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Water chemistry profile comparisons of early- and mid-successional forests in coastal British Columbia Binkley, Dan 1980

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WATER CHEMISTRY PROFILE COMPARISONS OF EARLY- AND MID-SUCCESSIONAL FORESTS IN COASTAL BRITISH COLUMBIA A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR- THE DEGREE OF ' MASTER OF SCIENCE in THE FACULTY OF 'GRADUATE STUDIES FACULTY OF FORESTRY We accept t h i s thesis as meeting the required standard THE UNIVERSITY OF BRITISH COLUMBIA March 20, 1980 (c) Daniel E. Binkley, 1980 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 D E - 6 B P 7 5 - 5 1 1 E i i i ABSTRACT A comparison of water chemistry p r o f i l e s was made between a mid-successional 70 to 90 year-old f o r e s t and an early-successional 18 year-old f o r e s t at the U.B.C. Research Forest. Western hemlock, Douglas-fir and western red cedar dominated the older ecosystem, while the younger ecosystem was composed of Douglas-fir and red alder. The concentrations of nutrients and other chemicals were compared i n throu g h f a l l , f o r e s t f l o o r and mineral s o i l leachates, saturated zone-water and stream-water. The younger ecosystem was found to have greater concentrations i n the intermediate stages of the p r o f i l e s , while stream-water concentrations were more s i m i l a r between the ecosystems. The o v e r a l l trend i n the water chemistry p r o f i l e s was best exempli-f i e d by the conductivity p r o f i l e s . Conductivity was assumed to be equal i n p r e c i p i t a t i o n f o r both ecosystems, and was almost i d e n t i c a l i n stream-water. The s o i l leachate i n the younger ecosystem, however, was two to three times greater i n conductivity than i n the older ecosystem. The major exception to th i s trend was the n i t r a t e p r o f i l e compari-sons, where stream-water concentrations were 17 times greater i n the younger than i n the older ecosystem. However, b i o l o g i c a l nitrogen f i x a t i o n by the red alder i n the younger ecosystem r e s u l t s i n substan-t i a l l y greater inputs• The concentrations of s i l i c a increased progressively through the p r o f i l e s of both ecosystems, but the l e v e l s were consistently 40% to 100% higher i n the younger ecosystem, suggesting a greater input of mineral cations to the younger ecosystem through s o i l mineral weather-ing. i i i The higher concentrations of nutrients within the s o i l leachate stages of the younger ecosystem, combined with the f a i l u r e of these higher l e v e l s to be observed i n the saturated zone-water and stream-water (with the exception of n i t r a t e ) , suggest that the younger ecosys-tem was r e l a t i v e l y more e f f i c i e n t at r e t a i n i n g dissolved nutrients than the older ecosystem. X V TABLE OF CONTENTS CHAPTER 1 INTRODUCTION 1 CHAPTER 2 DEFINITIONS AND LITERATURE REVIEW 3 2-1 D e f i n i t i o n s 3 2- 2 Water chemistry p r o f i l e changes through successional time 5 CHAPTER 3 DESCRIPTION OF STUDY AREAS 11 3- 1 General d e s c r i p t i o n 11 3-2 The younger ecosystem 13 3- 3 The older ecosystem 14 CHAPTER 4 METHODS 18 4- 1 F i e l d methods 18 4T-1-1 C o l l e c t i o n period and i n t e r v a l 18 4-1-2 P r e c i p i t a t i o n c o l l e c t i o n s 19 4-1-3 Throughfall c o l l e c t i o n s 19 4-1-4 S o i l leachate c o l l e c t i o n s 19 4-1-5 Saturated zone-water c o l l e c t i o n s 20 4-1-6 Stream-water c o l l e c t i o n s 21 4-2 Laboratory methods 21 4- 3 Sources of bias 22 CHAPTER 5 RESULTS AND DISCUSSION 24 5- 1 Water chemistry p r o f i l e comparisons 24 5-1-1 Concentration r a t i o s , younger:older ecosystem 24 5-1-2 Ratios of stream-water concentration to p r o f i l e maxima 24 5-1-3 Chloride 30 5-1-4 pH 32 5-1-5 Conductivity 32 5-1-6 N i t r a t e and ammonium 33 5-1-7 S i l i c a 35 -5-1-8 Calcium and magnesium 37 5-1-9 Potassium 37 5-2 Relative anion d i s t r i b u t i o n 38 5-3 Relative cation d i s t r i b u t i o n 39 5-4 Cation:anion balances 39 5-5 Comparisons with other water chemistry p r o f i l e studies 40 5-6 Dominant anions and cations 42 5-7 Nutrient depletion 44 5-8 Nutrient retention through successional time 45 5-9 Cr i t i q u e of the water chemistry p r o f i l e method 47 CHAPTER 6 CONCLUSIONS 50 LITERATURE CITED 53 APPENDIX 57 LIST OF TABLES Table 1. Mean concentration of chemicals i n p r e c i p i t a t i o n , t hroughfall and stream-water for s p r u c e - f i r and aspen ecosystems i n New Mexico 7 Table 2. Water chemistry p r o f i l e s for Douglas-fir-western hemlock ecosystems, 70 to 90 years-old and 450 years-old. 9 Table 3. pH, conductivity and s i l i c a water chemistry p r o f i l e s . 25 Table 4. Anion water chemistry p r o f i l e s 26 Table 5. Cation water chemistry p r o f i l e s 27 Table 6. Water chemistry p r o f i l e r a t i o s , younger ecosystem: older ecosystem 28 Table 7. Ratios of stream-water concentrations to the p r o f i l e maximum concentration 29 Table 8. Conductivity balance 41 Table A-•1 S o i l p r o f i l e d e s c r i p t i o n , younger ecosystem 58 Table A-•2 S o i l p r o f i l e d e s c r i p t i o n , older ecosystem 59 Table A-•3 S o i l chemical information averages 60 Table A-•4 Forest f l o o r biomass and nutrient content 62 Table A-•5 L i t t e r f a l l biOmass and nutrient content 63 Table A-•6 Species d i s t r i b u t i o n and biomass 66 Table A-•7 Aboveground net primary pr o d u c t i v i t y estimates 68 v i LIST OF FIGURES Figure 1. Mean monthly temperatures, U.B.C. Research Forest O f f i c e . 12 Figure 2. Monthly p r e c i p i t a t i o n , U.B.C. Research Forest O f f i c e . 12 Figure 3. Younger ecosystem estimated biomass pools and turnovers. 15 Figure 4. Older ecosystem estimated biomass pools and turnovers. 16 Figure 5. S i m p l i f i e d model of water flow through ecosystems. 49 Figure A - l . Regional map of the study areas 69 Figure A-2. U.B.C. Research Forest, study area locations 70 v i i ACKNOWLEDGEMENTS I g r a t e f u l l y acknowledge the e f f o r t s of my committee, Hamish Kimmins, Alan Carter and Tim B a l l a r d , i n t h e i r indefatigueable attempts to improve the grammar, organization, s t y l e and content of my t h e s i s . I appreciate t h e i r help..r ... . ; The execution of the project was greatly a s s i s t e d by discussions and f i e l d work help from fellow students: Paul Courtin, Jennifer DeGatanzaro, Lynn Husted, Fred Nuszdorfer, Chris P e r r i n , Kathy Pomeroy and Jane Richards. Laboratory and f i e l d methods also were developed with the help of Min Tsze, whose pragmatic approach to research was an e s s e n t i a l counter-balance. Min's analyses with the AutoAnalyzer were a great help on a major portion of my project. Greg Bohnenkamp was extremely h e l p f u l i n lo c a t i n g and supplying equipment, from rubben'.stoppers to airplanes. I also thank the s t a f f of the U.B.C. Research Forest for t h e i r assistance during my excursions. F i n a l l y , my gratitude i s extended to Henry the Grouse, whose annoyingly aggressive behavior o c c a s s i o n a l l y provided r e s p i t e from the r i g o r s of cold science. Further, Henrietta the black bear and her two cubs are thanked for eventually r e f r a i n i n g from destroying my i n s t a l l a t i o n s and allowing me to continue with the study. CHAPTER 1 INTRODUCTION The production of biomass i n forest ecosystems i s regulated i n part by the a v a i l a b i l i t y of nutrients. Nutrient transfers, additions and losses i n ecosystems are often associated with the flow of water. Water chemistry p r o f i l e s which examine the concentrations of chemicals at various stages of the water's passage through an ecosystem can pro-vide some insigh t s into the nutrient dynamics of the system. Water chemistry p r o f i l e s have been used to characterize undis-turbed ecosystems ( F e l l e r 1977, S o l l i n s et a l . i n press), to examine the e f f e c t s of c l e a r c u t t i n g and slashburning (Kimmins and F e l l e r 1976), to compare so l u t i o n chemistry mechanisms between ecosystems of d i f f e r -ent biomes (Johnson 1975) and to examine the e f f e c t s of acid p r e c i p i t a -tion on high elevation ecosystems (Cronan and Schofield 1979). This thesis reports on a comparison of water chemistry p r o f i l e s measured i n a 70 to 90 year-old mixed con i f e r forest by M. C. F e l l e r (1974, 1977) with those I measured i n an 18 year-old Douglas-fir plan-tation with red alder. These ecosystems were on s i m i l a r s i t e s , and the differences i n water chemistry p r o f i l e s can be attributed l a r g e l y to differences i n age and vegetation. The objectives were to: 1. Examine the changes i n chemical concentrations from one water chemistry p r o f i l e stage to the next, comparing the concentra-tions as r a t i o s of the younger ecosystem to the older eco-system. 2. Examine the e f f i c i e n c y with which each ecosystem retained dissolved nutrients, expressed as a r a t i o of the concentration in the stream-water leaving the ecosystem to the maximum con-centration i n the p r o f i l e . 3. Investigate the interpretations which could be made about eco-system nutrient dynamics through the water chemistry p r o f i l e method. Assess how this information on ecosystem nutrient dynamics compares with current ideas i n the l i t e r a t u r e . CHAPTER 2 DEFINITIONS AND LITERATURE REVIEW 2-1 D e f i n i t i o n s For the purpose of th i s t h e s i s , I have used the following d e f i n i -tions: 1. An ecosystem was defined by Whittaker (1976) as "a community and i t s environment treated together as a fu n c t i o n a l system of complemen-tary r e l a t i o n s h i p s , (with)transfer and c i r c u l a t i o n of energy and matter." As used i n this t h e s i s , ecosystem boundaries were four-dimensional. For the younger ecosystem, the s u r f i c i a l boundaries were the borders between the 18 year-old plantation and the surrounding older f o r e s t . This was not an en t i r e watershed. The s u r f i c i a l boundaries of the older ecosystem were lar g e l y the boundaries of the watershed, with the exception of areas within these boundaries which had younger vegetation (see F e l l e r 1974). The v e r t i c a l boundaries extended from the bedrock or compacted t i l l surfaces upward to the height of the t a l l e s t trees. The fourth dimension, time, covered the data c o l l e c t i o n periods. 2. Input and output of nutrients were generally defined as matter that crosses the defined boundaries of an ecosystem. The exceptions to t h i s d e f i n i t i o n (as used i n t h i s thesis) involved elements which are contained i n minerals. The release of cations from primary and secondary minerals constituted an input to the pool of nutrients p o t e n t i a l l y a v a i l a b l e f o r c y c l i n g within, or loss from, the ecosystem. S i m i l a r l y , cations combined i n the secondary formation of clay minerals would be considered an "output". Detection of th i s type of output was beyond the re s o l u t i o n of this study. A d d i t i o n a l l y , molecular nitrogen which was within the ph y s i c a l boundaries of the ecosystem would be considered an input when fixed to N H 3; d e n i t r i f i c a t i o n of combined nitrogen to molecular nitrogen or nitrous oxides would be an output. A d e t a i l e d discussion of ecosystem nutrient inputs and outputs was provided by Gorham et a l . (1979). 