a t e prec ip i ta t ion o c c u r r e d . Biological Removal As the lack of phospha t e in Powel l Lake c a n n o t b e exp l a ined by either ana ly t i ca l error, or as a result of inorgan ic r emova l , the possibility that it is b io log ica l l y cont ro l l ed must b e c o n s i d e r e d . Therefore , s o m e discussion of phosphorus u p t a k e b y b a c t e r i a a n d phy top l ank ton is required. Under cond i t i ons of h igh phosphorus l imitation w h i c h is c h a r a c t e r i z e d by the extraord inar i ly h igh C :N:P ratios of su r f a ce p l a n k t o n in Powe l l a n d Sak inaw Lakes , b a c t e r i a ac tua l l y t a k e up , rather t h a n release P O ^ w h e n d e g r a d i n g s u c h phosphorus-d e p l e t e o r g a n i c matter . This phosphorus u p t a k e of phosphorus by d e c o m p o s e r s w o u l d a p p e a r to o c c u r in Powel l Lake. The DIN:DIP ratios h a v e t w o m a x i m a in Powel l Lake (Fig. 4-11). The first is essent ia l ly t h e ent i re u p p e r 175 m, w h e r e the re is n o d e t e c t a b l e p h o s p h a t e ; this results artificially, in infinite DINDIP molar ratios. A t 175 m, phospha te is first d e t e c t a b l e a n d it is at this d e p t h that the lowest measurab le DIN:DIP ratio occurs . Below this d e p t h the DIN:DIP ratio g radua l l y increases with d e p t h , ind ica t ing that phosphorus is not b e i n g minera l i zed t o the s a m e extent as n i t rogen , i.e., it is b e i n g ass imi la ted by b a c t e r i a . Be low 175 m, SRP is r e l eased but in m u c h lower quant i t ies t h a n a m m o n i u m . The PON:PP ratio profile supports this (Fig. 4-11). Be low 200 m, PON:PP d e c r e a s e s with d e p t h a n d mirrors the DIN:DIP prof i le , i nd i ca t ing tha t phosphorus is m o v i n g f rom the dissolved f rac t ion to the par t icu la te f ract ion. Bac te r i a h a v e a m u c h lower C P ratio t han a l g a e . Fenche l a n d B lackburn (1979) report a n a v e r a g e C:P a t o m i c ratio of 48 for b a c t e r i a in gene ra l , whereas Bratbak (1985) f o u n d a t o m i c C : P ratios v a r y i ng b e t w e e n 8 a n d 56 for m i x e d b a c t e r i a l cu l tures , d e p e n d i n g o n whe the r their growth was phosphorus- or carbon-l imi ted, a n d G d c h t e r et a l . (1988) f o u n d a mo la r C:P ratio of 39 in natural lake assemblages of ba c t e r i a . A v e r a g e g r o w t h e f f i c i e n c y m a y a p p r o x i m a t e 5 0 % u n d e r a e r o b i c c o n d i t i o n s ( F enche l a n d B lackburn 1979). Therefore, assuming a bac te r i a l C:P ratio of 48, SRP should b e re leased only If the C :P ratio of the o rgan i c substrate is < 96. S ince the seston supp l i ed f rom the ep i l imn ion of b o t h Powe l l a n d Sak inaw Lakes has a C :P ratio cons ide r ab l y > 96, it is ev iden t tha t a t least in the u p p e r part of the mon imo l imn ion mineral izat ion processes c a n n o t l e a d to a n a c c u m u l a t i o n of SRP. Var ious researchers h a v e r e p o r t e d u p t a k e of SRP by a q u a t i c b a c t e r i a (e .g. Barsdate et a l . 1974; P lanas 1978; Fenche l a n d B lackburn 1979; Fleisher 1983). In the phot i c z o n e , b a c t e r i a c a n o u t c o m p e t e phy top lank ton in the up take of SRP, at least at low SRP concen t ra t ions (Currie a n d Kalff 1984; Lean a n d White 1983; a n d Lean 1984). Currie et a l . (1986) f o u n d tha t the bac te r i op l ank ton a re responsible for > 9 5 % of the o r thophospha te u p t a k e in situ, e x c e p t in lakes tha t a re not phosphorus-def ic ient , a n d o r thophospha te u p t a k e b y a l g a e w a s g rea t es t in t h e least phosphorus-de f i c i en t l akes s t u d i e d . H y p o l i m n e t i c d e c o m p o s e r s c a n rap id l y a n d a c t i v e l y t a k e u p PO4. k e e p i n g t h e phospho rus c o n c e n t r a t i o n so l ow tha t little phosphorus is a v a i l a b l e for i no rgan i c c o m p l e x a t i o n a t overturn (Levine a n d Schindler 1980; Doremus a n d C lescer i 1982). Sherr et a l . (1982) s h o w e d that mic rob ia l b r e a k d o w n of Peridinium cells w a s a c c e l e r a t e d by the a d d i t i o n of p h o s p h a t e , sugges t ing tha t d e c o m p o s e r s w e r e phosphorus-l imi ted. Kamp-Nie lsen (1974) f o u n d tha t p o i s o n e d sed iments s o r b e d less SRP t h a n un t r ea t ed systems, i n d i c a t i n g tha t phosphorus a c c u m u l a t i o n b y o rgan i sms con t i nues w h e n se t t l i ng p a r t i c l e s r e a c h t h e s e d i m e n t s u r f a c e . P r o d u c t i o n o f b i o m a s s b y . c h e m o a u t o t r o p h i c b a c t e r i a s u c h as Beggiatoa sp. a n d m e t h a n o g e n s will further cont r ibute t o SRP f ixation in lake sediments under app rop r i a t e redox condi t ions. In a study of the a e r o b i c d e c o m p o s i t i o n of the g r e e n a l g a Chlamydomonas reinhardii b y a m i x e d p o p u l a t i o n of l ake b a c t e r i a in b a t c h a n d c h e m o s t a t cultures, Uehlinger (1986) f o u n d that the bac ter ia l mineralization of a lga l c a r b o n is l inked with no or minor phosphorus re lease. Phosphorus up t ake by b a c t e r i a g rown o n heat-kil led a l g a e v a r i ed a c c o r d i n g to the C:P ratio of the a l g a e . A t a n a lga l C:P of 114, 5 5 % of the tota l so lub le phospho rus (TSP) w a s t a k e n u p b y the b a c t e r i a a t t h e b e g i n n i n g of a n exper iment , whi le a t a C :P of 2 2 7 , 6 0 % was ass imi lated, a n d at a C:P of 851, 8 4 % of the TSP was i n co rpo ra t ed . W h e n the bac t e r i a l popu l a t i on b e g a n t o d e c r e a s e b e c a u s e of sho r t age of f o o d , s o m e phosphorus w a s r e g e n e r a t e d . The c h e m o s t a t exper iments s h o w e d tha t a cont inuous supply of d e a d a l g a e p r e v e n t e d the d e c a y p h a s e of the b a c t e r i a l p o p u l a t i o n , a n d thus a n y net regenera t ion . Uehl inger (1986) sugges t ed that phosphorus in the ep i l imnion is f inal ly r e l eased by the graz ing act iv i ty of bac t i vo rous z o o p l a n k t o n or b y autolysis of the b a c t e r i a as a result of starvation. G a c h t e r a n d Mares (1985) f o u n d in the Swiss lakes Zug , Lucerne a n d Gre i fen that the C:P ratio of seston cons ide rab l y e x c e e d e d the Redf ie ld ratio (> 258 in Lucerne a n d G re i f en a n d -232 in Zug). However , this ratio d e c r e a s e d wi th inc reas ing w a t e r d e p t h ( a n d h e n c e increas ing a g e of the seston), a n d eventual ly b e c a m e as low as 25.8 in the a n o x i c hypo l imnion of Zug. A similar d e c r e a s e of the C:P ratio with increas ing sampl ing d e p t h w a s o b s e r v e d by Holm-Hansen (1972) in Lake Tahoe , ind i ca t ing that the seston takes u p SRP whi le settling. G a c h t e r a n d Mares (1985) sugges t ed that the up t ake of SRP b y sett l ing part ic les might h a v e c o n t r i b u t e d to the o b s e r v e d inc rease of pa r t i cu la te phosphorus flux with increas ing d e p t h . They also f o u n d that after par t i cu la te mat ter was d e p o s i t e d at the lake bo t tom it c o n t i n u e d to a c c u m u l a t e SRP. Tezuka (1986) s h o w e d that n o SRP is r e l eased f rom the seston of Lake B iwa , a s eve re l y P-l imited, m e s o t r o p h i c J a p a n e s e l a k e , du r i ng a e r o b i c d e c o m p o s i t i o n , a l t h o u g h DIN a c c u m u l a t e s abundan t l y in the hypo l imnion during t h e s tagna t ion pe r iod (Tezuka 1984, 1985). Tezuka (1985) sugges ted that this lack of SRP re lease is d u e to the h igh C:P (516) a n d N:P ratios (27 - 40) of the phy top lank ton in Lake Biwa. To illustrate this, phy top l ank ton a ssemb lages ( co l l e c t ed from Lake Biwa) with different C:N:P ratios (high (814:122:1), m e d i u m (266:38:1) a n d low (147:12:1)) w e r e g r o w n in the l abora tory a n d s u b s e q u e n t l y d e c o m p o s e d u n d e r a e r o b i c c o n d i t i o n s (Tezuka 1989a). The a l g a l a s s e m b l a g e with the highest N:P ratio (122) d i d not re lease SRP, whe reas that with the lowest N:P ratio (12) re leased SRP abundan t l y . N i t rogen b e h a v e d m u c h like phosphorus as DIN w a s a b u n d a n t l y r e l eased only f rom the a l ga l a s s e m b l a g e with the highest N:P ratio (122), whi le there w a s little or n o re lease of DIN f rom the a l g a l a s semb l ages with lower N:P ratios (38 a n d 12). Tezuka (1989a) further s tud ied the e f f ec t of C:N:P ratios of o r g a n i c substrates o n the regenera t ion of DIN a n d SRP by natural a s semb lages of l ake b a c t e r i a , using s imple o r g a n i c C , N a n d P c o m p o u n d s ( g l u c o s e , a s p a r a g i n e a n d sod ium g l y c e r o p h o s p h a t e ) . In these exper iments , w h e n the C : N a n d N:P ratios we re bo th lower t han 11.7 a n d 22 respect ively, bo th DIN a n d SRP were r egene ra t ed . However , w h e n the C :N a n d N:P ratios were higher than 17.6 a n d 55 respectively, neither DIN nor SRP we re regenera ted . O n the other h a n d , w h e n the C :N ratio was lower than 11.7 a n d the N:P ratio was higher t han 22, only DIN was regenera ted . In contras t , in Lake Kasumigaura , a highly eu t roph ic J a p a n e s e l ake , the seston has very low a v e r a g e C :N a n d N:P ratios of 7.1 - 8.1 a n d 14.4 - 22.5, respect ive ly (Aizaki a n d Otsuki 1987). W h e n p h y t o p l a n k t o n c o l l e c t e d f rom this lake w e r e d e c o m p o s e d ae rob i ca l l y they re leased bo th DIN a n d SRP (Aizaki a n d Takamura 1986). Tezuka (1989b) s h o w e d that bo th Microcystis (C:N:P= 191:29:1) a n d Anabaena (C:N:P= 150:18:1), two b lue g r e e n a l g a l spec ies w h i c h g r o w in eu t roph ic env i ronments a n d h a v e low C:N:P ratios, a lso re lease b o t h DIN a n d SRP a b u n d a n t l y dur ing a e r o b i c d e c o m p o s i t i o n . N o t e tha t the C:N:P ratios of Microcystis (119:29:1) a n d Anabaena (150:18:1) o b s e r v e d in t h e prev ious study a n d of the phy top l ank ton of Lake Kasumigau ra (Aizaki a n d Otsuki 1987) fall approx imate l y into the C:N:P r ange that releases b o t h DIN a n d SRP, whereas the C:N:P ratio (516:44:1) of the phy top lank ton in the north bas in of Lake B iwa in summer falls into the C:N:P r ange that releases DIN a lone . Thus it is ev ident that the C:N:P ratio of phy top lank ton is a n important pa r ame te r for determin ing the relative amounts of DIN a n d SRP re l eased b y a e r o b i c decompos i t i on . In a l l t h e e x a m p l e s of b a c t e r i a l phospho rus u p t a k e prev ious ly d i s c u s s e d , d e c o m p o s i t i o n took p l a c e u n d e r a e r o b i c cond i t i ons . Under a n a e r o b i c cond i t i ons , b a c t e r i a l g rowth e f f i c ienc ies a re only 5 - 3 0 % ( Fenche l a n d B lackburn 1979). H e n c e , m u c h m o r e o r g a n i c ma t t e r must b e d e c o m p o s e d for the b a c t e r i a t o assimilate the s a m e a m o u n t of c a r b o n a n d thus relatively more phosphorus is ass imi lated. Therefore, in a n a e r o b i c d e c o m p o s i t i o n phosphorus re lease genera l l y o c c u r s , as b a c t e r i a c a n a c q u i r e suff ic ient phosphorus e v e n f rom o r g a n i c ma t t e r wi th h igher C :P ratios. To illustrate this, B a cc in i (1985), using a l ga l mat ter l abe l l ed with M C a n d 3 2 P b a c t e r i a in the ox ic port ion of a sed iment c o r e s tored phosphorus a n d d e c r e a s e d the C:P ratio in this h o r i z o n . A s i g n i f i c a n t r e l e a s e of p h o s p h o r u s f r o m t h e s e d i m e n t o c c u r r e d s imu l taneous ly , bu t this phosphorus w a s u n l a b e l l e d a n d o r i g i n a t e d f r om d e e p e r , r e d u c e d sed imen t layers. The o r g a n i c mat ter in Powel l Lake is ext remely phosphorus-d e p l e t e d (C:P -300 - 400). Perhaps , e v e n a t lower g rowth e f f i c ienc ies , b a c t e r i a simply c a n n o t fulfil their phosphorus requirements w h e n C :P ratios a re so high. Therefore, in contrast t o c lass ica l theory , d e c o m p o s e r s d o not re lease, but t ake u p SRP. Why Powell and Sakinaw Are So Different The d i f f e r ences in phosphorus distr ibution b e t w e e n Powe l l a n d Sak inaw a re summar ized in Figs. 4-7 a n d 4-8. In the b o t t o m waters of Powel l Lake , t he proport ion of phosphorus in the par t i cu la te f rac t ion (5 - 20%) is m u c h greater t h a n in Sakinaw. In the latter, a l t h o u g h PP contr ibutes up to 2 6 % of the to ta l phosphorus a t t he in ter face a n d a r o u n d 2 0 % a b o v e , b e l o w the in te r face PP contr ibutes virtually noth ing t o the to ta l phosphorus p o o l . By the s a m e t o k e n , most of the phosphorus in Sak inaw is in the SRP f rac t ion (-80%), whe reas in Powel l it is half that m u c h . In light of the var ious studies d e s c r i b e d in the previous sec t i on , the small a m o u n t of phosphorus r e l eased in Powel l Lake b o t t o m waters is not tha t unusua l , as o r g a n i c ma t t e r in this lake is extremely P-deplete. Howeve r , this d o e s not exp la in w h y the t w o lakes a r e so d i f fe rent , as S a k i n a w p h y t o p l a n k t o n a l so h a v e very h igh C : P rat ios. c o n s i d e r a b l y h igher t h a n those of Powel l . Therefore , w h y has Powe l l d e v e l o p e d this unusual b o t t o m w a t e r c o n t a i n i n g h igh a m m o n i u m a c c o m p a n i e d wi th low p h o s p h a t e concen t ra t i ons , w h e n Sak inaw b o t t o m waters show a m u c h more norma l mineral izat ion of al l the nutrients as is usually seen in anox i c porewaters? The first c o n s i d e r a t i o n is tha t phosphorus input t o S a k i n a w is unlikely to b e a p p r e c i a b l y h igher t h a n in Powe l l Lake . A l t h o u g h Sak inaw su r face wate rs c o n t a i n d e t e c t a b l e quanti t ies of SRP, they a re still very low. The source for this SRP is most likely diffusion f rom the P-replete waters be l ow . A n t h r o p o g e n i c supply t o the more dense ly p o p u l a t e d S ak i naw Lake m a y serve as a n a d d i t i o n a l phosphorus s o u r c e , howeve r , cons ider ing the la rge a m o u n t of t ime that these lakes h a v e b e e n a n o x i c , the relatively r e c e n t i n f l u e n c e of a n t h r o p o g e n i c input shou ld b e n e g l i g i b l e . Phosphorus w a s m e a s u r e d a t f ive o ther stations in Powe l l (Fig. 4-13 a n d 4-14) to de te rmine if the low concen t ra t ions in the south bas in we re d u e to r emova l in the basins c loser to the h e a d . H o w e v e r , SRP w a s u n d e t e c t a b l e a t a l l d e p t h s in a l l basins. Both I P a n d PP w e r e extremely low. Even in the a n o x i c waters of the East bas in , I P concen t r a t i ons d i d not e x c e e d 0.7 p M . Therefore , phosphorus is ext remely l imiting th roughou t Powe l l Lake , e v e n in the river wa te r enter ing the lake. The d i f f e rence b e t w e e n the t w o lakes in the phosphorus chemistry m a y ref lect the vary ing c h e m i c a l histories of t he t w o lakes. A t present , neither Powel l nor Sak inaw h a v e a n y su lphate in their b o t t o m waters . Thus, the d e e p waters are essentially oxidant-s t a r ved , wi th f e rmen ta t i on b e i n g the on ly m e a n s of o r g a n i c mat te r d e c o m p o s i t i o n . Add i t i ona l s e a w a t e r input to Sak inaw s ince sill e m e r g e n c e w o u l d prov ide Sak inaw with extra ox idant supply , in the form of su lphate . This w o u l d result in more su lphate reduct ion in the b o t t o m waters , with a s s o c i a t e d minera l izat ion of nutrients. B e c a u s e Powel l has p r o b a b l y not h a d a n y input of su lphate s ince it was s e p a r a t e d f rom the Strait of G e o r g i a ~11000 years a g o , it has b e e n oxidant-starved for a m u c h longer p e r i o d , a n d thus less mineral izat ion has o c c u r r e d . However , h igh levels of a m m o n i u m d o o c c u r in Powel l a n d this must b e e x p l a i n e d . Both lakes a re o l i go t roph i c , with ext remely h igh sestonic C P ratios. P resumably , t h e lakes we re equa l l y phosphorus-l imited in their g e o l o g i c history, a n d thus C P ratios w e r e p robab l y a lways high. Ove r the long pe r i od of t ime that Powel l has b e e n i so l a t ed it e ven tua l l y b e c a m e ox idan t-s ta r ved , a n d al l t h e phosphorus reminera l ized v i a su lphate r educ t ion processes (prior t o su lphate exhaust ion) w a s likely e x h a u s t e d b y c h e m o a u t o t r o p h s s u c h as m e t h a n o g e n s a n d fe rmenters d e g r a d i n g phosphorus-dep le ted o r g a n i c matter . Fermenters w o u l d not h a v e to t a k e u p inorgan ic n i t rogen as the o r g a n i c mat ter b e i n g d e c o m p o s e d w o u l d con t a i n sufficient n i t rogen to satisfy their nutritional needs . The high levels of a m m o n i u m , therefore , ref lect t he m a n y years of reminera l iza t ion tha t h a v e t a k e n p l a c e b e f o r e t h e l ake b e c a m e ox idan t s t a r v e d . CHAPTER 5 SULPHUR CHEMISTRY 5.1 Introduction Sulphur c a n exist in a n u m b e r of v a l e n c e states b e t w e e n +6 a n d -2. The most a b u n d a n t forms of t he e l e m e n t in nature h a v e v a l e n c e s of +6 ( su lphates , su lphate esters), 0 ( e l e m e n t a l sulphur) , a n d -2 (sulphides, r e d u c e d o r g a n i c sulphur). Sulphur d iox ide a n d sulphite (+4) a n d polysulphur c o m p o u n d s with m ixed v a l e n c e states (eg . th iosu lpha te , polyth ionates ) o c c u r as transient spec ies . Powel l a n d Sak inaw Lakes a re idea l sites for the study of sulphur chemistry b e c a u s e their waters e n c o m p a s s a w i d e r a n g e of Eh, inc lud ing the low Eh env i ronment requ i red for pyrite fo rmat ion . Var ious sulphur c o m p o u n d s w e r e m e a s u r e d in Powel l a n d Sak inaw Lakes, a n d thus sulphur chemis t ry will b e briefly r e v i e w e d , be fo r e d iscuss ing the spec i f i c s of iron su lph ide format ion in the t w o lakes. Sulphur makes u p a b o u t 0.05% of the earth's crust, of w h i c h app rox ima te l y 90% o c c u r s in sed iments a n d d e e p o c e a n i c a n d sed imenta r y rocks as Se (nat ive ) , FeS2 (pyr i te) , PbS ( g a l e n a ) , HgS ( c i n n a b a r ) , ZnS (sphaler i te ) , C u 2 S ( c h a l c o c i t e ) , C u F e S 2 ( c h a l c o p y r i t e ) , CaSC>4»2H 20 (gypsum) , BaSO,* (barite) , a n d M g S C W H 2 0 ( epsomi te ) (Mort imer 1979)). The rema inde r occu r s largely as su lphate in seawa te r . The e l ement c y c l e s b e t w e e n reservoirs v i a a we l l d e f i n e d ox ida t ion-reduc t ion c y c l e ( G o l d h a b e r a n d K a p l a n 1974). Sulphur is a d d e d to natura l waters f rom the w e a t h e r i n g of rocks, fertilizers, a n d a t m o s p h e r i c p rec ip i t a t ion a n d dry depos i t i on (Wetzel 1983). Sulphides and/or free sulphur are ox id ized in the p resence of wate r to form sulphuric a c i d , v ia : FeS2 +7/202 +H 20-> FeSCU + H2SO4 2S° + 3O2 + 2HzO -> 2H2S04. La rge quant i t ies of r e d u c e d sulphur (as H2S) are r e l eased into t he a t m o s p h e r e f rom v o l c a n o e s a n d b i o g e n i c a n d industrial sources. The em i t t ed H 2S is ox id ized t o sulphur d iox ide (SOiD. sulphur tr ioxide (SO3), a n d sulphuric a c i d (H 2S04). A p p r o x i m a t e l y 95% of the sulphur e v o l v e d f rom the burning of fossil fuels is p r o d u c e d as S0 2, w h i c h is rapidly ox id ized t o sulphuric a c i d as it dissolves in a tmospher i c water . Sulphur is a n essential c o m p o n e n t of al l living matter ; t he S con t en t of organisms ranges f rom 0.05 - 5% (dry we igh t ) , a n d a v e r a g e s 0.2% (Wetzel 1983). The b i o l o g i c a l sulphur p o o l is gene ra l l y smal l c o m p a r e d t o the i no rgan i c forms of sulphur in most natura l waters , t h e p r e d o m i n a n t spec ies b e i n g su lphate . Most of t he sulphur in seston occu r s as ester sulphates a n d protein sulphur (Wetzel 1983), w h i c h cont r ibute up to 8 0 % of the recent l y d e p o s i t e d sed iment sulphur in p roduc t i v e lakes. The r e m a i n d e r of the sed imen t sulphur consists of pyrite, ac id-volat i le su lphides, sulphides d isso lved in pore wate rs , e l e m e n t a l sulphur, a n d d issolved su lphate . O r g a n i c sulphur c o m p o u n d s are more resistant t o d e c o m p o s i t i o n t han sulphur-free o rgan i c mat ter (Wetzel 1983). Sulphur Compounds There a re a l a rge n u m b e r of known sulphur-contain ing c o m p o u n d s , inc lud ing b o t h c o m p l e x o r g a n i c subs tances a n d simple inorgan ic spec ies . Howeve r , at the Eh, p H , a n d t empe ra tu r e va lues c o m m o n l y f o u n d in mar ine a n d lacustr ine sed iments , a n d at t h e r m o d y n a m i c equ i l ib r ium, on ly a smal l n u m b e r of c o m m o n d i sso l ved spec i e s (H 2S (aq), HS", a n d SO4) m a k e u p a lmost all of t h e to ta l sulphur in a q u e o u s solut ion (Thorstenson 1970). All o the r s p e c i e s , s u c h as S 2 O f , a r e p resent a t m u c h lower concen t r a t i ons . The pr inc ipa l sulphur spec i es in a e r o b i c sur face waters at neutra l pH should b e SO4 ,and in a n a e r o b i c waters in the pH range of 5 - 9, the p redominan t sulphur spec ies a re H ^ a n d HS". Inorganic Sulphur Species I no rgan i c su lphur s p e c i e s consist of t h e r e d u c e d c o m p o u n d s , i n c l u d i n g d issolved su lph ide , po lysu lph ide a n d par t i cu la te m e t a l sulphides, t he ox id ized spec ies , i n c l ud ing s u l p h a t e , su lphi te , po l y th iona te a n d th iosu lpha te , a n d e l e m e n t a l sulphur (Table 5-1). H ^ is m o d e r a t e l y soluble in wa te r a n d is a w e a k , d iprot ic a c i d in a q u e o u s solution. It ionizes in t w o steps: H2S(oq) <-> H+(aq) + HS' ( aq) \OQ K, = 7.02 HS" (oc l) «-» H+(0q) + S 2 " ^ log 1(2=18.57. This spec i a t i on is therefore pH d e p e n d e n t : at the pH of most natural waters (5-9 ) , the S2" spec ies is not very a b u n d a n t . The t w o p r i m a r y f o rms o f e l e m e n t a l su lphur a r e o r t h o r h o m b i c ( the t h e r m o d y n a m i c a l l y s t ab l e form) a n d c o l l o i d a l S. E l e m e n t a l su lphur is essent ia l ly insoluble in w a t e r but dissolves in a n u m b e r of o r g a n i c so lvents , most n o t a b l y CS 2 . Sulphur dissolves in solutions of soluble sulphides a n d forms a mixture of po lysu lph ide Table 5-1 Inorganic sulphur compounds commonly found in the aqueous environment Chemical Species Name Oxidation State SG-4 sulphate ion S (+6) SO? sulphite ion S (+4) HSO3 bisulphite ion s o 2 sulphur d iox ide S (+4) SnC? polyth ionate ion of length n SO3 (+5) e g . S4O? tet rath ionate c e n t r a l s (0) S2O32" th iosulphate ion t e rm ina l s (-2) cen t ra l S (+6) s 8 e l emen ta l sulphur S (0) polysulphide ion of length n t e rm ina l s (-1) e g . S f te t rasu lph ide centra l S (0) H2S h y d r o g e n su lphide S (-2) HS" bisulphide ion S2" sulphide ion FeS iron monosu lph ide S (-2) a m o r p h o u s , m a c k i n a w i t e . pyrrhotite Fe 3 S 4 gre ig i te S (-2) with 2 Fe (III) a n d 1 Fe(ll) FeS 2 pyrite or marcas i te S (-1) an ions , St, Sf" a n d S2," b e i n g the most c o m m o n (Bou legue 1976, 1977; Bou l egue a n d M i c h a r d 1978): HS" + l/8Sa <-> S| + H + HS" + l/4Se <-> £ + H + HS' + 3/8S8 <-> £ + H + HS" + l/2Sa «-> S| + H + HS' + 5/8Sa <-> £ + H + The S^ " spec ies c a n reac t with H + t o form HS jons (Boulegue a n d M i c h a r d 1978): St + H + <-» HS4 St + H + <-» H S A l t h o u g h po l y su lph ides c o n t a i n i n g o v e r a h u n d r e d su lphur a t o m s h a v e b e e n synthes ized, on ly po lysu lph ides with five sulphur a t oms or less a r e s tab le in a q u e o u s solution a t measu rab l e concent ra t ions for a n a p p r e c i a b l e length of t ime (Pickering a n d Tobolsky 1972). A t r o o m t e m p e r a t u r e , po lysu lph ides d e c o m p o s e in a c i d solut ion to y ie ld main ly H2S a n d free S. Reversibility has a lso b e e n seen by V o g e (1939) w h o f o u n d r ap id e x c h a n g e of r ad ioac t i v e ^S b e t w e e n dissolved sulphide a n d sulphur. A t a g iven p H , the tota l r e d u c e d sulphur (ST) is g iven by ( J acobs a n d Emerson 1982): ST = (HzS) + (HS") + (S2") + (£) + (St) + (£ ) + (S?) + (£ ) + (HSj + (HS5). The most s tab le fo rm of sulphur in a e r o b i c env i ronments is su lpha te , w h i c h is of ten a lso present in low concen t ra t ions in r e d u c e d waters. The th iosu lphate ion , S 2 O f , m a y b e r e g a r d e d as a sulphate ion in w h i c h o n e oxygen a t o m has b e e n r e p l a c e d by a sulphur a t o m (the prefix thio is used to n a m e any spec ies that m a y b e c o n s i d e r e d to b e de r i ved f rom another c o m p o u n d by rep l ac ing a n o x y g e n a t o m by a sulphur a tom) . The t w o sulphur a t o m s of the th iosu lphate ion a re not equ i va l en t . W h e n a th iosu lphate c o m p o u n d is p r e p a r e d f r om su lph i te a n d r a d i o a c t i v e su lphur ( 3 5S), a n d t h e n d e c o m p o s e d by ac id i f i c a t i on , all the act iv i ty occurs in the e l emen ta l sulphur: SO3 (oq) + S(S) -> ^ SSCfcaq) ^SSOicoq) + 2H+<oq) -» + SOxg) + H2O. The cent ra l sulphur a t o m in th iosulphate is genera l ly ass igned a n ox idat ion numbe r of +6 (as in the su lphate ion) , a n d the c o o r d i n a t e d sulphur is usually a ss igned a n ox ida t ion n u m b e r of -2 ( co r respond ing to the ox ida t ion n u m b e r of the o x y g e n it rep laces ) ; the a v e r a g e ox ida t ion state of sulphur in the ion is +2. Thiosulphate ion is readi ly ox id ized to the te t ra th ionate ion , SAOI. O the r th iona te ions a lso exist, e .g . d i t h i ona t e , S2O6. a n d trithionate, S3O?. Organic Sulphur Compounds O r g a n i c a l l y - c o m b i n e d sulphur is synthesized v i a d i rec t assimilat ion of su lphate b y l iving plants a n d b a c t e r i a . The synthesis of o r g a n i c sulphur b y mar ine organisms l eads t o a var ie ty of c o m p o u n d s compr i s ing main ly su lphur-conta in ing a m i n o a c i d s , su lphona t e s in w h i c h sulphur is d i rect ly b o n d e d to c a r b o n , a n d o r g a n i c esters of sulphuric a c i d w h i c h c o n t a i n a C-O-SO3H l inkage. O r g a n i c sulphur spec ies c o m m o n l y f o u n d dissolved in o c e a n i c waters inc lude d imethy l sulphide (DMS), d imethy l d isulphide (DMDS ) , c a r b o n d i s u l p h i d e (CS 2 ) , me thy l m e r c a p t a n ( m e t h a n e th io l - CH3SH), d i b e n z o t h i o p h e n e (DPT), n a p t h o b e n z o t h i o p h e n e , benzo th i azo l , t h i am ine , a n d biotin (Balzer 1981). A l t h o u g h o r g a n i c sulphur a c c o u n t s for less t h a n 10% of t h e to ta l sed imenta ry sulphur ( G o l d h a b e r a n d K a p l a n 1974). there is p r o b a b l y a la rge n u m b e r of as yet u n d e t e c t e d o r g a n i c sulphur c o m p o u n d s , espec ia l l y in c o m b i n e d or c o n d e n s e d fo rm, w h i c h t e n d t o a c c u m u l a t e in the humic f rac t ion of the mar ine sediments (N issenbaum a n d K a p l a n 1972). Current ly , three fract ions of o r g a n i c sulphur a re dist inguished using m e t h o d s b o r r o w e d f rom soil s c i e n c e (Williams 1975): a f r ac t i on that is r e d u c e d b y hydro iod i c a c i d t o H2S, consist ing mainly of ester sulphates a n d su lphamates ; a f rac t ion con ta in ing the c a r b o n - b o n d e d sulphur; a n d a f rac t ion wh i ch is cha r a c t e r i z ed as Raney-n i cke l- reduc ib le sulphur. The latter is a lso a subt rac t ion of c a r b o n - b o n d e d sulphur represent ing main ly the cystine a n d methionine in soil o rgan i c matter. The Sulphur Cycle The sulphur c y c l e in lakes is summar ized in Fig. 5-1. The b i o g e o c h e m i c a l sulphur c y c l e c a n b e d i v i d e d into assimi latory a n d dissimilatory p rocesses . In t h e fo rmer , i n o r g a n i c su lphur is t a k e n u p by m i c r o b e s , p lants a n d an ima l s ( v ia plants ) a n d t r ans fo rmed into a m i n o a c i d s , proteins a n d c o e n z y m e s . D u e t o its p r e d o m i n a n c e , virtually all assimilation of sulphur by b i o t a is as sulphate . During the synthesis of proteins by plants a n d an imals , su lphate is r e d u c e d t o sulphydryl (-SH), w h i c h is further r e d u c e d to H2S b y subsequen t d e c o m p o s i t i o n of this o r g a n i c mat te r b y var ious he te ro t roph ic b a c t e r i a (Wetzel 1983). B e c a u s e H 2S is ox id ized fairly rap id ly , little is f o u n d in a e r a t e d Surface runoff (SO/) Precipitation ft dry fallout (S0 4\ SOj) Outflow S (SO/) G'Oundwater s o ; Assimilation done* (Chiomatium.ChlofObium. Other photosynthetic and chemosynthetic S bacteria) ORGANIC S] SQ, -*-R SH TROPHOGENIC ZONE ThiobiioHuS th.oo«Kl,ins ThtobacilHis denilridcins 1 ^ N 0 3  Deposition ORGANIC? S TROPHOLYTIC ZONE SEDIMENTS Fig. 5-1 The sulphur c y c l e In a l ake , with emphas is o n the m i c rob io log i ca l processes. MS = me ta l sulphides, (from Wetze l 1983) waters . The turnover rates of assimilatory su lphate r e d u c t i o n a r e slow re lat ive t o the dissimilatory p rocesses , dur ing w h i c h sulphur c o m p o u n d s of va ry ing ox ida t i on states a re u sed as ei ther e l ec t ron donors or a c c e