3. Succession i s a process of s t r u c t u r a l development i n an ecosystem through time, i n v o l v i n g changes i n vegetation composition and dominance. Functional changes, such as increases or decreases i n p r o d u c t i v i t y and nutrient c y c l i n g rates, also occur through a successional sequence. The term primary succession i s used to describe ecosystem development on a s i t e unmodified by a previous vegetation. Secondary succession occurs when a disturbance has disrupted a vegetation but not removed a l l of the vegetation's e f f e c t s on the development of the s i t e . In t h i s t h e s i s , "older" and "younger" r e f e r to the time since the most recent i n i t i a t i o n of secondary succession. 4. Water chemistry p r o f i l e r e f e r s to the changes i n concentration of chemicals i n water as i t passes from one stage i n the ecosystem to another. These stages were p r e c i p i t a t i o n , t hroughfall, f o r e s t f l o o r and mineral s o i l leachates, saturated zone-water, and stream-water. P r e c i p i t a t i o n was the incoming water from the atmosphere as measured by •precipitation c o l l e c t o r s (described i n Methods, Chapter 3). Through-f a l l r e f e r s to water which passed through the canopies of both the overstory and understdry, where present. Forest f l o o r leachate r e f e r s to water which passed through the fo r e s t f l o o r and entered a lysimeter. Mineral s o i l leachate i n the younger ecosystem ref e r s to water which entered a lysimeter located 25 cm below the in t e r f a c e of the A and B horizons, and i n the older ecosystem into lysimeters placed 60 cm below the s o i l surface. I t should be noted that these lysimeter c o l -l e c t i o n s may not have been representative of a l l water passing these stages; periods of rapid flow may have been undersampled, j u s t as flows during periods of s o i l tensions greater than 0.1 atm (about 10 kPa) of tension would not have been sampled. Saturated zone-water refer s to water sampled from the saturated zone of the s o i l above the compacted t i l l layer (the term "groundwater" i s not used to avoid confusion with water deeper i n the earth's crust which i s beyond the defined l i m i t s of the ecosystem). F i n a l l y , stream-water refe r s to water exposed to the atmosphere i n the stream bed. P r e c i p i t a t i o n and throughfall c o l l e c t o r s , as well as the s o i l lysimeters, continuously c o l l e c t e d samples whenever conditions permit-ted; stream-water and saturated zone-water were sampled at d i s c r e t e i n t e r v a l s on the days of f i e l d c o l l e c t i o n s . The analyses presented here give equal weight to each c o l l e c t i o n period, disregarding d i f f e r -ences i n water volumes. Further, averages and standard errors are based on a combination of a l l samples without s t r a t i f i c a t i o n by time or lo c a t i o n . 2-2 L i t e r a t u r e Review, Water Chemistry P r o f i l e Changes Through Succes-s i o n a l Time The differences i n the vegetation between the two ecosystems of the comparisons presented i n t h i s thesis represent a common successional trend i n coa s t a l P a c i f i c Northwest forests (Franklin and Dyrness 1973, Klinka 1976). The differences i n water chemistry p r o f i l e s should re-v e a l trends which accompany the successional development of ecosystems on these s i t e s . Water chemistry p r o f i l e comparisons through successional time are currently absent from the l i t e r a t u r e . William Graustein (personal  communication) of the Department of Geology and Geophysics at Yale University made such a comparison on a mountain i n northern New Mexico. His water chemistry p r o f i l e comparisons involved an early-suc-cessional trembling aspen stand and an old-growth s p r u c e - f i r stand. The s p r u c e - f i r stand was 300 m higher than the aspen stand, but Graustein believed the majority of the differences i n the water chemistry p r o f i l e s could be a t t r i b u t e d to the e f f e c t s of the vegetation. During a two year c o l l e c t i o n period, he measured the chemistry of water at the pre-c i p i t a t i o n , t hroughfall, s o i l leachate and stream-water stages. His s o i l s o l u t i o n lysimeters were not r e p l i c a t e d , and so no measure of s p a t i a l v a r i a b i l i t y was a v a i l a b l e . However, his more intensive sampling of p r e c i p i t a t i o n , t hroughfall and stream-water chemistry revealed some i n t e r e s t i n g patterns. Table 1 presents Graustein's water chemistry p r o f i l e comparisons. With the exception of n i t r a t e , the concentration increased f o r a l l chemicals from p r e c i p i t a t i o n to throughfall. Through-f a l l concentrations were consistently greater for the s p r u c e - f i r eco-system, with n i t r a t e again being the only exception. N i t r a t e appeared to have been taken up by both canopies, with the s p r u c e - f i r canopy absorbing more than the aspen. While many of the ions i n throughfall originated from within the leaves, Graustein a t t r i b u t e d much of the increase i n concentration to the washing from plant surfaces of aerosol p a r t i c l e s which impacted on the vegetation before the r a i n . (One of the major objectives of his study was to quantify the aerosol impaction component of atmospheric nutrient input to these ecosystems.) Stream-water runoff was usually more concentrated from the s p r u c e - f i r ecosystem Table 1. Mean concentration of chemicals i n p r e c i p i t a t i o n , t h r o u g h f a l l and stream-water f o r s p r u c e - f i r and aspen ecosystems i n New Mexico. Data from W. Graustein (personal  communication), ueq £ - 1 . Spruce-Fir Aspen Chemical P r e c i p i t a t i o n Throughfall Stream-water Throup ;hf a l l Stream-water Na + 2.9 12.5 82 3. 7 124 K + 3.1 72 28 29 16 Mg"^ 3.4 31 129 11 91 C a ^ 18 121 178 39 158 S i 0 2 a 0.5 6.5 167 1. 4 243 N0 3" 18 2.6 8 8 2 H C O 3 " -11 43 256 40 280 C l " 9 49 12 14 15 soh~~ 34 122 123 35 50 Si02 data are expressed i n micromoles/liter. 8 than from the aspen ecosystem. Graustein proposed that a greater bio-mass accumulation rate i n the aspen stand probably accounted f o r these differences. This i s i n l i n e with the hypothesis of Vitousek and Reiners (1975, 1976) (discussed i n Chapter 5) of l a t e successional ecosystems being less e f f i c i e n t i n r e t a i n i n g incoming nutrients than e a r l i e r stages. No water chemistry p r o f i l e comparisons through successional time have been made for forests i n the P a c i f i c Northwest. Grier et a l . (1974) compared nutrient c y c l i n g between the 450 year-old Douglas-fir forest of Watershed 10 on the H. J. Andrews Experimental Forest i n Oregon with a 37 year-old Douglas-fir p l a n t a t i o n at the A. E. Thompson Research Center i n Washington. Water chemistry p r o f i l e data are now av a i l a b l e f or these s i t e s , but the differences i n parent material com-bined with the 170% greater p r e c i p i t a t i o n at the H. J. Andrews s i t e would obscure the differences i n water chemistry p r o f i l e s caused by the vegetation. As an a l t e r n a t i v e , Table 2 presents a comparison of the old-growth H. J. Andrews ecosystem p r o f i l e s with those measured by F e l l e r (1977) f o r the 70 to 90 year-old mixed conifer ecosystem used i n the comparison presented i n this thesis. The s o i l parent materials were d i f f e r e n t for the two ecosystems (volcanic t u f f s f o r the 450 year-old ecosystem and q u a r t z - d i o r i t e t i l l for the 70-90 year-old ecosystem), but p r e c i p i t a t i o n i s s i m i l a r . Table 2 reveals s u b s t a n t i a l differences i n p r e c i p i t a t i o n chemistry for the two ecosystems. P r e c i p i t a t i o n concentrations i n the 450 year-old ecosystem were f i v e times greater f o r H +, two-and-a-half times greater f or CI , and twelve times greater for NO3 than i n the 70 to 90 year-old ecosystems. 9 Table 2. Water chemistry p r o f i l e s for Douglas-fir-western hemlock ecosystems, 70 to 90 years-old and 450 years-old,. Data from F e l l e r a ( ] 977). and S o l l i n s et a l . ( i n press) , peq l - * . Stage PH CI NO3 Ca Mg K P r e c i p i t a t i o n 70-90 4.5 17 1 1 - 1 0 5 2 450 5.2 44 0.9 7 4 1 Throughfall 70-90 4.7 27 12 32 14 22 450 5.3 52 Trace 18 12 18 Forest Floor Leachate 70-90 450 5.8 61 5 157 41 37 5.8 81 Trace 58 23 33 Mineral S o i l Leachate 70-90, 60 cm 450, 100 cm 6.5 6.9 31 104 22 0.1 71 398 38 46 7 16 Springs, Saturated Zone 70-90 450 6.3 6.4 25 1 0.4 65 159 21 74 -2 8 Stream-Water 70-90 6.8 .450 6.7 23 4 1.4 75 160 26 69 2 9 Only data f o r mid- and lower-slope sampling s t a t i o n s included here. 10 The p r e c i p i t a t i o n cation concentration differences between the 450 year-old and the 70 to 90 year-old ecosystems were smaller. Below the throughfall stage, the older ecosystem cation concentrations were usually higher than the younger ecosystem's concentrations. Concentra-tions of potassium were s i m i l a r between the two ecosystems from precip-i t a t i o n through forest f l o o r stages. In subsequent stages, both eco-systems experienced decreasing K concentrations; however, the decreases were les s f o r the old growth ecosystem. Calcium and magnesium exhibited less s i m i l a r i t y . In the 70-90 year-old ecosystem (the older ecosystem of the present study), Ca and Mg reached t h e i r maximum concentrations i n the fo r e s t f l o o r leachate stage and then decreased through the rest of the p r o f i l e . In the old growth ecosystem, Ca and Mg stream-water concentrations exceeded the l e v e l s i n forest f l o o r leachate. However, the weathering rates (and hence cation input) for the two ecosystems may have d i f f e r e d . S i l i c a water chemistry p r o f i l e s would give some in s i g h t s , but no si l i c a data were c o l l e c t e d f o r the 450 year-old ecosystem. Data on the consumption of H + through the p r o f i l e also could be h e l p f u l ( S o l l i n s et a l . i n press), but the differences i n pr o d u c t i v i t y and nutrient c y c l i n g rates between the ecosystems make i t d i f f i c u l t to •distinguish between the b i o l o g i c and mineralogic consumption of H + ions. The comparison of these two ecosystems showed that the ecosystems differed in t h e i r water chemistry p r o f i l e s , but not enough information was a v a i l a b l e to d i f f e r e n t i a t e between the e f f e c t s of the vegetation and of the s i t e s . Comparisons of water chemistry p r o f i l e s through successional time are currently too l i m i t e d to synthesize a general picture of any trends which may occur. The present study, even with i t s l i m i t a t i o n s , was a step into a l a r g e l y unexamined f i e l d . 11 CHAPTER 3 DESCRIPTION OF THE STUDY AREAS The water chemistry p r o f i l e s used i n th i s study were measured i n three separate stands within a 500 m radius i n the Univ e r s i t y of B r i t i s h Columbia Research Forest. The U.B.C. Research Forest i s located approx-imately 60 km east of Vancouver near Haney, B.C. (maps on pages 69 and 70). 3-1 General Description F e l l e r (1977) presented a de s c r i p t i o n of the climate and geology of the area, a b r i e f summary of which i s given here. The study areas were between 100 and 300 m elevation, with a c l i -matic c l a s s i f i c a t i o n of C£, a f t e r Kopnen (1936). This designates a r b marine warm temperate rainy (mesothermal) climate. Summer i s the d r i e s t part of the year, but even the d r i e s t month receives an average of 3 cm of r a i n . More than 70% of the t o t a l p r e c i p i t a t i o n (about 250 cm) f a l l s during the period of October to March. Temperatures are mild. The average mean daily- temperature of the warmest month (July) i s 17°C; the coldest month (January) averages about 1°C. Fog and mists are common and probably add an undetermined amount of water (and nutrients) to these f o r e s t s (DeCatanzaro and Binkley, manuscript i n preparation). Snow accumulation i n winter i s usually minimal and r a r e l y l a s t s f o r more than two weeks at a time. Figures 1 and 2 present the mean monthly temperatures and monthly p r e c i p i t a t i o n for the 1972-1973 period of the older ecosystem WCP in v e s t i g a t i o n and the 197 8 period of the younger ecosystem study. The 1978 period was generally warmer and d r i e r than the 1972-1973 period. The q u a r t z - d i o r i t e bedrock i n the study areas i s overlain by a layer of compacted (basal) t i l l , which i s l a r g e l y impermeable to water 12 1973 1972 1978 Figure 1. Mean monthly temperatures, U.B.C. Research Forest O f f i c e . Note discontinuous time scale. 30-1973 1972 1978 Figure 2. Monthly p r e c i p i t a t i o n , U.B.C. Research Forest O f f i c e . Note discontinuous time scale. and i s not usually penetrated by roots. Some seepage through the t i l l probably occurs around bedrock outcrops and large boulders. A blanket of q u a r t z - d i o r i t e ablation t i l l m aterial o v e r l i e s the basal t i l l ; i t averages one meter i n depth. The s o i l s are Humo-Ferric Podzols by the Canadian System of S o i l C l a s s i f i c a t i o n (Canada S o i l Survey Committee 1978), which corresponds to the Typic Haplorthod subgroup of the U.S. System ( S o i l Survey Staff 1975). The textures range from predominantly loamy sand to sandy loam. The coarse (> 2 mm) fragment content of these s o i l s i s often 50% or more. The study areas are within the d r i e r subzone of the Coastal Western Hemlock Zone of Krajina (1965, 1969). Klinka (1976) c l a s s i f i e d the U.B.C. Research Forest into ecosystem units. Under his scheme, the study areas f a l l into the Polystichum-Western Red Cedar ecosystem type. This i s s i m i l a r to the Tsuga heterophy11a/Polystichum habitat type of the Tsuga heterophylla Zone of Franklin and Dyrness (1973). The s i t e index i s 52 m at 100 years (Klinka 1976). 3-2 The Younger Ecosystem The younger ecosystem was a 15 ha Douglas-fir plantation, estab-l i s h e d i n 1960. The s i t e was previously occupied by a fo r e s t which originated a f t e r a w i l d f i r e i n 1848; this stand was logged and the s i t e slashburned i n 1959. The dominant vegetation on the s i t e was Douglas-fir (Pseqdotsuga  menziesii (Mirb.) Franco), vine maple (Acer circinatum Pursh), red alder (Alnus rubra Bong.), b i t t e r cherry (Prunus emarginata Dougl.), and big l e a f maple (Acer macrophyllum Pursh.). The understory shrubs 14 were salmonberry (Rubus s p e c t a b i l i s Pursh) and elderberry (Sambucus  racemosa L.)- Swordfern (Polystlchum munitum (Kaulf.) Presl.) was the dominant fern, and various mosses were common. The younger ecosystem study s i t e was not an en t i r e watershed; subsurface seepage-water drained into the area from several hundred meters of upslope 70-110 year-old f o r e s t . Table A - l , i n the Appendix, presents a s o i l p r o f i l e d e s c r i p t i o n f o r a t y p i c a l s o i l p i t . 3-3 The Older Ecosystem F e l l e r (1974, 1977) measured water chemistry p r o f i l e s i n two nearby watersheds which supported 70-90 year-old fo r e s t s . These forests were established a f t e r a w i l d f i r e i n 1868. The dominant overstory species i n the older ecosystem were western hemlock (Tsuga heterophylla (Raf.) Sarg.), Douglas-fir, and western red cedar (Thuja p l i c a t a Donn). Vine maple and b i g l e a f maple were common understory species, and swordfern was the most common herbaceous species. 3-4 Biomass Pools and Turnovers Figures 3 and 4 present the estimated biomass pools and turnover rates f o r the younger and older ecosystems, respectively. These figures were derived from unpublished data and data from the l i t e r a t u r e f o r the older ecosystems (Kimmins, unpub. data, and DeCatanzaro 1979) and from data I c o l l e c t e d f o r the younger ecosystem. The d e t a i l s of these methods, as well as ad d i t i o n a l s i t e d e s c r i p t i o n information, are in the Appendix. No estimate was made of belowground biomass or nutrient turnovers, and belowground dynamics can exceed aboveground. For example, a 70 to 100 year-old Douglas-fir forest was estimated to pro-duce 8 to 10 tons h a - 1 y r _ 1 of fi n e roots as compared to 2 to 3 tons h a - 1 y r _ 1 of f o l i a g e (D. Santantonio, personal communication). Aboveground Deciduous Overstary Biomass 47,600 Aboveground Understory Biomass 7,000 Net Annual Aboveground| Increment 7,500 Net Annual Abovegroundj Production 15,500 Total Aboveground| L i t t e r f a l l 8,000 Forest Floor Biomass 20,200 Decomposition from Forest Floor 8,000 FIGURE 3. Younger ecosystem estimated biomass pools and turnovers, d e t a i l s In Appendix (kg/ha). Net Annual Aboveground Biomass Increment 5,500 Net Annual Aboveground Production •9.600 Tot a l Aboveground L i t t e r f a l l 3 ,500 Aboveground Coniferous Overstory Biomass 424,300 Abovegroun Understory Biomass ??? (minor) Forest Floor Biomass 35,000 {Decomposition [from Forest Floor 3 ,500 FIGURE 4. Older ecosystem biomass pools and turnovers, d e t a i l s i n Appendix (kg/ha). 17 The most important comparisons to be made between Figures 3 and 4 are the greater net annual aboveground biomass increment and greater net p r o d u c t i v i t y of the younger ecosystem. The younger ecosystem (Figure 3) accumulated aboveground biomass at about 7,500 kg ha" 1 y r - 1 , about 35% more than the 5,700 kg h a - 1 y r - 1 i n the older ecosystem (Figure 4). The annual net pr o d u c t i v i t y for the aboveground system was estimated by summing the biomass increment and the l i t t e r f a l l values. The net (aboveground) pr o d u c t i v i t y of the younger ecosystem was 15,500 kg h a - 1 y r - 1 while that of the older ecosystem was 9,200 kg h a - 1 y r - 1 . Productivity was about 7 0% greater i n the younger ecosystem. As emphasized i n the Appendix, these estimates are very approximate and are presented only for de s c r i p t i v e purposes. 18 CHAPTER 4 METHODS 4-1 F i e l d Methods Water samples were c o l l e c t e d at several stages of water's passage through the ecosystems: p r e c i p i t a t i o n , throughfall, f o r e s t f l o o r and mineral s o i l leachates, saturated zone-water and stream-water. P r e c i p i -t a t i o n and th r o u g h f a l l samples were c o l l e c t e d i n continuously open funnels, s o i l leachates from alundum d i s c lysimeters, saturated zone-water from p i t s (older ecosystem) and piezometers (younger ecosystem) and stream-water as grab samples at the downstream boundaries of the study areas. The 14 sampling stations for the younger ecosystem water chemistry p r o f i l e study were located randomly along fixed transects. Sites where Douglas-fir regeneration dominated were excluded according to the o r i g i n a l objectives of the younger ecosystem study. The 11 sampling stations used here from the older ecosystem were subjectively chosen by F e l l e r (1974) to represent biogeocoenotic units. 4-1-1 C o l l e c t i o n Period and Int e r v a l I c o l l e c t e d water chemistry p r o f i l e data for the younger ecosystem from March through November 1978. I extracted the data representing, the older ecosystem from a long term project by M. C. F e l l e r . The periods from March to July of 1973 and August to November 1972 were grouped to provide a period comparable to the younger ecosystem study. Older ecosystem throughfall data are from March through November of 1973, and stream-water values are the annual averages from June 1972 through May 1973. A c o l l e c t i o n i n t e r v a l of 2 weeks was planned; dry weather i n the summers lenghtened t h i s i n t e r v a l . 19 4-1-2 P r e c i p i t a t i o n C o l l e c t i o n s P r e c i p i t a t i o n was c o l l e c t e d only i n the older ecosystem study. The p r e c i p i t a t i o n chemistry reported i n th i s thesis i s from F e l l e r ' s sampling period of August 1972 to July 1973. P r e c i p i t a t i o n chemistry for part of the period of the younger ecosystem study was co l l e c t e d and analyzed from other locations i n the U.B.C. Research Forest by DeCantanzaro and Binkley (manuscript i n preparation) and by C. P e r r i n (personal communication); nutrient concentrations were s i m i l a r to those measured by F e l l e r (1977). For the purposes of the water chemistry pro-f i l e comparisons presented here, I have assumed that p r e c i p i t a t i o n chemical concentrations were the same for both periods. The p r e c i p i t a t i o n c o l l e c t o r s consisted of 15 cm diameter pol y e t h y l -ene funnels and 4 l i t e r polyethylene b o t t l e s . Nylon f i b e r plugs were used i n the necks of the funnels to reduce contamination. No b i o l o g i c i n h i b i t o r was used i n the water b o t t l e s i n these studies. 4-1-3 Throughfall C o l l e c t i o n s To reduce sample v a r i a b i l i t y , a double funnel c o l l e c t o r design was used i n the younger ecosystem study. Two funnels of the type used for p r e c i p i t a t i o n c o l l e c t i o n were connected to a 4 l i t e r b o t t l e . The funnels were located below the understory vegetation, catching water that had passed through both the overstory and shrub layers (where pre-sent). Single funnel c o l l e c t o r s were used i n the older ecosystem study. Nylon f i b e r plugs were used to reduce contamination. 4-1-4 S o i l Leachate C o l l e c t i o n s Tension lysimeters were used to c o l l e c t s o i l s o l u t i o n samples from the f o r est floor-mineral s o i l i n t e r f a c e and from the mineral s o i l . 20 F i f t e e n centimeter alundum dis c lysimeters without sidewalls were used i n the younger ecosystem, while those i n the older ecosystem employed 10 cm alundum discs with sidewalls. Tensions were supplied by hanging columns of water with heights of 90 to 100.cm, giving about 9 to 10 kPa of tension. Due to the shallow depth to basal t i l l , some lysimeters had only 70 cm columns i n the younger ecosystem. Mineral s o i l lysime-ters were located 10 cm below the A/;B horizon i n t e r f a c e i n the younger ecosystem, and at 60 cm below the surface i n the older ecosystem. 4-1-5 Saturated Zone-Water Co l l e c t i o n s Piezometers were i n s t a l l e d at 10 of the 14 sampling stations i n the younger ecosystem. The piezometers consisted of 5 cm diameter by 100 cm long p l a s t i c pipes, perforated near the base. Rubber stoppers placed on the top of the pipe i n h i b i t e d gas exchange with the atmosphere. Samples were obtained by i n s e r t i n g a tube into the piezometer and extracting water with a syringe. In the older ecosystem, F e l l e r (1974, 1977) sampled saturated zone-water from two covered s o i l p i t s . Unlike the throughfall and s o i l leachate c o l l e c t i o n s , the saturated zone-water was composed of water from within and beyond the ecosystem boundaries. The younger ecosystem was not an e n t i r e watershed, i t re-ceived flow from older upslope ecosystems. S i m i l a r l y , the older eco-system sampling stations were located i n mid- to lower-slope p o s i t i o n s , receiving flow from less productive upslope communities. Concentrations reported for saturated zone-water may la r g e l y r e f l e c t within system processes, but the. unquantified contribution from upslope seepage added unavoidable error. 