p t o r s in mic rob ia l me tabo l i sm. The different m e t a b o l i c t ypes i nc lude a n a e r o b i c dissimilatory su lphate (or sulphur, or th iosu lphate e tc . ) r e d u c t i o n , a n a e r o b i c p h o t o t r o p h i c sulphur o x i d a t i o n , a n d c h e m o l i t h o t r o p h i c sulphur ox ida t i on , w h i c h c a n b e b o t h a n a e r o b i c or a e r o b i c . Commun i t i e s of sulphur-r e d u c i n g a n d sulphur-oxidizing b a c t e r i a form su lphureta , w h i c h a re best d e s c r i b e d as mini , se l f-conta ined sulphur cyc l es . Sulphate-Reducing Bacteria Dissimilatory s u l p h a t e r e d u c t i o n is t he pr imary m e a n s of o r g a n i c c a r b o n minera l izat ion in a n o x i c waters a n d sed iments . The su lpha te-reduc ing b a c t e r i a ( eg . Desulfovibrio. Desulfotomaculum, Desulfomonas) a re strict a n a e r o b e s , a n d use su lphate as the termina l e l ec t ron a c c e p t o r in the ox idat ion of either o rgan i c matter or m o l e c u l a r h y d r o g e n : SO4 + 2CH2O + 2H+ -> 2CO2 + 2H2O + H2S SO4+4H2+2H+->4H20+H2S A3o= -251.2 k j . m o f ' . These r eac t i ons d o not use up o x y g e n d i rec t l y , but t h e H2S g e n e r a t e d is read i l y ox id i zed , w h i c h c o n s u m e s o x y g e n in a e r o b i c waters. The su lphate-reduc ing b a c t e r i a c a n also r e d u c e sulphite more rapidly ( and thiosulphate less rapidly) t h a n su lphate , a n d c a n r e d u c e co l l o ida l sulphur (but not or thorhombic sulphur) very slowly (Wetzel 1983). Sulphur-Oxidizing Bacteria The sulphur-oxidizing b a c t e r i a a re more diverse t h a n the reducers a n d c a n b e d i f fe rent ia ted into t w o groups , t he first be ing the colourless sulphur b a c t e r i a , w h i c h a re c h e m o s y n t h e t i c , a n d usually strict a e robes . These b a c t e r i a oxidize primarily H2S a n d c a n b e d i v i ded into t w o types , the first of w h i c h deposits sulphur inside the ce l l , v ia : H2S+1/202 -> S° + H20 AGo = -171.7 kJ»mof'. This sulphur a c c u m u l a t e s until H2S b e c o m e s d e p l e t e d , w h e n the internally stored sulphur is t h e n ox id ized t o su lphate : S° + 3/2O2 + hfeO -> SO4 +2H+ AGo= -494.0kJ.mol"1. Two g e n e r a w h i c h oxidize a n d store S° internally a re Beggiatoa, a l ong , f i lamentous b a c t e r i u m , a n d Thiothrix. The s e c o n d t y p e of chemosyn the t i c , sulphur-oxidizing b a c t e r i a deposits sulphur outs ide the c e l l , the most c o m m o n genus b e i n g Thiobacillus, w h i c h oxidizes su lph ide , S ° , a n d other r e d u c e d sulphur c o m p o u n d s such as th iosulphate: 2 s 2 o 2 ; + a -»2s°+2S04\ M a n y of the spec ies of Thiobacillus ( eg . T. thiooxidans) a re only f o u n d in a c i d i c waters (pH = 1 to 5), whi le others such as T. thioparus g row in neutral to a lkal ine condit ions. The sulphur-oxidizing b a c t e r i a are c o m m o n l y f o u n d adhe r ing to e l emen t a l sulphur particles. The s e c o n d g r o u p o f su lphu r-ox id i z i ng m i c r o b e s is t h e a n a e r o b i c p h o t o s y n t h e t i c b a c t e r i a , w h i c h a r e c o m p o s e d of t h e pu rp l e su lphur b a c t e r i a (Jhiorhodaceae) a n d t h e g r e e n sulphur b a c t e r i a (Chlorobacteriaceae).These organisms require light as a n energy source , a n d use H2S-sulphur as a n e l ec t ron donor in the photosynthet ic reduct ion of C 0 2 (Wetzel 1983): CO2 + 2H2S CH2O + H 2 0 + 2S° 2C02 + 2H2O + H2S 20-feO + SC2* +2H + . The g r een sulphur b a c t e r i a (eg . Chlorobium a n d Pelodictyon) a re genera l l y unicel lular , non-moti le , a n d depos i t sulphur extracel lularly. Unlike the purp le sulphur b a c t e r i a , the greens c a n to le ra te fairly h igh concen t r a t i ons of H2S. The purp le sulphur g r o u p ( eg . Chromatium a n d Thiocystis) c a n use other r e d u c e d sulphur c o m p o u n d s , e spec i a l l y th iosu lpha te , in p l a c e of H 2S as a n e l e c t ron donor . These b a c t e r i a a re l a rge , ac t i ve ly moti le a n d depos i t free S° intracellularly. The o c c u r r e n c e a n d distribution of the sulphur b a c t e r i a a re restricted by Eh a n d pH cond i t i ons , a c c o r d i n g to the a m o u n t of 0 2 present a n d the ox ida t ion state of the sulphur c o m p o u n d s (Fig. 5-2). The spec i f i c requirements for g rowth of sulphur b a c t e r i a o f ten result in distinct, thin layers of cer ta in bac te r i a l popu la t ions in the wate r co lumns of stratif ied lakes. The photosynthe t i c purp le b a c t e r i a a re o f t en f o u n d in a dense layer immed ia te l y a t the ox i c/anox i c inter face in meromic t i c lakes, b e l o w w h i c h a thin b a n d of g r e e n sulphur b a c t e r i a domina tes . Light levels at bacter ia-susta in ing interfaces are usually a b o u t 10% of those at the surface (Pfennig a n d W idde l 1982). Diagenesis of Sulphur The d i agenes i s of sulphur d e p e n d s o n the p r e s e n c e or a b s e n c e of d isso lved o x y g e n . Sulphur c a n b e a d d e d to sed iments ( a n d a n o x i c b o t t o m waters) as inorgan ic Fig. 5-2 G e n e r a l Eh-pH env i ronmenta l limits of: 1) c h e m o s y n t h e t i c (colourless) sulphur-oxidizing b a c t e r i a ; 2) photosynthet ic purp le b a c t e r i a ; 3) su lphate-reduc ing b a c t e r i a ; a n d 4) g r e e n sulphur b a c t e r i a (from Wetze l 1983). su lphate a n d as various o rgan i c sulphur c o m p o u n d s . In a e r o b i c env i ronments , o rgan i c sulphur is ox id i z ed t o su lpha te , w h i c h a d d s t o the su lpha te p o o l . Unde r a n a e r o b i c cond i t i ons , h o w e v e r , su lphate-reduc ing b a c t e r i a use su lphate as a termina l e l e c t ron a c c e p t o r , r e d u c i n g it t o su lph ide . O t h e r b a c t e r i a a lso p r o d u c e su lph ide b y the d e g r a d a t i o n of sulphur in o r g a n i c matter . The su lph ide p r o d u c e d m a y in terac t with various metals t o form insoluble sulphide minerals, or, d u e to migrat ion, it m a y c o m e into c o n t a c t wi th o x y g e n a n d b e ox id ized either ab iot i ca l l y or b y sulphur-oxidizing b a c t e r i a to sulphur c o m p o u n d s of var ious ox ida t ion states. The pr imary e n d p r o d u c t of sulphur d iagenes is in most systems is pyrite (FeS2). Iron Sulphides The c o m m o n iron su lph ide minerals w h i c h form unde r sed imen ta r y cond i t ions i n c l u d e py r i t e ( c u b i c FeS2), its o r t h o r h o m b i c d i m o r p h , m a r c a s i t e , a n d t h e monosu lph ides : a m o r p h o u s FeS (wh ich is p r o b a b l y a mixture of f ine-gra ined greigi te a n d mack inaw i t e (Morse et a l . 1987)), mack inaw i t e (also known as t e t r agona l su lphide, kansite, or hydrotroilite (FeSo.94) (Ward 1970)), greigite (also k n o w n as melnikovi te Fe3S4), a n d pyrrhotite (FeSu) . Fig. 5-3 shows the Eh-pS2" d i a g r a m for su lph id ic sed iments at a f ixed pH of 7.37. Not i n c l u d e d in this d i a g r a m a re mack inaw i t e a n d greigite b e c a u s e of their instability re lat ive t o pyrrhotite a n d pyrite. A u t h i g e n i c pyrrhotite is o c c a s i o n a l l y f o u n d in sediments (Berner 1971) a n d it has b e e n sugges ted that it is a precursor to pyrite fo rmat ion (R ickard 1969; S w e e n e y a n d K a p l a n 1973); howeve r , its o c c u r r e n c e is very rare. The monosu lph ides a re of ten referred t o as "acid-volat i le sulphides" d u e to their solubility in hot HCI. They a re more correct ly c a l l e d the metas t ab l e iron sulphides, s ince they transform to pyrite in the p resence of HS" a t concent ra t ions a b o v e pyrite saturation. W h e n excess su lph ide is not present , they c a n persist for long per iods of t ime (Berner 1974, 1981). Pyrite is t he s tab le minera l at t he low Eh a n d h igh sulphide concen t ra t i ons t y p i c a l of organic-r ich sediments . Detrital pyrite is c h e m i c a l l y a n d physica l ly unstab le , a n d is thus very rare in sediments. Sedimentary Pyrite Formation Sed imenta ry pyrite (FeS2) is a c o m m o n au th igen i c minera l in recent mar ine a n d lacus t r ine e n v i r o n m e n t s , as we l l as in s e d i m e n t a r y rocks . It t y p i c a l l y o c c u r s as m i c r o s c o p i c single crystal grains 1 t o 10 urn in size, as f r ambo ida l spherules u p to 250 urn in d i a m e t e r (Love a n d Amstutz 1966) a n d as groups of f r a m b o i d a l spheres t e r m e d I l l 0.00 -0.10 £ -0.30 -0.40 -0.50 --0.60 / Hematite / F e 2 0 3 Pyrite FeS2 / Magnetite / F e 3 0 4 Pyrrhotite F e S ^ Siderite F e C 0 3 H 2 1 1 1 l i i 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 Fig. 5-3 Eh-pS2" d i a g r a m for iron minerals at pH = 7.37. log Pccs= -2.40. T = 25°C. P = 1 a tm. Measu rements of natura l sulphidic mar ine sediments fall nea r the d a s h e d line, (from Berner 1971) po l y f r ambo ids (Love 1971). The te rm " f r ambo ida l " refers t o a u n i q u e , raspberry-like mic ro texture . The single crystals a n d f r ambo ids a re present in the c l a y a n d silt-size sed iment f r ac t ion , or as infillings of f o r a m , d i a t o m , a n d radio lar ian tests ( G o l d h a b e r a n d K a p l a n 1974). Berner (1970) p r o p o s e d a three s tep m e c h a n i s m for the format ion of pyrite: 1) r educ t ion of su lphate t o sulphide by bac t e r i a ; 2) r eac t ion of iron minerals with this sulphide to form iron monosulph ides ; a n d 3) r eac t ion of e l emen ta l sulphur with the iron monosulphides t o form pyrite. The net reac t ion c a n b e written as: FeS + S° -> FeSz. Pyrite is t h e on l y t h e r m o d y n a m i c a l l y s t ab l e p h a s e of t h e poss ib le iron-sulphur c o m p o u n d s in mar ine sediments (Berner 1967b). Laboratory Studies of Pyrite Formation A var ie ty of pyr i te synthesis s c h e m e s h a v e b e e n p r o p o s e d , i n c l ud ing t h e r eac t i on of m a c k i n a w i t e with e l e m e n t a l sulphur, the d issoc ia t ion of gre ig i te , a n d the direct r eac t ion of Fe 2 + with polysulphide (Fig. 5-4). F eOOH + HS" FeS 2 Framboidal FeS 2 Euhedral Fig. 5-4 Possible reac t ion pa thways of pyrite fo rmat ion , (from Raiswell 1982) A n u m b e r of expe r imenta l studies h a v e d e m o n s t r a t e d that pyrite c a n b e synthesized rapidly in o n e to a f e w days in inorgan ic solution under suitable condi t ions (Berner 1964a; Roberts et a l . 1969). As m e n t i o n e d a b o v e , pyrite format ion is genera l l y thought to require a precursor iron m o n o s u l p h i d e p h a s e , s u c h as m a c k i n a w i t e or g re ig i te , w h i c h t h e n reac ts wi th excess su lph ide a n d e l e m e n t a l sulphur t o form pyrite (Berner 1969, 1970; R ickard 1969), In the earliest exper imenta l work, pyrite w a s o b t a i n e d f rom H2S only w h e n air or F e 3 + w a s present (Berner 1964a); otherwise iron monosu lph ides w e r e f o r m e d . Berner (1964a) f o u n d n o pyrite format ion at pH > 7, e v e n over 200 days , whe reas at more a c i d i c p H , pyrite fo rmat ion c o u l d b e a c h i e v e d within 24 h. B e c a u s e mar ine sediments typ ica l l y fall in the pH range of 7-8, Berner (1970) hypothes ized that pyrite format ion must t a k e cons ide r ab l e t ime. However , Ha l lberg (1972) exper imenta l l y p r e c ip i t a t ed pyrite in short t ime per iods at pH values b e t w e e n 6 a n d 8. Rober ts et a l . (1969) f o r m e d pyrite rap id ly w h e n F e 3 + w a s m i x e d with H 2S; h o w e v e r , w h e n F e 2 + w a s used no pyrite was f o r m e d . These workers s u g g e s t e d that pyrite fo rmat ion requires fo rmat ion of po lysu lphide first, w h i c h then reacts very quick ly with Fe 2 + t o form pyrite. G o l d h a b e r a n d K a p l a n (1974) sugges ted that this m a y b e a major p a t h w a y of pyrite f o rma t i on . Roberts et a l . (1969) h ypo thes i zed tha t H 2 S 2 w a s the po lysu lph ide spec i es f o r m e d , but severa l studies h a v e shown that S2* d o e s not exist in solut ion at neutra l pH ( S c h w a r z e n b a c h a n d Fisher 1960; Teder 1969; P i cker ing a n d Tobolsky 1972) a n d therefore some other polysulphide must b e present. R i c k a r d (1975) s u g g e s t e d tha t m o n o s u l p h i d e s w e r e precursors t o pyr i te f o r m a t i o n , but tha t b o t h FeS a n d e l e m e n t a l sulphur must g o t h r o u g h dissolut ion r eac t i ons , w h e r e e l e m e n t a l sulphur dissolves in su lph ide solut ions, w h i c h p r o d u c e po l y su lph ide ions, a n d ferrous su lph ide dissolves t o form a q u e o u s ferrous ions a n d sulphur spec ies . Pyrite t h e n prec ip i ta tes direct ly th rough the reac t ion b e t w e e n ferrous ions a n d po lysu lph ide ions: SnS2" + &-» S^S 2" SrveS2" + SqS2" -> S^ 2 " * SpS2" FeS + H + -> Fe 2 + + HS" Fe 2* + sf + HS" -» FeS 2 + Si + HS". Howeve r , Berner (1964a) f o u n d that pyrite fo rmat ion only o c c u r r e d in the p r e s e n c e of excess e l emen t a l sulphur, a n d not w h e n polysulphides we re the only zerova lent sulphur present . S w e e n e y a n d K a p l a n (1973) f o u n d tha t w h e n gre ig i te r e a c t e d with o x y g e n f r a m b o i d a l pyrite f o r m e d , whi le G o l d h a b e r a n d Kap l an (1974) sugges t ed that euhed ra l pyrite resulted f rom the reac t i on of m a c k i n a w i t e with e l e m e n t a l sulphur. Berner et a l . (1979) a r g u e d tha t the convers ion of m a c k i n a w i t e a n d greigi te t o pyrite requires the p r e s e n c e of excess su lphide a n d if the concen t ra t i ons are low t h e n these me tas t ab l e phases m a y persist for some t ime. Pyrite m a y a l so b e f o r m e d direct ly without a m a c k i n a w i t e or greigite precursor u n d e r cond i t i ons w h e r e monosu lph ides a re unde r sa tu ra t ed ( G o l d h a b e r a n d K a p l a n 1974). Howarth (1979) initially f o u n d that pyrite is rapidly f o rmed in this manne r in salt marsh peats . S ince t h e n , several authors (Howarth a n d Teal 1979; Luther et a l . 1982; Gibl in a n d Howar th 1984) h a v e f o u n d that in such environments, w h i c h are cha rac t e r i zed by low pH (5 to 6.5), low dissolved sulphide concent ra t ions , h igh o rgan i c conten ts a n d rap id rates of su lpha te r e d u c t i o n , pyrite p rec ip i t a tes rap id ly a n d d i rec t l y w i thout f o rma t i on of precursor iron sulphide phases. Howarth (1979) a n d Berner et a l . (1979) have stressed the i m p o r t a n c e of l o w p H in c a u s i n g unde r sa tu r a t i on of i ron m o n o s u l p h i d e s wh i le ma in ta in ing supersa tura ted condi t ions for pyrite. The low su lph ide concen t r a t i ons a n d pH a re c a u s e d by p e r i o d i c o x y g e n a t i o n v i a marsh grass roots b e l o w the sed imen t sur face . During these events , highly reac t i ve polysulphides a n d e l e m e n t a l sulphur are f o r m e d w h i c h c a n r ea c t with ferrous iron; thus pyrite c a n p rec ip i t a t e rap id ly without c o m p e t i t i o n f rom iron monosu lph ides . A l t h o u g h it is c o m m o n in a n o x i c sed iments , pyrite has rarely b e e n s tud ied in a n o x i c w a t e r co lumns (Skei 1988). Sak inaw a n d Powel l Lakes a re c o n v e n i e n t natura l beakers in w h i c h t o study pyrite fo rmat ion d u e t o the c o - o c c u r r e n c e of dissolved Fe 2 + , d isso lved su lph ide , a n d highly r eac t i ve po lysu lphides , a n d also d u e t o the e x p a n d e d d e p t h , re lat ive t o sed imen t porewate rs , o ve r w h i c h the fo rmat ion of pa r t i cu l a te iron sulphides o c c u r . 5.2 Materials and Methods Water Collection Wate r samples we re c o l l e c t e d in 1.8 L or 9 L Niskin bottles e q u i p p e d with pressure fittings. Immediate ly after be ing brought o n b o a r d , the full bottles we re c o u p l e d through spec i a l fittings t o a n N 2 pressure line. Water was run direct ly f rom the Niskin bott les under a slight positive pressure of N 2 into a nitrogen-filled g love b a g a n d c o l l e c t e d in 10%-HCI-w a s h e d po l ye thy l ene or po l yp ropy l ene bott les tha t h a d b e e n previously f lushed with ni t rogen. All samples w e r e kept under n i t rogen during transport t o the lab . Samples that requi red filtration w e r e pressure-filtered in the g love b a g direct ly f rom the Niskin bot t le , th rough 0.4 jam p o l y c a r b o n a t e N u c l e p o r e m e m b r a n e filters. Al l n i t rogen used in the g l o v e b a g s w a s s c r u b b e d f ree of o x y g e n by pass ing it t h rough v a n a d o u s ch lo r ide solution prior t o enter ing the g love b a g . Sulphate Two ana l y t i ca l t e chn iques we re used. For b o t h t e chn iques , wa te r samples we re pressure-filtered in the g l o v e b a g a n d a n y H 2S present w a s p r e c i p i t a t e d as ZnS, w h i c h w a s later r e m o v e d by filtration be fore analysis. 1) Titration Techn ique Su lphate w a s first a n a l y z e d b y the titration m e t h o d of Howar th (1978). In this t e c h n i q u e , 3 mL of 0.0100 M EDTA a n d 4 mL of 0.4 M HCI were a d d e d to 1 mL of samp le , b o i l e d gent ly for 2 min to s p e e d the che l a t i on of a n y metals present , a n d t h e n c o o l e d after add i t i on of 10 mL of 0.05 M HCI. Then 5 mL of 10% BaCI 2 was a d d e d a n d the solution was left for 20 min to a l low the B a S 0 4 t o prec ip i ta te . The B a S 0 4 w a s then c o l l e c t e d o n a 0.45 n m Mi l l ipore filter (with interfer ing ca t i ons w a s h e d a w a y in t h e fi ltrate) a n d resolubil ized with 5.00 mL 0.0100 M EDTA a n d 4.0 mL NH 4 OH. The mixture was h e a t e d for 15 min t o a i d d issolut ion a n d af ter c o o l i n g t o r o o m t e m p e r a t u r e , 0.5 mL of pH 10 NH 4 CI/NH 4 OH buffer w a s a d d e d a n d the excess ( uncomp l exed ) EDTA t i t rated with 0.025 M M g C I 2 solut ion using a 2.5 mL G i lmont microburet te . The e n d p o i n t w a s d e t e r m i n e d using e r i och rome b l a c k T as a n indicator . C o p e n h a g e n S t anda rd S eawa te r was di luted with DDW for standards. All samples were b e l o w the the d e t e c t i o n limit of 0.5 m M . 2) C h r o m a f o a r a p h i c Analysis of Su lphate Su lpha te w a s r ede t e rm ined v i a ion c h r o m a t o g r a p h y using a D ionex 2110i Ion C h r o m a t o g r a p h . In this t e c h n i q u e , S 0 4 is a d s o r b e d to a n ion e x c h a n g e resin a n d then e lu ted with a 2.5 m M sod ium c a r b o n a t e a n d 3.1 m M sod ium b i c a r b o n a t e buffer. A 0.25 m M H2SO4 so lut ion w a s used as t h e a n i o n f iber suppressor r e g e n e r a n t . S t anda rds (N02S04) we re m a d e up in appropr ia te concent ra t ions of NaCI in DDW as a large CI p e a k interferes wi th resolution of the SO4 p e a k w h e n CI" is present at concen t r a t i ons > 2 m M . The d e t e c t i o n limit w a s < 1 j iM a t a salt concen t r a t i on of l%o a n d approx imate l y 5 n M at the m a x i m u m chlorinity of 9%o ( about 5 0 % that of seawater ) . The prec is ion w a s 0 .5% (1 a , rsd). Sulphite, Thiosulphate and Polythionate These sulphur oxyan ions w e r e de t e rm ined po la rograph i ca l l y in b o t h Powel l a n d S a k i n a w Lakes . In Powe l l L a k e su lphi te a n d t h i o s u l p h a t e w e r e a l so m e a s u r e d colourimetr ical ly. Samples we re run within 1 h after co l l ec t ion , a n d usually within 30 min. 1) Co lour imet r i c Analysis of Thiosulphate Th iosu lphate w a s d e t e r m i n e d b y the co lour imet r i c m e t h o d of U rban (1961), w h e r e th iosu lphate is c y a n o l i z e d using c u p r i c ch lo r ide as a cata lyst . The t h i o c y a n a t e f o r m e d is d e t e r m i n e d co lour imetr i ca l l y as its red ferric c o m p l e x . Wa te r w a s pressure-fi ltered into a bott le con ta in ing 1 M Z n A c 2 w h i c h h a d b e e n b u b b l e d with N 2 t o r e m o v e a n y d i sso l ved o x y g e n . The ZnS w a s f i l tered wi th 0.4 n m p o l y c a r b o n a t e N u c l e p o r e m e m b r a n e s whi le still in the g love b a g , a n d then 2.5 mL 1% N a C N , 1.5 mL 0.1 M C u C i 2 a n d 2.5 mL ferric nitrate r e agen t (0.74 M F e ( N 0 3 ) 3 in 2 2 % HNO3) we re a d d e d to 25 mL of samp le (neutral ized with 10% NH4OH t o pH 5). After mixing a n d dilution with DDW to 50 mL, the s amp l e was left for > 5 min in the dark (due to d e g r a d a t i o n of the ferric c o m p l e x in light) for co lou r d e v e l o p m e n t . The a b s o r b a n c e w a s then de t e rm ined at 460 n m in 10 c m cells. S tandards w e r e m a d e with Na2S 20 3«5H 20 in DDW. The d e t e c t i o n limit was 1 11M, a n d prec is ion w a s 1% ( l a , rsd). 2) Co lour imetr ic Analysis of Sulphite Sulphite was a n a l y z e d b y the colour imetr ic m e t h o d of West a n d G a e k e (1956) in w h i c h sulphite forms a s t ab l e d i su lph i tomercu ra te c o m p l e x tha t is resistant t o air ox idat ion for 12 h. In a g l o ve b a g , 10 mL of f i l tered samp le was a d d e d t o 25 mL of 0.1 M sod ium t e t r a ch lo romercu ra t e . Af ter a l l ow ing a t least 30 min for the sulphite c o m p l e x fo rmat ion , the s a m p l e was r e m o v e d from the g love b a g , a n y HgS f i l tered out , a n d 1 mL of 1% p-rosaniline a n d 1 mL of 0 .2% f o r m a l d e h y d e were a d d e d . C o l o u r d e v e l o p m e n t w a s e f f e c t e d for £ 30 min a n d then a b s o r b a n c e was de te rm ined at 560 nm in 10 c m cells. S t anda rds w e r e m a d e wi th N a 2 S 0 3 in DDW. The d e t e c t i o n limit w a s 0.25 \LM. a n d prec is ion w a s 1% ( l a , rsd). 3) Po l a rog raph i c Analysis of Sulphite. Thiosulphate. a n d Polvth ionate These sulphur oxyan ions w e r e m e a s u r e d v i a d i f ferent ia l pulse p o l a r o g r a p h y (DPP) using the t e c h n i q u e of Luther et a i . (1985). All measurements w e r e m a d e with a P r inceton A p p l i e d Resea r ch m o d e l 374 Po la rograph i c Ana lyzer a n d a m o d e l 303 static d r o p mercury e l e c t r ode (SDME). DPP was pe r fo rmed with a 5 mV»s'' s c a n rate a n d a 0.47 s d r o p t ime for the SDME in the d r o p p i n g mercury e l e c t r o d e m o d e . Tab le 5-2 show the re levant react ions of sulphur spec ies a t the mercury e l e c t rode . Table 5-2 Reactions at the mercury electrode (from Luther e ta l . 1986a) 1) 2S2O3 + Hg -» Hg(8*Oa£ + 2e" Ei/2 =-0.12 V 2) 2SO? + Hg Hg(S03)2 + 2e" Ei/2 = -0.60 V 3 ) S 4 0 2 : + 2e- -> 2S2O3" E1/2 =-0.32 V 4)HS" + Hg-> HgS + H + + 2e" E1/2 = -0.68 V 5) f£ + Hg -» HgS + (n-l)S + 2e" E1/2 = -0.68 V 6) 2RSH + Hg -> (RS)2Hg + 2 H + + 2e" E1 / 2 = -0.68 V 7) RSSR + 2e" -> 2RS* E1/2 =-0.54 V E1/2 for 1-3 are for 5 0 % pH 5 a c e t a t e buffer. E1/2 for 4-7 are for pH 10 buffer. E1/2 for 6 a n d 7 varies with R. Prepuri f ied "zero o x y g e n " n i t rogen (min imum purity 99.998%) w a s used for purg ing the ana l y t i ca l ce l l . Wa te r w a s pressure-filtered into bott les con ta in ing d e a e r a t e d Z n A c 2 in a g love b a g a n d the p r e c i p i t a t ed ZnS was then f i l tered out. Three mL of pH 5.0 a c e t a t e buffer w a s a d d e d to the ana l y t i ca l ce l l a n d p u r g e d with ni trogen for 10 min. Three mL of samp l e was t hen c o l l e c t e d through a small o p e n i n g in the g love b a g with a Finn p ipet te w h i c h h a d b e e n f lushed with n i t rogen a n d rinsed with s amp l e tw i ce . The s a m p l e was t h e n quick ly a d d e d t o the d e a e r a t e d a c e t a t e buffer in the e l e c t r ode ce l l , w h i c h was in c lose proximity to the g love b a g so that transfer invo lved min imum exposure to air. After stirring for 30 s (by purging with N 2 ) , t he p o l a r o g r a p h s w e e p was run. The initial s c a n was run b e t w e e n -0.45 t o -0.80 V to d e t e c t sulphite w h i c h has a ha l f-wave po ten t i a l of app rox ima te l y -0.6 V , b e c a u s e it is more easi ly ox id ized t h a n th iosulphate . Then a s c a n w a s run f rom 0 to -0.45 V to d e t e c t th iosulphate (E1/2 —0.1 V) a n d po ly th ionate ( E V 2 —0.3 V) . B e c a u s e t h e ion ic s t rength v a r i e d with d e p t h in the lacustr ine w a t e r c o l u m n s , s t anda rd addi t ions of Na 2 S 2 0 3 »5H 2 0 a n d N a ^ G a in DDW we re m a d e to e a c h samp le . S o m e samples we re a n a l y s e d without add i t i on of Z n A c 2 a n d sulphide was r e m o v e d by ac id i fy ing with d e a e r a t e d HCI if necessary (to bring the pH d o w n to a b o u t 5) a n d purging with n i t rogen . N o d i f f e r ence w a s s e e n b e t w e e n these samp les a n d those that h a d sulphide r e m o v e d as ZnS. The de t e c t i on limit was 2 \iM a n d 0.25 j iM for th iosulphate a n d sulphite respect ive ly , a n d the prec is ion was 1% ( l a , rsd) for bo th ions. Zerova lent Sulphur This f rac t ion inc ludes bo th e l ementa l sulphur a n d zerova lent sulphur c o n t a i n e d in polysulphides. This p r o c e d u r e fol lows that of Luther et a l . (1985) a n d involves r eac t i ng sulphur w i th sulphite a n d hea t to fo rm th iosu lpha te , w h i c h c a n t h e n b e m e a s u r e d po la rograph i ca l l y . The overal l r eac t ion is: H 2 0 + S? + (n-l)SOf -> HS" + (n-DSzOf + OH". In a g l o v e b a g , 10 mL of s a m p l e w a s a d d e d t o d e a e r a t e d a m p o u l e s c o n t a i n i n g d e a e r a t e d 1 M SOf (25 \il Powe l l , 55 i± Sakinaw) . A m p o u l e s we re c a p p e d with s e p t a a n d t h e n s e a l e d with a n oxygen-p ropane to r ch . Sea l ing h a d to b e d o n e outs ide the g love b a g ; howeve r , the c a p s we re r e m o v e d only w h e n the neck of the a m p o u l e was p l a c e d in the f l a m e a n d thus no in t roduct ion of air shou ld h a v e o c c u r r e d (the hea t drives N 2 out of the ampou l e ) . The ampou l e s were then immedia te l y immersed in a 60°C w a t e r b a t h for t w o hours t o c o m p l e t e the r e a c t i o n . S a m p l e s w e r e a n a l y z e d for th iosu lphate po l a rog raph i c a l l y as d e s c r i b e d a b o v e , with the e x c e p t i o n that dilutions w e r e m u c h h igher for m a n y of the samples . Polysulphide sulphur w a s d e t e r m i n e d f rom f i l t e red w a t e r a n d p a r t i c u l a t e e l e m e n t a l su lphur f r o m unf i l t e red s a m p l e s a f te r subtract ing the polysulphide sulphur. Therefore, the separa t ion b e t w e e n the two phases is o p e r a t i o n a l l y d e f i n e d , resulting in unde res t ima t ion of e l e m e n t a l su lphur , as the po l y su lph ide f r a c t i o n u n d o u b t e d l y con t a i n s s o m e c o l l o i d a l e l e m e n t a l sulphur. A n y th iosu lphate originally present in the w a t e r w a s sub t r a c t ed f rom these measurements . Three r ep l i c a t e a m p o u l e s (all t a k e n f rom the s a m e w a t e r samp le ) w e r e run for e a c h samp le . The convers ion e f f i c iency was f o u n d to fall b e t w e e n 98 - 9 9 % (± 5% l a , rsd) a n d the d e t e c t i o n limit was that of th iosu lphate (-1 \iM S). The samples w e r e not run until severa l weeks af ter co l l e c t i on a n d thus un t rea ted w a t e r w a s c o l l e c t e d a n d s tored in a m p o u l e s ident ica l l y a n d c h e c k e d for ox ida t ion a t t he s a m e t ime the samp les we re run. N o sulphite or th iosu lphate was f o u n d in a n y of the six a m p o u l e s t es ted ( inc luding s o m e f rom t h e most su lph id ic wa te r ) , i nd i ca t i ng tha t n o ox ida t i on o c c u r r e d dur ing hand l ing a n d storage. Dissolved Sulphide Dissolved su lphide was d e t e r m i n e d a c c o r d i n g to the m e t h o d of C l ine (1969). In this t e c h n i q u e , H 2S reacts with N.N d ime thy l -p-pheny l e r i ed i am ine su lpha t e in a c i d m e d i u m , w i t h F e C I 2 as a c a t a l y s t , t o fo rm m e t h y l e n e b lue w h i c h is m e a s u r e d colour imetr ica l ly . Wa te r w a s c o l l e c t e d in a g love b a g , a n d sulphide was t r a p p e d with d e a e r a t e d Z n A c 2 as ZnS, t o b e a n a l y s e d severa l weeks later. Different concen t r a t i ons of reagents a re required for different sulphide levels. B ecause C l ine (1969) only p rov i ded rec ipes for su lph ide concen t r a t i ons up to 1000 p.M, a n add i t i ona l m o r e c o n c e n t r a t e d r e a g e n t c o n t a i n i n g 10.0 g N,N d ime thy l -p-pheny l ened i am ine su lpha t e plus 15.0 g F e C I 3 » 6 H 2 0 in 100 mL 5 0 % (v/v) HCI w a s f o r m u l a t e d for t h e 3 - 5.5 m M su lph ide c o n c e n t r a t i o n s f o u n d in Powe l l a n d Sak inaw Lakes. S t anda rds w e r e m a d e f rom Na 2 S»9H 2 0 in d e a e r a t e d DDW, a n d we re t r ea t ed in the s a m e w a y as the samples (i.e. p r e c i p i t a t ed with Zn) a n d stored for a per iod of t ime be fo re analysis. The de t e c t i on limit was 0.3 \iM a n d precis ion was a b o u t 2% (1 a , rsd). Particulate Sulphide Analysis W a t e r samp les w e r e c o l l e c t e d in d e o x y g e n a t e d 4 L jugs in a g l o ve b a g . The jugs w e r e rinsed 3 t imes with s amp l e wate r , a n d we re then returned immed ia te l y t o the l ab . The p r o c e d u r e f o l l o w e d w a s that of Howar th a n d Jo rgensen (1984), mod i f i ed for w a t e r samples . This m e t h o d invo lved essentially four steps: 1) r emova l of S°; 2) co l l e c t i on of part iculates b y filtration; 3) co l l e c t i on of monosu lph ides v i a a c i d distillation; a n d 4) co l l e c t i on of pyrite b y ch romium reduct ion . All steps w e r e ca r r i ed out in nitrogen-filled g love bags , n S ° R e m o v a l Two L of s amp l e w a s stirred with 200 mL d e o x y g e n a t e d CS2 a t t h e highest s p e e d o n a m a g n e t i c stirrer for 1 hr. The o rgan i c CS2 layer con ta in ing the S° was t hen s e p a r a t e d f rom t h e a q u e o u s layer in a separa tory funnel . The separa t ion w a s not c o m p l e t e , with s o m e frothing occur r ing at the inter face of the t w o layers. H e n c e , c a r e was t a k e n not to co l l e c t a n y of the a q u e o u s f rac t ion that h a d large drops of CS2 in it. The v o l u m e of the a q u e o u s f rac t ion c o l l e c t e d was r e c o r d e d . 