21 4-1-6 Stream-water C o l l e c t i o n s No single stream drained the e n t i r e younger ecosystem. The stream chosen to represent the younger ecosystem surfaced within the area; approximately one-half of this stream's drainage basin was up-slope of the study area. Stream-water samples for the older ecosystem were collected by F e l l e r (1974, 1977) above the weirs of h i s study watersheds. Again, drainage from upslope ecosystems (within the water-shed but not sampled for throughfall or s o i l leachate) contribute to the stream-water. This boundary problem of the saturated zone- and stream-water samples represent a problem i n non-quantified inputs of nutrients to the defined ecosystems. The water chemistry p r o f i l e as used i n t h i s study cannot avoid such problems. 4-2 Laboratory Methods Water samples were analyzed f o r pH,.bicarbonate concentration ( t i t r a t a b l e a l k a l i n i t y to pH 4.5) and e l e c t r i c a l conductivity on the day of c o l l e c t i o n . Samples were then r e f r i g e r a t e d or frozen u n t i l the other analyses could be performed. Nothing was added to i n h i b i t b i o -l o g i c a c t i v i t y i n the samples during storage. F e l l e r (personal communi-cation) found no s i g n i f i c a n t changes i n concentrations during storage. Conductivity was measured with a Radiometer CDM 2e conductivity meter using a CDC 104 conductivity c e l l ( a l l measurements at 20° to 25°C). An Orion model 404 s p e c i f i c ion meter was used i n pH determinations. Bicarbonate as t o t a l a l k a l i n i t y was measured by t i t r a t i n g a 25 ml a l i -quot to a 4.5 pH endpoint with 0.0005 M HC1 standard. F e l l e r (personal communication) did a potentiometric t i t r a t i o n and found that an endpoint 22 of 4.5 pH may be lower than the true equivalence point, r e s u l t i n g i n an overestimate of bicarbonate concentration. Subsequent to the pH measurements of these studies, he discovered some anomalies with the pH electrode used. The pH values for the older ecosystem may be 0.3 units too low. Values for K, Ca, and Mg were determined by standard methods for atomic absorption spectrophotometry on a Varian Techtron AA-5. An air-acetylene flame was used for K and Mg and a nitrous oxide-acetylene flame was used f o r Ca. Ammonium, s i l i c a and anion concen-trations were determined with standard methods on a Technicon Auto-analyzer II ( d e t a i l s given by F e l l e r 1977). 4-3 Sources of bias Two unavoidable sources of bias are inherent i n the water chemistry p r o f i l e method, and one more crept into the experimental methods of t h i s study. The f i r s t inherent source of bias was in the use of water chem-i s t r y concentrations without a knowledge of water volumes. The calculated averages are unweighted with respect to the quantity of water they rep-resent i n the ecosystem. A dry period which produced a small volume of s o i l leachate with high concentrations received equal weight i n averaging with a sample from a wetter period with more d i l u t e concentrations. The second source of inherent bias also involved the c a l c u l a t i o n of averages. As presented i n t h i s comparison, averages were ca l c u l t e d as the means of a l l water samples analyzed f o r each stage of the eco-systems. These means were based on samples which d i f f e r e d i n both l o c a t i o n and time. Locations which consistently c o l l e c t e d water during dry weather received more weight i n the cal c u l a t i o n s of the averages than locations which c o l l e c t e d only s p o r a d i c a l l y . The water chemistry p r o f i l e comparisons presented here were mea-sured i n d i f f e r e n t years, introducing the t h i r d source of bias. D i f -ferences i n the quantity, timing and composition of p r e c i p i t a t i o n are unaccounted f o r i n the comparisons presented here. However, the chloride p r o f i l e s (as discussed i n Chapter 5) suggest the two time periods were hy d r o l o g i c a l l y s i m i l a r . These sources of bias were unavoidable given the constraints of the studies and should be kept i n mind when evaluating the comparisons which follow. 24 CHAPTER 5 RESULTS AND DISCUSSION 5-1 Water Chemistry P r o f i l e Comparisons The r e s u l t s of the water chemistry p r o f i l e comparisons are summar-ized i n Tables 3 to 7. Tables 3, 4 and 5 l i s t the average concentra-tions of the chemicals by p r o f i l e stage. Table 6 presents the r a t i o s of concentrations of the younger ecosystem to the older ecosystem for each p r o f i l e stage. Table 7 compares stream-water concentration with the highest concentration i n each p r o f i l e , providing a r e l a t i v e index of the reduction i n concentration of the chemicals before the water leaves the ecosystem i n the stream. 5-1-1 Concentration Ratios, Younger Ecosystem:Older Ecosystem Values i n Table 6 greater than 1.0 indi c a t e that the concentrations i n the younger ecosystem exceeded those of the older ecosystem. The o v e r a l l pattern showed higher concentrations i n the younger ecosystem's water. The magnitude of the difference varied greatly among the chemicals; chloride was con s i s t e n t l y within 40% of the older ecosystem's concentrations, while n i t r a t e reached 54 times greater concentrations i n the younger eco-system's forest f l o o r leachate. The other major feature of the r a t i o s of the two ecosystems was that the r a t i o s tended to decrease i n the lower part of the p r o f i l e s , i n d i c a t i n g a convergence i n the concentrations for several of the chemicals. 5-1-2 Ratios of Stream-Water Concentration to P r o f i l e Maxima Values i n Table 7 les s than 1.0 i n d i c a t e that the maximum concen-t r a t i o n of the chemical was i n a p r o f i l e stage other than stream-water. The maximum concentration i n the p r o f i l e - was commonly the forest f l o o r 25 Table 3. pH, c o n d u c t i v i t y and s i l i c a water chemistry p r o f i l e s , average (standard e r r o r ) . Conductivity SiC^ Stage ; pH US cm"1 n m o l ' l - 1 4.5 (<.l) 17 (<1) 2 (.2) P r e c i p i t a t i o n Throughfall Younger Older Forest Floor Leachate Younger Older Mineral S o i l Leachate Younger Older Saturated Zone-Water Younger Older 5.88(.05) 34 (2) 2 (.3) 4.7K.03) 27 (2) 2 (.2) 5.58(.05) 77 (11) 62 (8) 5.77(.13) 39 (2) 41 (5) 5.80(.ll) 73 (14) 73 (8) 6.5K.04) 23 (2) 46 (3) 5.65(.06) 27 (2) 95 (6) 6.3 (<.l) 19 ( 1) 47 (3) Stream-Water Younger Older 6.5K.06) 6.8 (<.l) 21 (2) 20 (1) 111 (10) 78 (2) Table 4. Anion water chemistry profiles,.average ueq 1 (standard e r r o r ) . Stage CI" N0 3~ HC0 3 SO '4 Tot a l P r e c i p i t a t i o n 17 ( <D 11(<D 5(<1) 28 (2) 61 (2.1) Throughfall Younger . Older 34 27 (2) (2) 4( 1) 12 (2) 151(13) 16(05) 108 (5) 73(11) 297 126 (14) (13) Forest Floor Leachate Younger Older 50 61 (7) (4) 270(36) 5 (2) 75 (8) 117(14) 77 120 (9) (6) 472 303 (39) (16) Mineral S o i l Leachate Younger Older 35 31 (3) (3) 136(23) 22 (7) 103(15) 126(14) 64 53 (7) (8) 338 232 (29) (18) Saturated Zone-Water Younger Older 36 25 (4) (1) 50(11) 1(<D 131(14) 77 (9) 58 35 (6). (2) 275 138 (20) (9) Stream-Water Younger Older 23 23 (2) (1) 63 (9) 4(<1) 128 (8) 128 (3) 37 44 (4) (2) 251 199 (13) (4) Table 5. Cation water chemistry p r o f i l e s , average ueq 1 (standard^error). + + + ++ ++ ---Stage - a K ,NH Ca Mg Td.tal P r e c i p i t a t i o n 31. 6(1. 5 ) a 2( .1) 0. 50(, .06) 10 (.4) 5 CD 49, .1 (1. 6) Throughfall Younger 2. 4(0. 4) 106 (8) 1. 60(, .22) 60 (5) 52 (6) 222. ,0 (11. 2) Older 24. 1(2. 2) 22 (4) 0. 20(. .07) 32 (5) 14 (2) 92. ,3 (7. 1) Forest Floor Leachate Younger 6. 3(2. 3) 69 (9) 1. 42(, .31) 275(29) 117(14) 468. ,7 (33. 5) Older 8. 0(1. 8) 37 (3) 0. 29(. ,07) 157(12) 41 (4) 243. ,3 (13. 1) Mineral S o i l Leachate Younger 4. 0(1. 1) 35 (7) 1. 35(. .25) 160(13) 79 (9) 279. .4 (17. 3) Older 0. 4(<. 1) 7 (1) 0. 19(. .09) 71 (7) 38 (3) 116. , 6 (7- 7) Saturated Zone-Water Younger 3. 2(0. 8) 24 (5) 1. 36(. .40) 81 (8) 35 (3) 144. 6 (9. 9) Older 0. 5 a 2( <D 0. IK. .03) 65 (2) 21 (1) 88. . 6 (2. 3) Stream-Water Younger 0. 3(<. 1) 5 (1) 0. 08(. .04) 83 (4) 33 (2) 121. ,4 (4. 6) Older 0. 2 a 2( <D 0. 11(, ,01) 75 (2) 26 (.4) 103. 3 (2. 0) These H concentrations converted from average pH values, not c a l c u l a t e d as averages of i n d i v i d u a l H concentrations. Table 6. Water chemistry p r o f i l e r a t i o s , younger ecosystemrolder ecosystem. Stage Cond. C l ~ N0 3- NH.+ 4 ++ Ca Mg"^ K+ S i 0 2 P r e c i p i t a t i o n (Assumed to be the same for both eco systems) Throughfall 0.1 1.3 1.3 0.3 8.0 1-9 3.7 4.8 1.0 Forest Floor Leachate 0.8 2.0 0.8 54. 4.9 1.8 2.9 1.9 1.5 Mineral S o i l Leachate 10.0 3.2 1.1 6.2 7.1 2.3 2.1 5.0 1.6 Saturated Zone-Water 6.4 1.4 1.4 50. 12.4 1.3 1.7 12.0 2.0 Stream-Water 1.5 1.0 1.0 16. 0.7 1.1 1.3 " 2.5 1.4 N3 00 Table 7. Ratios of stream-water concentration to the p r o f i l e maximum concentration. Conductivity C l " NC>3~ NH 4 + Ca 4 4" Mg"1"4" K + SiC>2 Younger Ecosystem 0.273 0.460 0.233 0.050 0.302 0.282 0.047 1.0 Older Ecosystem 0.5.13 0.377 0.182 0.550 0.478 0.634 0.091 1.0 30 leachate stage. S i l i c a was the only chemical which reached i t s maximum concentration at the stream-water stage. Table 7 shows that although the younger ecosystem often had greater concentrations i n fo r e s t f l o o r leachate than the older ecosystem, the reductions i n concentrations i n the younger ecosystem were generally r e l a t i v e l y greater than i n the older ecosystem. The chloride and n i t r a t e r a t i o s i n Table 7 are i n t e r e s t i n g l y very s i m i l a r f o r the eco-systems. However, while the absolute chloride concentrations i n the two ecosystems were very close, the n i t r a t e l e v e l s d i f f e r e d by more than an order of magnitude. On a r e l a t i v e scale, however, the younger eco-system's n i t r a t e concentrations were reduced as much as i n the older ecosystem. 5-1-3 Chloride The chloride water chemistry p r o f i l e s (Table 4) were very s i m i l a r . Both ecosystems showed increasing chloride concentrations from p r e c i p i -t a t i o n to throughfall to fo r e s t f l o o r leachate stages, followed by decreasing l e v e l s through the rest of the p r o f i l e . The maximum d i f f e r -ence i n chloride concentrations between the ecosystems was 40% (Table 6); the average diffe r e n c e was about 20%. Chloride has generally been considered non-reactive i n ecosystems, with chloride inputs balancing outputs (see Juang and Johnson 1967, Hem 1970, Bryck 1977, Johnson and Cole 1977, Likens et a l . 1977, and Vitousek 1977). Assuming the p r e c i p i t a t i o n and stream-water chloride concentrations i n the present study represent annual averages, the chloride balance suggests that evap'otranspiration equaled about 25% of p r e c i p i t a t i o n (or about 60-65 cm i n an average year). This estimate 31 coincides with estimates by McNaughton and Black (1973) for the U.B.C. Research Forest, suggesting that chloride inputs equal outputs. The chloride budget suggests that the ecosystems are not experienc-ing unmeasured inputs of chloride from aerosol impaction. The increase i n chloride concentration from p r e c i p i t a t i o n to throughfall probably r e f l e c t s "wash-out" of chloride from within the leaves, pointing to an intrasystem chloride cycle. U l r i c h and Mayer (1971) found a s i m i l a r intrasystem chloride cycle i n a 125 year-old beech forest i n Germany. They estimated an uptake of 27 kg h a - 1 y r - 1 of chloride from the s o i l , which balanced the l e v e l s of chloride found i n throughfall (after pre-c i p i t a t i o n chloride was subtracted). Although the mechanism responsible for the measured p r o f i l e s of chloride concentrations remains speculative,the chloride p r o f i l e compari-son i s a valuable part of t h i s study. If i t i s assumed that the mechan-ism (s) c o n t r o l l i n g the behavior of the chloride anions was the same for both ecosystems, then the s i m i l a r i t y of the concentration p r o f i l e s sug-gests that the water f l u x through each ecosystem was s i m i l a r . If the hydrologic behavior of both ecosystems was s i m i l a r , then the concentra-t i o n comparisons presented i n t h i s study should approximate r e a l r e l a -t i v e differences i n the quantities of the chemicals. Thus, although the comparisons are presented i n terms of concentrations, these comparisons might also hold true for quantities. F i n a l l y , the chloride p r o f i l e s ' s i m i l a r i t y suggests that the separate periods of the ecosystem studies were s i m i l a r , and that observed differences between the ecosystem are not completely confounded by time. 32 5-1-4 p.H Two s t r i k i n g features of the pH water chemistry p r o f i l e s (Table 3) were the increase i n pH i n the throughfall i n the younger ecosystem and the higher pH l e v e l s i n the older ecosystem's s o i l - and stream-waters. The large decrease i n a c i d i t y i n throughfall ( r i s e i n pH) beneath the canopy of the younger ecosystem was also accompanied by large increases i n HCO3 , K , and Mg concentrations (discussed l a t e r ) . The lower pH i n the s o i l s o l u t i o n of the younger ecosystem was accompanied by a higher decomposition rate (Figures 3 and 4) and a greater n i t r i f i c a t i o n rate (as discussed i n section 5-1-6).. Both pro-cesses tend to increase s o i l a c i d i t y (decrease pH). The s o i l pH be-neath deciduous forests i s commonly higher than the pH beneath c o n i f e r -ous forests on s i m i l a r s o i l s ( P r i t c h e t t 1979). However, the s o i l s beneath red alder are t y p i c a l l y one pH unit lower than under conifers (Franklin et a l . 1968). These lower pH l e v e l s i n s o i l s o l u t i o n of the younger ecosystem p a r a l l e l the lower pH l e v e l s found i n the s o i l chemi-c a l analyses (Appendix Table A-3). 5-1-5 Conductivity S p e c i f i c e l e c t r i c a l conductance i s a measure of a substance's a b i l i t y to conduct an e l e c t r i c current. Pure water has a very low con-d u c t i v i t y , a few hundredths microsiemenscm - 1 at 25°C (Hem 1970). The presence of ions increases the a b i l i t y of a so l u t i o n to conduct an e l e c t r i c current so that as the i o n i c concentration increases, the conductivity increases. Therefore, conductivity provides an index of the t o t a l i o n i c concentration of a s o l u t i o n . The conductivity p r o f i l e s (Table 3) showed a very i n t e r e s t i n g pat-tern. The conductivity of incoming p r e c i p i t a t i o n was assumed to be 33 i d e n t i c a l , and the conductivity of outgoing stream-water was found to be the same for both ecosystems. Intermediate i n the p r o f i l e s , however, large differences were exhibited. The co n d u c t i v i t i e s of for e s t f l o o r and mineral s o i l leachates were 2.0 and 3.2 times greater, re s p e c t i v e l y , i n the younger ecosystem. Interpretations about i n d i v i d u a l nutrient concentrations cannot be drawn d i r e c t l y from conductivity. Nonetheless, the conductivity water chemistry p r o f i l e s revealed much greater i o n i c concentrations within the younger ecosystem while output concentrations were i d e n t i c a l for both ecosystems. The shape of the conductivity p r o f i l e s suggested a greater degree of c y c l i n g within the younger ecosystem than within the older ecosystem. 5-1-6 Ni t r a t e and Ammonium The n i t r a t e water chemistry p r o f i l e s (Table 4) were usually greater than the ammonium water chemistry p r o f i l e s (Table 5) by at lea s t an order of magnitude at a l l stages of both ecosystems. The average ammonium l e v e l s were consistently higher i n the younger eco-system. The large decrease i n ammonium concentration from the younger ecosystem's seepage-water to the stream may have been due to stream processing through uptake by the bio t a or n i t r i f i c a t i o n . The two ecosystems were more d i s s i m i l a r i n t h e i r n i t r a t e p r o f i l e s than i n any other profile.. The lev e l s of n i t r a t e i n throughfall were lower i n the younger ecosystem than i n p r e c i p i t a t i o n , suggesting a net uptake of n i t r a t e by the hardwood f o l i a g e . Such an uptake was not apparent i n the older ecosystem, which suggests a second i n t e r p r e t a t i o n . No b i o l o g i c i n h i b i t o r was added to the throughfall c o l l e c t o r s , 34 therefore the observed decrease i n n i t r a t e l e v e l s i n the younger eco-system could be due to microbial uptake within the c o l l e c t o r . The lower pH of the older ecosystem's throughfall might have reduced such a c t i v i t y . The average n i t r a t e concentration i n the younger ecosystem forest f l o o r leachate was 270 yeq l - 1 compared to only 5 yeq l - 1 i n the older ecosystem. The maximum concentration recorded f o r the younger eco-system's forest f l o o r leachate was over 1,000 yeq l - 1 . High l e v e l s of n i t r a t e were not r e s t r i c t e d to the s o i l s o l u t i o n under red alder; one forest f l o o r lysimeter with no alder within 15 meters had peak n i t r a t e concentrations of over 500 yeq l - 1 . The r a t i o s of n i t r a t e concentrations i n two ecosystems presented i n Table 6 show decreasing r a t i o s from 54 at the forest f l o o r stage to 16 at the stream-water stage. Although the younger ecosystem had consist-ently higher n i t r a t e concentrations, the r e l a t i v e decrease i n n i t r a t e concentrations from one stage to the next was greater than i n the older ecosystem (Table 7). Contrary to the pattern i n the majority of the water chemistry pro-f i l e s , the n i t r a t e l e v e l s i n the younger ecosystem's stream averaged 16 times greater than the older ecosystem's stream. The younger ecosystem was not necessar i l y less capable of re t a i n i n g nitrogen. .The symbiotic nitrogen f i x a t i o n by the red alder would have greatly increased the input to the younger ecosystem. No attempt was made to measure nitrogen f i x a t i o n i n the younger ecosystem. In a study on Vancouver Island at 510 m elevation, Binkley (manuscript i n preparation) estimated the input of nitrogen from red alder to a 15 to 20 year-old Douglas-fir plantation. Based on the 35 acetylene reduction technique and the quantity of red alder nodules, a nitrogen f i x a t i o n estimate of 130 to 215 kg h a - 1 y r - 1 was derived. The red alder basal area was almost twice as high i n the Vancouver Island study than i n the present study (13.9 m2 h a - 1 vs. 7.6 m2 h a - 1 ) . Therefore as a rough approximation of the nitrogen f i x a t i o n input to the younger ecosystem, I estimate that between 65 and 110 kg-N h a - 1 y r - 1 enter the younger ecosystem v i a the red alder component of the ecosystem. This estimate i s many times greater than the p r e c i p i t a t i o n input of nitrogen to these ecosystems, estimated at 1-2 kg h a - 1 y r - 1 ( F e l l e r 1974). Although this, nitrogen f i x a t i o n rate i s only an estimate, i t does suggest much greater nitrogen.input to the younger ecosystem. Total nitrogen was not measured regu l a r l y ; however, organic n i t r o -gen accounted f o r 25% to 65% of the t o t a l nitrogen for a few samples which were analyzed. C l e a r l y , organic nitrogen i s a major component of the nitrogen p i c t u r e , and i t i s unfortunate that i t was not measured i n these studies. 5-1-7 S i l i c a S i l i c a i s not considered an e s s e n t i a l plant nutrient. It was of in t e r e s t i n th i s study, however, i n r e l a t i o n to the weathering release of other elements from s o i l minerals. S i l i c a does not d i s s o c i a t e into ionized s i l i c i c acid below pH 8.5. Therefore, the s i l i c a found i n the solutions of th i s study would be i n the hydrated nonionic (I^SiO^) form. This form i s t y p i c a l l y monomolecular, and has a s o l u b i l i t y of about 115 mg l - 1 at 25 ° C (Hem 1970). The primary source of s i l i c a i n the s o i l s o l u t i o n and stream-water i s from the weathering of s i l i c a t e minerals. 36 Once s i l i c a i s released from s i l i c a t e minerals, i t travels through the ecosystem with few in t e r a c t i o n s (Hem 1970). There are two possible exceptions to t h i s generalization. F i r s t , some accumulation of s i l i c a ("phytoliths") occurs i n many groups of the family Pinaceae, i n the grass family Poaceae and some other taxa (Klein and Geis 1978). The amount accumulated i n b i o l o g i c tissues i s probably a small portion of the amount released through mineral weathering i n the ecosystems of this study. Second, s i l i c a can recombine with aluminum and other metals to form secondary clay minerals (Birkeland 1974). Windsor (1969) found decreases i n s o i l leachate s i l i c a concentrations with depth i n a short-term lysimeter study. He assumed the decrease could not be due to changes i n the quantity of water, and hypothesized a recombination of s i l i c a with sesquioxides to form secondary clay minerals. The most s t r i k i n g feature of the s i l i c a water chemistry p r o f i l e s was t h e i r s i m i l a r i t y i n shape, with concentrations consistently 40 to 100% higher i n the younger ecosystem (Table 3). There are two possible explanations for the difference i n weathering release of s i l i c a . The mineralogic composition of the q u a r t z - d i o r i t e t i l l parent materials may d i f f e r between the two ecosystems. A l t e r n a t e l y , the higher s i l i c a release could be the r e s u l t of more rapid mineral weathering due to lower pH or more active organic chelation i n the younger ecosystem. For the purposes of t h i s study, the s i l i c a p r o f i l e comparison demonstrates the weathering release of s i l i c a (and of nutrient cations) should not be assumed to have been equal for both ecosystems. The younger ecosystem may have experienced a greater input (weathering release) of nutrient cations. 