7) Filtration The a q u e o u s f rac t ion from 1) was fi ltered through 0.4 urn Nuc l epo re membranes . B e c a u s e of the l a rge a m o u n t of o r g a n i c "fluff" present in the b o t t o m waters of b o t h lakes (as was n o t e d in all filtrations d o n e o n this water ) , the filters c l o g g e d easily a n d h a d to b e c h a n g e d frequently. For the approx imate l y 8 L of wa te r f i l tered for e a c h s a m p l e , as m a n y as 25 filters w e r e requ i red . Before r emov ing filters f rom v a c u u m , they we re rinsed wel l with d e a e r a t e d DDW to r e m o v e dissolved sulphide. Filters we re f o l d e d a n d a d d e d to the d e a e r a t e d distillation appa ra tus flask in the g love b a g . 3) Monosu lDh ide The r e a c t i o n flask w a s h o o k e d u p t o t h e disti l lation a p p a r a t u s (a W h e a t o n c y a n i d e disti l lation a p p a r a t u s w h i c h h a d previously b e e n f lushed with N 2) a n d then f lushed with N 2 for 15 min. D e a e r a t e d c o n c e n t r a t e d HCI (30 mL) was then a d d e d with a syringe a n d r e l eased H 2S w a s t r a p p e d wi th Z n A c 2 . After 15 min , the r eac t i on flask was brought to boi l ing to re lease a n y greigite sulphur. The reac t ion was a l l o w e d to p r o c e e d for ano the r 45 min , after wh i ch the hea t was r e m o v e d a n d the t w o Z n A c 2 traps (in series) w e r e r e m o v e d . A t r ap con t a i n i ng 100 mL of 1 M pH 4 p h o s p h a t e buffer was instal led b e t w e e n the c o l d f inger a n d the Zn traps to r emove HCI vapour . 4) Pyrite After r ep l a c ing the t w o Z n A c 2 t raps a n d letting the distillation appa r a tus c o o l for 15 min , 20 mL of EtOH a n d 60 mL of 1M C r C b , bo th d e a e r a t e d , we re a d d e d . Fifteen min after r eagen t add i t i on , hea t was a p p l i e d a n d the samp le was bo i l ed gent ly for 45 min. S a m p l e s c o l l e c t e d as ZnS w e r e m e a s u r e d as d e s c r i b e d a b o v e for so lub le sulphides. The d e t e c t i o n limit w a s d e p e n d e n t o n the v o l u m e of w a t e r f i l tered; for a n a v e r a g e s a m p l e v o l u m e of 7700 mL, it w a s 0.8 n M S, or 1.6 n M FeS2. B e c a u s e s a m p l e analysis t ook so long (from start t o finish -6 - 7 h per samp le ) , repl icates we re not d o n e . O n e pyrite measu remen t w a s r ep l i c a t ed d u e to loss of the monosu lph ide port ion of the s a m p l e a n d the t w o measurements d i f fered by 3.7% (41.59 n M versus 40.09 nM) . No te that this t e c h n i q u e is spec i f i c t o inorgan i c su lphides, as o r g a n i c sulphur is not r e d u c e d v i a this p r o c e d u r e (Zhabina a n d Vo lkov 1978; Howar th a n d Jo rgensen 1984; C a n f i e l d et a l . 1986). O n e serious p rob l em with this ana ly t i ca l f rac t ionat ion s c h e m e used is t h e hot a c i d distil lation tha t is requ i red to solubiiize greigite. B e c a u s e greigi te is the thiospinel of iron (Fe 2 + Fe 3 + Fe 3 + S4). w h e n hot HCI is a d d e d Fe 3 + is r e l eased , w h i c h c a n then oxidize H2S t o S°. The S° g e n e r a t e d is not volat i l ized v i a a c i d , howeve r , a n d ins tead it is r e d u c e d by c h r o m i u m in the s e c o n d distil lation. Thus, s o m e of the su lph ide f rom the ac id-vo la t i l e phases is m e a s u r e d in the c h r o m i u m - r e d u c e d "pyrite" f r ac t i on (Berner 1964a, 1974), resulting in the pyrite f rac t ion be ing ove res t imated , a n d the monosu lph ide f rac t ion underes t imated . To obv i a t e this, SnCb, w h i c h r educes the F e 3 + , c a n b e a d d e d , the reby p ro tec t ing the H2S f rom ox idat ion ( C h a n t o n a n d Martens 1985). However , w h e n pyrite is b o i l e d in a c i d in the p r e s e n c e of SnCI 2 . s o m e of the pyrite is r e l eased to the m o n o s u l p h i d e f r ac t i on . This results in m o n o s u l p h i d e b e i n g o v e r e s t i m a t e d a n d pyrite underes t imated . W h e n the a c i d distillation is ca r r ied out with SnCb at r oom tempera tu re , howeve r , no pyrite is r e l eased t o the monosu lph ide poo l . This cons ide ra t ion also has a d r a w b a c k : gre ig i te c a n n o t b e re l eased without hea t (R. Berner pers. c o m m . , c i t e d in Howar th a n d J0rgensen 1984). Therefore , monosu lph ides a re a g a i n unde r e s t ima t ed a n d pyrite is o ve res t ima ted . This c o n u n d r u m w a s so l ved by Howar th a n d J0rgensen (1984) b y performing a n add i t iona l CS2 extract ion after the a c i d distillation to r emove the e l e m e n t a l sulphur f o r m e d dur ing the ac id i f i ca t ion step. B e c a u s e of the low par t i cu la te sulphur concen t ra t ions in the lakes a n d the difficulty in dea l i ng with the large vo lumes of w a t e r requi red t o co l l e c t e n o u g h mater ia l for analysis, this extra step was not ca r r ied out in this study. Therefore, it is possible that the pyrite f rac t ion has b e e n ove res t ima ted in this s tudy a t t h e e x p e n s e of the monosu lph ide f rac t ion . It shou ld a lso b e n o t e d that s o m e pyr i te m a y b e e x t r a c t e d by the hot a c i d disti l lat ion b e c a u s e this solut ion is unde r sa tu r a t ed with r e spec t t o pyrite; thus, t he ex t rac t ion is a k ine t i ca l l y-domina ted process (Morse a n d Cornwe l l 1987). Iron and Manganese Bott les for t h e c o l l e c t i o n of t r a c e me ta l s w e r e n e w p o l y p r o p y l e n e or po lye thy lene bottles w h i c h h a d b e e n w a s h e d in hot 2 0 % HNO3 a n d rinsed with Nanopure w a t e r . S a m p l e w a t e r w a s pressure-fi ltered into bot t les c o n t a i n i n g a n a p p r o p r i a t e v o l u m e of Ultrapure Seastar® HNO3 t o bring the pH to 2. Wa te r samples we re a n a l y z e d using g raph i t e f u r n a c e a t o m i c absorp t ion spec t romet ry . Sak inaw Lake samples we re a n a l y z e d v i a d i rect inject ion into pyrol i t ica l ly-coated graph i te tubes using a Perkin Elmer 560 A A with deu te r ium b a c k g r o u n d co r rec t i on a n d s tandards p r e p a r e d in a c i d i f i e d , c h e l e x e d artif icial s eawa te r at the app rop r i a t e salinities. The d e t e c t i o n limit for M n w a s 3.6 n M a n d prec i s ion 2 % ( l a , rsd), w h e r e a s for Fe it w a s 9 n M a n d 2%. Powel l Lake samp les we re a n a l y z e d with a Va r i an S p e c t r A A 300 s p e c t r o p h o t o m e t e r with Z e e m a n b a c k g r o u n d co r r e c t i on a n d a PSD 96 au tosamp le r using pyrolit ic g raph i t e tubes with L'vov p la t forms a n d a p a l l a d i u m modi f ie r (9.39 m M Pd in 1% HCI a n d 1% HNO3) t o r e m o v e matrix e f fects . S t andards w e r e p r e p a r e d in 0 . 1 % HNO3 N a n o p u r e wate r . Al l dissolved me ta l concen t ra t ions we re a b o v e the d e t e c t i o n limit. Speciation and Solubility Calculations S p e c i a t i o n of iron a n d m a n g a n e s e , as wel l as the saturat ion state of iron a n d m a n g a n e s e solid phases was c a l c u l a t e d using MINEQL as d e s c r i b e d in A p p e n d i x 1. 5.3 Results Powell Lake Thiosu lphate a n d sulphite a re u n d e t e c t a b l e th roughou t t h e w a t e r c o l u m n of Powel l Lake. Su lphate occu r s a t a concen t r a t i on of a b o u t 8 m-M in the u p p e r ox ic waters (Fig. 5-5), increases sharply t o 11.3 |xM at the ox i c/anox ic in ter face , a n d then dec reases rap id ly wi th d e p t h , b e c o m i n g u n d e t e c t a b l e a t 185 m. Dissolved su lph ide (H 2S) is first d e t e c t a b l e b e t w e e n 145 a n d 150 m. The concen t r a t i on remains low (< 10 n.M) to 180 m, b e l o w w h i c h it increases t o a m a x i m u m of 3.1 m M in the b o t t o m water . Polysulphide (Si^) is first d e t e c t e d a t a d e p t h of 160 m, a n d then increases marked ly t o m a x i m u m levels of 2.2 m M in t h e b o t t o m w a t e r (Fig. 5-5). The rat io of to ta l d i sso lved su lph ide t o to ta l d isso lved ze rova l en t sulphur d e c r e a s e s slightly f rom just b e l o w the in te r face (-2.0) t o the b o t t o m waters (-1.4) (Fig. 5-7). Dissolved iron concen t r a t i ons a re typ ica l l y 0.04 p.M in the ox i c waters with a sur face m a x i m u m of 0.09 j i M (Fig. 5-9). Concen t r a t i ons increase rapid ly just a b o v e the in ter face at 145 m, r e a c h i n g a m a x i m u m of 171 \iM a t 210 m. Be low this d e p t h , the iron con ten t d e c r e a s e s sharply t o 0.06 | iM at the bo t t om . From mode l l i ng ( A p p e n d i x 1), iron o c c u r s pr imari ly (98-99%) as f ree F e 2 + in the ox i c waters (Fig. 5-11). The e l e m e n t is increasingly c o m p l e x e d with CI" with d e p t h t o a m a x i m u m of 3 4 % as FeCI + in the b o t t o m water . Dissolved m a n g a n e s e is also low in the uppe r ox ic waters with concen t ra t ions of a b o u t 0.03 n M (Fig. 5-9). Levels b e g i n t o increase a t 100 m, a n d a very large increase in c o n c e n t r a t i o n is o b s e r v e d b e t w e e n 125 m d e p t h a n d the inter face . The c o n c e n t r a t i o n then remains fairly invariant at a b o u t 27 j iM to a d e p t h of 250 m, b e l o w w h i c h the e lement is d e p l e t e d t o a min imum of 0.7 | iM at the bo t tom. M a n g a n e s e is present as free M n 2 + in the u p p e r ox ic waters; in the b o t t o m sulphidic waters , MnHS i c o m p l e x e s p r e d o m i n a t e , compr i s ing 7 8 % of the tota l M n (Fig. 5-13). O the r m a n g a n e s e spec ies i n c lude M n H C 0 3 + (max. 8%), M n C I + (max. 18%) a n d MnSf" (max. 10%) (see A p p e n d i x 1 for descr ip t ion of ca l cu l a t i ons ) . Part iculate iron monosulph ides are u n d e t e c t a b l e a b o v e a d e p t h of 200 m (4 nM) (Fig. 5-15). The c o n c e n t r a t i o n t h e n increases to a m a x i m u m of 240 n M a t 275 m, b e l o w w h i c h it rapidly dec l ines t o 84 n M a t the bo t tom. Pyrite is first d e t e c t a b l e a t 150 m (41 nM) , increases t o a m a x i m u m of 435 n M at 250 m, a n d then dec reases rapidly to 150 n M at the b o t t o m . Sakinaw Lake Thiosulphate a n d sulphite a re also u n d e t e c t a b l e throughout the w a t e r c o l u m n of S a k i n a w Lake . Su lpha te is present in the u p p e r ox i c waters of S ak i naw Lake at a c o n c e n t r a t i o n of a b o u t 50 n M (Fig. 5-6), a n d increases rather sharply just a b o v e the in ter face t o 64 \iM be fo re dec l in ing rapidly b e l o w the interface. The ion is u n d e t e c t a b l e b e l o w 50 m. Both sulphide a n d polysulphide sulphur first a p p e a r at 30 m d e p t h a n d their profiles are similar in shape . Concen t ra t ions increase rapidly b e t w e e n 40 a n d 60 m, a n d rema in a p p r o x i m a t e l y cons tan t (H 2S - 5.3 m M , Sv, - 4.5 m M ) to the b o t t o m . Dissolved su lph ide concen t r a t i ons a re a lmost t w o t imes those of Powel l Lake. The ratio of tota l d issolved sulphide t o polysulphide sulphur is fairly cons tant with d e p t h (-1.2) b e l o w 40 m (Fig. 5-8). Dissolved iron a n d m a n g a n e s e concen t r a t i ons are lower t h a n in Powel l Lake. Dissolved iron is present in the ox ic waters , with a m a x i m u m c o n c e n t r a t i o n of 0.3 j iM at 5 m (Fig. 5-10). Be low this hor izon, the concen t r a t i on dec reases to 0.04 | iM until just b e l o w the inter face at 32.5 m where it rapidly rises to a max imum of 6.7 \iM. Be low this d e p t h the c o n c e n t r a t i o n rap id ly falls t o a b o u t 0.09 jxM, a n d remains fairly cons tan t b e l o w 75 m. M a n g a n e s e is u n d e t e c t a b l e in the sur face waters , first a p p e a r i n g at the inter face at 30 m. It t hen rapidly increases to a m a x i m u m concen t r a t i on of approx imate l y 6 j iM at 45 m a n d remains fairly cons tan t at greater d e p t h . The s p e c i a t i o n of Fe a n d M n is similar t o tha t c a l c u l a t e d for Powe l l Lake ( A p p e n d i x 1). In the oxic waters bo th Fe a n d M n are present a lmost entirely as the free spec ies (Fig. 5-12,5-14). In the anox i c waters, iron occurs as FeCI + (-28%) (Fig. 5-12), while M n is c o m p l e x e d primarily as MnHSli in the sulphidic b o t t o m waters (-87%), with minor contributions from M n C l \ M n H C O s , a n d MnSl" (all < 10%) (Fig. 5-14). Iron m o n o s u l p h i d e is first d e t e c t e d at 40 m d e p t h (124 nM) (Fig. 5-16), a n d gradua l l y Increases in concen t ra t i on to 543 n M at a d e p t h of 100 m. Below this horizon the c o n c e n t r a t i o n d e c r e a s e s a n d a g a i n increases t o 545 n M nea r the b o t t o m . Pyrite is first d e t e c t e d right a t the interface (30 m), increases to a max imum of 80 n M at 60 m a n d then d e c r e a s e s with d e p t h . Fig.5-5 Dissolved sulphur spec ies in Powel l Lake Su lphate (piM) Dissolved Su lph ide (mM) Polysulphide Sulphur (mM) Fig. 5-6 Dissolved sulphur spec ies in Sak inaw Lake Fig. 5-7 Ratio of total dissolved sulphide (S(-2)) to d issolved zerovalent polysulphide (S(0)) in Powel l Lake Fig. 5-8 Ratio of tota l dissolved sulphide (S(-2)) to dissolved zerova lent po lysu lphide (S(0)) in Sakinaw Lake Fig. 5-9 Dissolved iron a n d m a n g a n e s e in Powell Lake Fe . M n ^ " QiM) Percent Dissolved Iron Fig. 5-11 Pe rcen tages of free a n d c o m p l e x e d dissolved iron in Powel l Lake. All other c o m -plexes we re < 1% of the tota l dissolved iron. Percent Dissolved Iron Fig. 5-12 Pe rcen tages of free a n d c o m p l e x e d dissolved iron in Sakinaw Lake. All other c o m -plexes were < 1% of the to ta l d issolved iron. Percent Dissolved M a n g a n e s e Fig. 5-13 Pe rcen tages of free a n d c o m p l e x e d dissolved m a n g a n e s e in Powel l Lake. All other comp l exes were < 1% of the total dissolved m a n g a n e s e . Fig. 5-14 Pe rcen tages of f ree a n d c o m p l e x e d dissolved m a n g a n e s e in Sak inaw Lake. All other comp l exes were < 1% of the to ta l dissolved m a n g a n e s e . Fig. 5-15 Particulate sulphur in Powell Lake Fig. 5-16 Part iculate sulphur in Sakinaw Lake Fig. 5-17 Saturation state of iron sulphides in Powel l Lake. Log (K *IAP) > 0 = super-satura ted , < 0 = undersaturated. Log (K s p * IAP) -15 -10 -5 0 5 10 15 -i r i i | i i i i | i i i i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -i - | 1 ( Sakinaw < . . . . i , . . . i . . . . . " 0 - % • r • o -t • o -( I i i — : -1 • 1 1 4 • o -FeS 2 / 6 ; i • • O -\ i y • o -•' ' • i • • • • i • ' ' • Fig. 5-18 Saturation state of iron sulphides in Sak inaw Lake. Log (K *IAP) > 0 = super-5 p saturated, < 0 = undersaturated. Fig. 5-19 Saturation state of m a n g a n e s e sulphides in Powel l Lake. Log (K *IAP) > 0 = super-s p sa tura ted , < 0 = undersaturated. Log (K s p * IAP) -15 -10 -5 0 5 10 15 i i i i i i i i i i i MnCO, 20 40 60 80 100 120 140 I f / i / ' ' MnS Mn(OH). f ^ m i l i •' ' 1 *' • ' 1 i i i i i i i i i i i i 1 1 OXIC anoxic Sakinaw MnS, Fig. 5-20 Saturation state of m a n g a n e s e sulphides in Sak inaw Lake. Log (K *IAP) > 0 = super-s p saturated, < 0 = undersaturated. 5.4 Discussion Sulphur Oxyanions Sulphate Despi te b e i n g the the s e c o n d most a b u n d a n t an ion in s eawa te r (at S = 3 5 % 0 , the SO4 c oncen t r a t i on is 28 m M ) , sulphate is d e p l e t e d at d e p t h in bo th lakes (Figs. 5-5 a n d 5-6). S u c h dep le t i ons ref lect the f a c t that su lphate is the major e l e c t r o n a c c e p t o r for a n a e r o b i c resp i ra t ion in s t ra t i f i ed , o x y g e n - d e p l e t e d w a t e r masses a n d a n o x i c sed imen t s ; m u c h of t h e d e c o m p o s i t i o n in near-shore mar ine sed iments a n d salt marshes is m e d i a t e d by sulphate-reducing b a c t e r i a (J0rgensen 1977,1982; Howarth a n d Teal 1979; Howar th a n d Gib l in 1983). There a re three sources for su lphate in the oxic waters of Powel l a n d Sak inaw Lakes: d i rect a tmospher i c input, river input a n d diffusion u p w a r d a n d ox ida t ion of sulphide f rom the anox i c b o t t o m waters. The higher su lphate concen t ra t ions a b o v e 30 m in Sak inaw Lake are most likely d u e t o the larger amoun t of su lph ide present in the b o t t o m wa te r , w h i c h supports a m u c h h igher u p w a r d flux of r e d u c e d sulphur t o the oxic sur face layer where ox ida t ion to SOt c a n o c c u r . However , Sak inaw Lake is a lso c loser t o the Strait of G e o r g i a w h e n c e su lphate c o u l d b e supp l ied by seaspray . In a d d i t i o n , Sak inaw extends less farther in land t h a n Powe l l Lake , w h i c h must result in less dilution of the salt aeroso l input. The su lphate m a x i m u m that occurs at the inter face of bo th lakes is p robab l y d u e t o c y c l i ng of sulphur spec ies at the inter face . As sulphide diffuses upwards , it is ox id ized bo th c h e m i c a l l y by c o n t a c t with dissolved o x y g e n a n d iron a n d m a n g a n e s e oxides as wel l as b io log ica l l y v i a chemosyn the t i c b a c t e r i a , such as Beggiatoa spp . The latter are o b l i g a t e a e r o b e s a n d thus a re only f o u n d a b o v e the ox i c /anox i c in te r face . O n c e ox id i zed to su lpha te , sub-interface su lphate-reduc ing b a c t e r i a will r e d u c e SO2," w h i c h diffuses d o w n w a r d from the max imum. C o n t i n u e d u p w a r d diffusion of sulphide results in a c y c l i n g of sulphur a t t he ox i c /anox i c b o u n d a r y . The in te r face in b o t h lakes is t o o d e e p for photosynthe t i c b a c t e r i a t o survive, a n d , in f a c t , no purple b a c t e r i a c o u l d b e visual ly o b s e r v e d . Su lphate coexists with sulphide in bo th lakes, a l though in Sak inaw Lake the zone of over lap is m u c h shallower (30 - 45 m) than in Powel l Lake (150- 180 m)(Figs. 5-5 a n d 5-6). This reflects t he sharper in ter face in Sak inaw Lake. Diffusion processes a l one are unlikely to a c c o u n t for t h e p r e s e n c e of su lphate u p to 30 m b e l o w the ox i c/anox i c in ter face , a n d thus sufficient oxidants must b e present t o gene ra t e su lphate at these depths. Likely oxidants are iron a n d m a n g a n e s e oxides w h i c h interact with sulphur spec ies a c c o r d i n g t o the fo l lowing equat ions (Aller a n d Rude 1988): 1) 5H + + 2FeOOH + HS" -» 2Fe 2 + + S° + 4H2O 2) 10H + + 6FeOOH + S° -> 6Fe* + S 0 4 + 8H2O 3) 16H+ + 8FeOOH + FeS -> 9Fe 2 + + SO* + I2H2O 4) 3H + + MnOz + HS" -> Mn 2 * + S° + 2HzO 5) 4 H + + 3MnG2 + S° -» 3 M n 2 + + SO4 + H2O 6) 8H + + 4 M n 0 2 + FeS - > 4 M n 2 + + SO? + Fe 2 + + 4H2O. A n equ i va l en t set of reac t ions c a n b e written f o r M n O O H or for o ther M n 3 + or M n 4 + c o m p o u n d s . R e a c t i o n 1) is a b i o g e n i c a n d wel l-known f rom laboratory a n d f ie ld studies (Berner 1964a; Land ing a n d Lewis 1990; Pyzik a n d Sommer 1981; R ickard 1974). C o m p l e t e ox idat ion such as in 2) a n d 3) (with Fe 3 + as reactant ) has b e e n d o c u m e n t e d at low pH in n o n m a r i n e env i ronments a n d at h igh pH in pyrite ox ida t ion exper iments , but not in natura l mar ine sed iments (Berner 1970; Brock a n d Gusta fson 1976; Pyzik a n d Sommer 1981; Moses e t a l . 1987). Al ler a n d Rude (1988) h a v e shown that c o m p l e t e anox i c ox ida t ion of sulphide to su lphate c a n o c c u r in the a b s e n c e of f ree O2. w h e n Mn-oxides are physical ly mixed or in otherwise c l o se c o n t a c t with su lph id ic , a n o x i c mar ine sed iment . A l t h o u g h l imited c o m p a r a b l e ox ida t i on c o u l d also t a k e p l a c e in the p r e s e n c e of Fe-oxides, Al ler a n d Rude (1988) f o u n d n o e v i d e n c e for this. Their exper iments impl ied that Mn 4 + -ox ides are m o r e e f f ec t i ve t h a n M n 3 + (as M n 3 0 4 / M n O O H ) in oxidiz ing su lph ide . These ox ida t i on reac t ions c a n b e e x p e c t e d to o c c u r in a n o x i c basins like Powel l a n d Sak inaw whe re ox ide-bear ing or d iscrete ox ide part ic les a re m ixed wi th a n o x i c , sulphur-rich mater ia l . The reac t ion of Mn-oxide with HS" is rap id (< 1 min half-life HS" in p r e s e n c e of excess Mn-ox ide ) a n d p r o d u c e s S° as a pr imary, a l t h o u g h not exc lus ive , p r o d u c t (Burdige a n d N e a l s o n 1986). Such a n o x i c su lphide ox ida t ion is inhibi ted by the m e t a b o l i c inhibitors az ide a n d 2,4-dinitrophenol (DNP) but not by ch lora te (or p r o d u c e d chlorite) , ind icat ing tha t the r eac t i on is b io log ica l l y m e d i a t e d , possibly b y th iobac i l l i or a similar g r o u p of chemo l i t ho t roph i c b a c t e r i a . Thus, t he su lphate distributions o b s e r v e d in Powel l a n d Sak inaw Lakes c a n b e a t t r i bu ted t o d i r e c t ae roso l a n d su r f a ce runoff inputs, a n d u p w a r d di f fus ion a n d o x i d a t i o n of su lph ide a t or nea r t he o x i c / a n o x i c b o u n d a r y , t h e r e b y estab l i sh ing a steady-state su lpha te m a x i m u m . Thiosulphate, Sulphite and Polythionates The par t ia l l y o x i d i z e d forms of sulphur m a y b e p r o d u c e d b y a va r ie ty of react ions , inc lud ing the ox idat ion of H2S ( C h e n a n d Morris 1972a,b; Ho f fmann 1977), the ox ida t ion of su lphide minerals ( G o l d h a b e r 1983), a n d mic rob ia l processes ( G o l d h a b e r a n d K a p l a n 1974). Despite this variety of potent ia l format ion pa thways for partly ox id ized sulphur c o m p o u n d s , in this s tudy, th iosu lpha te , sulphite a n d po ly th iona tes we re not d e t e c t e d a t a n y d e p t h in either lake . This is a n u n e x p e c t e d result, g i v e n that these spec i es a re intermediates in the ox ida t ion of bo th sulphide ( C h e n a n d Morris 1972a,b) a n d pyr i te ( G o l d h a b e r 1983; Moses et a l . 1987) t o su lpha te . Su lphi te ( SO? ) a n d tetrath ionate (S^Of) are known to o c c u r , a lbeit rarely, in natural environments. Bou legue et a l . (1982) a n d Luther et a l . (1985,1986a) , for e x a m p l e , f o u n d small amounts of sulphite ( 7 - 4 0 \iM) in a f e w salt marsh po rewa te r samples , a n d Luther et al . (1986b) f o u n d up to 300 p.M te t ra th ionate in the porewate rs f rom o n e salt marsh co re . In contrast t o these in te rmed ia te spec i es , th iosu lphate is a signif icant c o m p o n e n t ( typical ly 20 - 700 nM) of dissolved sulphur at al l dep ths in salt marsh porewaters (Bou legue et a l 1982; Howar th a n d Teal 1980; Howarth et a l 1983; Luther et a l . 1985,1986a,b), subt idal porewaters (Luther et a l . 1985), l ake po rewa te r s (Nr iagu et a l . 1979) a n d s o m e a n o x i c w a t e r co lumns ( J a c o b s 1984). Th iosu lphate is o n e of t h e first p r o d u c t s of t h e ox ida t i on of pyrite ( G o l d h a b e r 1983; Moses et a l . 1987; Luther 1987), a n d is a lso p r o d u c e d f rom the d e c o m p o s i t i o n of po l y su lph ides ( C h e n a n d Morris 1972a). Unde r w e a k l y a c i d i c cond i t i ons , s u c h as those in b o t h Sak inaw a n d Powe l l Lakes, th iosu lphate is readi ly ox id ized t o te t ra th ionate by w e a k oxidizing agents (Lyons a n d Nickless 1968), viz: 2S2O2: + H + + I/2O2 -> S4CI + H2O. Po ly th ionates a r e relat ively s tab le unde r a c i d i c cond i t ions (Lyons a n d Nickless 1968; Dowson a n d Jones 1974). The distributions of sulphur oxyan ions in Powel l a n d Sak inaw Lakes are similar t o the B lack S e a , whe re no S 20 2T,S406 or S O l a re d e t e c t a b l e a t a n y d e p t h (Luther et a l . 1990c). This is in spite of t he f a c t tha t Luther et a l . (1990c) f o u n d a n a e r o b i c sulphide ox ida t ion in s tored samples . This observa t ion ind ica tes that the in te rmed ia te oxidat ion-state sulphur oxyanions are either not f o r m e d , or, if they are p r o d u c e d they are oxid ized rapidly a n d essentially quant i tat ive ly , or pe rhaps used as a l te rnate e l e c t ron a c c e p t o r s (Truper 1982). However , Luther et a l . (1990c) obse r ved that th iosu lphate w a s g e n e r a t e d w h e n air w a s pu rpose l y a l l o w e d t o c o n t a c t their samp les . The p a u c i t y of sulphur oxyan ions in b o t h the B lack S e a a n d Powel l a n d Sak inaw Lakes is consistent with a n a p p a r e n t l a c k of a p p r o p r i a t e c h e m i c a l ox idants (O2, Fe(lll), Mn(IV)) in the a n o x i c waters . The inabi l i ty t o d e t e c t a n y of these spec i e s ind i ca tes tha t ox ida t i on of the samples d i d not o c c u r in the f ie ld , or in the various manipu la t ions of t he s amp l e wa te r such as a m p o u l i n g . Reduced Sulphur Species Dissolved Sulphide Dissolved sulphide concent ra t ions are almost tw i c e as high in Sak inaw Lake as in Powel l (Figs. 5-5 a n d 5-6). B e c a u s e ch lor ide a n d other major ion concen t ra t i ons in the former a re a b o u t two-thirds those of Powel l , Sak inaw Lake must h a v e h a d a n add i t i ona l su lphate source s ince it was cu t off f rom the o c e a n approx imate l y 11000 years a g o . The most likely source is f rom o c c a s i o n a l intrusions of s eawa te r over the bare ly e m e r g e d sill. Howeve r , su lphide levels m a y also b e higher in Sak inaw b e c a u s e of l imitation on iron-sulphide fo rmat ion d u e t o l a ck of iron. The sulphide c o n c e n t r a t i o n m a x i m a in the two lakes differ by 2500 | iM whereas the d i f fe rence in m a x i m u m iron contents is only 160 n M . This order of m a g n i t u d e d i f fe rence ind ica tes that the higher concen t ra t ions of sulphide in Sak inaw are most likely attr ibutable t o a n add i t iona l sulphate source. No te it has b e e n assumed that the ana ly t i ca l m e t h o d used (Cl ine 1969) measures all d i sso lved su lph ide , i n c lud ing the te rmina l S 2 "of po lysu lph ides . H o w e v e r , J a c o b s (1984) a n d Luther et a l . (1985) f o u n d that only approx imate ly 20 - 2 5 % of S$ a d d e d to H2S-b e a r i n g solutions w a s d e t e c t a b l e (74% of Na2S2). P resumab ly , t he e l e m e n t a l sulphur l ibe ra ted w h e n the a c i d i c r eagen t is a d d e d t o the samples inhibits the d e v e l o p m e n t of the methy l ene b lue colour . C l ine (1969) i nd i c a t ed that th iosulphate , but not sulphite, has a similar e f f ec t o n co l ou r d e v e l o p m e n t . Thus, this t e c h n i q u e underest imates to ta l S(-2) w h e n po l y su lph ides a re present . To a v o i d this p r o b l e m I a t t e m p t e d to m e a s u r e dissolved sulphide po l a rog raph i ca l l y as in Luther et a l . (1985), a t e c h n i q u e w h i c h does not suffer f rom s u c h in ter ferences a n d is a lso m u c h m o r e sensit ive t h a n the C l i ne t e c h n i q u e . Howeve r , dur ing the short t ime b e t w e e n c o l l e c t i o n of samp les a n d their del ivery t o the nea rby l ab , a large a m o u n t of the H2S h a d b e e n lost (when c o m p a r e d to the C l i ne m e t h o d ) . This is most likely d u e t o the str ipping of H 2S f rom t h e samp les by v igorous outgass ing of m e t h a n e as samples are brought t o the sur face f rom d e p t h . The a m o u n t of H2S lost w a s d e p e n d e n t o n pH: a t lower depths , whe re the pH was less a c i d i c (6.8), only a b o u t 2 5 % w a s lost d u e t o the p r e s u m e d outgass ing. At mid-depths , whe re the pH r a n g e d f rom 5.9 - 6.4, there was 40 - 6 4 % loss. A t the u p p e r more a c i d i c dep ths (pH 5.7), u p t o 7 5 % of the H 2S m e a s u r e d v i a the C l i ne t e c h n i q u e w a s not d e t e c t e d po la rograph ica l l y . This is d u e to the m u c h larger proport ion of sulphide occur r ing as the H 2S spec ies (95% at pH 5.7 versus 4 5 % at pH 6.8) at t he more a c i d i c pH levels. As no th iosu lpha te or sulphite w e r e d e t e c t e d , su lph ide loss d i d not a p p e a r to b e d u e to oxidat ion. If all of the polysulphide present was S4 (see next sect ion) a n d therefore , the d isso lved su lph ide concen t r a t i ons are p r o b a b l y a b o u t 2 5 % unde re s t ima ted (Luther et al . 1985). Zerovalent Sulphur Po lysu lph ides a r e impor t an t in te rmed ia tes in pyri te f o r m a t i o n (G ib l in 1988; Howarth 1979; Lord a n d Chu r ch 1983; Luther et a l . 1982; Rickard 1975; Sweeney a n d Kap lan 1974), a n d a re a lso potent ia l l y impor tant in the c y c l i n g of meta ls d u e to their h igh c o m p l e x i n g abi l i ty ( Bou l egue et a l . 