37 5-1-8 Calcium and Magnesium The p r o f i l e s for calcium and magnesium (Table 5) were s i m i l a r and are discussed together. As with s i l i c a , the patterns f o r the two eco-systems were remarkably s i m i l a r , with the younger ecosystem's p r o f i l e s c o n s i s t e n t l y higher. However, the p r o f i l e s f o r the ecosystems converged at the saturated zone and stream-water stages. Although calcium and magnesium concentrations i n stream-water were 10% and 30% greater, r e s -p e c t i v e l y , i n the younger ecosystem, the s i l i c a concentration d i f f e r e n c e of 40% suggested greater mineral weathering rates i n the younger eco-system. Refering to Table 6, the r a t i o s for calcium and magnesium in the younger to older ecosystem decreased from the mineral s o i l leachate stage to saturated zone and stream-water stages. These decreases were proport i o n a l l y greater i n the younger ecosystem, suggesting t h i s system may r e t a i n a greater proportion of the dissolved cations. 5-1-9 Potassium The shapes of the potassium p r o f i l e s (Table 5) were sim i l a r for the ecosystems; the major d i f f e r e n c e was the much greater wash-out from the deciduous canopy of the younger ecosystem. The greater wash-out could have been regulated by leaf c h a r a c t e r i s t i c s , such as leaf area or c u t i c l e .layer composition. Int e r e s t i n g l y , there was a f i v e - f o l d decrease i n potassium concen-t r a t i o n s i n the younger ecosystem from the saturated zone to the stream-water stages. The potassium ion i s highly l a b i l e within ecosystems, and I have no explanation for the surp r i s i n g decrease i n concentrations. However, both ecosystems appear to be e f f i c i e n t l y r e t a i n i n g potassium, as shown by the large reductions i n concentrations through the lower p r o f i l e s . 38 5-2 Relative Anion D i s t r i b u t i o n The p r o f i l e s f o r the t o t a l anion concentrations (Table 4) show major differences between the ecosystems. Sulfate dominated i n pre-c i p i t a t i o n , followed by chloride, n i t r a t e and bicarbonate. Two impor-tant differences between the ecosystems were found at the thr o u g h f a l l stage. F i r s t , an apparent net uptake of n i t r a t e from p r e c i p i t a t i o n by the crowns i n the younger ecosystem decreased the importance of th i s anion while bicarbonate became the dominant anion. This was accompanied by an increase of almost one-and-a-half pH units. In the older ecosystem, s u l f a t e dominated the throughfall anions. The differences between the two ecosystems persisted through the rest of the p r o f i l e s . The anion ranking f or the younger ecosystem's s o i l leachate was N 0 3 ~ > H C 0 3 ~ = S0h~~ > C l ~ . Along with increasing pH and decreasing NO3 through the younger eco-system's p r o f i l e , bicarbonate became the dominant anion in saturated zone- and stream-water. In the older ecosystem, however, a consistent pattern was present from the f o r e s t f l o o r leachate through stream-water : H C 0 3 ~ > SOL, -" > C l ~ > N 0 3 ~ . Not s u r p r i s i n g l y , the major differences between the anionic r a t i o s of the two ecosystems involved the n i t r a t e and bicarbonate ions. The l a t t e r r e f l e c t e d i n part the change i n hydrogen ion concentrations that accompanied the changes i n n i t r a t e concentrations. 39 5-3 Relative Cation D i s t r i b u t i o n The cation d i s t r i b u t i o n s were more s i m i l a r between the ecosystems than were anion d i s t r i b u t i o n s . The r e l a t i v e magnitudes of. the calcium, magnesium and potassium concentrations were s i m i l a r for both eco-systems. O v e r a l l , calcium concentrations were greater than magnesium concentrations which i n turn exceeded potassium concentrations. The hydrogen ion was important p r i m a r i l y i n p r e c i p i t a t i o n and, i n the older ecosystem, i n throughfall. The major exception to t h i s o v e r a l l s i m i -l a r i t y was found at the throughfall stage, where potassium dominated i n the younger ecosystem while hydrogen ions dominated i n the older ecosystem. 5-4 Cation:Anion Balances In order to maintain e l e c t r i c n e u t r a l i t y , the t o t a l equivalents of cations must balance the t o t a l equivalents of anions. Comparisons of the t o t a l columns of Tables 4 and 5 show several discrepancies i n t h i s balance. Three basic reasons are advanced to explain the d i f f e r -ences. F i r s t , not a l l of the inorganic ions present in the water samples were measured. Sodium, ir o n and manganese made up a substan-t i a l portion of the cation t o t a l for the older ecosystem but were not measured for the younger ecosystem. These elements contributed 20% of the cation t o t a l i n the forest f l o o r leachate in F e l l e r ' s (1977) study, which n i c e l y balances the forest f l o o r anion t o t a l from Table 4. Second, the bicarbonate estimates (as t o t a l a l k a l i n i t y ) may have been too high ( F e l l e r , personal communication). Further, organic ions could be of importance i n the cation:anion balances. The sum of the c o n d u c t i v i t i e s of the measured ions can be com-pared to the measured conductivity of a solution as a check for the presence of unmeasured ions. Using standard values for the conducti-v i t i e s of the i n d i v i d u a l ions (Golterman and Cly-mo 1969), I calculated i o n i c sum c o n d u c t i v i t i e s for each stage of each ecosystem. These calculated c o n d u c t i v i t i e s are presented i n Table 8 together with the measured c o n d u c t i v i t i e s . Where the measured conductivity exceeds the calculated, the presence of unmeasured species or a n a l y t i c a l error i s suggested. Based on F e l l e r ' s (1977) cation t o t a l s , sodium, i r o n and manganese might add from 5% to 10% to the calculated c o n d u c t i v i t i e s . No other major inorganic ions were unmeasured, suggesting considerable importance f o r unmeasured organic ions i n the f o r e s t f l o o r and mineral s o i l leachates of the younger ecosystem. Organic anions have been found to be important species i n other studies (Johnson 1975, Cronan and Schofield 1979), where they have been used to account for the d i f -ferences i n charge balance between the measured cations and anions. The presence of organic ions, as indicated by the conductivity comparisons, along with the organic nitrogen found i n the few samples for which i t was analyzed, combine to underscore the importance of organic compounds i n water chemistry p r o f i l e s . 5-5 Comparisons With Other Water Chemistry P r o f i l e Studies Aside from the two research projects compared here, no other studies have examined water chemistry p r o f i l e s i n low elevation coastal forests i n B r i t i s h Columbia. Several investigations have, however, examined nutrient concentrations i n s o i l leachate and stream-water. Bourgeois and Lavkulich (1972), Klinka (1976) and Otchere-Boateng and B a l l a r d (1978) presented data on s o i l s o l u t i o n nutrient concentrations fo r ecosystems i n the U.B.C. Research Forest which were s i m i l a r to the 41 Table .8. Conductivity balance, us cm - i Stage Younger Ecosystem Older Ecosystem P r e c i p i t a t i o n Throughfall Forest Floor Leachate Mineral S o i l Leachate Saturated Zone-Water Calculated Measured 17 17 33 34 63 77 40 26 73 27 Calculated Measured 17 ' 17 22 27 37 39 21 15 23 19 Stream-Water 22 21 20 20 Sum of the c o n d u c t i v i t i e s of hydrogen, calcium, magnesium, potassium n i t r a t e , c h l o r i d e , bicarbonate and s u l f a t e . Contributions to con-d u c t i v i t y from ammonium, phosphate and hydroxyl ions was n e g l i g i b l e . 42 older ecosystem of t h i s study. There appear to be no major d i f f e r e n -ces which would suggest that the older ecosystem data i n t h i s study are not representative of s i m i l a r mixed conifer stands. Johnson (1975) provided water chemistry p r o f i l e data for a 45 year-old Douglas-fir p l a n t a t i o n i n the A. E. Thompson forest near Seattle, Washington. His s i t e was less productive than the ecosystems of the present study, but the t o t a l anion and cation concentrations followed s i m i l a r patterns to those of my study. His t o t a l concentra-tions were intermediate between the concentrations of the younger and older ecosystems of my study; chloride concentrations were consistently higher, but followed a very s i m i l a r pattern through the p r o f i l e , while n i t r a t e was below detection l i m i t s a f t e r the p r e c i p i t a t i o n stage i n Johnson's study. W. Graustein's (personal communication) comparisons of early suc-cessional aspen and l a t e successional s p r u c e - f i r ecosystems in New Mexico, discussed i n Chapter 2, found greater stream-water concentra-tions of cations and nitrogen i n his older ecosystem. The differences between his two ecosystems are more pronounced than found i n t h i s study. However, his older ecosystem was an old-growth f o r e s t , while •the older ecosystem of the present study would s t i l l be considered to be growing at a rapid rate. 5-6 Dominant Anions and Cations Cole and Johnson (1979) state that the dominant anion i n s o i l leachates i n Douglas-fir ecosystems i s bicarbonate. This conclusion i s based on studies on a low p r o d u c t i v i t y , Site Class IV ecosystem. The older ecosystem of the present study was much more productive, and 43 bicarbonate was s t i l l the dominant anion i n mineral s o i l leachate, saturated zone-water and stream-water. However, fo r e s t f l o o r leachate bicarbonate concentrations were matched by s u l f a t e concentrations. Further, i n the younger ecosystem n i t r a t e dominated the s o i l leachates anions; but again, bicarbonate was dominant i n the saturated zone and stream-water. In the old-growth Douglas-fir f o r e s t at the H. J. Andrews Experi-mental Forest i n Oregon, the pattern i s d i f f e r e n t . Chloride i s the dominant anion i n p r e c i p i t a t i o n , throughfall and f l o r e s t f l o o r leach-ates and s u l f a t e dominated i n the mineral s o i l leachates ( S o l l i n s et a l . i n press). Not a l l major anions were determined f o r saturated zone and stream-water for t h i s ecosystem. The late-successional s p r u c e - f i r water chemistry p r o f i l e s of Graustein (personal communication) also showed a pattern that d i f f e r e d from the dominant bicarbonate anion p r o f i l e . Reliable chloride data are not a v a i l a b l e , but s u l f a t e dominated i n p r e c i p i t a t i o n , throughfall, and mineral s o i l leachate. Only i n stream-water did the dominance s h i f t to the bicarbonate anion. In Graustein's early-successional aspen ecosystem, bicarbonate dominated from the throughfall stage through to the stream-water stage. Just as the dominant anion s h i f t e d from n i t r a t e to bicarbonate i n the successional comparison of the present study, the dominant anion s h i f t e d from bicarbonate to s u l f a t e i n the northern New Mexico study. The r e l a t i v e dominance of cations i n Graustein's study did not greatly d i f f e r between his two ecosystems, and the pattern of Ca > Mg > K i s i d e n t i c a l to the pattern found for both ecosystems of the present study. It appears that r e l a t i v e anion dominance i s strongly influenced by the successional stage (vegetation) of an ecosystem, while the pattern of cation dominance, Ca > Mg > K, appears to be less s e n s i -t i v e to vegetational changes. Anion dominance appears regulated i n part by the b i o t a of the ecosystem, and cation dominance l a r g e l y by geochemical processes. 5-7 Nutrient Depletion Cole et a l . (1978) presented estimates of calcium leaching below the rooting zone for a 38 year-old alder ecosystem and a 48 year-old Douglas-fir ecosystem. They estimated a 25% greater loss of Ca from the alder ecosystem. Calcium concentrations i n the saturated zone water of the present study averaged 25% greater i n the younger ecosys-tem (Douglas-fir-red a l d e r ) , while stream-water concentrations were about 10% greater. Franklin et a l . (1968) compared s o i l properties beneath red alder and Douglas-fir. The s o i l pH beneath the alder was about one unit lower than beneath the Douglas-fir. Their alder ecosystem s o i l also had only one-third the exchangeable calcium and one-sixth the exchange-able magnesium found i n th e i r Douglas-fir ecosystem's s o i l . Franklin et a l . (1968) did not measure the Ca and Mg contained i n biomass, and speculated that unless the decreased Ca and Mg were accumulated i n biomass, the lower s o i l pH of the alder ecosystem could be depleting the s i t e of these minerals. S i m i l a r l y , Cole et a l . (1978) found 14% less exchangeable Ca beneath t h e i r alder ecosystem. However, the vegetation and f o r e s t f l o o r of the alder ecosystem contained 65% more calcium than the Douglas-fir ecosystem. Summing the biomass and s o i l exchangeable pools, their alder ecosystem had one-third more calcium. Despite the 10-25% greater calcium concentrations i n the waters leaving the younger ecosystem of the present study, there was no e v i -dence of calcium depletion from the s i t e . On a meq 100 g - 1 of s o i l b asis, exchangeable calcium i s s i m i l a r f o r both ecosystems (Appendix Table A-3). The younger ecosystem returned almost three times as much Ca i n aboveground l i t t e r f a l l (Appendix Table A-5). The calcium content of the aboveground standing biomass was not estimated. Fur-ther, the s i l i c a p r o f i l e suggested that mineral nutrient release from primary and secondary minerals may have been greater i n the younger ecosystem. The increase could have been due to differences i n mineral composition; however, the greater a c i d i t y (one-half unit lower pH) i n the younger ecosystem suggests increased rates of weathering may have been occurring. In addition, the a c t i v i t y of organic chelating agents could have been greater i n the younger ecosystem. The decreases i n exchangeable calcium and magnesium observed by Franklin et a l . (1968) and Cole et a l . (197 8) may be due to a greater accumulation of these elements i n biomass and a s h i f t i n cation d i s t r i b u t i o n s on exchange s i t e s due to the lower s o i l pH. These apparent decreases i n Ca and Mg may be more than o f f s e t by increased input from mineral weathering, r e s u l t i n g i n a net increase i n nutrient cation pools. 5-8 Nutrient Retention Through Successional Time In 1969, Odum published a summary of trends to be expected through successional time. One such trend was that the a b i l i t y of ecosystems to r e t a i n incoming nutrients increased through successional time. He did not specify i f th i s applied to primary or secondary succession, or both. Vitousek and Reiners (1975, 1976) countered this statement 46 through the l o g i c a l argument that: i f the retention of nutrients by ecosystems i s proportional to the accumulation of nutrients i n b i o -mass, then an ecosystem with a steady state accumulation of biomass (climax community) must be less e f f i c i e n t at r e t a i n i n g nutrients than some previous successional stage. Vitousek and Reiners (1975, 1976) presented a graphical model of ecosystem biomass accumulation, and hypothesized that nutrient retention would follow i n synchrony. Gorham, Vitousek and Reiners (1979) elaborated this hypothesis by l i s t i n g f a c t o r s which regulate nutrient retention and vary through successional time. Bormann and Likens (1979) further elaborated on the n u t r i e n t -retention-and-successional-time theme, d i v i d i n g the biomass accumula-tio n model into four phases representing successional development. The Reorganization Phase begins secondary succession, and i s character-ized by a net loss of biomass and nutrients from the ecosystem. An Aggradation Phase ra p i d l y follows, with maximum rates of biomass and nutrient accretion. If undisturbed, an ecosystem would then pass through a negative biomass accumulation T r a n s i t i o n Phase into a Steady State Phase. Both ecosystems of the present study would f a l l into Bormann and •Likens' (1979) Aggradation Phase, where net ecosystem production i s p o s i t i v e . In addition, the 450 year-old Douglas-fir ecosystem d i s -cussed i n Chapter 2 also had a p o s i t i v e net ecosystem p r o d u c t i v i t y (Grier and Logan 1977); i t too f a l l s within the Aggradation Phase. Yet the water chemistry p r o f i l e s of these ecosystems d i f f e r e d sub-s t a n t i a l l y . From the study of water chemistry p r o f i l e s presented here, i t appears that s i m p l i f i e d generalizations of ecosystem nutrient retention through successional time are of limited usefulness when confronted with the d i v e r s i t y of nutrient input, output and c y c l i n g rates of successional ecosystems. A more useful conceptualization could be derived from the characterization of factors which influence these properties i n s p e c i f i c ecosystems, a f t e r Gorham et a l . (1979). Fac-tors such as s o i l development, nitrogen f i x a t i o n and hydrologic pro-cesses can change with successional time, and biomass accumulation rates cannot serve as surrogate.measures of these factors. 5-9 C r i t i q u e of the Water Chemistry P r o f i l e Method The water chemistry p r o f i l e method presented by Kimmins and F e l l e r (1976) and used here does not address the problems of water quantities; only concentrations are examined. S o l l i n s et a l . (in press) calculated nutrient fluxes by combining water chemistry p r o f i l e concentrations with a computer simulation model of t h e i r ecosystem's hydrology. This approach assumes that the water sampled at each pro-f i l e stage i s representative of a l l the water passing through -that stage. However, numerous studies have demonstrated that water move-ment through s o i l s can be a combination of rapid saturation flow through s o i l micropores and slower movement through the s o i l matrix (e.g. F e l l e r 1974, Beasley 1976, Harr 1977, De Vries and Chow 1978). Haines and Wade (1979) compared tension and tensionless lysimeters i n a c l e a r c u t t i n g study in North Carolina. At the forest f l o o r leachate stage, tensionless lysimeters c o l l e c t e d seven times more water than the tension lysimeters. Concentrations were also greater from the tensionless lysimeters. The pattern reversed at the mineral s o i l stage, where the tension lysimeters c o l l e c t e d twice the water volume 48 c o l l e c t e d by the tensionless lysimeters. A f t e r c l e a r c u t t i n g , the mineral s o i l tensionless lysimeters indicated that the treatment i n -creased s o i l leachate concentrations, while the mineral s o i l tension lysimeters indicated that s o i l leachate concentrations had been re-duced by the treatment! These authors concluded that t h e i r study may have to l d more about lysimetry than about c l e a r c u t t i n g e f f e c t s on s o i l s o l u t i o n . Figure 5 presents a s i m p l i f i e d diagram of water passage through an ecosystem; uptake and evapotranspiration are not included, but would account for removal of water from every compartment. The water sampled at each p r o f i l e stage i s the product of several f a c t o r s , and these fac-tors vary i n importance through time. Water chemistry p r o f i l e s can give, however, some insigh t s into processes with ecosystems. The mobility of anions i n s o i l s can regu-l a t e the losses of cations. Johnson and Cole (197 7) used water chem-i s t r y p r o f i l e information to develop a model pr e d i c t i n g the e f f e c t s of changes i n anion input rates on s o i l s . Cronan and Schofield (1979) used water chemistry p r o f i l e s to assess the impact of acid p r e c i p i t a -t i o n on high elevation ecosystems i n the Northeast. F i n a l l y , water •chemistry p r o f i l e s can be used for comparative purposes, as was done i n the present study. The observed differences i n concentration were useful i n i d e n t i f y i n g differences between the ecosystems. The younger ecosystem was found to have higher nutrient concentrations i n s o i l leachate than the older ecosystem, while stream-water nutrient concen-tratio n s were more s i m i l a r . 49 lAlIXCi OVERSTORY CANOPY I L>UNDERSTORY CANOPY •THROUGHFALL FOREST FLOOR CHANNEL FLOW FOREST FLOOR MATRIX FLOW MINERAL SOIL CHANNEL FLOW V MINERAL SOIL MATRIX FLOW .MINERAL SOIL LEACHATE SAMPLE 'SATURATED ZONE-WATER STREAM-WATER UPSLOPE SATURATED FLOW Figure 5. S i m p l i f i e d model of water flow through ecosystems. Uptake and evapotranspiration are not included i n the diagram, but account f o r removal of water from every compartment l i s t e d . Exchanges between compartments f l u c t u a t e over time.. Sampling stages are underlined. CHAPTER 6 CONCLUSIONS 1. The younger ecosystem's water chemistry p r o f i l e s were often r i c h e r at most stages. However, the younger ecosystem's stream-water concen-tratio n s approached those of the older ecosystem. The conductivity p r o f i l e best exemplified the o v e r a l l trend; the greater concentrations i n t h roughfall and s o i l leachate of the younger of the ecosystems were not found i n stream-water. This pattern suggests a greater c y c l i n g and a v a i l a b i l i t y of nutrient species within the younger ecosystem without equivalent increases i n stream-water output concentrations. 2. Defining nutrient retention e f f i c i e n c y as the r a t i o of the stream-water concentration to the maximum p r o f i l e concentration, the younger ecosystem was consistently more e f f i c i e n t . 3. The water chemistry p r o f i l e s also suggested more luxuriant nutrient regimes i n the younger ecosystem. Nitrogen l e v e l s were much higher, probably due to the nitrogen f i x a t i o n of the red alder over the pre-vious 18 years. Higher nitrogen a v a i l a b i l i t y would have many d i r e c t and i n d i r e c t e f f e c t s on ecosystematic function rates. 4. The dominant cations i n the water chemistry p r o f i l e s i n both eco-systems followed the general pattern Ca > Mg > K . The anions d i f f e r e d s u b s t a n t i a l l y both between ecosystems and from one water pro-f i l e stage to another. 5. The chloride p r o f i l e s were s i m i l a r f o r the two ecosystems, suggest-ing hydrologic s i m i l a r i t y for the two ecosystems and f o r the separate periods in which the p r o f i l e s were measured. The mechanisms respon-s i b l e for the observed patterns are undetermined, but an intrasystem c y c l i n g of chloride i s suggested. 51 6. The s i l i c a water chemistry p r o f i l e s indicated that the weathering release of s i l i c a from s i l i c a t e minerals have been 40% higher i n the younger ecosystem. This weathering difference could have been due to several f a c t o r s : differences i n mineralogic composition of the s o i l s , increased a c i d i t y , or differences i n organic chelating a c t i v i t y . The transfer of nutrient cations from the unavailable mineral l a t t i c e to more ava i l a b l e forms i s d i f f i c u l t to measure. However, the s i l i c a p r o f i l e does suggest that the input of nutrient cations from weather-ing processes may have d i f f e r e d for the two ecosystems. The greater stream-water outputs from the younger ecosystem of Ca (10%) and Mg (30%) may have been less than the differences i n weathering input. Therefore, these cation differences do not indicate s i g n i f i c a n t d i f f e r -ences i n cation depletion between the ecosystems. 