1982: B o u l e g u e a n d Denis 1983). Po lysu lph ide concent ra t ions a re extremely h igh in bo th Powel l a n d Sak inaw Lakes, mak ing u p a large f rac t ion of t he to ta l inorgan ic sulphur p o o l (Figs. 5-5 a n d 5-6). Free e l ementa l sulphur was not d e t e c t e d in either lake. The very large quant i ty of polysulphide-sulphur m a y h a v e interfered with the de te rminat ion of S°, however , s ince in this study the e l ementa l sulphur f rac t ion is operat iona l l y d e f i n e d as the zerova lent sulphur w h i c h is re ta ined o n a 0.4 |im N u c l e p o r e filter. The f ree S° is d e t e r m i n e d by d i f f e r e n c e b e t w e e n to t a l ze rova l en t sulphur a n d d isso lved ze rova l en t sulphur, but the h igh polysulphide-sulphur c o n t e n t w o u l d p r o b a b l y interfere b y s w a m p i n g a n y small a m o u n t of f ree S° present. A lso , a n y co l lo ida l S° present w o u l d b e m e a s u r e d as polysulphide. The po lysu lph ide concen t r a t i ons f o u n d in b o t h Sak inaw a n d Powe l l Lakes are extremely h igh (Figs. 5-5 a n d 5-6) w h e n c o m p a r e d to those r epo r t ed for other anox i c basins, w h i c h rarely h a v e po lysu lph ide present. For e x a m p l e , in the hypersal ine anox i c basins of the Eastern Me d i t e r r ane an S e a , H2S r e aches 3 a n d 2.2 m M respect ive ly in the B a n n o c k a n d Tyro bas in brines a n d yet no in termedia te ox ida t ion state c o m p o u n d s of sulphur CSzOl", SO3, a n d Srf) a re d e t e c t a b l e (Luther et a l . 1990b). The l a ck of these intermediates is p robab l y d u e to the pauc i t y of oxidants in the uppe r f e w metres of the br ines, i m m e d i a t e l y b e l o w the ox i c /anox i c in te r face . In the B lack S e a , Luther et a l . (1990c) d i d d e t e c t low levels (< 60 nM) of par t i cu la te S° , but we re unab l e t o d e t e c t a n y po lysu lph ide sulphur. J a c o b s et a l . (1985) also d i d not f ind a n y zerova lent sulphur in the a n o x i c w a t e r c o l u m n of Framvaren Fjord in southern Norway. Polysulphides c a n b e g e n e r a t e d v i a t w o major pa thways : 1) the ox idat ion of dissolved sulphide a n d sulphide minerals; a n d 2) the reac t ion of e l emen ta l sulphur with hydrogen sulphide ( G i g g e n b a c h 1972). 1) E l emen ta l sulphur dissolves in a q u e o u s sod ium su lph ide solut ion a n d c o m b i n e s readi ly with su lphide to form polysu lphide ions, e .g . s i " , S3, S4 a n d Sf (Peschansk i a n d Va lens i 1949). Po lymer izat ion d o e s not e x c e e d the Sf s t age a n d e l e m e n t a l sulphur remains in excess , fo rming a sa tu ra ted po lysu lph ide solution m a d e u p primarily of St a n d sf", whi le St a n d S? a re either t o o low in c o n c e n t r a t i o n or unstab le a n d are thus sub jec ted to rap id d isproport ionat ion ( S chwa rzenbach a n d Fischer 1960), viz: 3S|" + 2H2O <-» 2HS" + 20H" + S4 3S2; + hbO <-> HS" + 20H" + 2S4. The fo rmat ion of po lysu lph ide ions has a n a u t o c a t a l y t i c e f f ec t o n the rate of sulphur dissolution, s ince in the r eac t i on s e q u e n c e HS' + S <-> £ + H + Si" + S <r> S? Sf + S <-» s£ S 4 + S <-» s l e a c h p r o d u c t is a lso a r eac t an t for the next step. Thus, autocata lys is is t o b e e x p e c t e d if react ions after the first o n e are rap id ( C h e n a n d Morris 1972a). 2) A l o n g with th iosu lphate , po lysu lphide a n d e l emen ta l sulphur a re important p roduc ts of the i n c o m p l e t e ox ida t ion of H2S in natura l waters. They are f o r m e d f rom the reac t ion of sulphide with zerova lent sulphur f o rmed from sulphide ox idat ion (Boulegue 1972; C h e n a n d Morris 1972a; Gou rme lon et a l . 1977; Hof fmann 1977), viz: 2HS" + O2 -> V4Se + 20H" HS" + (rvl)/8S8 ^ S 2 " + H + St + 0 s + H2O -> S2O! + S i^ +2H+ 2HS" + 2O2 - * S2O! + H2O. As t h e c h a i n l ength (n) increases , polysulphides d e c o m p o s e t o e l e m e n t a l sulphur a n d su lph ide ( G i g g e n b a c h 1972). These reac t ions p r o c e e d easi ly a n d rap id ly in natura l wa te r s , a n d , there fo re , po lysu lph ide ions shou ld b e f o u n d in r e d u c i n g env i ronments whe re the ox idat ion of H2S has b e e n incomp le te . B o u l e g u e a n d Denis (1983) show tha t po lysu lph ides c a n const i tu te a la rge f rac t ion of the to ta l r e d u c e d sulphur spec ies , a n d are stable e v e n at very low sulphide concent ra t ions ( about lO^-lO^ M) (Teder 1971; G i g g e n b a c h 1972; Bou legue a n d M i c h a r d 1978). The c o n c e n t r a t i o n of polysulphide ions mainly d e p e n d s o n the phys ica l state of e l emen ta r y sulphur (i.e. co l l o ida l vs. rhombic ) p r o d u c e d dur ing the ox ida t ion process (Gourme lon et a l . 1977). E lementa l sulphur is mostly f o u n d as stable rhomb ic sulphur (S8 a) a n d me tas t ab l e co l l o ida l sulphur (Ssc). The G i b b s free energy of Sea is zero , whi le that of Sac is larger t h a n 3.5 kJ»mof' (Boulegue 1976,1978). Thus, a c c o r d i n g to the reac t ion (n-l)/8S8 + HS' <-> Sh + H + the a m o u n t of polysulphide ions in the p resence of co l lo ida l e l ementa l sulphur will b e at least tw i c e the a m o u n t in the p re sence of rhomb ic sulphur, a n d this has b e e n f o u n d in the f ield (Bou legue 1977; Bou legue et al . 1982). The oxidat ion of H2S by o x y g e n , b a c t e r i a , M n 0 2 a n d iron(lll) minerals is the ma in source of co l lo ida l e l emen ta l sulphur. The p e a k of polysulphide concent ra t ions fall within the pH range 6.6 - 7.4 a n d dec reases drastical ly in b o t h a c i d i c a n d a lka l ine solutions ( C h e n a n d G u p t a 1973). Under o n e a t m o s p h e r e pressure of o x y g e n a n d sulphide concen t ra t ions of 1 m M to 10 m M , the co r r espond ing m a x i m u m y ie ld of polysu lphide varies f rom 14 t o 8% of the to ta l H2S. B e c a u s e they are highly r eac t i ve a n d t h e r m o d y n a m i c a l l y unstab le in na ture , po lysu lph ides a re further ox id ized t o fo rm more s table p roduc ts like S2O?.SO4 a n d sulphur. Howeve r , Bou legue a n d M i c h a r d (1978) f o u n d that polysulphide ions a re stable p r o v i d e d n o ox idant enters the system a n d f o u n d no c h a n g e in spec i a t i on in stored samples ove r the course of a year . Bowers et a l . (1966) sugges ted that po lysu lphide ions a re m u c h more suscept ib le t o r eac t i on with o x y g e n t h a n H2S spec ies . H igh leve ls of po l y su lph ides a re usual ly f o u n d in ox id iz ing env i ronments . Bou l egue et a l . (1979) m e a s u r e d sulphur spec ies in the waters of Puzzichel lo (France) , w h i c h a re c h a r a c t e r i z e d by a tmosphe r i c ox idat ion of a n initially sulphide-rich water . In , t h e ear l y s t ages of t h e o x i d a t i o n p r o c e s s , t hey f o u n d ma in l y po l y su lph ide a n d th iosu lphate ; in the f inal s t a g e , su lphate w a s the m a i n p roduc t . Bou l egue (1977) a lso f o u n d po lysu lph ide ions a n d th iosulphate in the g r o u n d waters of a F rench freshwater spring (Enghien), a n d Bou legue a n d Denis (1983) n o t e d the o c c u r r e n c e of polysulphides a n d S° in po r e wate rs of sed iments f rom the Walvis Bay , N a m i b i a . They suggest the p r e s e n c e of po lysu lph ide in these porewaters m a y b e d u e to a n input of S° resulting f rom t h e ac t i v i t y of su lphide-oxid iz ing b a c t e r i a in t h e sed iments (Beggiatoa we re present) a n d a g i n g of the p r o d u c e d co l lo ida l sulphur. Luther et a l . (1986b) f o u n d polysulphide levels of > 300 \M in the pore waters of G r e a t Marsh , D e l a w a r e a n d Luther et a l . (1985) f o u n d that marsh samples consistently c o n t a i n h igher levels of S(0) t h a n subt ida l porewaters . They suggest that this d i f f e rence results f rom t h e t w o di f ferent m e c h a n i s m s of po l y su lph ide f o r m a t i o n . In sub t ida l p o r e w a t e r s , po l ysu lph ides a re f o r m e d f rom t h e r e a c t i o n of S° w i th b i su lph ide ion ( G i g g e n b a c h 1972), whe reas , in salt marsh porewaters , they should form primarily f rom t h e o x i d a t i o n of h y d r o g e n su lph ide ( C h e n a n d Morris 1972a,b) . Exposure to the a t m o s p h e r e a n d infi ltration by t i da l w a t e r a l l serve t o de l i ve r ox idan t s t o marsh sed iment . These ox idants c a n r ea c t with sulphides to p r o d u c e var ious ox id ized a n d part ial ly ox id ized sulphur c o m p o u n d s so that polysulphides are readi ly a va i l ab l e in the u p p e r port ions of the sed iments (Gibl in a n d Howar th 1984). H o w e v e r , po lysu lph ide sulphur concen t r a t i ons in G r e a t Marsh we re present e v e n in the strongly r educ ing z o n e (Luther e t a l . 1986b). In v i e w of these numerous prev ious studies, it is diff icult t o exp l a i n w h y the po l y su lph ide levels in Powe l l a n d S ak i naw a re so h igh . Both lakes represent fairly s t a g n a n t bas ins , m u c h like the B lack S e a , t he M e d i t e r r a n e a n br ines, or F r amva ren , w h e r e levels of po lysu lphides a re low d u e t o the l ack of ox idants . Yet , the extremely h igh concen t ra t ions of polysulphide obse r ved in the t w o lakes c o u l d only b e g e n e r a t e d b y ox ida t ion . There is no readi ly a p p a r e n t source of ox idant in the b o t t o m waters of these lakes. To con f i rm these results, the re fo re , t h e first c o n s i d e r a t i o n must b e to d e t e r m i n e w h e t h e r m e a s u r e d levels a re a c c u r a t e , or ref lect a r t e f ac t s i n t r o d u c e d during samp l i ng , or dur ing the ana ly t i ca l p r o c e d u r e , i.e.. d o they mere ly ref lect ox id ized d i sso lved su lph ide . There is cons ide rab l e e v i d e n c e that the m e a s u r e d concen t ra t ions are cor rec t . 1) There w e r e no p rob l ems wi th ox ida t i on in a n y of t h e o ther ana lyses p e r f o r m e d th roughout this study. N o th iosu lphate or sulphite w e r e ever d e t e c t e d in a n y samples , b o t h b e i n g c o m m o n p roduc t s of su lph ide ox ida t ion . Usually, o x i d a t i o n of su lph ide g e n e r a t e s t h i o s u l p h a t e t o g e t h e r w i th p o l y s u l p h i d e a n d not just p o l y s u l p h i d e . Unfor tunate ly , b e c a u s e t h e ind i rect m e t h o d for de t e rm in ing po l y su lph ide involves convers ion to th iosu lphate , the p resence of th iosulphate c o u l d not b e direct ly c h e c k e d o n t h e p o l y s u l p h i d e s a m p l e s themse l ves . H o w e v e r , a m p o u l e s w e r e f l u shed wi th n i t rogen prior t o s a m p l e in t roduct ion a n d those tha t w e r e not u sed for po lysu lph ide analysis s h o w e d n o e v i d e n c e of ox ida t ion . A lso , the samples f rom the t w o lakes we re c o l l e c t e d in t w o di f ferent years. Therefore , t o p r o d u c e the o b s e r v e d po lysu lph ide concent ra t ions , the s a m e d e g r e e of ox idat ion w o u l d h a v e h a d to o c c u r at t w o different t imes, in t w o different p l a ces . A lso , a m u c h more erratic po lysu lphide profile w o u l d b e e x p e c t e d if ox ida t ion of su lphide was significant. Instead, the profiles a re s m o o t h , with little sca t te r , a n d no c lear l y a n o m a l o u s points. The po lysu lph ide profiles a lso d o not c o m p l e t e l y mimic those of d issolved sulphide. In the lowermost dep ths of Powel l Lake , po lysu lph ide concen t r a t i ons d o not b e c o m e cons tant until the b o t t o m 10 m, whe reas sulphide levels are constant for the bo t tom 25 m. 2) N o p r e c i p i t a t e w a s o b s e r v e d in t h e a m p o u l e s . Bes ides p o l y s u l p h i d e a n d th i o su lpha te . S ° is a c o m m o n p r o d u c t of su lph ide ox ida t ion . In d u p l i c a t e a m p o u l e s w h i c h w e r e not o p e n e d , there w a s no prec ip i ta te up to two years after co l l ec t ion ; after four years , s o m e h a d a p p e a r e d , ind ica t ing that su lph ide w a s eventua l l y ox id ized (or th iosulphate was d i ssoc ia ted to S° a n d S O f ) . 3) Sulphite r e m a i n e d in the a m p o u l e s . A smal l excess of sulphite w a s a d d e d t o the a m p o u l e s at the t ime of s a m p l e co l l e c t ion to reac t with the zerova lent sulphur. Sulphite is ox id ized easi ly b y O2 (on the order of 100 mo le^L '^min " 1 ) a n d has b e e n used as a n o x y g e n s c r u b b e r for this r eason . O n al l p o l a r o g r a p h runs, su lphi te w a s p resen t , i nd i ca t ing that it h a d not b e e n e x p o s e d t o ox idat ion . However , ox ida t ion of sulphite is inhibited by the p r e sence of sulphide, the half-life at 5 x 1 0 5 M S O f b e i n g i n c r eased from a f e w minutes t o hours at pH 8.4 in the p r e sence of 0.25 m M sulphide ( C h e n a n d Morris 1972a). Therefore a n y ox idant present might h a v e b e e n exhaus ted in oxidizing sulphide. 4) The b o t t o m w a t e r of b o t h lakes has a dist inct straw c o l o u r , w h i c h i nd i ca tes the p r e s e n c e of polysulphides (Morse et a l . 1987). However , the co lour c o u l d b e d u e to the p r e s e n c e of h u m i c ma te r i a l , w h i c h a lso t ends t o impar t a ye l l ow c o l o u r to w a t e r (Williams 1975). Both lakes h a v e very h igh levels of D O C ( C h a p t e r 3) , a n d so the latter cons ide ra t ion c a n n o t b e d i s coun ted . The ye l low co lou r diminishes s o m e w h a t , a l though not ent i re ly , u p o n o x i d a t i o n , i n d i c a t i n g tha t a l a rge por t ion of it is likely d u e to polysulphides, a l though the remain ing co lour must b e d u e to o rgan i c matter. 5) The most persuasive e v i d e n c e that polysulphides o c c u r in h igh concen t ra t ions is that w h e n samp les we re run into bott les con t a i n i ng either c o n c e n t r a t e d HCI, or H N 0 3 (for d i sso lved meta l s ana lyses ) , a wh i t e-co lou red p r e c i p i t a t e f o r m e d i m m e d i a t e l y (the prec ip i ta te was slightly ye l low-coloured in Powell) . This w a s at t r ibuted to ac id i f i ca t ion of po lysu lph ide , w h i c h releases the sulphide as H 2S, the reby f ree ing the zerova lent sulphur w h i c h t hen prec ip i ta tes . A n y d issolved su lphide present shou ld also b e c o n v e r t e d to H 2S a n d quick ly d e g a s , part icular ly cons ider ing that , a t the pH of the waters s tud ied (< 6.8), most of t he d i sso lved su lph ide must o c c u r as H 2S. H o w e v e r , Sholkov i tz (1976) s h o w e d tha t a c id i f i c a t i on of natura l organic-r ich waters ( lowering the pH to b e l o w 3), c auses hum i c mat te r t o prec ip i ta te . To c h e c k this possible cont r ibut ion , the p rec ip i ta te w a s f i l tered a n d a n a l y z e d o n a C N S ana l yze r a n d f o u n d t o b e 100% sulphur in the Sak inaw b o t t o m wa te r a n d 9 2 % sulphur (8% c a r b o n ) in Powel l Lake. In summary , it w o u l d a p p e a r tha t there is a la rge store of ze rova len t sulphur present in b o t h lakes. It shou ld b e n o t e d that some of this sulphur m a y b e co l l o ida l S° rather t h a n po lysu lph ide sulphur, as the f rac t ion is opera t iona l l y d e f i n e d as that w h i c h passes t h r o u g h a 0.4 p.m N u c l e p o r e filter. Usually, e l e m e n t a l sulphur co-exists wi th po l ysu lph ides ( Bou l egue a n d M i c h a r d 1978). S p e c i a t i o n c a l c u l a t i o n s wi th MINEQL ( A p p e n d i x 1) i n d i c a t e d that a lmost all the polysulphide in b o t h lakes should b e present as St. As n o t e d earl ier, the re must b e , or h a v e b e e n , s o m e ox idan t a v a i l a b l e w h i c h c o u l d h a v e c a u s e d the gene ra t i on of the zerova lent sulphur. Ox idants m a y h a v e b e e n i n t r o d u c e d t o S ak i naw Lake b y o c c a s i o n a l intrusions of s e a w a t e r ove r the sill. Such inputs t o d e e p waters h a v e likely o c c u r r e d severa l t imes s ince Sak inaw was s e p a r a t e d f rom t h e Strait of G e o r g i a . D u e to the high levels of su lph ide , t he ox idants m a y h a v e b e e n e x h a u s t e d in oxid iz ing the su lph ide t o sulphur as we l l as th iosu lpha te , ( a n d possibly t o su lphate ) . B e c a u s e there is a shor tage of e l ec t ron a c c e p t o r s in the b o t t o m wate rs , a n y th iosu lpha te so g e n e r a t e d w o u l d likely h a v e b e e n rap id ly r e m o v e d by su lpha te- reduc ing b a c t e r i a , most of w h i c h a re c a p a b l e o f r e d u c i n g sulphite a n d th iosulphate (Truper 1982). In Powel l Lake , howeve r , it is m u c h more difficult t o establish a n ox idant source. It is we l l k n o w n tha t b o t h iron a n d m a n g a n e s e oxides oxidize su lph ide rapidly . I ndeed , Land ing a n d Lewis (1990) s h o w e d exper imenta l ly that m ic romo la r sulphide levels almost ins tantaneous ly r e d u c e so lub le Fe(lll). Thus they be l i e ve there is little so luble Fe(lll) present b e l o w 110 m (the su lph ide inter face ) in the B lack Sea . Burd ige a n d Nea l son (1986) f o u n d c h e m i c a l r educ t ion of Mn(IV) b y sulphide to b e rap id a n d c o m p l e t e , with al l su lph ide b e i n g ox id ized p redominan t l y t o S° within 5-10 min. B e c a u s e these me ta l oxides a re r e d u c e d so rapidly in the p resence of su lph ide , howeve r , they should all b e r e d u c e d just b e l o w t h e o x i c / a n o x i c i n t e r f a c e in Powe l l L ake . This o b s e r v a t i o n essential ly rules out the pa r t i c ipa t ion of Fe a n d M n oxides as oxidants a t d e p t h in the lake . In b o t h lakes, the ratio of sulphide to sulphur dec reases with d e p t h (Figs. 5-7 a n d 5-8). This is u n e x p e c t e d , g i ven that the source of most oxidants is at the in ter face . The lowest S(-2):S(0) va lues w o u l d therefore b e e x p e c t e d to o c c u r just b e l o w the inter face . A lso, the lower ratio in Sak inaw Lake ind icates that a greater proport ion of the sulphide p o o l the re consists of polysulphides. This is consistent with the hypo thes i zed spo rad i c inject ion of ox ic wa te r into Sak inaw d e e p waters. Luther et a l . (1990c) h a d similar difficulty in f inding a n ox idant to exp la in a sub-in ter face zerova lent sulphur m a x i m u m in the B lack Sea . The low levels of S(0) a n d the inability t o d e t e c t sulphur oxyanions (typical ly < 200 nM) are consistent with the a p p a r e n t l a c k of t y p i c a l c h e m i c a l ox idants (O2. Fe(lll), Mn(IV)) in t h e a n o x i c / n o n s u l p h i d i c transition zone . Despi te this, Luther et a l . (1990c) f o u n d that su lphide is ox id ized in situ a t d e p t h in the B lack S e a a n d suggests that the ox idant m a y b e CO2 ( J a rgensen et a l . 1990b, c i t ed in Luther et a l . 1990c; R e p e t a et a l . 1989) or oxidized organ ic matter. M a n g a n e s e c o m p o u n d s m a y b e responsible for the a b i o t i c , a n o x i c su lph ide ox ida t ion o b s e r v e d in the B lack S e a a n d Eastern Med i t e r r anean S e a brines by Luther et a l . (1990b,c) . These authors hypothesize that soluble c o m p o u n d s or c o m p l e x e s such as Mn( l l l )-organic c o m p l e x e s or Mn( l l )-organic c o m p l e x e s w i th u n s a t u r a t e d o r g a n i c ma t t e r (e .g . c a r b o x y l i c a c i d s , olef ins, e tc . ) , m a y a c t as the e l e c t r o n a c c e p t o r s for su l ph ide o x i d a t i o n . L i g a n d - c e n t r e d o x i d a t i o n of Mn( l l ) t o Mn(l l l ) in m a n g a n e s e c o m p l e x e s c o n t a i n i n g c a r b o x y l a t e l igands has b e e n d e m o n s t r a t e d by Richert et a l . (1988), a n d in this m e c h a n i s m , a n e lec t ron f rom Mn(ll) is a c c e p t e d by a ca rboxy l i c a c i d l i gand . Luther et a l . (1990c) suggest that Mn(lll) p r o d u c e d in this m a n n e r c a n reac t with a n d ox id ize su lph ide . O x i d a t i o n of Mn(l l ) w o u l d not b e o b s e r v e d in situ b e c a u s e su lph ide w o u l d r e d u c e the ox id ized m a n g a n e s e readi ly. Overa l l t he process shou ld l e a d to the reduc t ion of unsaturated (oxidized) o rgan i c matter (R) a n d the net ox idat ion of su lphide with Mn(ll) as the cata lyst , viz: (R)-Mn"-S -»(R)"-Mn'"-S -+ (R)"-Mn"-S+-> products ( r e d u c e d o rgan i c matter , SO 2") + Mn(ll) M a n y different o rgan i c e lec t ron a c c e p t o r s w o u l d b e a b l e to c a u s e the net ox idat ion of su lph ide b e c a u s e of the c a t a l y t i c e f f e c t of Mn(ll). This p rocess is a n a l o g o u s t o the t r ace-meta l-ca ta l yzed ox idat ion of su lphide by o x y g e n (Luther 1990a). There is a la rge quant i ty of o rgan i c matter in the bo t tom wa te r of bo th Powel l a n d Sak inaw Lakes, some of w h i c h m a y a c t as a source of oxidants. The p roduc t i on of sulphur in termediates in b o t t o m wate rs u n d e r these a n o x i c cond i t i ons shou ld l e a d t o their r ap id u p t a k e or d ispropor t ionat ion by organisms w h i c h require t h e m as a source of ene rgy ( Jargensen e t a l . 1990b). In s u m m a r y , t h e on l y sou rces of o x i d a n t t ha t c o u l d g e n e r a t e the h igh po lysu lph ide concen t r a t i ons o b s e r v e d at d e p t h in Powel l Lake a re o rgan i c c o m p l e x e s s u c h as the Mn(ll)- a n d Mn(l l l )-organic c o m p l e x e s p r o p o s e d by Luther et a l . (1990c). B e c a u s e of the h igh concen t ra t ions of o rgan i c mat te r a n d m a n g a n e s e in Powel l Lake b o t t o m waters , a n d the long pe r iod of t ime that the wa te r has b e e n anox i c , it is possible that these c o m p o u n d s might h a v e g e n e r a t e d sufficient ox idant t o c a u s e the h igh level of po lysu lph ide f o u n d a t d e p t h in this lake. In Sak inaw Lake , o c c a s i o n a l incursions of s eawa te r over the sill w o u l d a d d cons iderab ly to the ox idant poo l . Iron and Manganese The sub-interface dissolved iron m a x i m a in Powel l a n d Sak inaw Lakes (Figs. 5-9 a n d 5-10) arise f rom the reduct i ve dissolution of me ta l oxides settling f rom the overlying ox ic wa te r , f o l l o w e d b y prec ip i ta t ion or adsorpt ion on to solid phases a t d e p t h ( J a cobs et a l . 1987). These profiles a re t y p i c a l of transition metals w h i c h exhibit r edox c yc l i ng of m e t a l ox ide part ic les a n d d issolved m e t a l spec ies a t the O2/H2S i n te r f ace , a n d m e t a l su lphide format ion ( J a cobs et a l . 1985). In ox ic waters , iron a n d m a n g a n e s e are present primarily as the extremely insoluble Fe(lll) a n d Mn(IV) a n d Mn(lll) oxyhydroxides. These part ic les a re r e d u c e d w h e n they e n c o u n t e r a n o x i c waters in me rom i c t i c lakes or seas , a n d so prov ide a source of soluble me ta l cat ions w h i c h a re t ranspor ted a t c o m p a r a b l e rates b o t h u p w a r d t o b e o x i d i z e d a n d d o w n w a r d t o w a r d s d e e p e r waters . This so lub i l izat ion a t or n e a r t h e c h e m o c l i n e a n d the two-way t ranspor t c a u s e s the cha rac te r i s t i c m a x i m u m in the c o n c e n t r a t i o n - d e p t h profi les of t h e so lub le spec ies . D i sso l ved Fe(ll) a n d Mn(l l ) in t h e sub-oxic z o n e di f fuse u p w a r d a l o n g a s t e e p concen t r a t i on grad ient a n d are ox id ized t o Mn(IV) a n d Fe(lll) at or a b o v e the inter face. Highly insoluble phases , s u c h as 8 M n 0 2 a n d Fe (OH) 3 a re f o r m e d w h i c h resettle t o w a r d the anox i c zone . As iron is r e d u c e d , howeve r , it is p rec ip i t a ted as iron sulphide phases in the p r e s e n c e of H2S a n d is thus r e m o v e d f rom cyc l i ng a t the inter face . D u e t o the high solubil i ty of t he least so lub le Mn(ll ) p r e c i p i t a t e (MnS2), M n 2 + is rarely r e m o v e d v i a prec ip i ta t ion . C o m p a r i s o n of the m a n g a n e s e a n d iron profiles reveals that the large increase in iron c o n c e n t r a t i o n d e v e l o p s b e t w e e n 150 a n d 200 m in the w a t e r c o l u m n in Powel l Lake , whi le tha t of m a n g a n e s e beg ins earl ier at 125 m (Figs. 5-9 a n d 5-10). In Sak inaw L a k e , t h e t w o s t e e p g rad i en t s o v e r l a p d u e t o t h e m u c h sha rpe r i n t e r f a ce . The d i f f e rence in the behav iou r of these t w o metals reflects their different redox chemistries, a n d is consistent wi th the f a c t that m a n g a n e s e r educ t i on o c c u r s a t s o m e w h a t higher (more oxidizing) potentia ls t han does the reduc t ion of Fe (Stumm a n d M o r g a n 1981). Severa l studies h a v e i n d i c a t e d that Fe(lll) a n d Mn(lll) r educ t ion in natural waters a n d sediments is b io log i ca l l y-med ia ted (Kamura et a l . 1963; Serensen 1982; Jones et a l . 1983; Bu rd ige a n d N e a l s o n 1985; Myers a n d N e a l s o n 1988). G e n e r a l l y , t h e net a c c u m u l a t i o n of Fe(ll) in w a t e r a n d sed iment is not o b s e r v e d until af ter the r emova l of d isso lved o x y g e n a n d nitrate a n d the a c c u m u l a t i o n of Mn(ll) ( P o n n a m p e r u m a 1972; Y o s h i d a 1975), a n d this has b e e n e x p l a i n e d as a preferent ia l r e d u c t i o n of e l e c t r on a c c e p t o r s in o rder of d e c r e a s i n g ene rgy y ie ld. Thus, Mn(IV) r educ t ion p r e c e d e s Fe(lll) r educ t i on (see Tab le 3-1). The latter p h e n o m e n o n has a lso b e e n e x p l a i n e d as resulting f rom compe t i t i v e exc lus ion of Fe(l l l )-reducing b a c t e r i a b y other organisms ( H a m m a n n a n d O t tow 1974; P o n n a m p e r u m a 1972; Yosh ida 1975). Lovley a n d Phillips (1988) found that dissimilatory Fe( l l l )-reducing organisms c a n r e d u c e Fe(lll) in the p r e s e n c e of Mn(IV), a n d t h e y suggest tha t the d o m i n a n t f a c t o r p reven t ing the a c c u m u l a t i o n of Fe(ll) in sed iments tha t c o n t a i n microbia l ly r educ ib l e Mn(IV) is t he n o n e n z y m a t i c ox idat ion of Fe(ll) by Mn(IV). A l t h o u g h m u c h of t h e Fe(lll) a n d Mn(IV) r e d u c t i o n in na tura l env i ronments a p p e a r s t o b e microb ia l l y c a t a l y z e d , these e l ements c a n a lso b e r e d u c e d abiot ica l ly b y c o m p o u n d s s u c h as sulphide (Ehrtich 1981; Burdige a n d Nea l son 1986; Land ing a n d Lewis 1990). Var ious o r g a n i c c o m p o u n d s a re a lso c a p a b l e of c h e m i c a l l y r e d u c i n g Fe(lll) a n d Mn(IV) ( M o r g a n a n d Stumm 1964; Stone a n d M o r g a n 1984a, b). M ic robes c a n c a t a l y z e iron a n d m a n g a n e s e r e d u c t i o n by e x c r e t i n g r e d u c e d m e t a b o l i c e n d p roduc t s such as su lphide a n d o r g a n i c c o m p o u n d s , w h i c h t hen r eac t ab io t i ca l l y with me ta l oxides (Burdige a n d Nea lson 1985). Iron a n d m a n g a n e s e ox ida t i on a re a lso t hough t t o b e primari ly b io log i ca l l y m e d i a t e d - p r o c e s s e s . S e ve r a l s tudies sugges t t ha t b i o l o g i c a l ca ta l ys i s must b e occu r r ing (Emerson et a l . 1979, 1982; Wollast et al.1979; Tebo et a l . 1984)) b e c a u s e the rates a r e t o o fast t o b e e x p l a i n e d b y pure ly i n o r g a n i c m e c h a n i s m s . H o w e v e r , adso rp t i on a n d a u t o c a t a l y t i c ox ida t i on of m a n g a n e s e o c c u r s ( M o r g a n 1967; Wilson 1980; Kessick a n d M o r g a n 1975; Sung a n d M o r g a n 1981). The d e p l e t i o n of iron a t d e p t h in b o t h lakes (Figs. 5-9 a n d 5-10) is d u e to p rec ip i t a t i on of iron sulphides. The Fe(ll) g e n e r a t e d in t h e a n o x i c waters reac ts with su lph ide , or more likely with the highly reac t i ve po lysu lph ide , t o form either FeS or FeS 2. This c a n b e s e e n by c o m p a r i n g the iron a n d su lph ide profiles in b o t h lakes: as iron concen t ra t ions d e c r e a s e sulphide increases (Figs. 5-5, 5-6 versus 5-9,5-10). The f a c t that iron is a lmost entirely d e p l e t e d a t d e p t h ind ica tes that iron su lph ide fo rmat ion is iron-l imited in bo th of these lakes. The ult imate source of iron a n d m a n g a n e s e to the lakes is sur face run off, a n d dissolved iron a n d m a n g a n e s e levels are m u c h higher in the anox i c wate rs of Powe l l t h a n in Sak inaw Lake . The h e a d w a t e r s of b o t h lakes d ra in a reas d o m i n a n t l y unde r l a i n b y h o r n b l e n d e g ranod io r i t e ( M a t h e w s 1962; N o r t h c o t e a n d Johnson 1964); input of iron a n d m a n g a n e s e should b e similar for the t w o lakes. Ruby Lake is ups t r eam of S ak inaw , a n d thus m a y t r ap iron b io log i ca l l y b e f o r e it r e a c h e s Sak inaw Lake. However , t he situation for Powel l Lake is similar as wa te r f rom Powel l River travels th rough several other basins be fore r each ing the southernmost bas in . The higher concen t ra t ions of iron in Powel l Lake most likely reflect the extremely diffuse inter face as c o m p a r e d t o the sharp in te r face in Sak inaw Lake. In Sak inaw , the zones of iron a n d su lphate r educ t i on very near ly ove r l ap : therefore as iron is r e d u c e d , it is immed ia t e l y p r e c i p i t a t e d as iron sulphides a n d r e m o v e d from the system. This results in a very sharp p e a k in iron c o n c e n t r a t i o n just b e l o w the in te r f ace (Fig. 5-9). In Powe l l L ake , the o x i c / a n o x i c i n t e r f a ce a n d t h e c h e m o c l i n e a r e s e p a r a t e d by o ve r 100 m. H e n c e , su lph ide c o n c e n t r a t i o n s a re l ow in the z o n e of iron r e d u c t i o n a n d iron c a n c y c l e b e t w e e n ox id ized a n d r e d u c e d forms, a n d thus r e a c h higher concent ra t ions . Metal Complexes The c o m p u t e d spec ia t ion of iron a n d m a n g a n e s e in the t w o lakes (Figs. 5-11 a n d 5-12) is similar t o tha t c a l c u l a t e d for the Black S e a by Land ing a n d Lewis (1990). Soluble Fe(ll)-sulphide c o m p l e x e s w e r e o m i t t e d f rom the c a l cu l a t i ons s ince e v i d e n c e f rom F ramvaren Fjord suggests that these c o m p l e x e s , as wel l as Fe(ll) c o m p l e x e s with thiols, D O C , or polysulphides, a re not important in s tab le , sulphidic mar ine basins (Landing a n d Wester lund 1988). The d e c r e a s e in d issolved iron c o n c e n t r a t i o n with inc reas ing to ta l su lph ide c o n c e n t r a t i o n is charac te r i s t i c of a transit ion m e t a l tha t d o e s not c o m p l e x signif icantly with r e d u c e d su lphide (Emerson et a l . 1983). This results in a c o n c e n t r a t i o n m a x i m u m of the me ta l at low su lphide levels. The results for the B lack S e a h a v e b e e n c o r r o b o r a t e d b y Luther et a l . (1990c ) , w h o f o u n d tha t b o t h "free" a n d m e t a l " c o m p l e x e d " forms of su lphide exist in the w a t e r c o l u m n . Thus, su lph ide in the u p p e r ox i c w a t e r c o l u m n (0-100 m) of the B lack S e a is " c o m p l e x e d " b y meta ls , whe reas the su lph ide b e l o w 100 m is p redominan t l y "free" (H 2S, HS"). B a sed o n expe r imen ta l d a t a a n d t h e r m o d y n a m i c cons idera t ions (Dyrssen 1988), Luther et a l . (1990c) suggest that M n 2 + shou ld b e the m e t a l w h i c h has the best oppor tun i ty t o c o m p l e x su lph ide , a n d there fore , Mn(ll)-sulphide c o m p l e x e s we re i n c l uded in spec i a t i on ca l cu la t ions . The equ i l ib r ium t r a c e m e t a l m o d e l l i n g d i s cussed a b o v e i n c l u d e d only the ef fects of inorgan ic l igands, but me ta l ions c a n also b e c o m p l e x e d by o rgan i c l igands. s u c h as h u m i c subs tances or thiols. L and ing a n d Lewis (1990) f o u n d tha t in a m o d e l system, Mn(ll) a n d Fe(ll) a re c o m p l e x e d with nitri lotriacetic a c i d (NTA), a n a n a l o g u e for mar ine h u m i c subs tances . They o b t a i n e d similar results using cys te ine ( a thiol) as the m o d e l l i g a n d ; but in this c a s e , on ly Fe w o u l d b e likely t o c o m p l e x w i th cys te ine at natural ly occur r ing levels. A cursory a t t empt was m a d e to measure thiols in Powel l Lake , a n d n o n e w e r e d e t e c t e d , a l t h o u g h t h e t e c h n i q u e u s e d w a s not ve ry sensit ive (m in imum d e t e c t i o n limit -0.5 nM) . Total thiol concen t r a t i ons of severa l h u n d r e d n M h a v e b e e n r epo r t ed in the a n o x i c waters of the Black S e a ( M o p p e r a n d Kieber 1988; Luther et a l . 1990c), suggest ing that only Fe(ll)-thiol c o m p l e x a t i o n might b e e x p e c t e d to b e signif icant. Land ing a n d Lewis (1990) d e t e c t e d some an ion i c Fe(ll) spec ies (10 - 30%) ; h o w e v e r , t h e y sugges t tha t s u c h c o m p l e x e s a re k inet ica l ly ve ry l ab i le . Therefore, c o m p l e x a t i o n b y o rgan i c c o m p o u n d s was not i n c l u d e d in the ca l cu la t ions d u e to lack of t h e r m o d y n a m i c a n d f ie ld d a t a for those potent ia l l igands. Particulate Sulphides Both pyrite a n d iron monosu lph ides are present in the w a t e r c o l u m n of Powel l a n d Sak inaw Lakes (Figs. 5-15 a n d 5-16). X-ray di f f ractometry of the sediments in Powel l s h o w e d tha t pyrite is t h e d o m i n a n t crystal l ine p h a s e in the large ly o r g a n i c o o z e , quant i t a t i ve l y e x c e e d i n g e v e n detr i ta l s i l icates (T. Pede r sen pers. c o m m . ) . In b o t h Powel l a n d Sak inaw Lakes, pyrite w a s d e t e c t e d at a higher level in the w a t e r c o l u m n t h a n the d e p t h of first de t e c t i on of iron monosu lph ide . In Powel l , monosu lph ides are first d e t e c t a b l e at 200 m d e p t h . 50 m b e l o w the horizon w h e r e pyrite is ana ly t i ca l l y first o b s e r v e d (i.e. right at the interface) . In Sak inaw Lake , however , monosu lph ides o c c u r at the next sampl ing d e p t h b e l o w the level of first a p p e a r a n c e of pyrite. The a p p e a r a n c e of m o n o s u l p h i d e s c o r r e s p o n d s w e l l w i t h t h e i n c r e a s e in d i s s o l v e d s u l p h i d e c o n c e n t r a t i o n . It w o u l d a p p e a r that in t he uppe r horizons of Powel l a n d Sak inaw Lakes, pyrite o u t c o m p e t e s monosu lph ides for iron w h e n H2S concen t ra t ions are low. O n c e the H2S levels inc rease (to ~100's of n M in this c a se ) , monosu lph ide c a n t h e n prec ip i ta te . In Sak inaw Lake , su lph ide concen t ra t ions increase with d e p t h m u c h more quick ly d u e to the sharper in te r f ace , a n d thus monosu lph ides a p p e a r at sha l lower dep ths relat ive t o pyrite. P r esumab l y t h e m o n o s u l p h i d e f o r m e d c a n t h e n r e a c t wi th po l ysu lph ide or sulphur t o form pyrite. This f o r m a t i o n of pyrite w i thout a p p a r e n t m o n o s u l p h i d e precursors has a lso b e e n o b s e r v e d in var ious sed iments , espec i a l l y in salt marshes (Bou legue et a l . 1982; Cu t te r a n d Vel insky 1988; Dav ison et a l . 1985; Howar th 1979; Howar th a n d Gib l in 1983; Howar th a n d Mar ino 1984; Howar th a n d Merke l 1984; King 1988; Lord a n d C h u r c h 1983; Luther e t a l . 1982; Skyring a n d Lup ton 1984). Howa r th a n d Tea l (1979) f o u n d , v i a r ad io t r a ce r studies, tha t pyrite forms very rap id ly (hours t o days ) in marsh sed iments , suggest ing d i rect r eac t i on b e t w e e n iron a n d polysulphides rather t h a n format ion by the s low m e c h a n i s m s o b s e r v e d in o ther situations. Salt marshes a re c h a r a c t e r i z e d by a l a rge supply of ox idants requ i red for pyrite fo rmat ion d u e to a ) t h e d i rec t diffusion of o x y g e n into the a n o x i c sed iments w h e n the depos i ts a re e x p o s e d dur ing low t ide ( D a c e y a n d Howes 1984); b) infiltration of o x y g e n a t e d t ida l water ; a n d c ) 0 2 release from the marsh-grass rhizosphere, resulting in the fo rmat ion of polysulphides a n d e l emen ta l sulphur. Iron c a n then directly reac t with polysulphides to form pyrite without the n e e d for FeS in te rmed ia tes , viz: Fe 2 + + S* + HS" <-» FeS2 + + H +. Marsh porewate rs c a n c o n t a i n polysu lphides in concen t r a t i ons far a b o v e e x p e c t e d equi l ibr ium va lues , as o b s e r v e d in Powel l a n d Sak inaw Lakes, imply ing p r o d u c t i o n v i a sulphide ox idat ion as discussed earlier (Boulegue et a l 1982; Luther et a l . 1985). The o c c u r r e n c e of s u s p e n d e d pyrite in the a b s e n c e of monosu lph ides in the lakes contrasts with most mar ine sed iments whe re soluble sulphides (H 2S, HS") a n d iron monosu lph ide (FeS) a re the major short-term e n d p roduc ts of su lphate r educ t i on , a n d whe re pyrite forms slowly th rough the slow r eac t i on of FeS with S° (Berner 1970). As a n e x a m p l e , f rom 80 t o 100% of t h e S O * r e d u c e d dur ing o n e - d a y i n c u b a t i o n s w a s r e c o v e r a b l e as m o n o s u l p h i d e s in b l a c k , h ighly r e d u c i n g m u d s f rom W o o d s Ho le ha rbour (Howarth 1979) a n d f rom the Peru upwel l ing system (Rowe a n d Howar th 1985). Similar results w e r e o b t a i n e d for Long Island S o u n d (Westr ich a n d Berner 1988), t w o Danish fjords (Kysing Fjord a n d Limfjorden) (Howarth a n d J0 rgensen 1984), shal low-water c a r b o n a t e sed iments in Austra l ia (Ferguson et a l . 1983) a n d sediments f rom the North Sea-Baltic transition ( Jargensen et a l . 1990a). A l t hough pyrite makes up the bulk of the sulphur in t hese s ed imen t s , FeS a n d S° usually d e c r e a s e w i th d e p t h , whi le pyrite inc reases , sugges t ing tha t FeS 2 forms f rom the slow convers ion of iron monosu lph ides (Howar th a n d J a r g e n s e n 1984). G e n e r a l l y , o x y g e n c a n en te r sub t i da l a n d l ake sed iments only b y diffusion a n d by the ac t ions of ben th i c an imals (Aller 1978) a n d thus the ox ida t ion of sulphides t o form polysulphides a n d e l emen ta l sulphur m a y b e primarily l imited t o slow react ions with detrital iron ox ide minerals. The l imited avai labi l i ty of S° a n d polysulphides results in s low format ion of pyrite. The inability t o d e t e c t monosu lph ide a t the shal lower dep ths in t h e Powel l a n d Sak inaw w a t e r co lumns where pyrite occurs does not necessari ly m e a n that the mineral is not fo rming a t these h igher levels; r ap id conve r s ion t o pyrite c o u l d r e m o v e it as q u i c k l y as it is p r o d u c e d , thus m a s k i n g its f o r m a t i o n . H o w e v e r , c o n v e r s i o n of monosu lph ides t o pyrite is thought to b e a s low process (Berner 1970) a n d therefore , if m o n o s u l p h i d e p rec ip i t a t ion o c c u r s , s o m e quant i ty of FeS shou ld b e d e t e c t e d . Berner (1964b) s u g g e s t e d tha t this o c c u r s in the S a n t a C a t a l i n a Basin w h e r e s igni f icant concen t r a t i ons of pyrite but not of iron monosu lph ides o c c u r in the sur face sediments (Kap lan et a l . 1963). B e cause the sed iment a c c u m u l a t i o n rate in this bas in is low, longer exposure t o oxid iz ing cond i t ions nea r the sed iment-water in te r face m a y result in a n a b u n d a n t supply of zerova lent sulphur. A sufficiently slow rate of depos i t ion w o u l d a l low the t rans format ion of FeS t o FeS 2 t o g o t o c o m p l e t i o n a t t he u p p e r su r f ace of the sed iment , a n d thus no b l a c k transition z o n e w o u l d result. However , a p p a r e n t a b s e n c e of m o n o s u l p h i d e s in reg ions wi th l ow sed imen t a c c u m u l a t i o n rates m a y a lso b e exp l a i ned by the undersaturat ion of such phases d u e to the lower dissolved sulphide (or pe rhaps iron) concen t r a t i ons charac te r i s t i c of such cond i t ions . In the S a n t a C a t a l i n a Basin, sed iments a re t yp i ca l l y ox i c t o subox i c a n d the interstitial waters c o n t a i n low levels of su l ph ide (usual ly u n d e t e c t a b l e ) ; h e n c e , m o n o s u l p h i d e s a re likely to b e undersa tura ted , resulting in d irect prec ip i tat ion of pyrite. Solubility c a l cu l a t i ons w e r e p e r f o r m e d using MINEQL t o see if t he t heo re t i c a l d e g r e e of saturat ion of iron monosu lph ide a n d pyrite as a func t ion of d e p t h in the lakes co r responds to their a p p e a r a n c e in b o t h w a t e r co lumns . It has b e e n sugges t ed that , d u e t o t h e unce r t a in t y in t h e s e c o n d d i ssoc i a t ion c o n s t a n t of su lph ide , solubil ity ca l cu l a t i ons for m e t a l sulphides should b e d o n e using the c o n c e n t r a t i o n of b isulphide ion rather than that of S2" (Emerson et a l . 1983) a c c o r d i n g to the fol lowing equa t ion : H + + MS «-> M 2 + + HS" I A P = ( M ) ( H S " ) / ( H + X W H S / Y H ) where M is the m e t a l of interest (Fe 2 + in this c ase ) , ( ) is solute c o n c e n t r a t i o n a n d y is the t o t a l a c t i v i t y c o e f f i c i e n t . Seve ra l lAPs w e r e r e c a l c u l a t e d in this m a n n e r a n d no d i f fe rence w a s f o u n d in the saturat ion state of the iron sulphides. Thus, those c a l c u l a t e d with S2" v i a MINEQL are g iven here. As c a n b e seen in Figs. 5-17 a n d 5-18, the saturation index of bo th monosulph ides a n d pyri te co r r e sponds fairly we l l w i th t h e d e t e c t i o n of these spec i e s in the wa te r co lumns . In Sak inaw Lake , pyrite is supersaturated throughout the a n o x i c port ion of the w a t e r c o l u m n , whe reas mack inaw i t e a n d greigite d o not b e c o m e sa tu ra ted until 40 m d e p t h , w h e r e m o n o s u l p h i d e s a r e first d e t e c t e d . In Powe l l L a k e , pyr i te is a lso supersa tura ted throughout the anox i c port ion of the wa te r c o l u m n , whi le greigite a n d mack inaw i t e d o not r e a c h saturation until 210 m dep th . Pyrite was d e t e c t e d at all depths in the a n o x i c z o n e , whe reas monosu lph ide first a p p e a r s in the w a t e r c o l u m n at 200 m, w h e r e greigi te is very near ly sa turated. Very low levels of monosu lph ide w e r e f o u n d at this d e p t h (4 nM) (Fig. 5-15), ind icat ing that the spec ies we re just at saturat ion. The d a t a m a t c h the p r e d i c t e d solubilities extremely we l l , espec ia l l y cons ider ing the uncertaint ies in the ca l cu l a t i ons a n d the small d i f ferences of K,p va lues a m o n g most of the minera l phases . A l so , these c a l cu l a t i ons w e r e d o n e assuming i no rgan i c c o m p l e x a t i o n only. O the r iron minera l solubilities w e r e a lso c a l c u l a t e d (FeS i0 3 , F e O H 2 , F e C 0 3 , F e 3 ( P 0 4 ) 2 . Ca 2 Fe(P04)2); all of these minerals we re undersa tura ted , with the e x c e p t i o n of a n a p a i t e (Ca 2 Fe (P04 ) 2 ) in the bottom-most waters of Sak inaw Lake. B e cause iron sulphides form so rapidly , it is unlikely that this mineral w o u l d r emove significant amounts of iron, a n d , to my k n o w l e d g e , a n a p a i t e has not b e e n repor ted in mar ine sediments. The saturat ion ca l cu la t ions ind i ca te that w h e n the solubility p roduc t of the least so luble ac id-volat i le su lphide phase is not e x c e e d e d (pyrite in equi l ibr ium with excess e l e m e n t a l su lphur is m a n y orders of m a g n i t u d e less so l ub l e t h a n g re ig i t e or mack inaw i t e ) pyrite c a n form direct ly, without compe t i t i on f rom monosu lph ides for iron. Therefore , t he w a t e r c o l u m n s of Powe l l a n d Sak inaw Lakes c a n b e d i v i d e d into t w o zones of pyrite fo rmat ion : 1) the u p p e r z o n e whe re pyrite prec ip i ta tes a n d monosu lph ide is undersa tu ra ted ( a n d non-detectab le ) (150 - 200 m PL, 30 - 40 m SL); a n d 2) the d e e p e r waters whe re bo th iron monosu lph ides a n d pyrite are sa tura ted a n d thus b o t h c a n form. These o b s e r v a t i o n s c o r r e s p o n d t o t h e t w o p rev ious l y p r o p o s e d p a t h w a y s of pyr i t izat ion, t he first b e i n g d i rec t r e a c t i o n b e t w e e n Fe(ll) a n d po lysu lph ides y ie ld ing single pyrite crystals (Howarth 1979) a n d the s e c o n d be ing p roduc t i on of pyrite v i a the slower r eac t i on with a monosu lph ide precursor (Berner 1970). Cut te r a n d Velinsky (1988) o b t a i n e d similar results In sediments f rom the G rea t Marsh , D e l a w a r e , w h e r e the depths of t he FeS a n d Fe 3 S 4 m a x i m a c o i n c i d e w i th p r e d i c t e d m a c k i n a w i t e a n d gre ig i te saturat ion (Berner 1967b; Bou legue et a l 1982; Lord a n d C h u r c h 1983). Cut ter a n d Velinsky (1988) f o u n d ove r l app ing greigite a n d pyrite peaks in the d e e p e r G r ea t Marsh sed iment , a distr ibution w h i c h is consistent with the s low pyrit ization m e c h a n i s m p r o p o s e d by S w e e n e y a n d K a p l a n (1973), in w h i c h greigite is thought t o b e a necessary precursor to the f r a m b o i d a l fo rm of pyrite. In this r eac t i on s e q u e n c e , m a c k i n a w i t e c o m b i n e s with e l emen ta l sulphur (in the form of polysulphides) t o p r o d u c e greigite (Berner 1967a): 3FeS + S° <-> FeaS* Gre ig i t e in turn p r o d u c e s f r a m b o i d a l pyr i te , e i ther t h rough d i spropor t iona t ion or b y further r eac t i on with e l emen ta l sulphur (as polysulphides): Fe3S4 <-> 2FeS + FeS2 FeaSa + 2S° <-> 3FeS2. Morse a n d Cornwe l l (1987), however , h a v e sugges ted that the convers ion of greigite to pyrite c a n n o t b e the major m e c h a n i s m for fo rmat ion of f r a m b o i d a l pyrite, as they c o u l d not f ind greigi te in a w i d e var iety of d iagenet i ca l l y-ac t i ve sed iments w h e r e f r ambo ids o c c u r . Effect of pH on Pyrite Formation Berner et a l . (1979) has stressed that a n a c i d i c env i ronment is requi red for rap id pyrite fo rmat ion without monosu lph ide intermediates, not ing that pyrite w o u l d only form in l a b expe r imen t s w h e n the pH w a s < 6. Unde r m o r e a lka l ine c o n d i t i o n s , on ly monosu lph ides f o r m e d . Other researchers h a v e also f o u n d that a c i d cond i t ions favour the r ap id fo rmat ion of FeS2 (Roberts et a l . 1969; G o l d h a b e r a n d K a p l a n 1974; R i ckard 1975). H o w e v e r , pH c a n h a v e n o d i rec t e f f e c t o n t h e nature of t he iron su lph ide p r o d u c e d ; it c a n only a f f e c t the nature of the iron or sulphur spec ies in solution or the nature of the initial mack inaw i t e surface. The pH has no e f fec t o n the iron spec ies (at the pH r a n g e c o m m o n l y f o u n d in natura l waters a n d sed iments ) , a n d its e f fec ts o n the sulphide spec i es a re simply t o c h a n g e dominan t HS' (at pH > 7) t o dominan t H2S (pH < 7) a n d d e c r e a s e t h e a m o u n t of S2" as p H d e c r e a s e s . Howar th (1979) p r o d u c e d pyrite rather t h a n monosu lph ide a t pH 7.5 w h e n the part ia l pressure of H2S was m a i n t a i n e d at 0.4 a t m (vs. 1 a tm) . Therefore, as Howar th (1979) o b s e r v e d , t h e t e n d e n c y for pyrite t o form at lower pH a n d iron monosulphides a t higher pH only reflects the e f fec t of pH o n S2' activity. Dec r eas i ng the pH dec reases the concen t r a t i on ( a n d activity) o f S2* relative t o other su lphide spec ies ; thus iron monosu lph ides a re more likely t o b e undersa tu ra ted at lower pH . These observat ions co l lec t i ve ly exp la in r ap id fo rmat ion of pyrite in salt marsh sed iments , as the pH in these deposits is usually b e t w e e n 5 a n d 6.5. In summary , severa l factors i nd i ca t e that pyrite is forming direct ly in the u p p e r anox i c waters of Powel l a n d Sak inaw Lakes, rather t h a n v i a a monosu lph ide precursor: 1) pyrite occu r s a t shal lower depths t h a n monosu lph ide ; 2) wa te rs a t these d e p t h s a re unde r sa tu r a t ed wi th r e spec t t o m o n o s u l p h i d e ( a n d satura ted with respect to pyrite); a n d 3) highly r eac t i ve polysulphides a n d F e 2 + a re present , a n d concen t r a t i ons of d issolved sulphide are low. In add i t i on , the pH is low, dec reas ing the activity of S2". In the d e e p e r waters w h e r e monosu lph ide is sa tu ra ted , pyrite c a n form v i a the more g r a d u a l convers ion of FeS. It is c l e a r tha t t he un ique s e p a r a t i o n of t h e o x i c / a n o x i c i n t e r f a ce a n d the c h e m o c l i n e in Powel l a n d Sak inaw Lakes al lows better resolution of the t w o regimes in w h i c h the a l t e rna te p a t h w a y s of pyrite fo rmat ion d o m i n a t e . In contras t , t he relat ive compress i on of t he a n o x i c z o n e in p o r e w a t e r profiles obv ia tes s u c h a de l i nea t i on of fo rmat ion pa thways . Organic Sulphur N o a t t emp t was m a d e in this study to de te rmine o rgan i c sulphur. In b o t h Powel l a n d Sak inaw Lakes the inorgan ic sulphur p o o l is extremely large (~3 m M in the former a n d 5.5 m M in the latter). However , there are also very high levels of D O C a n d P O C in the b o t t o m waters of these lakes (Figs. 3-2 a n d 3-3), a n d thus, there m a y b e a large quant i ty of a s s o c i a t e d o r g a n i c sulphur present . High c o n c e n t r a t i o n s of thiols (2.4 m M ) h a v e b e e n f o u n d in salt ma r sh p o r e w a t e r s (Luther et a l . 1986b). H o w e v e r , a l t h o u g h o rganosu lphur c o m p o u n d s m a y m a k e u p a s izable cont r ibu t ion of t he to ta l sulphur p o o l , it is unlikely tha t they pa r t i c i pa t e d i rect ly in iron su lph ide f o rma t i on , as iron will p re ferent ia l l y r e a c t wi th the- l a rge quant i t ies o f h ighly r e a c t i v e po lysu lph ides a n d dissolved inorgan ic su lphide that a re present. Ox id i zed organosu lphur c o m p o u n d s c a n indirect ly p l a y a role in pyrite f o rma t i on , a c t i n g as e l e c t ron a c c e p t o r s for su lpha te r e d u c t i o n , t h e r e b y b e i n g c o n v e r t e d to dissolved su lph ide tha t c o u l d t h e n r e a c t with i ron, as has b e e n s u g g e s t e d for Everg lades pea t s (Altschuler et a l . 1983). Therefore , a l t h o u g h the o r g a n i c sulphur p o o l m a y b e la rge in Powe l l a n d Sak inaw Lakes, this f rac t ion is unlikely t o p lay a direct role in pyrite format ion. Manganese Sulphides In t h e b o t t o m waters of Powel l Lake m a n g a n e s e a p p e a r s t o b e r e m o v e d at d e p t h (Fig. 5-9). The t w o m a n g a n e s e sulphide minerals, a l a b a n d i t e (MnS) a n d haurite (MnS2), b o t h of w h i c h a re relatively soluble , a re undersa tu ra ted in b o t h lakes, a l t hough hauri te d o e s a p p r o a c h saturat ion in Powel l Lake b o t t o m waters (Figs. 5-19 a n d 5-20). M n C 0 3 a p p r o a c h e s , but d o e s not at ta in saturat ion in Powel l Lake a n d M n O H 2 is highly undersa tu ra ted in bo th lakes. The lAPs for M n S i 0 3 a n d M n 3 ( P 0 4 ) 2 we re also c a l c u l a t e d , but these minerals a re e v e n less sa tu ra ted . The only k n o w n o c c u r r e n c e of MnS is in r ecen t sed iments of t h e Balt ic S e a (Suess 1979); MnS is otherwise on ly k n o w n f rom hydro the rma l depos i t s ( P a l a c h e et a l 1952). H igh d isso lved M n 2 + c o n c e n t r a t i o n s are t yp i ca l of Balt ic S e a basins (Baker 1978; Djafari 1976, c i t ed in Suess 1979), a n d , therefore , MnS m a y prec ip i ta te in this env i ronment rather t h a n iron sulphides as is usually the c a s e under anox i c mar ine condi t ions. A n o t h e r m e c h a n i s m for m a n g a n e s e r emova l is adsorpt ion a n d cop re c i p i t a t i on with ano the r minera l phase . M a n g a n e s e c a n cop re c i p i t a t e with C a C 0 3 (Pingitore et a l . 1988; Thomson et a l . 1986), however , as was discussed in C h a p t e r 4, C a C 0 3 format ion in Powe l l Lake is unlikely. J a c o b s et a l . (1985) suggest that f r a m b o i d a l pyrite part ic les prec ip i ta t ing in F ramvaren Fjord a c t as a carrier phase for M n 2 + , as f r ambo ids c o l l e c t e d from the fjord w a t e r c o l u m n h a v e m a n g a n e s e contents of 1.0%. S ince f r a m b o i d a l pyrite is present in the w a t e r c o l u m n of Powel l Lake (T. Pedersen pers. c o m m . ) , pe rhaps this is h o w the m a n g a n e s e is b e i n g r e m o v e d f rom the d e e p waters. Pyrite concen t ra t i ons in Powe l l Lake a re m u c h higher t h a n those in Sak inaw a n d this m a y exp la in why M n 2 + is d e p l e t e d a t d e p t h in Powel l Lake only. C o m p a r i s o n of the M n 2 + a n d FeS2 profiles in Powel l Lake (Figs. 5-9 a n d 5-15) shows that bo th are r e m o v e d from the wa te r c o l u m n b e l o w 250 m , sugges t i ng tha t similar p rocesses a r e r e m o v i n g b o t h spec i e s ; c o p r e c i p i t a t i o n of M n 2 + w i th FeS 2 is t h e mos t p l aus ib l e e x p l a n a t i o n . The d e c r e a s e in pyr i te ( a n d monosu lph ide ) nea r the c h e m o c l i n e is p r o b a b l y d u e to f l o c cu l a t i on a n d rap id settling where there is a n abrupt c h a n g e in salinity as desc r i bed in C h a p t e r 3. CHAPTER 6 SUMMARY AND CONCLUSIONS Powel l a n d Sak inaw Lakes are meromic t i c ex-fjords w h i c h we re s e p a r a t e d f rom the Strait of G e o r g i a approx imate l y 11000 years a g o d u e to isostatic uplift fol lowing the last d e g l a c i a t i o n . Both are stably stratif ied, with a n o x i c , highly sulphidic b o t t o m waters under ly ing fresh, o x y g e n a t e d waters. Sak inaw Lake has a m u c h sharper ox i c/anox i c in te r face t h a n Powel l Lake , w h i c h reflects pe r iod i c incursions of s eawa te r into Sak inaw s ince sill e m e r g e n c e , w h e r e a s t h e rel ict s e a w a t e r in Powe l l L ake is that original ly t r a p p e d . This d i f f e r ence in the a g e s of t h e b o t t o m w a t e r of t h e t w o lakes results in seve ra l n o t a b l e d i f f e r ences in chemist ry . The most o b v i o u s c o n s e q u e n c e is tha t S ak inaw Lake has a lmost t w i c e t he c o n c e n t r a t i o n of su lph ide , e v e n t h o u g h it has f r eshened cons ide rab l y more t h a n Powe l l , ref lect ing a n add i t i ona l source of su lphate . G e o t h e r m a l hea t ing has p r o d u c e d w a r m b o t t o m waters in b o t h lakes, wh i ch c r e a t e a mid-depth t empera tu re min imum in bo th basins. However , d u e to the higher salinity of the b o t t o m waters , t he w a t e r c o l u m n remains stably stratif ied in spite of the higher t empera tu re at d e p t h . A l t hough bo th lakes h a v e f reshened , the ratios of the major ion concent ra t ions in their mon imo l imn i a , relat ive t o chlorinity, a re similar to those of present-day seawate r . There a r e s o m e d i f f e rences , h o w e v e r , a n d these c a n b e part ly e x p l a i n e d b y the d i f f e rences in m o l e c u l a r diffusivities for e a c h of the spec i es . M a g n e s i u m , c a l c i u m , b o r a t e , a n d stront ium a re a l l re lat ive ly e n r i c h e d wi th r e s p e c t t o c h l o r i de w h e n c o m p a r e d t o t h e c o n c e n t r a t i o n s e x p e c t e d f rom t h e c o n s t a n t c o m p o s i t i o n of s e a w a t e r . These distr ibut ions h a v e b e e n e x p l a i n e d as result ing f rom the lower diffusivities of these ions, w h i c h results in their b e i n g lost more slowly v i a diffusion to the u p p e r , fresher waters . Potass ium, o n t h e other h a n d , is relatively d e p l e t e d , d u e t o its h igher diffusivity a n d thus faster u p w a r d diffusion. In cont ras t , t he N a + t o CI" rat io is cons t an t , w h i c h is consistent with the iden t i ca l diffusivities of ch lo r ide a n d sod ium. A m a t h e m a t i c a l m o d e l of the history of the freshening in Powel l Lake only partially explains the d i f fe rences b e t w e e n o b s e r v e d major ion concen t r a t i ons a n d those p r e d i c t e d o n the basis of their differential rates of diffusion (Sanderson et al . 1986), w h i c h in part , m a y ref lect non-conservat ive behav iou r of some of the ions. The b o t t o m waters of Powel l a n d Sak inaw Lakes are c h e m i c a l l y similar t o m a n y a n o x i c mar ine a n d lacustr ine sed iment porewaters . Very h igh levels of d isso lved a n d par t i cu la te o rgan i c c a r b o n are f o u n d toge ther with high concent ra t ions of alkalinity a n d nutrients (with t h e e x c e p t i o n of PO4 in Powe l l Lake ) , d e r i v e d f rom t h e a n a e r o b i c d e c o m p o s i t i o n of o rgan i c matter. The low growth yields of a n a e r o b i c b a c t e r i a (relative t o ae robes ) usually results in grea ter re lease of nutrients; b e c a u s e the w a t e r c o l u m n is so stably stratif ied, these nutrients are virtually t r a p p e d a t d e p t h a n d h e n c e increase t o ve ry h igh levels. The h igher a n d more v a r i e d pa r t i cu l a t e C : N ratios in Powe l l Lake ind i ca te that the b r e a k d o w n of o rgan i c matter is occur r ing in the wa te r c o l u m n , whereas the cons tan t C : N ratios (with dep th ) in the m u c h shal lower Sak inaw Lake suggest that most o r g a n i c m a t t e r d e c o m p o s i t i o n o c c u r s pr imari ly in t h e sed iments . The h igh alkalinities o b s e r v e d in b o t h lakes ref lect a c t i v e su lphate r e d u c t i o n a n d a m m o n i u m format ion. These processes a re also the c a u s e of the large increase in pH with d e p t h . Extremely high par t icu la te C:P a n d N:P ratios o c c u r in bo th lakes, ind ica t ing that p h y t o p l a n k t o n a re severe l y phosphorus l imi ted . Unlike S a k i n a w , Powe l l Lake has ex t r eme l y l ow c o n c e n t r a t i o n s of p h o s p h a t e in its b o t t o m waters . C o m p a r i s o n of par t i cu la te N:P t o d issolved N:P ratios shows that at d e p t h , phosphorus is c o n c e n t r a t e d in the par t i cu la te p h a s e , ref lect ing the u p t a k e , or non-release, of phosphorus relative to n i t rogen dur ing the d e c o m p o s i t i o n of o rgan i c matter. Cons ide ra t ion of the solubilities of va r ious p h o s p h o r u s minera ls i n d i c a t e t ha t s u c h p r e c i p i t a t i o n p rocesses c a n n o t a c c o u n t for the r e m o v a l of phosphorus f rom t h e b o t t o m waters of Powe l l Lake . The d i f f e r ence in t h e behav i ou r of phosphorus in the t w o lakes m a y ref lect the different c h e m i c a l histories. B e c a u s e Sak inaw Lake has h a d more recen t s e a w a t e r input t h a n P o w e l l , it has b e e n less ox idan t-s t a r ved a n d thus m o r e p h o s p h o r u s has b e e n remob i l i zed v i a con t inu ing d e c o m p o s i t i o n of o r g a n i c matter . D u e t o inhibi ted nutrient r e g e n e r a t i o n b e c a u s e of t h e l a ck of ox idan t s , a n d d u e t o t h e h i g h d e g r e e of phosphorus l imitation in Powel l Lake a n d preferent ia l up take of p h o s p h a t e f rom bo t tom waters by b a c t e r i a , ove r t ime the a m m o n i u m c o n c e n t r a t i o n has i n c r eased relative to p h o s p h a t e , a n d , there fore , s ince the bas in has b e e n ox idant s t a r ved , a m m o n i u m has not b e e n d e p l e t e d in the bo t tom waters of Powel l . Sulphur s p e c i e s of i n t e rmed i a t e o x i d a t i o n s ta te ( th iosu lpha te , sulphi te a n d po ly th ionate ) a re not d e t e c t a b l e in bo th lakes. Part iculate e l emen ta l sulphur is also not f o u n d , a l t h o u g h la rge quant i t ies of S° a r e present in the form of po lysu lphides in the a n o x i c b o t t o m waters of Powe l l (2.2 m M ) a n d Sak inaw (4.7 m M ) Lakes. Thus, a la rge p ropor t ion of the d issolved su lphide f r ac t ion consists of highly r eac t i v e polysulphides . So lub le c o m p o u n d s or c o m p l e x e s such as Mn(lll)- or Mn( l l )-organic c o m p l e x e s wi th unsa tura ted o rgan i c matter m a y a c t as the e l ec t ron a c c e p t o r s for ox idat ion of sulphide to zerova lent sulphur in polysulphides (Luther et a l . 1990a) Iron monosu lph ides a n d pyrite form in the w a t e r co lumns of b o t h Powel l a n d S a k i n a w Lakes as e x p e c t e d f rom t h e c o - o c c u r r e n c e of r e d u c e d i ron, h y d r o g e n su lph ide , a n d highly reac t i ve polysulphides. The distributions of these two minerals in the w a t e r co lumns corre lates wel l with their c a l c u l a t e d saturat ion states. Pyrite prec ip i tates direct ly wi th no monosu lph ide precursor at dep ths where sulphide concen t ra t ions are low a n d monosu lph ides a re undersa tura ted . As soon as su lphide levels increase to the sa tura t ion th resho ld , pa r t i cu l a t e iron m o n o s u l p h i d e s a p p e a r in t h e w a t e r c o l u m n . M a n g a n e s e m a y b e r e m o v e d a t d e p t h in Powe l l Lake v i a c o - p r e c i p i t a t i o n wi th f r a m b o i d a l pyrite. The e x t e n d e d d i s t ance b e t w e e n the ox i c/anox i c in te r face a n d the c h e m o c l i n e in Sak inaw (~10 m) a n d espec i a l l y in Powel l (-100 m) relat ive t o that of sed iment pore waters a l lows exce l lent resolution of these processes. This study has d e m o n s t r a t e d tha t g e o c h e m i c a l processes s u c h as au th igen i c su lphide fo rma t i on , w h i c h a re known to o c c u r in c o a s t a l a n d h e m i p e l a g i c sed iments , c a n b e d e f i n e d in a c o m p r e h e n s i v e m a n n e r by v i e w i n g t h e w a t e r c o l u m n s of m e r o m i c t i c lakes as essentially s imple a n a l o g u e s of chemical ly-strat i f ied deposits . The ma jo r o r ig ina l o b j e c t i v e of t h e p ro j e c t , t o d e f i n e the c h e m i c a l c o n d i t i o n s a n d pa thway (s ) of pyrite fo rmat ion in a n o x i c sed imenta ry systems, has b e e n met : pyrite forms b o t h by d i rec t prec ip i ta t ion where low dissolved sulphide concen t ra t ions preva i l , a n d indirect ly d e e p e r in the w a t e r c o l u m n whe re su lph ide concen t r a t i ons are higher a n d thus iron monosu lph ides are sa tura ted . These f indings a d d grea te r insight to extant hypotheses r ega rd ing the fo rmat ion a n d distribution of au th i gen i c su lphide phases in mar ine sed iments . APPENDIX 1 SOLUBILITY AND SPECIATION CALCULATIONS The d e g r e e of saturat ion with respect t o solid phases was d e t e r m i n e d f rom the pH a n d the to ta l concen t r a t i ons of the dissolved c o m p o n e n t s v i a ca l cu l a t i ons b a s e d o n mass b a l a n c e equa t i ons a n d equi l ibr ium constants for e a c h so luble spec ies . The m o d e l i n g w a s d o n e using MINEQL (version 2.0. a k a EASEQL). w h i c h iteratively solves the severa l h u n d r e d s imul taneous equa t ions invo l ved using a m o d i f i e d Newton-Raphson p r o c e d u r e . These c a l c u l a t i o n s y i e ld f ree ion c o n c e n t r a t i o n s a n d t h e ion ac t i v i t y p roduc ts (IAP) of solid phases w h i c h c o u l d b e in equi l ibr ium wi th t h e lacustr ine waters. The equi l ibr ium constants c h o s e n for the mode l l i ng we re c o l l e c t e d f rom the l iterature, a n d a r e g i v e n in Tables A- l a n d A-2. The input for EASEQL cons i s t ed of the to ta l d i sso lved c o n c e n t r a t i o n s of all c o m p o n e n t s t o b e m o d e l e d , a n d the d a t a b a s e of equil ibrium constants for the format ion of solution spec ies a n d solid phases consist ing of comb ina t i ons of t h e bas i c c o m p o n e n t s . The constants for su lph ide-conta in ing spec ies we re c o r r e c t e d using p K a ^ f o r H ^ of 18.57 ( S choonen a n d Barnes 1988). The formats for constants involving O H " we re written as in the fo l lowing examples : M + n H 2 0 <-> M(OH)n + nH + K' = (M(OH)n)(H+ ) n/(M) M + nhfeO <-» M(OH><s) + nH + K' = (H+ ) n/(M) whi le all other constants we re written as format ion constants: M + n L M L K' = (ML)/(M)(L) n M + nL«-» MU*) K '= l/(M)(L) n. Ionic s t rength e f f ec t s w e r e c o r r e c t e d using the Dav ies e q u a t i o n t o c o n v e r t t he equi l ibr ium constants (at ionic strength = 0) into "apparent " constants a t the appropr i a te ionic strength (Stumm a n d M o r g a n 1981): logy=-0.5z 2 (Vl/( l +Vl)-0.2I) where z = cha rge of ion or comp lex I = ionic strength •y = act iv i ty coe f f i c i en t Ionic strength w a s c a l c u l a t e d f rom the chlorinity using the fo l lowing e q u a t i o n (Stumm a n d M o r g a n 1981): I = 0.00147 + 0.03592*(CD + 0.000068*(CD2 a n d v a r i e d b e t w e e n 0 a n d 0.337. The Davies e q u a t i o n was a lso used t o conve r t ion c o n c e n t r a t i o n p roduc t s t o ion act iv i ty p roduc ts so as t o c a l c u l a t e the saturat ion index = (log K^p*IAP). Temperature a n d pressure effects o n the constants we re not i n c l u d e d , s ince t empera tu re var iat ion in the bo t tom waters was small a n d the pressure ef fects o n the equil ibrium constants are difficult t o determine without de t a i l ed d a t a o n part ial molar vo lumes for all the c o m p o n e n t s a n d spec ies . In g e n e r a l , at lower tempera tures (5°C to 25°C), the me ta l spec i a t i on shifts towards higher p e r c e n t a g e s of the free meta l ca t i on i c spec i e s , wi th spec i a t i on c h a n g e s o n the order of less t h a n 10% (Byrne et a l . 1988). For these ca l cu l a t i ons , a n d g i ven tha t the samples c o n s i d e r e d in this thesis w e r e f i l tered, solid phases w e r e not a l l o w e d to p rec ip i t a te or dissolve (ie. " e l im ina te " sett ing in the program) . However , the saturat ion state with respect to all solid phases was c a l c u l a t e d . It should b e n o t e d that several ambiguit ies limit the interpretation of such results in terms of the a c t u a l ex is tence of a solid in the solution. Publ ished solubility p roducts are o f t en insufficiently a c c u r a t e to m a k e pred ic t ions b a s e d o n a c o m p a r i s o n with ion p r o d u c t s un re l i ab l e , a n d satura t ion or supersa tura t ion m a y not c a u s e o b s e r v a b l e prec ip i ta t ion of a solid if kinetics are very slow or nuc lea t ion surfaces are absent . Table A-l Stability constants used in MINEQL calculations. I = ionic strength Reactants Products logK T ° C 1 Reference H2S(g) H2S(oq) -0.99 25 0 Smith a n d Martel l (1976) S2" +2H + H2S(aq) 25.59 25 0 Smith a n d Martel l (1976) S 2 -+H + HS" 18.57 25 0 S c h o o n e n a n d Barnes (1988) 1/4S8 + S2" S f 31.07 25 0 Bou legue a n d M i c h a r d (1978) 3/8S8 + S2" S42" 28.09 25 0 Bou legue a n d M i c h a r d (1978) 1/2S8 + S2" s f 27.98 25 0 Bou legue a n d M i c h a r d (1978) 5/8S8 + S2" sf 28.19 25 0 Bou legue a n d M i c h a r d (1978) 3/8S8 + S2" + H + HS; 21.09 25 0 Bou legue a n d M i c h a r d (1978) 1/2S8 + S2" + H + HS5" 21.88 25 0 Bou legue a n d M i c h a r d (1978) SO 2" + H + HS04 2.20 25 0 Morel (1983) H + + HCO3 H2C03 16.50 25 0 Morel (1983) H + + C O f H c a 10.20 25 0 Morel (1983) PO4 +3H + H 3P04 21.90 25 0 More l (1983) PO< + 2H + H2P04 19.90 25 0 More l (1983) PO4 + H + HP04 12.50 25 0 More l (1983) N H 3 + H + NH4 9.00 25 0 Morel (1983) SiOs + H + HSiOs 13.1 25 0 More l (1983) S i O f + 2 H + HzSiOs 22.96 25 0 More l (1983) Fe 2 + + CI" FeCI + 0.90 25 0 Morel (1983) Fe 2 + + SO4 FeSOS 2.30 25 0 More l (1983) Fe 2 + + N H 3 F e N H 2 + 1.30 25 0 More l (1983) Fe 2 + + 2NH 3 Fe(NH 3>r 2.10 25 0 Morel (1983) Fe 2 + + 4NH3 FeCNHa)? 3.60 25 0 More l (1983) Fe 2 + + P 0 4 + H + FeHPOS 16.0 25 0 More l (1983) Fe 2 + + PO4 + 2H + FeH 2 PO l 22.3 25 0 More l (1983) Fe 2 + + OH" F e O H + -8.60 25 0 More l (1983) F e^ + S2" FeS 0 13.3 25 0 Dyrssen (1988) .Fe^ + f f + H* FeHS + 19.97 25 0 Dyrssen (1988) Fe 2 + + 2S 2 "+2H + Fe(HS) ° 46.04 25 0 Dyrssen (1988) F e 2 + + 2S2" + H + Fe(HS)S + 39.84 25 0 Dyrssen (1988) Fe 2 + + 2S2" FeS 2" 31.54 25 0 Dyrssen (1988) M n ^ + C O f + H* M n H C 0 3 12.10 25 0 Morel (1983) Mn2+ + SOt MnSO 0 , 2.30 25 0 Morel (1983) M n 2 + + C f MnC I + 1.10 25 0 More l (1983) M n 2 + + 2C f MnCI° 1.10 25 0 More l (1983) Mn 2 * + 3CT MnC I 3 0.60 25 0 Morel (1983) M n 2 + + N H 3 M n N H 2 + 0.70 25 0 Morel (1983) M n 2 + + 2NH 3 Mn(NH 3 ) 2 + 1.20 25 0 More l (1983) M n 2 + + P 0 4 + H + M n H P O " 16.20 25 0 More l (1983) Mn2+ + OH" M n O H + -10.10 25 0 More l (1983) M n 2 + + 3 0 H " M n ( O H ) 3 -34.20 25 0 Morel (1983) M n 2 + + S2" MnS° 11.4 25 0 Dyrssen (1988) M n 2 + + S2" + H + M n H S + 18.07 25 0 Dyrssen (1988) M n 2 + + 2S2" + 2H + Mn(HS) ° 25.57 25 0 Dyrssen (1988) Mn2+ + 2S2" + H + Mn(HS)S" 37.94 25 0 Dyrssen (1988) M n 2 + + 2S2" MnS 2 " 29.64 25 0 Dyrssen (1988) N a + + C O f NaCOs 1.20 25 0 More l (1983) N a + + C 0 3 + H + NaHCO° 10.08 25 0 More l (1983) N a + + P04 + H + N a H P 0 4 13.5 25 0 More l (1983) N a + + S04 N0.SO4 0.7 25 0 More l (1983) C o 2 * +CO3 CaOCb 3.00 25 0 Morel (1983) Ca2+ + COt + H + CaHCO^ 11.60 25 0 More l (1983) C a 2 + + S04 CaSOS 2.30 25 0 More l (1983) C a 2 + + N H 3 C a N H 2 + -0.10 25 0 More l (1983) C a 2 + + 2NH 3 CaflMHs) 2* -0.70 25 0 More l (1983) C a 2 + + 3NH 3 C c X N H ^ f -1.50 25 0 More l (1983) C a 2 + + 4 N H 3 C a C N H ^ f -2.60 25 0 More l (1983) C c f + PO3*" C a P O i 6.5 25 0 More l (1983) C a 2 + + P 0 4 + H + CaHPOS 14.60 25 0 More l (1983) C a 2 + + P 0 4 + 2 H + C a H 2 P O ; 21.60 25 0 More l (1983) CO2++SJO? CaSiO° 4.2 25 0 More l ( 1983) C a 2 + + SiO? + H + CaHSiOs 14.1 25 0 More l ( 1983) C a 2 + + 2S iO ?+2H + CaH 2 (S i0 3 ) ° 29.9 25 0 More l ( 1983) G c r + OH" C a O H + -12.20 25 0 More l ( 1983) Mg 2 + + C O ? MgCO° 3.20 25 0 More l ( 1983) M g 2 + + C O ? + H + M g H C 0 3 + 11.60 25 0 More l ( 1983) M g 2 + + SO 2" M g S O ° 2.4 25 0 More l ( 1983) M g 2 + + N H 3 M g N H 3 2 + 0.10 25 0 More l ( 1983) M g 2 + + 2NH 3 M g ( N H 3 ) 2 + 0 25 0 Morel ( 1983) M g 2 + + 3 N H 3 M g ( N H 3 ) 2 + -0.30 25 0 More l ( 1983) M g 2 + + 4 N H 3 M g ( N H 3 ) f -1.00 25 0 Morel ( 1983) M g 2 + + PO4 M g P O ; 4.8 25 0 More l ( 1983) M g 2 + + P04+H + MgHPO° 15.10 25 0 Morel ( 1983) M g 2 + + P O * + 2H + M g H 2 P 0 4 + 20.8 25 0 Morel ( 1983) M g 2 + + SiO? MgSiO° 5.3 25 0 Morel ( 1983) M g 2 + + SiO? + H + M g H S i 0 3 14.3 25 0 More l ( 1983) M g 2 + + SiO? + 2H + M g H z S i O f 30.8 25 0 More l ( 1983) M g 2 + + OH" M g O H + -11.20 25 0 More l ( 1983) 163 Table A-2 Solubility products used in MINEQL calculations. I = ionic strength Mineral Products Reactants logK T ° C 1 Reference sider i te FeCOs Fe 2 + + C C ? -10.20 25 0 Rob i ee t a l . ( 1978 ) v iv ianite Fe3(PO-4)2 3Fe 2 + + 2 P 0 4 -36.00 25 0 Nriagu(1972) Fe (OH) 2 Fe 2 + + 2 0 H ' 12.10 25 0 More l (1983) a m o r p h o u s FeS Fe^ + S2" -21.62 25 0 Berner (1967) m a c k i n a w i t e FeS Fe^ + S2" -22.21 25 0 Berner (1967) pyrrhotite FeS Fe^ + S2" -24.52 25 0 R o b i e e t a l . (1978) gre ig i te Fe 3 S 4 SFe^ + SS^+S" -68.88 25 0 Berner (1967) pyrite FeS 2 Fe^ + S^ + S 0 -34.97 25 0 R o b i e e t a l . (1978) rhodoch ros i t e MnCOs M n 2 + + C O ? -10.40 25 0 More l (1983) r edd ing ite M n 3 ( P 0 4 ) 2 3 M n 2 + + 2 P O | -31.81 25 0 Tessenow (1974) M n ( O H ) 2 M n 2 + + 2 0 H ' 14.50 25 0 More l (1983) a l a b a n d i t e M n S M n ^ + S2" -18.96 25 0 R o b i e e t a l . (1978) haurite M n S 2 M n 2 + + S2" + S° -20.17 25 0 R o b i e e t a l . (1978) c a l c i t e C a C O s C a ^ + C O ? -8.30 25 0 More l (1983) C a S 0 4 C a 2 + + S 0 4 ^1.70 25 0 More l (1983) brushite C a H P 0 4 C a ^ + P O * + H + -19.30 25 0 More l (1983) CcuHCPO^s ACa2* + 3P<04 + H + -48.20 25 0 More l (1983) h y d r o x y a p a t i t e CasCPO^OH 5CQ 2* + 3 P 0 4 +OH" -45.10 25 0 More l (1983) a n a p a i t e C a 2 F e ( P 0 4 ) 2 20a2" + Fe 2 + + 2 P 0 4 -34.90 25 0 N r i a g u a n d Dell (1974) C a ( O H ) 2 C a ^ + ^ H " 21.90 25 0 More l (1983) r hodoch ros i t e M g C 0 3 M g 2 + + C O f -5.40 25 0 More l (1983) Mg3(PG-4)2 3 M g 2 + + 2PO s ; -28.40 25 0 More l (1983) newbery i t e M g H P 0 4 M g 2 + + P C M + H + -18.01 25 0 A b b o n a e t a l . (1982) struvite M g N H 4 P 0 4 M g 2 + + N H 3 + P 0 4 + H + -22.44 25 0 A b b o n a et al. (1982) M g ( O H ) 2 M g 2 + + 20H" 16.40 25 0 More l (1983) APPENDIX 2 DATA TABLES Table A-3 Physical and major ion data for Powell Lake All samples we re c o l l e c t e d in April 1984. z C a M g N a K B Sr a Salinity T Densi ty Diss. 0 2 (m) ( m M ) ( m M ) ( m M ) ( m M ) 0 i M ) (JIM) ( m M ) ( % ° ) ( °C) ( m g O ( j iM) 0 0.0189 0.0109 0.070 0.0052 0 0 0.818 0.052 7.55 999.96 1 0.0194 0.0109 0.070 0.0057 0 0 0.818 0.052 999.96 5 0.0192 0.0113 0.074 0.0057 3.57 0 0.818 0.052 7.31 999.99 95.536 10 0.0196 0.0136 0.080 0.0061 0.66 0 0.818 0.052 7.24 1000.00 93.408 25 0.0189 0.0118 0.079 0.0061 1.75 0 0.818 0.052 6.44 1000.02 95.648 50 0.0203 0.0158 0.120 0.0063 0.66 0 0.846 0.054 4.97 1000.06 89.152 75 0.0223 0.0222 0.187 0.0074 0 0 0.903 0.058 4.90 1000.07 82.320 100 0.0308 0.0595 0.520 0.0121 1.10 0 1.13 0.078 4.76 1000.08 63.728 125 0.0503 0.141 1.080 0.0204 2.57 0.15 1.81 0.116 4.80 1000.11 29.232 140 0.0722 145 0.0831 150 0.107 0.272 2.65 0.0451 1.84 0.514 3.10 0.199 4.95 1000.18 0 155 0.118 0.317 2.98 0.0501 1.02 0.514 3.36 0.215 4.96 1000.19 0 160 0.135 0.351 3.40 0.0576 2.84 0.695 4.23 0.271 5.04 1000.24 0 165 i7n 0.145 0.430 4.08 0.0674 3.20 0.786 4.68 0.3 5.14 1000.26 1 /U 175 0.197 0.566 5.53 0.0961 3.20 1.058 6.04 0.387 5.22 1000.33 0 IOU 185 ion 0.243 0.798 7.40 0.128 4.30 1.785 6.89 0.441 5.30 1000.36 200 9 i n 0.341 1.132 10.8 0.176 7.57 2.512 10.50 0.672 5.57 1000.54 0 Z IU 225 0.650 2.151 18.9 0.333 15.95 4.328 18.32 1.172 5.99 1000.92 230 0.716 250 1.200 4.188 35.2 0.651 30.53 8.506 33.96 2.171 6.63 1001.69 260 1.526 275 2.100 7.470 57.7 1.152 57.75 15.59 67.67 4.319 7.21 1003.36 300 4.500 19.83 149 2.578 140.9 38.04 159.7 10.151 8.20 1007.86 320 6.400 26.71 208 3.701 195.3 51.61 250.2 15.833 8.94 1012.21 325 6.904 330 6.860 26.94 215 3.844 202.3 53.43 259.8 16.429 9.19 1012.65 335 6.800 26.49 221 4.011 202.7 53.43 260.3 16.465 9.30 1012.66 340 7.077 27.73 228 4.011 203.8 54.34 261.8 16.555 9.41 1012.72 345 6.900 27.73 217 4.011 206.0 54.33 262.2 16.579 9.40 1012.74 Table A-4 Nutrient, carbon, pH, and alkalinity data for Powell Lake All samples were co l l e c t ed in April 1984. e x c e p t for P O * . Particulate P a n d Total P. wh i ch we re co l l e c t ed in July 1987 a n d p H , for wh i ch identical profiles were ob ta ined in April 1984, A u g . 1985 a n d Sept. 1986. z (m) (|iM) 1NO2" OiM ) NO3" ( f iM) Si(OHXi O iM) POA (UM) Partic. P Q iM ) Total P (UM) DOC (mg.L ' ' ) P O C (ng-L' 1) PON (ug»L"') p H Alkalinity (meq»L" ) z (m) 0 0 0 2.91 42.50 0 0.005 0 5.60 100.2 9.73 5.7 0.08 0 1 0 0 4.13 42.32 5.7 1 5 0 0 3.51 42.77 5.7 5 10 0 0 5.93 42.86 5.7 10 25 0.33 0 4.97 42.05 0 0.0078 0.015 1.58 47.47 3.98 5.7 0.09 25 50 0 0 8.70 42.23 0 0.0117 0 1.44 41.15 4.32 5.7 0.07 50 75 0 0 2.68 42.95 0 0.0069 0 5.7 0.09 75 100 0 0 2.68 45.38 0 0.0075 0 0.96 31.90 2.18 5.7 0.11 100 125 0.50 0 2.64 48.14 0 0.0087 0 0.16 125 140 0 0.0128 0.160 1.13 49.46 6.44 0.56 140 150 24.33 0 0.073 53.95 0 0.0089 0.055 1.43 48.07 7.20 5.7 0.47 150 155 31.71 0 0.071 54.95 5.7 155 160 89.98 0 0.120 57.11 0 0.0069 0.05 5.7 160 165 56.54 0 0.075 59.10 5.7 165 175 86.9 0 0.120 64.60 0.078 0.0083 0.064 3.16 52.05 6.20 5.7 0.90 175 185 177.0 0 0 71.37 5.9 185 200 175.8 0 0 80.93 0.097 0.008 0.214 4.56 46.74 9.14 5.9 1.49 203 225 369.2 0 0 97.35 0.097 0.0066 0.613 6.4 225 230 3.34 230 250 660.0 0 0 133.1 0.1 0.0172 0.332 6.4 250 260 15.28 128.3 7.74 6.82 260 275 1230.5 0 0 177.8 0.187 0.0213 0.634 6.8 275 290 49.07 276.1 18.39 10.71 290 300 2337 0 0 227.3 0.321 0.0484 0.838 6.8 300 320 3749 0 0 260.7 6.8 320 325 0 0 0.731 0.0410 2.322 48.01 258.1 12.47 31.73 325 330 3652 0 0 277.4 6.8 330 335 3988 0 0 266.9 6.8 335 340 3631 0 0 297.5 23.10 211.8 13.20 6.8 31.16 340 345 3591 0 0 272.6 0.569 0.1374 3.663 6.8 31.20 345 Table A-5 Phosphorus data for stations other than the South basin in Powell Lake All samples were c o l l e c t e d in July 1987. z W e s t Bear tooth M c M i l l a n H e a d East z (m) Basin Basin Basin of Lake Basin (m) Total P Part iculate Total P Part iculate Total P Part iculate Total P Par t icu late Total P Part iculate (UM) P (uM) (>iM) P (*iM) (jiM) P (jiM) QiM) P (nM) (|iM) P (nM) 0 0.166 0.0125 0.197 0.0042 0.171 0.0021 0.197 0.0032 0 0.0089 0 5 0.083 0.0034 5 25 0.057 0.0168 0.093 0.0096 0 0.0145 0.180 0.0115 25 50 0.051 0.0075 0.244 0.0128 0.197 0.0208 0 0.0068 50 75 0.181 0.0168 0 0.0171 0 0.0146 0 0.0145 75 ICO 0.181 0.0077 0 0.0162 0.025 0.0048 0 0.0078 100 150 0.015 0.0087 0.179 0.0153 0.031 0.0096 0.055 0.0121 150 150 0.0134 0.0072 0.0049 150 200 0.083 0.0102 0.005 0.0154 0.036 0.0159 0.521 0.0093 200 250 0 0.0137 0.041 0.0095 0.181 0.0133 0.475 0.0626 250 300 0 0.0071 0.690 300 Table A-6 Sulphur and trace metal data for Powell Lake All samples we re c o l l e c t e d in June-July 1987, e x c e p t for t h e H2S d a t a , w h i c h are a v e r a g e d for samples c o l l e c t e d in Apri l 1984, A u g . 1985, Sept. 1986 a n d July 1987. 2 SO4 H 2S Po lysu lph ide M o n o - Pyrite F e 5 + M n 2 + z (m) (U.M) (u.M) S ° su lph ide (nM) Q i M ) O i M ) (m) O iM ) (nM) 0 9.33 0 0 0 0.093 0.018 0 25 7.57 0 0.040 0.030 25 50 7.76 0 0 0 0.039 0.015 50 75 7.99 0 0.036 0.034 75 100 8.82 0 0 0 0.012 0.206 100 125 8.76 0 0.038 1.621 125 130 0 0 0 0 130 140 9.14 0 0 140 145 9.40 0 0 2.145 18.72 145 150 11.16 0 0 0 41.6 7.642 19.54 150 150 40.1 150 155 7.29 2.36 0 15.73 20.96 155 160 5.04 4.79 2.4 20.25 22.08 160 165 1.99 5.15 3.0 0 33.0 165 170 9.91 4.8 33.22 20.51 170 175 0.701 9.98 5.2 175 180 0.613 12.05 6.2 0 109 39.03 24.78 180 185 0 12.11 185 190 0 14.30 7.8 41.56 25.53 190 200 0 16.90 9.4 4.2 149 48.38 26.60 200 210 20.63 10.4 171.4 24.75 210 225 0 34.67 18 1.6 191 39.78 18.62 225 250 0 153.4 65 26.7 435 15.70 27.07 250 275 0 394.3 331 238 330 11.35 16.08 275 300 0 2276 1404 177 187 0.552 10.12 300 320 3119 320 325 0 3127 1744 190 248 0.211 1.688 325 330 3023 330 335 2956 2153 0.140 0.818 335 340 3153 340 345 0 2961 2097 84 148 0.057 0.742 345 Table A-7 Physical and major Ion data for Sakinaw Lake All samples were c o l l e c t e d in June 1985. z C a M g N a K a Salinity T Densi ty Diss. 0 2 z (m) ( m M ) ( m M ) ( m M ) ( m M ) ( m M ) (%o) ( °C ) (mg.L- 1 ) (|iM) (m ) 0 0.127 0.070 0.468 0.0150 0.422 0.027 19.12 998.47 618.75 0 1 0.127 0.070 0.468 0.0150 0.422 0.027 18.5 998.59 622.32 1 5 0.127 0.076 0.468 0.0150 0.423 0.027 17.96 998.69 633.04 5 10 0.127 0.079 0.516 0.0154 0.423 0.027 7.34 999.98 771.43 10 20 0.127 0.0909 0.610 0.0164 0.423 0.027 5.34 1000.04 533.93 20 22.5 0.127 0.0929 0.643 0.0167 0.027 5.1 1000.06 493.75 22.5 25 0.127 0.0944 0.647 0.0171 0.423 0.027 4.82 1000.06 455.36 25 27.5 0.134 0.100 0.735 0.0193 0.423 0.027 5.01 1000.06 335.71 27.5 30 0.137 0.226 0.928 0.0230 0.846 0.054 5.09 1000.07 130.36 30 32.5 0.228 0.259 2.273 0.0492 2.313 0.149 5.37 1000.14 0.00 32.5 35 0.331 0.613 5.683 0.113 5.699 0.364 5.75 1000.30 0.00 35 40 0.887 2.826 24.25 0.506 27.935 1.787 6.29 1001.41 0 40 50 2.591 10.87 92.84 1.802 101.35 6.458 6.48 1005.10 0 50 75 3.952 17.10 144.21 3.121 168.49 10.705 9.15 1008.21 75 100 3.969 17.62 144.41 3.121 168.72 10.718 9.39 1008.19 100 no 3.976 17.62 145.68 3.121 170.21 10.812 9.35 1008.27 110 120 4.007 17.62 145.93 3.121 170.44 10.826 9.39 1008.28 120 125 3.985 17.62 145.93 3.121 170.44 10.808 9.44 1008.26 125 130 3.995 17.76 145.93 3.121 170.44 10.826 9.45 1008.27 130 135 3.997 17.10 145.93 3.121 170.44 10.826 9.49 1008.27 135 Table A-8 Nutrient, carbon, pH and alkalinity data for Sakinaw Lake All samples were c o l l e c t e d In June 1985, e x c e p t for Pot. Part iculate P a n d Total P, w h i c h w e r e c o l l e c t e d In June 1988. z NO2 NCb Si(OH) 4 POA Partic. Total P DOC POC (ng-L'') PON P H Alkalinity z (m) (|iM) OaM) (UM) (|iM) P(nM) (*iM) (mg.L" ' ) (ng-L"') ( m e q » L ) (m) 0 0 0 0.4 33.9 5.7 0.36 0 1 5.2 0 0.71 35.3 3.12 145.2 23.39 5.7 0.12 1 5 4.8 0 0.67 35.6 0.055 0.0039 0.110 5.7 5 10 2.6 0 0.16 33.7 0.060 0.0401 0.219 2.97 322.8 43.84 5.7 0.34 10 20 0.2 0 2.19 41.3 0.064 0.0606 0.339 2.78 204.2 31.17 5.7 0.38 20 25 0 0.03 3.67 43.0 0.060 0.0248 0.548 2.92 150.6 24.02 5.7 0.57 25 27.5 0 0 6.67 44.3 0.060 0.0152 0.304 5.7 0.45 27.5 30 0.2 0.24 8.00 50.8 0.211 0.1464 0.601 2.95 442.7 79.53 5.7 0.48 30 32.5 40.2 0 0.55 86.1 2.08 0.0166 2.96 5.7 0.49 32.5 35 83.6 0 0.18 140 8.65 0.0094 7.97 3.72 193.4 34.80 5.7 0.85 35 37.5 25.62 0.0072 32.75 5.7 0.98 37.5 40 933 0 0 418 44.53 0.0098 48.87 4.58 188.9 33.62 6.2 3.17 40 45 102.5 0.0091 137.9 45 50 4160 0 0 820 156.3 0.0118 237.6 8.84 276.9 45.62 6.5 13.66 50 60 204.6 0.0048 347.1 60 75 7642 0 0 940 284.8 0.0048 364.6 11.53 237.7 36.47 6.5 27.17 75 ICO 7782 0 0 955 282.2 0.0042 389.1 15.95 232.1 35.65 6.5 27.53 ICO 110 7666 969 282.9 0.0037 413.5 6.5 27.63 no 120 7735 966 293.4 0.0033 363.7 12.16 250.8 41.66 6.5 27.70 120 125 0 0 265.7 0.0037 374.4 6.5 27.63 125 130 7316 979 253.3 0.0030 291.4 6.5 27.62 130 135 7235 828 211.3 0.0034 350.6 12.74 237.0 38.04 6.5 27.67 135 Table A-9 Sulphur and trace metal data for Sakinaw Lake All s amp les w e r e c o l l e c t e d in J une 1988, e x c e p t for the H 2S d a t a , wh i ch are a v e r a g e d for samples co l l e c t ed in June 1985 a n d June 1988. z SC-4 HzS Po l ysu lph ide M o n o - Pyrite Fe* M n 2 + z (m) (JIM) (UM) S ° GxM) su lph ide (nM) ( j iM) (UM) (m) (nM) 0 0 0 0 0 0 5 46.50 0 0 0 0 0.297 0 5 10 48.34 0 0 0.245 0 10 20 51.04 0 0 0.045 0 20 25 54.87 0 0 0.062 0 25 27.5 60.38 0 0 0.030 0 27.5 30 63.57 9.47 3.5 0 24 0.045 0.532 30 32.5 37.11 127.6 38 6.725 3.852 32.5 35 9.92 306.4 187 5.266 4.313 35 37.5 2.08 725.6 543 37.5 43 2.48 1166 1231 124 37 1.681 4.433 40 45 1.59 2704 2876 45 50 0 3946 4375 290 31 0.340 5.708 50 60 0 4929 4517 267 80 60 75 0 5299 4498 397 48 0.070 5.539 75 100 0 5316 4385 543 23 0.085 5.869 100 110 5458 4255 260 41 0.095 5.521 110 120 5259 4369 408 20 0.045 5.400 120 125 0 5299 4420 125 130 5244 4584 0.121 5.396 130 135 0 5291 4621 548 25 0.097 5.438 135 REFERENCES A B B O N A F.. LUNDAGER M A D S E N H.E. a n d BOISTELLE R. 1982. Crysta l l izat ion of t w o m a g n e s i u m p h o s p h a t e s , s t ruv i te a n d n e w b e r y i t e : e f f e c t o f p H a n d concent ra t ion . J. Crystal Growth 57: 6-14. AIZAKI M. a n d OTSUKI A . 1987. Character is t i c of variat ions of C :N:P :Ch l ratios of seston in eut roph ic shal low Lake Kasumigaura . Jpn. J. Limnol. 48: S99-S106. AIZAKI M . a n d T A K A M U R A N. 1986. Nutrient r egene ra t i on by d e c o m p o s i t i o n of lake p h y t o p l a n k t o n . Res. Rep. Natl. Environ. Stud. Jpn. 96: 29-44 (in J a p a n e s e with English summary) . ALEXANDER G.R. 1978. The rat ionale for a b a n o n de te rgen t p h o s p h a t e in the G r e a t Lakes Basin. In Phosphorus in the Environment: Its Chemistry and Biochemistry. A C i b a Foundat ion Sympos ium. Elsevier. A m s t e r d a m , p p 269-284. ALEXANDER M. 1965. Nitrification. Agronomy 10:307-343. ALLER R.C. 1978. Exper imenta l studies of c h a n g e s p r o d u c e d by depos i t feeders o n pore wate r , sed iment , a n d overlying wate r chemistry. Am. J. Sci. 278: 1185-1234. ALLER R.C. 1980. Quant i f y ing solute distributions in the b i o t u r b a t e d z o n e of mar ine sed iments by de f in ing a n a v e r a g e mic roenv i ronment . Geochim. Cosmochim. Acta 44:1955-1965. ALLER R.C. a n d RUDE P.D. 1988. C o m p l e t e o x i d a t i o n of sol id p h a s e sulf ides by m a n g a n e s e a n d b a c t e r i a in a n o x i c mar ine sediments . Geochim. Cosmochim. Acta 52: 751-765. ALTSCHULER Z.S. 1973. The w e a t h e r i n g of p h o s p h a t e depos i t s - g e o c h e m i c a l a n d env i ronmenta l aspec ts . In Environmental Phosphorus Handbook. E.J. Griffith, A . Bee ton a n d J . M . Spence r eds. J . Wiley a n d Sons, N e w York. p p . 33-96. ALTSCHULER Z.S., SCHNEPFE M.M. , SILBER C . C . a n d S IMON F.O. 1983. Sulfur d iagenes is in Everglades p e a t a n d origin of pyrite in c o a l . Sci. 221:221-227. ANDERSON L.G.. DYRSSEN D. a n d SKEI J . 1987. Format ion of c h e m o g e n i c ca l c i t e in super-anox i c seawa te r - F ramvaren . Southern Norway. Mar. Chem. 20:361-376. BACCINI P. 1985. Phospha te interact ions a t the sediment-water in ter face . In Chemical Processes in Lakes. W. S tumm e d . Wi ley-lnterscience, N e w York, p p 189-205. B A C O N W.R. 1957. G e o l o g y of lower Jervis Inlet, British C o l u m b i a . British Columbia Dept. Mines Bull. No. 39.45 p p . BALZER W. 1978 U n t e r s u c h u n g e n ube r A b b a u o rgan i s che r M a t e r i e u n d Ndhrstoff -Freusetzung a m B o d e n d e r Kieler Bucht b e i m U b e r g a n g v o m ox i s chen zum a n o x i s c h e n Mi l ieu. Ph.D. dissertation. Kiel University. BALZER W. 1981. O r g a n i c sulphur In the mar ine envi ronment . In Marine Organic Chemistry E. K. Duursma a n d R. Dawson eds. p p . 395-414. BARNES M.A. a n d Barnes W .C . 1981. O x i c a n d a n o x i c d i agenes i s of d i te rpenes in lacustrine sediments. In Advances in Organic Geochemistry, p p 289-298. BARROW N.J. 1983. O n the reversibility of p h o s p h a t e sorption by soils. J. Soil Sci. 34: 751-758. - BARSDATE R.J., FENCHEL T. a n d PRENTKI R.T. 1974. Phosphorus c y c l e of m o d e l ecosys tems: s ign i f i cance for d e c o m p o s e r f o o d cha ins a n d a f f e c t of bac te r i a l grazers. Oikos 25: 239-251. BERNER R.A. 1964a. Iron sulfides f o r m e d from a q u e o u s solution at low temperatures a n d a tmospher i c pressure. J. Geol. 72:293-306. BERNER R.A. 1964b. Distribution a n d d iagenes is of sulfur in some sediments f rom the Gulf of California. 1: 117-140. BERNER R.A. 1967a. Diagenes is of iron sulfide in r ecen t mar ine sediments . In Estuaries: Am. Assoc. Adv. Sci. Publ. 83: 268-272. BERNER R.A. 1967b. The rmodynamic stability of sed imentary iron sulfides. Am. J. Sci. 265: 773-785. BERNER R.A. 1969. Migrat ion of iron a n d sulfur within a n a e r o b i c sed iments dur ing early diagenesis . Am. J. Sci. 267: 19-42. BERNER R.A. 1970. Sedimentary pyrite format ion. Am. J. Sci. 268: 1-23. BERNER R.A. 1971. Principles of Chemical Sedimentology. McGraw-Hi l l , N e w York. 240 p p . BERNER R.A. 1973. Phospha te r emova l f rom s e a wa te r by adsorp t ion o n v o l c a n o g e n i c ferric oxides. Earth Planet. Sci. Lett. 18: 77-86. BERNER R.A. 1974. Iron sulfides in P l e i s tocene d e e p B lack S e a sed iments a n d their p a l e o o c e a n o g r a p h i c s ign i f i cance . In The Black Sea - Geology. Chemistry and Biology. E.T. D e g e n s a n d D.A. Ross eds . A m . Assoc . Pet. G e o l . M e m o i r 20. p p 524-531. BERNER R.A. 1975. Kinetic mode ls for the early d iagenes is of n i t rogen, sulfur, phosphorus, a n d si l icon in a n o x i c mar ine sediments . In: The Sea. Vo l . 5. E.D. G o l d b e r g e d . Wiley, N e w York, p p 427-450. BERNER R.A. 1981. A n e w g e o c h e m i c a l c lass i f icat ion of sed imenta ry env i ronments . J. Sed. Petrol. 51:359-365. BERNER R.A., BALDWIN T. a n d HOLDREN JR. G.R. 1979. A u t h i g e n i c iron sulfides as paleosal inity indicators. J. Sed. Petrol. 49: 1345-1350. BERNER R.A. a n d WESTRICH J.T. 1985. B ioturbat ion a n d the ear ly d iagenes is of c a r b o n a n d sulfur. Am. J. Sci. 285:193-206. BICK H. 1958. The possibility of in f luenc ing ce l l mate r i a l d e c o m p o s i t i o n a n d of the d e v e l o p i n g c i l iate f a u n a b y add i t i on of i no rgan i c ferti l ization mater ia ls t o trial waters. Arch. Mikrobiol. 29:311-338. BLUM J.J. 1966. Phospha t e u p t a k e by phosphate-s ta rved Euglena. J. Gen. Physiol. 49: 1125-1137. BOISTELLE R. a n d A B B O N A F. 1981. Mo rpho logy , habi t a n d growth of newbery i te crystals (MgHP0 4 «3H20). J. Crystal Growth 54:275-295. , BOSTRUM B., ANDERSEN J . M . . FLEISCHER S. a n d J A N S S O N M. 1988. E x c h a n g e of phosphorus across the sediment-water interface. Hydrobiologia 170: 229-244. BOULEGUE J . 1972. Mise e n e v i d e n c e et d o s a g e des polysulfures a u cours d e I 'oxydation d e I 'hydrogene sulfure dans I'eau d e mer. C.R. Acad. Sc. Paris 275C: 1335-1338. BOULEGUE J . 1976. Equilibres dans le systeme H2S-S8 c o l l o i d e - H 2 0 . C.R. Acad. Sc. Paris 283D: 591-594. BOULEGUE J . 1977. Equil ibria in a sulf ide r ich w a t e r f rom Enghien-les Bains, F rance . Geochim. Cosmochim. Acta 41:1751-1758. BOULEGUE J . 1978. Solubility of e l emen ta l sulfur in wa te r at 298 K. Phosphorus and Sulfur 5: 127-128. BOULEGUE J . , CIABRINI J.-P., FOUILLAC C . M ICHARD G. a n d OUZOUNIAN G . 1979. Field titrations of d isso lved sulfur spec i es in a n o x i c env i ronments - geochem i s t r y of Puzzichel lo waters (Cors i ca , France) . Chem. Geol. 25: 19-29. BOULEGUE J . a n d DENIS J . 1983. Sulf ide spec i a t ions in upwe l l ing areas . In Coastal Upwelling, Its Sediment Record. Part A: Responses of the Sedimentary Regime to Present Coastal Upwelling. eds. E. Suess a n d J . Thiede. p p 439-454. BOULEGUE J . , LORD III C.J . a n d C H U R C H T.M. 1982. Sulfur spec ia t ion a n d assoc i a t ed t r a ce meta l s (Fe, C u ) in t h e p o r e waters of G r e a t M a r s h , D e l a w a r e . Geochim. Cosmochim. Acta 46:453-464. BOULEGUE J . a n d M ICHARD G . 1978. Constantes d e format ion des ions polysulfures S?, Sf et si e n phase aqueuse . J. Francois d'Hydrologie 9: 27-34. BOWERS J.W., FULLER M . J .A . ' and PACKER J.E. 1966. Au tox ida t i on of a q u e o u s sulphide solutions. Chem. Ind. J an . 8:65-66. BRATBAK G . 1985. Bac t e r i a l b i o v o l u m e a n d b i o m a s s es t imat ions . Appl. Environ. Microbiol. 49: 1488-1493. BROCK T.D. 1979. Biology of Microorganisms, 3rd e d . Prentice-Hall. Inc., E n g l e w o o d Cliffs, 802 pp . BROCK T.D. a n d GUSTAFSON J . 1976. Ferric iron r educ t ion by sulfur- a n d iron-oxidizing bac te r i a . Appl. Environ. Microbiol. 32: 567-571. BROECKER W.S. 1971. A k inet ic m o d e l for c h e m i c a l c o m p o s i t i o n of sea-water . Quat. Res. 1:188-207. BROENKAW W.W. 1969. The distributions of non-conserva t i ve solutes r e l a t e d t o the d e c o m p o s i t i o n of o r g a n i c ma te r i a l in a n o x i c m a r i n e basins. Ph.D. Thesis. University of Wash ington . BURDIGE D.J. a n d NEALSON K.H. 1985. M ic rob ia l m a n g a n e s e r educ t ion by enr i chment cultures f rom coas t a l mar ine sediments. Appl. Environ. Microbiol. 50: 491-497. BURDIGE D.J. a n d NEALSON K.H. 1986. C h e m i c a l a n d m i c rob io log i ca l studies of sulfide-m e d i a t e d m a n g a n e s e reduct ion . Geomicrobiol. J . 4: 361-387. BURNETT W.C . 1977. Geochemis t r y a n d origin of phosphor i te deposi ts f rom off Peru a n d Chi le . Geol. Soc. Amer. Bull. 88: 813-823. BURNISON K.B. 1975. M i c rob ia l ATP studies. Int. Ver. Theor. Angew. Umnol. Verh. 19: 286-290. BUTLER E.E. a n d TIBBITTS S. 1972. C h e m i c a l survey of the Tamar Estuary. 1. Properties of the waters. J. Mar. Biol. Assoc. U.K. 52:681-699. BYRNE R.H., KUMP L.R. a n d CANTRELL K.J. 1988. The inf luence of t empera tu re a n d pH o n t r a ce meta l spec ia t ion in seawater . Mar. Chem. 25: 163-168. CALVERT S.E.C. a n d KARLIN R. 1990. S u l p h u r / c a r b o n re la t ionships in B l ack S e a sediments . Geochim. Cosmochim. Acta in press. CANFIELD D.E.. RAISWELL R.. WESTRICH J.T.. REAVES C M . a n d BERNER R.A. 1986. The use of c h r o m i u m reduc t ion in the analysis of r e d u c e d inorgan ic sulfur in sed iments a n d shales. Chem. Geol. 54: 149-155. C A R I G N A N R. 1984. S ed imen t g e o c h e m i s t r y in a e u t r o p h i c l ake c o l o n i z e d by the s u b m e r g e d m a c r o p h y t e Myriophyllum spicatum. Can. J. Fish. Aquat. Sci. 42 : 1303-1311. CEMBELLA A . D . , ANTIA N.J. a n d TAYLOR F.J.R. 1986. The d e t e r m i n a t i o n of t o t a l phosphorus in s eawa te r by nitrate ox idat ion of the o rgan i c content . Wat. Res. 20: 1197-1199. C H A N Y.K. a n d CAMPBELL N.E.R.1978. Phytop lankton up take a n d excret ion of assimilated nitrate in a small C a n a d i a n Shield lake. Appl. Environ. Microbiol. 35: 1052-1060. C H A N T O N J.P. a n d MARTENS C.S. 1985. The e f fec ts of h e a t a n d s tannous ch lo r ide a d d i t i o n o n the a c t i v e distillation of a c i d volat i le sulfide f rom pyrite-rich mar ine sed iment samples . Biogeochem. 1: 375-383. C H E N K.Y. a n d GUPTA S.K. 1973. Format ion of polysulphides in a q u e o u s solution. Environ. Lett. 4: 187-200. CHEN K.Y. a n d MORRIS J .C . 1972a. Kinetics of ox idat ion of a q u e o u s sulfide by 0 2 . Environ. Sci. Technol. 6: 529-537. C H E N K.Y. a n d MORRIS J .C . 1972b. Ox ida t ion of sulfide by 0 2 : Catalys is a n d inhibition. J. Sanit. Eng. Div. Proc. Amer. Soc. Civ. Eng. 98:215-227. CLINE J .D . 1969. S p e c t r o p h o t o m e t r i c de te rm ina t i on of h y d r o g e n su lph ide in natura l waters. Limnol. Oceanogr. 14:454-458. CLINE J .D . 1973. Deni t r i f icat ion a n d i sotop ic f r a c t i ona t i on in t w o cont ras t ing mar ine environments: the eastern t rop ica l North Pac i f i c O c e a n a n d the C a r i a c o Trench. Ph.D. Thesis. University of Ca l i forn ia . ' C L O E R N J.E.. C O L E B.E. a n d OREMLAND R.S. 1983. Seasona l c h a n g e s in the chemistry a n d b io logy of a meromic t i c lake (Big S o d a Lake . N e v a d a , USA). Hydrobiologia 105. 195-206. C L O E R N J.E.. C O L E B.E. a n d WIENKE S.M. 1987. Big S o d a Lake (Nevada ) . 4. Vert ica l fluxes of par t i cu la te matter : Seasonal i ty a n d variat ions across the c h e m o c l i n e . Limnol. Oceanogr. 32: 815-824. C M I E C H H.A. 1981. Ultrastructural c h a n g e s in f reshwater popu l a t i ons of p l ank ton i c C y a n o p h y c e a e du r i ng c e l l d i f f e rent i a t ion a n d d e v e l o p m e n t . Ph.D. Thesis. University of Leeds. U.K. 163 pp . C O L E C .V . . OLSEN S.R. a n d SCOTT C O . 1953. The nature of p h o s p h a t e sorpt ion by c a l c i u m c a r b o n a t e . 17: 352-356. COLE J .A. a n d BROWN C M . 1980. Nitrite reduct ion to a m m o n i a by fermentat ive bac te r i a : a short circuit in the b io log i ca l nitrogen c y c l e . FEMS Microbiology Letters 7. 65-72. C O R N W E L L J . C 1987. Phosphorus c y c l i n g in A r c t i c l ake sed imen t : adso rp t i on a n d auth igen ic minerals. 109:161-179. CULVER D.A. a n d BRUNSKILL G.J. 1969. Fayettevi l le G r e e n Lake , N e w York. V. Studies of p r imary p r o d u c t i o n a n d z o o p l a n k t o n in a m e r o m i c t i c ma r l l ake . Limnol. Oceanogr. 14: 862-873. CURRIE D.J., BENTZEN E. a n d KALFF J . 1986. Does a lga l-bacter ia l phosphorus partit ioning vary a m o n g lakes? A c o m p a r a t i v e study of o r thophospha te up take a n d alkal ine phospha tase activity in freshwater. Can. J. Fish. Aquat. Sci. 43: 311-318. CURRIE D.J. a n d KALFF J . 1984. A compar i son of freshwater a l g a e a n d bac t e r i a to acqu i re a n d retain phosphorus. Limnol. Oceanogr. 29: 298-310. CUTTER G .A . a n d VELINSKY D.J. 1988. Tempora l var iat ions of s ed imen ta r y sulfur in a De l aware salt marsh. Mar. Chem. 23:311-327. D A C E Y J .W.H. a n d HOWES B.L 1984. W a t e r u p t a k e by roots contro ls w a t e r t a b l e m o v e m e n t a n d sed iment ox idat ion in short Spartina marsh. Sci. 224:487-490. D 'ANGLE JAN B.F. 1968. Phospha te d iagenes is of c a r b o n a t e sediments as a m o d e of in situ f o rma t i on of mar ine phosphor i te : Observat ions in a c o r e f rom the eastern Paci f ic . Can. J. Earth Sci. 5:81-87. DAV I SON W., L ISHMAN J .P. a n d HILTON J . 1985. Fo rma t i on of pyr i te in f reshwater sediments: Implications for C/S ratios. Geochim. Cosmochim. Acta49: 1615-1620. DE BOER R.D. 1977. In f luence of s e e d crystals o n the p r e c i p i t a t i on of c a l c i t e a n d aragoni te . Am. J. Sci. 277: 38-61. DE KANEL J . a n d MORSE J .W. 1978. The chemist ry of o r t h o p h o s p h a t e u p t a k e f rom seawa te r on to ca l c i t e a n d aragoni te . Geochim. Cosmochim. Acta 42: 1335-1340. DEVOL A .H . 1975. B io log ica l ox ida t ion in ox ic a n d a n o x i c mar ine env i ronments : Rates a n d processes . Ph.D. Thesis. University of Wash ington . ' DILLON P.J. a n d RIGLER F.H. 1974. The phosphorus-ch lorophy l l re lat ionship in lakes. Limnol. Oceanogr. 19: 767-773. DJAFARI D. 1976. M a n g a n - E isenakkumulate in d e r Kieler Bucht. Ph.D. dissertation. Kiel University. DOREMUS C . a n d CLESCERI L.S. 1982. M i c rob ia l me tabo l i sm in sur face sediments a n d its role in t h e immob i l i z a t i on of phospho rus in o l i g o t r o p h i c l ake sed iments . Hydrobiologia91:261-268. D O W S O N W.M. a n d JONES W.F. 1974. Studies in qual i tat ive inorgan ic analysis - Part XLIII. The alkali me ta l salts of the sulfur oxyac ids . Mikrochim. Acta (Wien). p p 339-368. DREVER J.I. 1982. The Geochemistry of Natural Waters. Prentice-Hal l , E n g l e w o o d Cliffs. 388 pp . DYRSSEN D. 1965. A G r a n titration of seawa te r o n b o a r d SAGITTA. Acta Chem. Scand. 19: 1265. DYRSSEN D. 1988. Sulfide comp l exa t i on in surface seawater . Mar. Chem. 24: 143-153. EHRLICH H.L. 1981. Geomicrobiology. M a r c e l Dekker, N e w York. 393 pp . ELDERFIELD H., M C C A F F R E Y R.J., LUEDTKE N., BENDER M. a n d TRUESDALE V.W. 1981. C h e m i c a l d iagenes is in Narraganset t Bay sediments. Am. J. Sci. 281: 1021-1055. ELLIS-EVANS J . C . a n d L E M O N E.C.G. 1989. S o m e aspec t s of iron c y c l i n g in mar i t ime anta rc t i c lakes. Hydrobiologia 172: 149-164. EMERSON S. 1976. Early d iagenes is in a n a e r o b i c lake sediments: C h e m i c a l equi l ibr ia in interstitial waters. Geochim. Cosmochim. Acta 40:925-934. EMERSON S., C R A N S T O N R.E. a n d LISS P.S. 1979. Redox spec i e s in a r e d u c i n g fjord: Equilibrium a n d kinetic considerat ions. Deep-Sea Res. 26A: 859-878. EMERSON S. a n d HEDGES J.I. 1988. Processes control l ing the o r g a n i c c a r b o n con ten t of o p e n o c e a n sediments. Paleoceanography 3: 621-634. EMERSON S., J A C O B S L. a n d TEBO B. 1983. The behav io r of t r a ce metals in mar ine anox ic waters : Solubilities a t the oxygen-hydrogen sulfide in te r face . In Trace Metals in Sea Water. C.S. W o n g e d . p p 579-608. EMERSON S., KALHORN S., J A C O B S L, TEBO B.M., NEALSON K.H. a n d ROSSON R.A. 1982. Env i ronmenta l ox ida t i on rate of manganese ( l l ) ; b a c t e r i a l catalys is . Geochim. Cosmochim. Acta 46: 1073-1079. EMERSON S. a n d WIDMER G . 1978. Early d iagenes is in a n a e r o b i c lake sed iments - II. The rmodynami c a n d kinetic factors control l ing the fo rmat ion of iron phospha t e . Geochim. Cosmochim. Acta 42.1307-1316. EPPLEY R.W. a n d RENGER E.H. 1974. N i t rogen assimi lat ion of a n o c e a n i c d i a t o m in nitrogen-limited cont inuous culture. J. Phycol. 10. 15-23. ' FAYE G.H. . M A N N I N G P.G. a n d NICKEL E.H. 1968. The polar ized op t i c a l absorpt ion spec t r a of t o u r m a l i n e , co rd i e r i t e , ch lo r i t o id a n d v i v ian i te : ferrous-ferric e l e c t r o n i c interact ion as a source of p leochro ism. Am. Mineralogist 53: 1174-1201. FENCHEL T. a n d BLACKBURN T.M. 1979. Bacteria and Mineral Cycling. A c a d e m i c Press, London. 255 p p . FERGUSON J . . CHAMBERS L.A. a n d BURNE R.V. 1983. Heavy-meta l enr ichments , bac te r i a l su lpha te r e d u c t i o n a n d iron su lph ide f o rma t i on in sha l low-water c a r b o n a t e sediments offshore f rom a smelt ing c o m p l e x a t Port Pirie, South Austral ia. Chem. Geo/. 40:117-134. FLEISCHER S. 1983. M i c r o b i a l p h o s p h o r u s r e l ea se du r i ng e n h a n c e d g lyco lys is . Naturwissenschaften 70:415. FLEISCHER S. 1985. M i c rob ia l med i a t i on of phosphorus e x c h a n g e at the sediment-water in ter face . In 13th Nordic Symposium on Sediments. M. Enell, W. Grane l i a n d L.-A. Hansson eds. p p 9-16. FLEISCHER S. 1986. A e r o b i c u p t a k e o f F e ( l l l ) - p r e c i p i t a t e d p h o s p h o r u s b y microorganisms. Arch. Hydrobiol. 107: 269-277. FLORENTZ M. , G R A N G E R P. a n d HARTEMANN P. 1984. Use of 3 1 P n u c l e a r m a g n e t i c r e s o n a n c e a n d e l e c t r o n m i c r o s c o p y t o s tudy p h o s p h o r u s m e t a b o l i s m of microorganisms from waster-water. Appl. Environ. Microbiol. 47: 519-525. FORSBERG C . 1989. Impor tance of sediments in unders tand ing nutrient c y c l i ng in lakes. Hydrobiologia 176/177:263-277. FORSBERG C , RYDING S.-O., CLAESSON A. a n d FORSBERG A . 1978. Wa te r c h e m i c a l analyses and/o r a l g a l assay? - S e w a g e effluent a n d po l lu ted lake w a t e r studies. Mitt. int. Ver. Limnol. 21:352-363. FREVERT T. 1979. The p E redox c o n c e p t in natura l sed iment-water systems; its role in control l ing phosphorus release f rom lake sediments. Arch. Hydrobiol. (suppl.) 55: 278-297. FROELICH P.N., KLINKHAMMER G.P., BENDER M.L . LUEDTKE N.A., HEATH G.R., CULLEN D., DAUPHIN P., H A M M O N D D.. HARTMAN B. a n d M A Y N A R D V. 1979. Early ox idat ion of o r g a n i c ma t t e r in p e l a g i c sed iments of t h e eas te rn e q u a t o r i a l A t l an t i c : Suboxic d iagenesis . Geochim. Cosmochim. Acta 43: 1075-1090. FUHS G.W. . DEMMERLE S.D.. CANELLI E. a n d C H E N M. 1972. C h a r a c t e r i z a t i o n of phosphorus- l imi ted p l a n k t o n a l g a e (with re f lec t ions o n t h e limiting-nutrient c o n c e p t ) . In: Nutrients and Eutrophication: The Limiting-Nutrient Controversy. G.E. Likens e d . A m . Soc . Limnol. O c e a n o g r . Spec . Symp. 1: 113-133. GACHTER R. a n d BLOESCH J . 1985. Seasona l a n d ver t i ca l va r ia t ion in the C:P ratio of s u s p e n d e d a n d settling seston of lakes. Hydrobiologia 128: 193-200. G A C H T E R R. a n d MARES A . 1985. D o e s sett l ing ses ton r e l ease so lub le r e a c t i v e phosphorus in the hypol imnion of lakes? Limnol. Oceanogr. 30:364-371. ' GACHTER R.. MEYER J.S. a n d MARES A. 1988. Cont r ibut ion of b a c t e r i a t o re lease a n d fixation of phosphorus in lake sediments. Limnol. Oceanogr. 33: 1542-1558. GAUDETTE H.E. a n d LYONS W.-B. 1980. Phospha te geochemis t r y in nearshore c a r b o n a t e sediments: a suggest ion of apa t i t e format ion. Soc. Econ. Pal. Min. 29: 215-225. GIBLIN A.E. 1988. Pyrite format ion in marshes dur ing ear ly d iagenesis . Geomicrobiol. J. 6: 77-97. GIBLIN A.E. a n d HOWARTH R.W. 1984. Porewater e v i d e n c e for a d y n a m i c sed imentary iron c y c l e in salt marshes. Limnol. Oceanogr. 29:47-63. GIESKES J . M . a n d ROGERS W.C . 1973. Alkal inity de te rm ina t i on in interstitial waters of mar ine sediments. J. Sed. Petrol. 43: 272-277. G I G G E N B A C H W. 1972. O p t i c a l spec t ra a n d equil ibrium distribution of polysulphide ions in aqueous solution at 20°C. Inorg. Chem. 11:1201-1207. GOLDHABER M.B. 1983. Exper imenta l s tudy of m e t a s t a b l e sulfur o x y a n i o n fo rma t i on during pyrite oxidat ion at pH 6-9 a n d 30°C. Am. J. Sci. 283: 193-217. GOLDHABER M.B.. ALLER R . C . C O C H R A N J.K.. ROSENFELD J.K.. MARTENS C.S. a n d BERNER R.A. 1977. Sulfate r e d u c t i o n , diffusion a n d b io tu rba t ion in Long Island S o u n d sediments: Report of the F O A M Group . Am. J. Sci. 277: 193-237. GOLDHABER M.B. a n d KAPLAN I.R. 1974. The sulfur c y c l e . In The Sea. Vo l . 5. E.D. G o l d b e r g e d . Wiley, N e w York, p p 569-655. G O L D M A N J . C , M C C A R T H Y J.J. a n d PEAVY D.G. 1979. G r o w t h rate in f luence o n the c h e m i c a l compos i t ion of phytop lankton in o c e a n i c water . Nat. 279:210-215. G O L T E R M A N H.L. 1964. Minera l izat ion of a l g a e under sterile cond i t ions or b y bac t e r i a l b r e a k d o w n . Verh. Internat. Verein. Limnol. 15:544-548. G O L T E R M A N H.L. 1975. Phys io logica l l imnology. A n a p p r o a c h to the phys io logy of lake e c o s y s t e m s . Developments in Water Science 2. Elsevier Sc i . Pub l . C o . A m s t e r d a m . 489 p p . G O U R M E L O N C , BOULEGUE J . a n d MICHARD G . 1977. Ox ida t ion partiel le d e I 'hydrogene sulfure e n phase aqueuse . C.R. A c a d . Sc. Paris 284C: 269-272. GRASSHOF K. 1976. Methods of Seawater Analysis. Ve r l ag C h e m i e , N e w York, 317 p p . GREEN W.J., CANFIELD D.E., LEE G.F. a n d JONES R.A. 1986. M n , Fe, C u a n d C d distributions a n d r e s idence t imes in c l o s e d bas in Lake V a n d a (Wright Va l l e y , An ta r c t i c a ) . Hydrobiologia 134:237-248. GREENFIELD L J . 1963. Me tabo l i sm a n d c o n c e n t r a t i o n of c a l c i u m a n d m a g n e s i u m a n d prec ip i ta t ion of c a l c i u m c a r b o n a t e by a mar ine bac t e r i um . Ann. N.Y. Acad. Sci. 109:23-45. GULBRANDSEN R.R. 1969. Phys ica l a n d c h e m i c a l fac tors in t h e f o rma t i on of mar ine apat i te . Econ. Geol. 64:365-382. ' HALLBERG R.O. 1972. Iron a n d z inc sulfides f o r m e d in a con t inuous cul ture of sulfate-reduc ing bac te r i a . N. Jahrbuch f. Mineralogie. Monatshefte 31:481-500. H A M M A N N R. a n d OTTOW J . C . G . 1974. Reduc t i ve dissolution of F e 2 0 3 by saccha ro l y t i c Clostridia a n d Bacillus po l ymyxa under a n a e r o b i c condi t ions. Z. Pflanzenernaer. Bokenkd. 137:108-115. H A M N E R W . M . , GILMER R.W. a n d H A M N E R P.P. 1982. The p h y s i c a l , c h e m i c a l a n d b i o l o g i c a l charac te r i s t i cs of a strat i f ied, sa l ine , sulf ide lake in P a l a u . Limnol. Oceanogr. 27: 896-909. HANDSCHUH G.J. a n d ORGEL L.E. 1973. Struvite a n d preb iot i c phosphory la t ion. Sci. 179: 483-485. HARRIS G.P. 1976. Phytoplankton Ecology. C h a p m a n a n d Hall , N e w York. 384 p p . H A R T M A N N M. , MULLER P.J.. SUESS E. a n d V A N DER WEIJDEN C.H. 1973. Ox ida t i on of o rgan i c mat ter in recent marine sediments. Meteor Forsch. Reihe CI2: 74-86. HARTMANN M., MOLLER P.J., SUESS E. a n d V A N DER WEIJDEN C.H. 1976. Chemistry of Late Q u a t e r n a r y s e d i m e n t s a n d their interstit ial w a t e r s f r o m t h e N W A f r i c a n cont inenta l marg in : Meteor Forsch. Ergebnisse C(24): 1-67. H A S A N S.M. a n d HALL J.B. 1975. The phys i o l og i c a l f u n c t i o n of nitrate r e d u c t i o n in Clostridium perfringens. J. Gen. Microbiol. 87: 120-128. HATCHER P .G. . SPIKER E.C., SZEVERENYI N .M. a n d MAC I EL G.E. 1983. S e l e c t i v e preservat ion a n d origin of petroleum-forming a q u a t i c kerogen . Nat. 305:498-501. HEALEY F.P. a n d HENDZEL L.L. 1975. Effect of phosphorus de f i c i ency o n t w o a l g a e growing in chemostats . J. Phycol. 11:303-309. HEALEY F.P. a n d HENDZEL L.L. 1979. Indicators of phosphorus a n d n i t rogen de f i c i ency in five a l g a e in culture. Can. J. Fish. Aquat. Sci. 36: 1364-1369. HEALEY F.P. a n d HENDZEL L.L. 1980. Physio logica l indicators of nutrient de f i c i ency in lake phytoplankton. Can. J. Fish. Aquat. Sci. 37:442-453. HERBERT R.A., G U N N G . M . a n d BROWN C M . 1980. The phys io logy of nitrate dissimilating b a c t e r i a f rom the Tay Estuary. Proc. Royal Soc. Edinburgh 78B. 79-87. HERCZEG A.L. a n d HESSLEIN R.H. 1984 Determinat ion of h y d r o g e n ion c o n c e n t r a t i o n in sof twater lakes using c a r b o n d iox ide equi l ibr ia. Geochim. Cosmochim. A c t a 48: 837-846. H O F F M A N N M.R. 1977. Kinetics a n d m e c h a n i s m of ox ida t i on of h y d r o g e n sulfide by h y d r o g e n perox ide in a c i d i c solution. Environ. Sci. Technol. 11: 61-66. HOLDREN JR. G . C . a n d A R M S T R O N G D.E. 1986. Interstitial ion c o n c e n t r a t i o n s as a n i nd i c a to r of phosphorus re lease a n d minera l f o rmat ion in lake sed iments . In Sediments and Water Interactions. P.G. Sly e d . Spr inger-Ver lag, N e w York, p p 133-147. HOLMES G.S. 1981. The l imitation of a c c u r a t e "thin-film" X-ray f l uo r e s cence analysis of natural par t icu late matter: problems a n d solutions. Chem. Geol. 33: 333-353. HOLM-HANSEN O . 1972. The distr ibut ion a n d c h e m i c a l c o m p o s i t i o n of pa r t i cu l a t e mater ia l in mar ine a n d fresh waters. Mem. 1st. ital. Idrobiol. Suppl. 29: 37-51. HOLTAN H.. KAMP-NIELSEN L. a n d STUANES A . O . 1988. Phosphorus in soil , w a t e r a n d sed iment : a n overv iew. Hydrobiologia 170: 19-34. HOWARTH R.W. 1978. A rap id a n d prec ise m e t h o d for de te rmin ing sulfate in seawa te r , estuarine waters , a n d sediment pore waters. Limnol. Oceanogr. 23: 1066-1069. HOWARTH R.W. 1979. Pyrite: Its r ap id fo rmat ion in a salt marsh a n d its i m p o r t a n c e in e cosys tem metabo l i sm. Sci. 203: 49-51. HOWARTH R.W. a n d GIBLIN A . 1983. Sulfate r educ t i on in the salt marshes at S a p e l o Island, G e o r g i a . Limnol. Oceanogr. 28: 70-82. HOWARTH R.W., GIBLIN A. , G A L E J . , PETERSON B.J. a n d LUTHER III G.W. 1983. R e d u c e d sulfur c o m p o u n d s in t h e p o r e wa te r s of a N e w E n g l a n d salt marsh . In Environmental Biogeochemistry. R. Hal lberg e d . Eco l . Bull. (S tockholm) 35: 135-152. HOWARTH R.W. a n d J 0 R G E N S E N B.B. 1984. Format ion of ^S- labe l led e l e m e n t a l sulfur a n d pyrite in c o a s t a l mar ine sediments (Limfjorden a n d Kysing Fjord, Denmark ) dur ing short-term  xSOt r educ t ion measurements . Geochim. Cosmochim. Acta 48: 1807-1818. HOWARTH R.W. a n d M A R I N O R. 1984. Sulfate r e d u c t i o n in salt marshes , with s o m e c o m p a r i s o n s t o su l fa te r e d u c t i o n in m i c r o b i a l mats . In Microbial Mats: Stromatolites, p p 245-263. HOWARTH R.W. a n d MERKEL S. 1984. Pyrite fo rmat ion a n d the measu remen t of sulfate reduct ion in salt marsh sediments. Limnol. Oceanogr. 29: 598-608. HOWARTH R.W. a n d TEAL J . M . 1979. Sulfate r educ t i on in a N e w E n g l a n d salt marsh. Limnol. Oceanogr. 24:999-1013. HOWARTH R.W. a n d TEAL J . M . 1980. Energy f low in a salt marsh e cosys t em: the role of r e d u c e d inorganic sulfur c o m p o u n d s . Amer. Naturalist 116: 862-872. HURD D.C. 1972. Factors a f fect ing solution rate of b i ogen i c o p a l in seawater . Earth Planet. Sci. Lett. 15:41 M l 7. HUTCHINSON G.E. 1957. A Treatise on Limnology. I. Geography. Physics, and Chemistry. J o h n Wiley & Sons, Inc., N e w York, 1015 p p . H Y N D M A N R.D. 1976. H e a t f l ow m e a s u r e m e n t s in the inlets of southwes te rn British C o l u m b i a . J. Geophys. Res. 81:337-349. ISHAQ M. 1985. Hydro log ica l a n d mineral budge t i ng in Da l Lake. Ph.D. Thesis. University of Kashmir. Sr inagar. _ ISHAQ M. a n d KAUL V. 1988. C a l c i u m a n d magnes i um in Da l Lake , a h igh a l t i tude marl l ake in Kashmir Himalayas . Int. Revue zes. Hydrobiol. 73:431-439. J A C O B S L.A. 1984. M e t a l geochemis t ry in anox i c mar ine basins. Ph.D. Thesis. University of Wash ington . 217 p p . J A C O B S L.A. a n d EMERSON S. 1982. Trace me ta l solubility in a n anox i c fjord. Earth Planet. Sci. Lett. 60: 237-252. J A C O B S L.A., EMERSON S. a n d HUESTED S.S. 1987. T race m e t a l g e o c h e m i s t r y in the C a r i a c o Trench. Deep-Sea Res. 34: 965-981. J A C O B S L A . , EMERSON S. a n d SKEI J . 1985. The partit ioning a n d transport of metals across the O2/H2S in te r face in a pe rmanen t l y a n o x i c bas in ; F ramvaren Fjord, Norway . Geochim. Cosmochim. Acta 49:1433-1444. JENSEN T.E. 1968. E lectron m i c r o s c o p y of p o l y p h o s p h a t e bod i e s in a b lue-green a l g a , Nostoc pruniform. Arch. Microbiol. 62: 144-152. JONES J . G . , GARDENER S. a n d S IMON B.M. 1983. Bacter ia l r educ t ion of ferric iron in a stratified eutrophic lake. J. Gen. Microbiol. 129:131-139. J0RGENSEN B.B. 1977. Bacter ia l sulfate reduct ion within r e d u c e d micron iches of oxid ized sediments. Mar. Biol. 41 : 7-17. J0RGENSEN B.B. 1982. Mineral izat ion of o rgan i c matter in the sea b e d - the role of sulfate reduct ion. Nat. 296:643-645. J0RGENSEN B.B., B A N G M. a n d BLACKBURN T.H. 1990a. A n a e r o b i c minera l izat ion in mar ine sediments from the Baltic Sea-North Sea transition. Mar. Ecol. 59: 39-54. J0RGENSEN B.B. a n d C O H E N Y. 1977. Solar Lake (Sinai). 5. The sulfur c y c l e of ben th i c c y a n o b a c t e r i a l mats. Limnol. Oceanogr. 22: 657-666. J0RGENSEN B.B.. FOSSING H.. WIRSEN C O . a n d J A N N A S C H H.W. 1990b. Sulfide ox idat ion in t he a n o x i c B lack S e a c h e m o c l i n e . Deep-Sea Res. in press. J0RGENSEN B.B. a n d S0RENSEN J . 1985. Seasona l cyc les of 0 2 , N0 3 " a n d SO4 r educ t ion in estuar ine sediments : t h e s ign i f i cance of a n NO3' r e d u c t i o n m a x i m u m in spring. Mar. Ecol. 24: 65-74. K A G A W A H.. TOGASHI M. . a n d K A W A B A T A Z. 1988. C o m p a r i s o n of P. C a a n d M g c o n t e n t s of p h y t o p l a n k t o n b e t w e e n the h e a d s of t w o river reservoirs wi th different phosphorus loadings. Verh. Internal Verein. Limnol. 23:1022-1027. KAMP-NEILSEN L. 1974. Wa te r e x c h a n g e of p h o s p h a t e a n d other ions in und is turbed sed iment cores a n d factors a f f ec t ing the e x c h a n g e rates. Arch. Hydrobiol. 73: 213-237. K A M U R A T., TAKAI Y. a n d ISHIKAWA K. 1963. M i c rob i a l r educ t i on m e c h a n i s m of ferric iron in p a d d y soils I. So/7 Sci. Plant Nutr. (Tokyo) 9: 171 -175. ' K A P L A N I.R., EMERY K.O. a n d RITTENBERG S.C. 1963. The distr ibut ion a n d i so top ic a b u n d a n c e o f sulphur in r e c e n t mar ine sed iments off sou thern Ca l i f o rn i a . Geochim. Cosmochim. Acta 27: 297-331. KATO K. 1969. Behav ior of dissolved sil ica in c o n n e c t i o n with ox idat ion-reduct ion c y c l e in lake water. Geochem. J. 3:87-97. KELTS K. a n d HSU K.J. 1978. Freshwater c a r b o n a t e sed imenta t ion . In Lakes: Chemistry. Geology, Physics. A . Lerman e d . p p 295-323. KESSICK M.A. a n d M O R G A N J.J. 1975. M e c h a n i s m of auto-ox idat ion of m a n g a n e s e in a q u e o u s solution. Environ. Sci. Technol. 9: 157-159. KING G . M . 1988. Patterns of sulfate reduct ion a n d the sulfur c y c l e in a South Ca ro l i na salt marsh. Limnol. Oceanogr. 33:376-390. KITANO Y., O K U M U R A M. a n d IDOGAKI M. 1978. Up take of p h o s p h a t e ions by c a l c i u m c a r b o n a t e . Geochem. J. 12: 29-37. KITTREDGE J.S. a n d ROBERTS E. 1969. A carbon-phosphorus b o n d in nature. Sci. 164: 37-42. K J ENSMO J . 1988. Post-g lac ia l sed iments a n d the s t a g n a t i o n history of t h e iron-meromic t i c Lake Skjennungen, Eastern Norway. Arch. Hydrobiol. 113:481-499. KOIKE I. a n d HATTORI A . 1978. Denitr i f icat ion a n d a m m o n i a f o rma t i on in a n a e r o b i c c o a s t a l sediments. Appl. Environ. Microbiol. 35: 278-282. KOROLEFF F. 1976. De te rm ina t i on of nutrients. In Methods of Seawater Analysis. K. Grasshof e d . Ve r l ag C h e m i e , N e w York, p p 126-133. K R O M M.D. a n d BERNER R.A. 1980. A d s o r p t i o n of p h o s p h a t e in a n o x i c ma r i ne sediments. Limnol. Oceanogr. 25: 797-806. K R O M M.D. a n d SHOLKOVITZ E.R. 1977. Na ture a n d reac t ions of d i sso lved o r g a n i c mat ter in the interstitial waters of mar ine sediments. Geochim. Cosmochim. Acta 41: 1565-1573. LALOU C . 1957. Studies of b a c t e r i a l p rec ip i ta t ion of c a r b o n a t e s in s e a wate r . J. Sed. Petrol. 27: 190-195. LANDING W.B. a n d LEWIS B.L 1990. The rmodynamic m o d e l i n g of t r a c e m e t a l spec i a t i on in the B lack Sea . Deep-Sea Res. in press. LAND ING W.B. a n d WESTERLUND S. 1988. The solution chemistry of iron(ll) in F ramvaren fjord. Mar. Chem. 23:329-343. LEAN D.R. 1984. M e t a b o l i c indicators for phosphorus l imitation. Int. Ver. Theor. Angew. Limnol. Verh. 22:211-213. LEAN D.R. a n d WHITE E. 1983. C h e m i c a l a n d r ad io t r ace r m e a s u r e m e n t of p h o s p h a t e up take by lake phytoplankton. C a n . J. Fish. Aquat. Sci. 38:224-232. LEE G.F.. JONES R.A. a n d RAST W. 1980. Avai labi l i ty of phosphorus t o phy top lank ton a n d its impl icat ions for phosphorus m a n a g e m e n t strategies. In Phosphorus Strategies for Lakes. R.C. Loehr, C.S. Mart in a n d W. Rast eds. A n n Arbor Sci . . A n n Arbor, p p 259-308. LEVENTHAL J.S. 1983. A n interpretat ion of c a r b o n a n d sulphur relationships in Black S e a sed iments as indicators of env i ronments of depos i t ion . Geochim. Cosmochim. Acta 47:133-137. LEVIN G.V. a n d SHAPIRO J . 1965. M e t a b o l i c u p t a k e of phosphorus by waste-water organisms. J. Wat. Pollut. Control Fed. 37: 800-821. LEVINE S.N. a n d SCHINDLER D.W. 1980. R a d i o c h e m i c a l analysis of o r t h o p h o s p h a t e concen t ra t ions a n d seasona l c h a n g e s in the flux of o r thophospha te to seston in two C a n a d i a n Shield lakes. Can. J. Fish. Aquat. Sci. 37:479-487. LEWIN R.A. 1962. Physiology and Biochemistry of Algae. A c a d e m i c Press, N e w York, 929 p p . LI W.C . , A R M S T R O N G D.E., WILLIAMS J .D.H. , HARRIS R.F. a n d SYERS J.K. 1972. Ra te a n d extent of inorgan ic p h o s p h a t e e x c h a n g e in lake sed iments . Proc. Soil Sci. Soc. Amer. 36: 279-285. LI Y.H. a n d G R E G O R Y S. 1974. Diffusion of ions in sea wa te r a n d in deep-sea sediments. Geochim. Cosmochim. ActaZS: 703-714. LIJKLEMA L. 1980. Interact ion of o r thophospha te with iron(lll) a n d a luminum hydroxides. Environ. Sci. Tech. 14:537-541. LI JKLEMA L , GELENCSER P. a n d SZILAGYI F. 1983. Sed iments a n d sed iment-wa te r in teract ion. In Eutrophication of Shallow Lakes: Modelling and Management. L. Som l yody e d . Internat. Inst, for A p p l . Systems A n a l . L axenbu rg , Austr ia, p p 81-100. LODER T.C., LYONS W.B., MURRAY S. a n d MCGUINNESS H.D. 1978. Si l icate in anox i c pore waters a n d oxidat ion effects during sampl ing. Nat. 273:373-374. LOFGREN S. a n d RYDING S.O. 1985a. A p a t i t e ion ic p r o d u c t s in d i f ferent eu t roph i c sediments. Verh. Internat. Verein. Limnol. 22:3323-3328. LOFGREN S. a n d RYDING S.O. 1985b. A p a t i t e solubil ity a n d m i c r o b i a l act iv i t ies as regulators of internal l o a d i n g in sha l low, eu t roph ic lakes. Verh. Internat. Verein. Limnol. 22:3329-3334. LORD III C. J . a n d C H U R C H T.M. 1983. The geochemis t r y of salt marshes: Sed imentary ion di f fus ion, sulfate r e d u c t i o n , a n d pyrit ization. Geochim. Cosmochim. Acta47: 1381-1391. LOVE L.G. 1971. Early d i a g e n e t i c po l y f r ambo ida l pyrite, pr imary a n d r edepos i t ed , f rom the W e n l o c k i a n D e n b i g h Grit g roup , C o n w a y , North Wales , UK. J. Sed. Petrol. 41 : 1038-1044. LOVE L.G. a n d AMSTUTZ G . C . 1966. Rev iew of m i c roscop i c pyrite. Fortschr. Miner. 43: 273-309. LOVLEY D.R. a n d PHILLIPS E.J.P. 1988 N o v e l m o d e of m i c rob i a l e n e r g y m e t a b o l i s m : O r g a n i c c a r b o n o x i d a t i o n c o u p l e d t o d iss imi latory r e d u c t i o n of iron or m a n g a n e s e . Appl. Environ. Microbiol. 54: 1472-1480. LUTHER 111 G .W. 1987. Pyrite o x i d a t i o n a n d r e d u c t i o n : m o l e c u l a r o rb i ta l t heo r y considerat ions. Geochim. Cosmochim. Acta 51: 3193-3199. LUTHER III G.W. 1990a. The frontier-molecular-orbital theory a p p r o a c h in g e o c h e m i c a l processes. In Aquatic Chemical Kinetics, e d . W. Stumm. p p 173-198. LUTHER III G.W., C A T A L A N O G. , DE LANGE G . a n d WOITTIEZ J.R.W. 1990b. R e d u c e d sulfur in the hypersal ine anox i c basins of the Med i t e r r anean Sea . Mar. Chem. in press. LUTHER III G.W., C H U R C H T.M., GIBLIN A.E. a n d HOWARTH R.W. 1986a. S p e c i a t i o n of d isso lved sulfur in salt marshes by p o l a r o g r a p h i c me thods . In Organic Marine Geochemistry. M . Sohn e d . A C S Symposium Series. Vo l . 305. p p . 339-355. LUTHER III G.W.. C H U R C H T.M. a n d POWELL D. 1990c. Sulfur s p e c i a t i o n a n d su lph ide ox idat ion in the wa te r c o l u m n of the B lack Sea . Deep-Sea Res. in press. LUTHER III G.W., C H U R C H T.M., SCUDLARK J.R. a n d C O S M A N M. 1986b. Inorganic a n d o rgan i c sulfur c yc l i ng in salt-marsh pore waters. Sci. 232: 746-749. LUTHER III G.W., GIBLIN A. , HOWARTH R.W. a n d RYANS R.A. 1982. Pyrite a n d ox id ized iron m ine ra l p h a s e s f o r m e d f rom pyrite o x i d a t i o n in salt marsh a n d es tuar ine sediments. Geochim. Cosmochim. Acta 46: 2665-2669. LUTHER III G.W., GIBLIN A.E. a n d V A R S O L O N A R. 1985. Po l a rog raph i c analysis of sulfur spec ies in mar ine porewaters. Limnol. Oceanogr. 30: 727-736. LYONS D. a n d NICKLESS G . 1968. The lower oxy-ac ids of sulfur. In Inorganic Sulfur Chemistry. G . Nickless e d . Elsevier, Ams te rdam, p p 509-533. LYONS W.B. a n d GAUDETTE H.E. 1979. Sulfate reduct ion a n d the nature of o rgan i c matter in estuarine sediments. Org. Geochem. 1: 151-155. M A C F A R L A N E G.T. a n d HERBERT R.A. 1982. Nitrate dissimilation by Vibrio spp . i so la ted from estuarine sediments. J. Gen. Microbiol. 128: 2463-2468. M A C L E O D R.A. a n d ONOFREY E. 1956. Nutrition a n d me tabo l i sm of mar ine b a c t e r i a II. Observa t ions o n the re lat ion of s e a w a t e r to the g rowth of mar ine b a c t e r i a . J. Bact. 71:661-667. M A C L E O D R.A., ONOFREY E. a n d NORRIS M.E. 1954. Nutrition a n d me tabo l i sm of mar ine bac t e r i a I. Survey of nutritional requirements. J. Bact. 68:680-686. M A L O N E P.H.G. a n d TOWE K M 1970. M i c rob ia l c a r b o n a t e a n d p h o s p h a t e prec ip i tates from seawa te r cultures. Mar. Geol. 9:301-309. MANHE IM FT. 1974. Studies o n mar ine interstitial waters with spec i a l r e fe rence to mar ine drilling. Ph.D. Thesis. University of S tockholm. 378 p p . MANHE IM F.. ROWE G.T. a n d JIPA D. 1975. Mar ine phosphor i te format ion off Peru. J. Sed. Petrol. 45:243-251. MARA IS G.V.R. . LOEWENTHAL R.E. a n d SIEBRITZ IP. 1983. Obse r va t i ons suppor t i ng phosphorus r emova l b y b io l og i ca l excess u p t a k e - a review. Wat. Sci. Tech. 15: 15-41. MARTENS C.S.. BERNER R.A. a n d ROSENFELD J.K. 1978. Interstitial w a t e r chemist ry of a n o x i c Long Island S o u n d sed iments 2. Nutrient r egene ra t i on a n d p h o s p h a t e remova l . Limnol. Oceanogr. 23:605-617. MARTENS C.S. a n d HARRISS R.C. 1970. Inhibition of apa t i t e p rec ip i t a t ion in the mar ine env i ronment by m a g n e s i u m ions. Geochim. Cosmochim. Acta 34: 621-625. MATHEWS W.H. 1962. Ba thymet ry of Powe l l Lake . British C o l u m b i a . Inst. O c e a n o g r . University of British C o l u m b i a Ms. Rept. No . 13. MATHEWS W.H., FYLES J . G . a n d NASMITH H.W. 1970. Pos tg l ac i a l crusta l m o v e m e n t s in southwestern British C o l u m b i a a n d a d j a c e n t Wash ington State. Can. J. Earth Sci. 7. 690-702. M C C A F F R E Y R.J.. MEYERS A . C . . DAVEY E.. MORRISON G. , BENDER M.. LUEDTKE N.. CULLEN D., FROELICH P. a n d KLINKHAMMER G . 1980 The relationship b e t w e e n pore wa te r chemistry a n d ben th i c fluxes of nutrients a n d m a n g a n e s e in Nar raganset t Bay. Rhode Island. Limnol. Oceanogr. 25: 31-44. M C C A R T H Y J.J. 1981. The kinetics of nutrient utilization. Can. Bull. Fish. Aquat. Sci. 210: 211-233. MERILAINEN J . 1969. Distr ibution of d i a t o m frustules in r e cen t sed imen ts of s o m e meromic t i c lakes. Mitt. Internat. Verein. Limnol. 17: 186-192. MOPPER K. a n d KIEBER D.J. 1988. Distribution a n d up take of low mo lecu l a r we ight o rgan i c c o m p o u n d s in the w a t e r c o l u m n of the B lack Sea . EOS, Transactions of the American Geophysical Union 69: 1240 MOREL F.M.M. 1983. Principles of Aquatic Chemistry. Wi ley-lntersc ience, N e w York. 446 p p . M O R G A N J.J. 1967. C h e m i c a l equi l ibr ia a n d kinetic propert ies of m a n g a n e s e in natural wafers . In Principles and Applications of Water Chemistry. S.D. Faust a n d J .V. Hunter eds . Wiley. M O R G A N J.J. a n d STUMM W. 1964. Co l l o id-chemica l propert ies of m a n g a n e s e d iox ide . J. Colloid Sci. 19:347-359. MORITA R.Y. 1980. C a l c i t e prec ip i tat ion by mar ine bac te r i a . Geomicrobiol. J. 2. 63-81. MORRIS I.. GLOVER H.E.. KAPLAN W.A.. KELLY D.P. a n d WEI G HTM A N A . L 1985. M i c rob ia l activity In the C a r i a c o Trench. Microbios 42:133-144. MORSE J.W. a n d C O O K N. 1978. The distribution a n d form of phosphorus in North At lant ic O c e a n d e e p - s e a a n d con t inen ta l s lope sediments. Limnol. Oceanogr. 23: 825-830. ' MORSE J.W. a n d CORNWELL J .C . 1987. Analysis a n d distribution of iron sulfide minerals in . recent anox i c mar ine sediments. Mar. Chem. 22: 55-69. MORSE J.W., MILLERO F.J.. CORNWELL J . C . a n d RICKARD D. 1987. The chemistry of the ' h y d r o g e n sulf ide a n d iron sulf ide systems in na tura l waters . Earth-Science Reviews 24: 1-42. MORTIMER C.E. 1979. Chemistry. A Conceptual Approach. 4th e d . D. V a n Nostrand C o . . Toronto. 815 p p . MORTIMER C.H. 1941. The e x c h a n g e of dissolved substances b e t w e e n m u d a n d wa te r in lakes (Parts I a n d II). J. Ecol. 29:280-329. MORTIMER C.H. 1942. The e x c h a n g e of dissolved substances b e t w e e n m u d a n d wa te r in lakes (Parts III. IV, summary, a n d references). J. Ecol. 30: 147-201. MOSES C O . , NORDSTROM D.K., H E R M A N J.S. a n d MILLS A.L. 1987. A q u e o u s pyrite ox ida t ion by dissolved o x y g e n a n d by ferric iron. Geochim. Cosmochim. Acta 51: 1561-1571. MURPHY J . a n d RILEY J.P. 1962. A mod i f i ed single solution m e t h o d for the determinat ion of phospha te in natural waters. Anal. Chim. Acta 27:31-36. MURPHY T.P., HALL K.J. a n d YESAKE I. 1983. Coprec ip i t a t i on of phospha t e with ca l c i t e in a naturally eut rophic lake. Limnol. Oceanogr. 28: 58-69. MURRAY J.W., GRUNDMANIS V. a n d SMETHIE JR. W.M. 1978. Interstitial wa te r chemistry in the sediments of Saan i ch Inlet. Geochim. Cosmochim. Acta 42: 1011-1026. MYERS C.R. a n d NEALSON K.H. 1988. Bacter ia l m a n g a n e s e reduc t ion a n d growth with m a n g a n e s e ox ide as the sole e l ec t ron a c c e p t o r . Sci. 240: 1319-1321. NAES K., SKEI J . M . a n d W A S S M A N N P. 1988. Total pa r t i cu l a t e a n d o r g a n i c fluxes in anox i c Framvaren waters. Mar. Chem. 23:257-268. NISSENBAUM A . , BAEDECKER M.J. a n d KAPLAN I.R. 1972. Studies o n d isso lved o r g a n i c mat te r f rom interstitial wa te r of a r educ ing mar ine fjord. Adv. in Org. Geochem. 1971:427-440. NISSENBAUM A . a n d K A P L A N I.R. 1972. C h e m i c a l a n d isotopic e v i d e n c e for the in situ origin of mar ine humic substances. Limnol. Oceanogr. 17: 570-582. NORTHCOTE T.G. a n d HALL K.J. 1983. L imno log i c a l contrasts a n d a n o m a l i e s in t w o a d j a c e n t saline lakes. Hydrobiologia 105: 179-194. NORTHCOTE T.G. a n d J O H N S O N W.E. 1964. O c c u r r e n c e a n d distribution of s e a wa te r in Sak inaw Lake. British C o l u m b i a . J. Fish. Res. Board Can. 21:1321-1324. NORVELL W.A. 1974. Insolubilization of inorgan ic p h o s p h a t e by a n o x i c lake sediments. Proc. Soil Sci. Amer. 38:441-445. NR IAGU J .O . 1972. Stability of v iv ianite a n d ion-pair fo rmat ion in the system Fe 3(PCM) 2-H3PO4-H2O. Geochim. Cosmochim. Acta 36:459-470. ' NR IAGU J . O . , C O K E R R.D. a n d KEMP A.L.W. 1979. Th iosu l fa te , p o l y t h i o n a t e a n d rhodanese act iv i ty in Lakes Erie a n d Ontar io sediments . Limnol. Oceanogr. 24; 383-389. NRIAGU J .O . a n d DELL C . 1974. D i agene t i c format ion of iron phospha tes in recent lake sediments. Am. Mineral. 59: 934-946. O R E M W . M . , HATCHER P.G.. SPIKER E.C.. SZEVERENYI N .M. a n d MAC IEL G.E. 1986. Dissolved o r g a n i c mat te r in anox i c po re waters f rom M a n g r o v e Lake , Be rmuda . Geochim. Cosmochim. Acta 50:609-618. O R E M L A N D R.S., CLOERN J.E., SOFER Z., SMITH R.L, CULBERTSON C.W., ZEHR J . , MILLER L, C O L E B., HARVEY R., IVERSEN N., KLUG M „ DES MARAIS D.J. a n d RAU G . 1988. M i c r o b i a l a n d b i o g e o c h e m i c a l p rocesses in Big S o d a L a k e , N e v a d a . In Lacustrine Petroleum Source Rocks. A. J . Fleet, K. Kelts a n d M.R. Ta lbot eds. G e o l . Soc . Spec . Publ. No. 40. p p 59-75. OSBORN D.W. a n d NICHOLLS H.A. 1978. Opt imisat ion of the a c t i v a t e d s ludge process for the b io l og i ca l r emova l of phosphorus. Prog. Wat. Tech. 10: 261-277. OSTROFF R. a n d HENRY B.S. 1939. The uti l ization of n i t rogen c o m p o u n d s by mar ine bac te r ia . J. CellComp. Physiol. 13:353-371. OTSUKI A . a n d H A N Y A T . 1972a. P roduct ion of dissolved o rgan i c mat ter f rom d e a d g reen a lga l cells. I. A e r o b i c mic rob ia l decompos i t i on . Limnol. Oceanogr. 17: 248-257. OTSUKI A . a n d H A N Y A T . 1972b. P roduct ion of dissolved o rgan i c mat ter f rom d e a d g reen a l g a l cells. II. A n a e r o b i c m ic rob ia l d e c o m p o s i t i o n . Limnol. Oceanogr. 17: 258-264. OTSUKI A . a n d WETZEL R.G. 1972. Coprec ip i t a t i on of phospha t e with c a r b o n a t e s in a marl lake. Limnol. Oceanogr. 17: 763-766. OZRETICH R.J. 1976. A n invest igat ion of the transition from a e r o b i c to nitrate respiration in mar ine b a c t e r i a in cont inuous culture. Ph.D. Thesis. University of Wash ington. PALACHE C .H . . BERMAN H. a n d FRONDEL C . 1952. In The System of Mineralogy. J.J. D a n a a n d E.S. D a n a eds. Wiley. Vo l . 1: 207-208. PERRY M.J. 1976. P h o s p h a t e uti l ization b y a n o c e a n i c d i a t o m in phosphorus-l imited c h e m o s t a t cu l ture a n d in the o l igo t roph ic waters of t he cen t ra l North Pac i f i c . Limnol. Oceanogr. 21:88-107. PESCHANSKI D. a n d VALENSI M .G . 1949. Cont r ibu t ion a I ' e lec t roch imie des solutions aqueuses d e polysulfures. J. Chim. Phys. 46:602-619. PFENNIG N. a n d WIDDEL F. 1982. The b a c t e r i a of the sulphur c y c l e . Phil. Trans. R. Soc. Lord. B298:427-435. P ICKERING T.L a n d TOBOLSKY A .V . 1972. Inorganic a n d o r g a n i c sulfides. In Sulfur in Organic and Inorganic Chemistry. Vo l . 3. A . Senning e d . M a r c e l Dekker , N e w York, p p 19-38. ' PINGITORE JR. N.E., EASTMAN M.P., SANDIGE M. . O D E M K. a n d FREIHA B. 1988. The c o p r e c i p i t a t i o n of manganese ( l l ) w i th c a l c i t e : a n e x p e r i m e n t a l study. Mar. Chem.25:107-120. PLANAS D. 1978. Phosphorus u p t a k e rates in p l ank ton i c commun i t i e s r e l a t ed to light gradient . Int. Ver. Theor. Angew. Limnol. Verh. 20: 2731-2736. POCKL INGTON R. a n d LEONARD J .D. 1979. Terrigenous o rgan i c matter in sediments of the St. L a w r e n c e estuary a n d the S a g u e n a y fjord. J. Fish. Res. Board Can. 36: 1250-1255. P O M E R O Y L.R., SMITH E.E. a n d GRANT C M . 1965. The e x c h a n g e of p h o s p h a t e b e t w e e n estuarine wa te r a n d sediments. Limnol. Oceanogr. 10: 167-172. P O N N A M P E R U M A F.N. 1972. The chemistry of s u b m e r g e d soils. Adv. Agron. 24: 29-96. POSTMA D. 1982. Pyrite a n d siderite f o rma t i on in b rack i sh a n d f reshwater s w a m p sediments. Am. J. Sci. 282: 1151-1183. PRESLEY B.J. a n d K A P L A N I.R. 1968. C h a n g e s in d i s so l ved su l fa te , c a l c i u m , a n d c a r b o n a t e f r o m interst i t ia l w a t e r of near-shore s e d i m e n t s . Geochim. Cosmochim. Acta 32:1037-1048. PRICE N.B. 1976. C h e m i c a l d iagenes is in sediments. In Chemical Oceanography. Vol.6 J.P. Riley a n d R. Ches ter eds. A c a d e m i c Press, N e w York, p p 1-58. PYZIK A . J . a n d S O M M E R S.E. 1981. S e d i m e n t a r y iron monosu l f i des : k inet ics a n d m e c h a n i s m of format ion. Geochim. Cosmochim. Acta 45: 687-698. RAISWELL R. 1982. Pyrite texture, isotopic compos i t i on a n d the avai labi l i ty of iron. Am. J. Sci. 282: 1244-1263. RAISWELL R. a n d PLANT J . 1980. The incorpora t ion of t r a c e e lements into pyrite dur ing diagenesis of B lack Shales, Yorkshire, Eng land. Econ. Geol. 75:684-699. REDFIELD A . C . , KETCHUM B.H. a n d RICHARDS F.A. 1963. The inf luence of organisms o n the compos i t i on of seawater . In The Sea. Vo l . 2. M.N. Hill e d . Wiley, London , p p 26-77. REPETA D.J, S IMPSON D.J., J 0 R G E N S E N B.B. a n d J A N N A S C H H.W. 1989. E v i d e n c e for a n o x y g e n i c photosynthesis f rom the distribution of bac te r ioch lo rophy l l s in the Black Sea. Nat. 342:69-72. RHEE G.-Y. 1973. A con t inuous cul ture study of p h o s p h a t e u p t a k e , g rowth rate a n d po l yphospha t e in Scenedesmus sp. J. Phycol. 9: 495-506. RHEE G.-Y. 1978. Effects of N:P a t o m i c ratios a n d nitrate l imitation o n a l g a l g rowth , ce l l compos i t i on , a n d nitrate uptake . Limnol. Oceanogr. 23: 10-25. RICHARDS F.A. 1965. A n o x i c basins a n d fjords. In Chemical Oceanography. Vo l . 2. J.P. Riley a n d G . Skirrow eds. A c a d e m i c Press, N e w York, p p 611-645. R ICHARDS F.A., CL INE J . D . , B R O E N K A W W.W. a n d ATK INSON L. 1965. S o m e c o n s e q u e n c e s of the d e c o m p o s i t i o n of o r g a n i c ma t t e r in Lake- Nit inat, a n anox i c fjord. Limnol. Oceanogr. 10. R185-R201. RICHERT S.A., T S A N G P.K.S. a n d SAWYER D.T. 1988. L i g a n d - c e n t e r e d ox ida t i on of manganese ( l l ) comp lexes . Inorg. Chem. 27: 1814-1818. R ICKARD D.T. 1969. The chemis t ry of iron su lph ide f o rma t i on a t l ow tempera tu res . Stockholm Contributions to Geology 20: 67-95. RICKARD D.T. 1974. Kinetics a n d m e c h a n i s m of the sulfidation of goeth i te . Am. J. Sci. 274. 941-952. R ICKARD D. T. 1975. Kinetics a n d m e c h a n i s m of pyrite fo rmat ion at low temperatures . Am. J. Sci. 275: 636-652. RIGLER F.H. 1956. A t r ace r study of the phosphorus c y c l e in lake water . Ecology 37: 550-562. RITTENBERG E.C., EMERY K.O. a n d ORR W.L 1955. Regenera t ion of nutrients in sed iments of mar ine basins. Deep-Sea Res. 3: 23-45. ROBERTS W.M.B. , WALKER A.L. a n d B U C H A N A N A.S. 1969. The chemis t r y of pyr i te fo rmat ion in a q u e o u s solution a n d its relat ion to the depos i t iona l env i ronments . Mineral. Deposita4:18-29. ROBIE R.A., H E M I N G W A Y B.S. a n d FISHER J.R. 1978. T h e r m o d y n a m i c proper t ies of minerals a n d re l a ted substances at 298.15 K a n d 1 ba r (10 s Pascals) pressure a n d at higher temperatures. U. S. Geologic Surv. Bull. No. 1452.457 p p . RODHE W. 1948. Environmental requirements of freshwater p lankton a l g a e . Exper imental studies in the e c o l o g y of p lank ton a l g a e . Exper imenta l studies in the e c o l o g y of phy top lankton . Symol. Bot. Upsalien. 10(1). 149 p p . ROSS D.A. a n d DEGENS E.T. 1974. Recen t sediments of the B lack Sea . In The Black Sea -Geology, Chemistry and Biology. E.T. D e g e n s a n d D.A. Ross eds . Am. Assoc. Pet. Geol. Mem. Vo l . 20: 183-199. ROWE G.T. a n d HOWARTH R.W. 1985. Early d iagenes is of o r g a n i c mat te r in sed iments off the coas t of Peru. Deep-Sea Res. 32:43-55. S A K S H A U G E., ADRESEN K., MYKLESTAD S. a n d OLSEN Y. 1983. Nutr ient status of phy top l ank ton communi t i es in No rweg i an waters (mar ine, brackish a n d fresh) as r e v e a l e d by their c h e m i c a l compos i t ion . J. Plankton Res. 5: 175-196. SANDERSON B., PERRY K. a n d PEDERSEN T. 1986. Ver t i ca l diffusion in me rom i c t i c Powel l Lake , British C o l u m b i a . J. Geophys. Res. 91: 7647-7655. SCHIFF S.L a n d ANDERSON R.F. 1987. L imnocorra l studies of c h e m i c a l a n d b i o l og i c a l a c i d neutral izat ion in t w o freshwater lakes. C a n . J. Fish. Aquat. Sci. 44 (suppl . l ) : 173-187. SCHINDLER D.W. 1977. Evolution of phosphorus limitation in lakes. Sci. 195: 260-262. SCHIPPEL F.A., HALLBERG R.O. a n d O D E N S. 1973. Phosphate e x c h a n g e a t the sediment-wa te r interface. OikosSuppl. 15: 64-67. S C H O O N E N M.A.A. a n d BARNES H.L. 1988. A n approx imat ion of the s e c o n d dissociat ion constant for H2S. Geochim. Cosmochim. Acta 52: 649-654. S C H W A R Z E N B A C H G . a n d FISCHER A. 1960. Die a c i d i t a t d e r su i f ane u n d d i e z u s a m m e n s e t z u n g wasser ige r po l ysu l f id losungen . Helvetica Chem. Acta 5: 1365-1390 SHAPIRO J . 1967. I n d u c e d rap id re lease a n d up take of p h o s p h a t e by microorganisms. Sci. 155: 1269-1271. SHERR B.F., SHERR E.B. a n d B E R M A N T. 1982. D e c o m p o s i t i o n of o r g a n i c detritus: A se lect ive role for microf lage l la te p ro tozoa . Limnol. Oceanogr. 27: 765-769. SHOLKOVITZ E. 1973. Interstitial wa te r chemistry of the Santa Ba rba ra Basin sediments . Geochim. Cosmochim. Acta 37:2043-2073. SHOLKOVITZ E. 1976. F loccu la t ion of d issolved o rgan i c a n d inorgan ic mat te r dur ing the mixing of river wa te r a n d seawater . Geochim. Cosmochim. Acta 40: 831-845. SHUKLA S.S., SYERS J.K.. WILLIAMS J .D .H . . A R M S T R O N G D.E. a n d HARRIS R.F. 1971. Sorption of inorgan ic p h o s p h a t e by lake sediments. Proc. Soil Sci. Soc. Amer. 35: 244-249. SEVER R. 1962. Sil ica solubility, 0-200°C, a n d the d iagenesis of silicious sediments. J. Geol. 70:127-150. SKEI J . M . 1988. Format ion of f r a m b o i d a l iron sulfide in the wa te r of a pe rmanent l y anox i c fjord - Framvaren, South Norway. Mar. Chem. 23:345-52. SKERMAN T.M. 1963. Nutrit ional patterns in mar ine bac t e r i a l popu la t ions . In Symposium on Marine Microbiology. C .H. O p p e n h e i m e r e d . Thomas, Springfield, p p 685-698. SKYRING G.W. a n d LUPTON F.S. 1984. A n a e r o b i c m i c rob i a l p rocesses in per i t ida l a n d subt ida l sed iments of Hame l in Poo l (Shark Bay, Western Austral ia) . Ann. Rep., Baas Becking Geobiological Lab. p p 3-12. SMITH R.M. a n d MARTELL A.E. 1976. Critical Stability Constants. Vol. 4. Inorganic Complexes. P l enum Press, N e w York. 257 p p . S0RENSEN J . 1978. C a p a c i t y for denitr i f icat ion a n d reduc t ion of nitrate to a m m o n i a in a coas t a l mar ine sediment . Appl. Environ. Microbiol. 35: 301-305. S0RENSEN J . 1982. Reduc t i on of ferric iron in a n a e r o b i c mar ine sediments a n d interact ion with reduct ion of nitrate a n d sulfate. Appl. Environ. Microbiol. 43:319-324. S0RENSEN J . 1987. Nitrate r educ t ion in mar ine sediment : Pa thways a n d interact ion with iron a n d sulfur cyc l ing . Geomicrobiol. J. 5:401-421. S T A M M H.H. a n d KOHLSCHUTTER H.W. 1965. Sorpt ion of p h o s p h a t e ions on iron(lll) hydroxide. J. Inorg. Nucl. Chem. 27:2103-2108. STAUFFER R.E. 1986. L i nkage b e t w e e n t h e phosphorus a n d s i l i ca c y c l e s in Lake M e n d o t a . Wisconsin. Wat. Res. 20: 597-609. STIRLING H.P. a n d W O R M A L D A.P. 1977. Phosphorus sed iment in te rac t ion in Tolo a n d L a n d Harbours , H o n g K o n g , a n d its role in estuar ine phosphorus avai labi l i ty . Estuahne Coastal Mar. Sci. 5: 631-642. STONE A T . a n d M O R G A N J.J. 1984a. Reduc t i on a n d dissolution of manganese ( l l l ) a n d manganese ( IV ) oxides by organics : 1. Reac t i on with hyd roqu inone . Environ. Sci. Tech. 18:450-456. STONE A T . a n d M O R G A N J.J. 1984b. Reduc t i on a n d dissolution of manganese ( l l l ) a n d manganese ( IV ) oxides by organ ics : 1. Survey of react iv i ty of organ ics . Environ. Sci. Tech. 18:617-624. STRICKLAND J .D.H. a n d PARSONS T.R. 1972. Determinat ion of reac t i ve phosphorus. In A Practical Handbook of Seawater Analysis. Fish. Res. Boa rd C a n . Bull. 167. p p 49-52. STUMM W. 1973. S ign i f i cance of phosphorus in lakes a n d c o a s t a l w a t e r sed iments a n d benthos. Wat. Res7: 131-144. STUMM W. a n d LECKIE J . O . 1970. Phospha te e x c h a n g e with sed iments ; its role in the product iv i ty of sur face waters. In Adv. Water Pollut. Res. Proc. Fifth Int. Conf. Vo l . 2. part III p p . 26/1 -26/16. STUMM W. a n d M O R G A N J.J . 1981. Aquatic Chemistry. 2nd e d . J . Wiley & Sons, N e w York. 780 pp . STYAN W.B. 1976. P lankton a n d fat ty a c i d d iagenes is in a fjord l ake , British C o l u m b i a . Unpubl . B.Sc. Thesis. Univ. British C o l u m b i a . 55 p p . SUESS E. 1970. Interact ion of o r g a n i c c o m p o u n d s with c a l c i u m c a r b o n a t e . I. Assoc ia t ion p h e n o m e n a a n d g e o c h e m i c a l impl icat ions . Geochim. Cosmochim. Acta 34: 157-168. SUESS E. 1976. Nutrients nea r the depos i t iona l inter face . In The Benthic Boundary Layer. I.N. M c C a v e e d . P lenum, p p 57-79. SUESS E. 1979. Minera l phases f o r m e d in a n o x i c sediments by mic rob ia l d e c o m p o s i t i o n of o rgan i c matter. Geochim. Cosmochim. Acta 43:339-352. SUNG W. a n d M O R G A N J.J. 1981. Ox idat i ve remova l of Mn(ll) f rom solution c a t a l y z e d by the Y-FeOOH ( lep idocroc i te ) surface. Geochim. Cosmochim. Acta 45: 2377-2383. SUTTLE C A . a n d HARRISON P.J. 1986. P h o s p h a t e u p t a k e rates of p h y t o p l a n k t o n a s semb lages g r o w n a t different di lution rates in semicont inuous culture. C a n . J. Fish. Aquat. Sci. 43: 1474-1481. SWEENEY R.E. a n d KAPLAN I.R. 1973. Pyrite f r a m b o i d format ion: Laboratory synthesis a n d mar ine sediments. Econ. Geol. 68:618-634. TAKAHASHI T.. BROECKER W.S. a n d LANGER S. 1985. Redf ie ld ratios b a s e d o n c h e m i c a l d a t a f rom isopycna l surfaces. J. Geophys. Res. 90: 6907-6924. ' TEBO B.M.. NEALSON K.H.. EMERSON S. a n d J A C O B S L. 1984. M ic rob ia l med i a t i on of Mn(ll) a n d Co( l l ) p rec ip i t a t ion a t the 0 2 / H 2 S interfaces in two a n o x i c fjords. Limnol. Oceanogr. 29; 1247-1258. TEDER A. 1969. The spec t r a of a q u e o u s polysulfide solutions. Part II: The e f fec t of alkalinity a n d stoichiometr ic compos i t ion a t equil ibrium. Arkev. forkemiZY. 173-198. TEDER A. 1971. The equi l ibr ium b e t w e e n e l ementa r y sulfur a n d a q u e o u s po lysu lph ide solutions. Ada Chem. Scand. 25: 1722-1728. TERRY K.L 1983. Tempera ture d e p e n d e n c e of a m m o n i u m a n d p h o s p h a t e up t ake , a n d their interact ions in the mar ine d i a t o m Phaeodactylum triconnutum Bohlin. Mar . Biol. Left. 4: 309-320. TESSENOW U. 1966. Unte rsuchungen uber d e n Kieselsdurehaushalt de r B innengewdsser . Arch. Hydrobiol. (suppl.) 32: 1-136. TESSENOW U. 1974. Losungs-, Diffusions- u n d Sorptionsprozesse in d e r O b e r s c h i c h t v o n Seesed imen ten : IV. Reak t ionsmech i smen u n d G l e i c h g e w i c h t e im System Eisen-M a n g a n - P h o s p h a t in Hinbl ick auf d i e V iv ian i t-akkumulat ion im Ursee: Arch. Hydrobiol. Suppl. 47: 1-79. TEZUKA Y. 1984. S e a s o n a l var iat ions of d o m i n a n t p h y t o p l a n k t o n , ch lo rophy l l a a n d nutrient levels in the p e l a g i c regions of Lake Biwa. Jpn. J. Limnol. 45:26-37. TEZUKA Y. 1985. C:N:P ratios of seston in Lake Biwa as indicators of nutrient de f i c i ency in phy top l ank ton a n d d e c o m p o s i t i o n process of hypo l imnet i c par t i cu la te matter. Jpn. J. Umnol. 46:239-246. TEZUKA Y. 1986. Does the seston of Lake B iwa re lease dissolved inorgan i c n i t rogen a n d phosphorus dur ing a e r o b i c d e c o m p o s i t i o n ? Its imp l i ca t ion for eu t roph i ca t i on . Ecol. Res. 1:293-302. TEZUKA Y. 1989a. The C:N:P ratio of phy top l ank ton determines the relat ive amounts of d i s s o l v e d i n o r g a n i c n i t r o g e n a n d p h o s p h o r u s r e l e a s e d d u r i n g a e r o b i c d e c o m p o s i t i o n . Hydrobiologia 173: 55-62. TEZUKA Y. 1989b. The C:N:P ratio of Microcystis and Anabaena (Blue-green a l g a e ) a n d its i m p o r t a n c e for nutrient r egene r a t i on b y a e r o b i c d e c o m p o s i t i o n . Jpn. J. Umnol. 50: 149-155. THOMSON J . , H IGGS N.C., HYDES D.J., COLLEY S. a n d WILSON T.R.S. 1986. The behav iour of m a n g a n e s e in A t l an t i c c a r b o n a t e sediments . Geochim. Cosmochim. Acta 50: 1807-1818. THORSTENSON D.C. 1970. Equil ibrium distribution of small o r g a n i c mo lecu l e s in natura l waters. Geochim. Cosmochim. Acta 34: 745-770. TROPER H.G. 1982. M i c r o b i a l p rocesses in t h e sulfur c y c l e t h rough t ime. In Mineral Deposits and the Evolution of the Biosphere, eds . H.D. H o l l a n d a n d M. Schidlowski. p p 5-30. TSUNAGAIS . , NISHIMURA M. a n d N A K A Y A S. 1968. C o m p l e x o m e t r i c titration of c a l c i um in the p r e sence of larger amounts of magnes ium. Talanta 15:385-390. UEHLINGER U. 1981. Exper imentel le Unte rsuchungen zur Au tdko log i e v o n Aphan i zome-n o n f los-aquae. Arch. Hydrobiol. Suppl. 60: 260-288. UEHLINGER U. 1986. Bac te r i a a n d phosphorus r egene ra t i on in lakes. A n exper imenta l study. Hydrobiologia 135: 197-206. UPPSTROM L.R. 1968. A mod i f i ed m e t h o d for de terminat ion of Boron with c i r cumin a n d a simplified wate r el imination p rocedure . Anal. Chim. A c t a 43:475-486. URBAN P.J. 1961. Color imetry of sulphur anions. Part I. A n i m p r o v e d co lor imetr ic m e t h o d for the determinat ion of thiosulphate. A. analyt. Chem. 179:415-422. VALLENTYNE J.R. 1962. Solubility a n d the d e c o m p o s i t i o n of o r g a n i c mat te r in nature. Arch. Hydrobiol. 58:423-434. V O G E H. 1939. Exchange react ions with radio sulfur. J. Am. Chem. Soc. 61: 1032-1035. W A R D J . C . 1970. The structure a n d propert ies of s o m e iron sulfides. Rev. Pure Appl. Chem. 20: 175-206. WEST P.W. a n d GAEKE G . C . 1956. Fixation of sulfur d iox ide as disulf itomercurate( l l ) a n d subsequent color imetr ic ox idat ion. Anal. Chem. 28: 1816-1819. WESTRICH J.T. a n d BERNER R.A. 1988. The e f f e c t of t e m p e r a t u r e o n rates of sulfate reduct ion in mar ine sediments. Geomicrobiol. J. 6: 99-117. WETZEL M .C . . LOTTER L.H., LOEWENTHAL R.E. a n d MARAIS G.V.R. 1986. M e t a b o l i c behav iou r of Acinetobacter spp . in e n h a n c e d b io log i ca l phosphorus r emova l -a b i o c h e m i c a l m o d e l . Water SA 12: 209-224. WETZEL R.G. 1983. Limnology. Saunders C o l l e g e Publishing, Ph i lade lph ia . 767 p p . WETZEL R.G., RICH P.H., MILLER M.C . a n d ALLEN H.L 1972. Me t abo l i sm of dissolved a n d par t i cu la te detrital c a r b o n in a t e m p e r a t e hard-water lake. Mem. 1st. Ital. Idrobiol. 29(suppl): 185-243. WILLIAMS C . H . 1975. The c h e m i c a l na tu re of sulfur c o m p o u n d s in soils. In Sulfur in Australia Agriculture. K.D. M c L a c h l a n d e d . p p 21-30. WILLIAMS J .D.H. , SYERS J.K., HARRIS, R.F. a n d A R M S T R O N G D.E. 1970. Adso rp t i on a n d deso rp t ion of inorgan ic phosphorus by lake sed iments in a 0.1 M NaC I system. Environ. Sci. Tech. 4: 517-519. WILLIAMS P.J.LeB. 1975. B io log ica l a n d c h e m i c a l a spec t s of d issolved o r g a n i c mater ia l in seawater . In Chemical Oceanography. Vo l . 2. J.P. Riley a n d G . Skirrow eds. p p 301-364. WILLIAMS P.M.. MATHEWS W.H. a n d P ICKARD G.L. 1961. A l ake in British C o l u m b i a conta in ing o ld seawater. Nat. 191:830-832. WILSON D.E. 1980. Sur face a n d c o m p l e x a t i o n ef fects o n the rate of Mn(ll) ox idat ion in natural waters. Geochim. Cosmochim. Acta 44: 1311-1317. WOLLAST R.B.. BILLEN G . a n d DUINKER J .C . 1979. Behav iour of m a n g a n e s e in the Rhine a n d Schedl t estuaries. Estuarine Coastal Mar. Sci. 9: 161-169. YOSHIDA T. 1975. M i c rob i a l metabo l i sm of f l o o d e d soils. In Soil Biochemistry. Vo l . 3. E.A. Paul a n d A .D. McLa r en eds. Dekker, N e w York, p p 83-122. ZEHR J.P., HARVEY R.W.. OREMLAND R.S.. CLOERN J . E.. G E O R G E L H . a n d LANE J.L. 1987. Big S o d a Lake (Nevada ) . I. P e l ag i c bac te r i a l heterot rophy a n d biomass. Limnol. Oceanogr. 32: 781-793. ZHABINA N.N. a n d V O L K O V I.I. 1978. A m e t h o d of d e t e r m i n a t i o n of var ious sulfur c o m p o u n d s in s e a sediments a n d rocks. In Environ. Biogeochem. Geomicrobiol. Vol . 3. p p . 735-745. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0053308/manifest

Comment

Related Items