7. The measures of exchangeable cations for the two ecosystems' s o i l s are s i m i l a r , despite the d i f f e r e n t extractants used. Without measures of bulk d e n s i t i e s , however, a comparison of exchangeable bases per hectare was not possible. Franklin et a l . (1968) found the s o i l s beneath red alder stands were depleted i n exchangeable calcium and magnesium. This does not appear to hold true i n the present study. 8. Total nitrogen analyses of water samples indicated that a major portion of the dissolved nitrogen i n the water chemistry p r o f i l e s was i n an organic form. The lack of organic nitrogen determinations re-sulted i n very incomplete pictures of the o v e r a l l nitrogen water chem-i s t r y p r o f i l e s . 9. Comparisons of the measured conductivity with that calculated from the c o n d u c t i v i t i e s of the i n d i v i d u a l l y measured ions revealed that a s u b s t a n t i a l portion of the i o n i c constituents in the s o i l s olution of the younger ecosystem were u n i d e n t i f i e d . As a l l major inorganic ions were accounted f o r , organic ions would appear to be important compo-nents of the t o t a l water chemistry p r o f i l e . The agreement between measured and calculated conductivity was closer f or the older eco-system, suggesting a less important (though perhaps s i g n i f i c a n t ) role of organic ions. 10. The younger ecosystem cycles i t s nutrient more r a p i d l y than the older ecosystem. Higher nutrient concentrations i n f o r e s t f l o o r leachate than i n saturated zone-water or stream-water suggest that the younger ecosystem-was more e f f i c i e n t l y r e t a i n i n g dissolved n u t r i -ents. Higher rates of b i o l o g i c uptake probably account for the major-i t y of this regulation. If the vegetation were disturbed, as i n the spraying of a herbicide, the r a p i d l y c y c l i n g nutrients normally re-tained within the ecosystem by plant uptake would be a v a i l a b l e for leaching from the system. 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Ph.D. Thesis. U n i v e r s i t y of Washington, Sea t t l e . 188 pp. Zavitkovski, J. and M. Newton. 1971. L i t t e r f a l l and l i t t e r accumulation i n red alder stands i n western Oregon. Plant and S o i l 35:257-268. 57 APPENDIX A - l S o i l Descriptions A-l-1 S o i l P r o f i l e Descriptions Tables A - l and A-2 present s o i l p r o f i l e descriptions for the younger and older ecosystems. I selected p i t number one as being t y p i c a l of the younger ecosystem, and F e l l e r (1977) chose his p i t number 9. A-l-2 S o i l Chemical Analyses Cation exchange capacity and exchangeable cations were determined on s o i l samples from both ecosystems. I chose a neutral s a l t (1 N NaCl) extraction (Lavkulich 1976); F e l l e r (1974) used pH 7 ammonium acetate. Cation exchange capacity i s pH dependent, and so no comparison of the cation exchange capacities was made. Table A-3 l i s t s the average re-su l t s from 12 p i t s i n the younger ecosystem and 9 p i t s i n the older. A-l-3 Forest Floor Biomass and Nutrient Content I made c o l l e c t i o n s of the younger ecosystem's f o r e s t f l o o r at two times: A p r i l and November 1978. Two 25 x 25 cm samples of the L+F were c o l l e c t e d at each of the WCP sampling s t a t i o n s , giving a t o t a l of 28 samples per c o l l e c t i o n . The sampling l o c a t i o n was systematically 1.5 meters (downslope) from the forest f l o o r lysimeter. The quadrat s i z e prevented sampling of large debris such as logs or stumps. Any woody material within the quadrat was sampled. F e l l e r (1974) did not measure forest f l o o r biomass f o r the older ecosystem. To obtain a representative estimate of the fo r e s t f l o o r biomass f o r a s i m i l a r ecosystem, I sampled the forest f l o o r of the older ecosystem immediately upslope from the younger ecosystem. In 58 Table A - l . S o i l p r o f i l e d e s c r i p t i o n , younger ecosystem p i t #1. Deptt\ cm Horizon Description 3-0 LF Recent alder and salmonberry leaf and twig l i t t e r ; F layer w e l l developed; clear boundary; few roots. 0-9 Ah Dark brown (10 YR 3/3); s i l t y loam, 50% c f ; f i n e , weak granular structure; very f r i a b l e ; c l e a r , smooth boundary; abundant f i n e roots. 10-40 Bhf Olive brown (2.5 YR 4/4); s i l t y loam, 50% cf f i n e , weak granular structure; very f r i a b l e ; gradual, smooth boundary; p l e n t i f u l roots. 40-100 BC Light o l i v e brown (2.5 YR 5/4); s i l t y loam, 50% cf; f i n e , weak granular structure; very f r i a b l e ; abrupt, wavy boundary; few roots. 100+ IIC Compacted basal t i l l . 59 Table A-2. S o i l p r o f i l e F e l l e r 1977), de s c r i p t i o n , older ecosystem p i t //9 (from Depth, cm Horizon Description 15-0 LFH Fresh western hemlock and Douglas-fir l i t t e r ; F layer w e l l developed with yellow mycelia; f r i a b l e ; abrupt, wavy boundary, abundant fin e roots. 0-5 Ae Grey (5 YR 5/1); sandy loam, 62% cf; medium, weak subangular, blocky structure; f r i a b l e ; abrupt, broken boundary; few roots. 5-50 Bfh Reddish brown (5 YR 4/4); sandy loam, 71% cf; moderate, f i n e , angular, blocky structure; firm; c l e a r , i r r e g u l a r boundary; abundant roots. 50-100 Bf Yellowish brown (10 YR 5/4); loamy sand, 94% cf; weak, f i n e , granular structure; very abrupt, i r r e g u l a r boundary; few roots. 100+ R Quartzdiorite bedrock. Table A-3. S o i l chemical information averages . Extractable Horizon pH(H 90) Org. Mat.*3 C a ^ Mg^ K + NHi,+ CEC % -meq 100" 1  Forest f l o o r Younger 4.36 56 18.8 2.8 1.8 0.4 51.1 Older 4.21 84 17.2 3.0 1.1 Ah Younger 4.34 16 5.5 0.4 0.9 0.1 28.4 Older 4.49 20 5.6 0.9 0.4 Bf Younger 4.71 7 0.8 0.1 0.3 < .1 12.2 Older 5.11 3 0. 3 < .1 0.1 BC-C Younger 4.64 6 0.7 < .1 0.3 < .1 10.6 Older 5.27 3 0.4 < .1 0.1 aAverage based on 12 s o i l p i t s for the younger, 9 for the older ecosystems. k% organic matter calculated as lo s s - o n - i g n i t i o n at 450°C for 2 hours. C l N NaCl extraction used f or younger ecosystem samples, pH 7 ammonium acetate e x t r a c t i o n used for older. February, 1979, 30 random samples of.the L+F (25 x 25 cm) were c o l -lected. A discontinuous humus horizon was present i n t h i s older eco-system; the boundary between the H and Ah was i n d i s t i n c t and gradual. Only the L+F horizons are reported i n Table A-4. These f o r e s t f l o o r samples were oven dried at 70°C to a constant weight and ground to pass a 2 mm sieve. Percent organic matter was determined as l o s s - o n - i g n i t i o n at 475°C f o r two hours. Total cations were determined by atomic absorption spectrophotometry on a 28% HC1 extract. T o t a l nitrogen and phosphorus were determined on a micro-Kjeldahl digest using the Autoanalyzer. A-2 Turnover Rates A-2-1 L i t t e r f a l l Biomass and Nutrient Content C o l l e c t i o n s of l i t t e r f a l l i n the younger ecosystem were made by removing the accumulated leaf and twig l i t t e r from the mineral s o i l exposed by the forest f l o o r c o l l e c t i o n s . Two c o l l e c t i o n s were made, one i n August (to cover A p r i l to August) and one i n November, 1978 (to cover September to November). The sample number was 28 for each c o l l e c t i o n . Leaching and p a r t i a l decomposition of the l i t t e r between c o l l e c t i o n s would r e s u l t i n an underestimate of the t o t a l biomass and nutrient content of the l i t t e r f a l l . Also, leaf f a l l was only about 90-95% complete at the time of the November c o l l e c t i o n . F i n a l l y , the sampling scheme was not designed to provide a precise estimate of large woody l i t t e r f a l l . For these reasons, the l i t t e r f a l l data pre-sented i n Table A-5 are underestimates. L i t t e r f a l l biomass data for the older ecosystem up slope of the younger were co l l e c t e d by Kimmins (unpublished data). The biomass and Table A-4. Forest f l o o r biomass and nutrient content, kg ha Biomass N P K Ca Mg C/N Younger Ecosystem A p r i l 1978, L+F 20,760 (2,180) h 338 27 20 195 48 34 November 1978, L+F 19,900 (2,340) 340 29 19 144 40. 34 Older Ecosystem February 1979, L+F 18,610 (1,475) 140 21 9 57 30 77 H 16,290 (2,325) 190 20 9 106 18 50 Tot a l 34,900 330 41 18 163 48 No humus layer present i n the younger ecosystem. 'Standard error of the mean. Table A-5. L i t t e r f a l l biomass and nutrient content, kg h a ' yr '. Biomass N P K Ca Mg C/N Younger Ecosystem 7,740 (640) b 168 12 18 102 21 27 (2 c o l l e c t i o n total) Older Ecosystem 3,530 29 2 6 30 2 71 'Assuming, 'standard 58% carbon i n biomass-error of the mean-64 nutrient values i n Table A-5 for the older ecosystem are the average of two years of c o l l e c t i o n s . The values i n Table A-5 are the best estimates possible for l i t t e r -f a l l biomass and nutrient content within the constraints of this study. They should not be considered more r e l i a b l e than the above q u a l i f i c a -tions allow. Analyses were done using the same methods as for the fo r e s t f l o o r samples. A-2-2 Forest Floor Decomposition Rate No d i r e c t measurements of decomposition were made for either eco-system. However, some rough estimates may be made based on forest f l o o r accumulation and l i t t e r f a l l estimates. From A p r i l to November of 1978 almost eight tons per hectare of aboveground l i t t e r f a l l was measured i n the younger ecosystem; and yet no s i g n i f i c a n t change i n forest f l o o r biomass was measured. Based on th i s l i m i t e d sampling, the forest f l o o r biomass appeared to be i n steady-state (neither accumulating nor l o s i n g biomass). Further e v i -dence of approximate steady state forest f l o o r biomass i s that annual aboveground l i t t e r f a l l i n the 18 year-old ecosystem was 40% of the biomass of the f o r e s t f l o o r . If s u b s t a n t i a l accumulation of the f o r e s t f l o o r were occurring, annual aboveground l i t t e r f a l l would not be ex-pected to be such a large proportion of the forest f l o o r . Zavitkovski and Newton (1971) measured aboveground l i t t e r f a l l and f o r e s t f l o o r biomass i n a time seri e s of red alder stands. They found steady-state forest f l o o r dynamics were reached i n year s i x , with a biomass of 19 tons h a - 1 (1.5 to 2.5 years of l i t t e r f a l l ) . My r e s u l t s appear to f i t the same pattern. For these reasons, the best estimate of annual forest f l o o r decomposition i s the same as the annual aboveground 65 l i t t e r f a l l rate. However, th i s estimate does not take into account the turnover of large woody debris. Aboveground l i t t e r f a l l and f o r e s t f l o o r accumulation i n the older ecosystem was estimated at 4.1 and 27.3 tons h a - 1 , r e s p e c t i v e l y . Annual aboveground l i t t e r f a l l i s 15% of the accumulated f o r e s t f l o o r of t h i s 100+ year-old ecosystem. Some accumulation or decrease i n the fo r e s t f l o o r may have been occurring. However, given the age of the ecosystem and the magnitude of the aboveground l i t t e r f a l l i n r e l a t i o n to the accumulated f o r e s t f l o o r , annual f o r e s t f l o o r inputs and outputs were probably s i m i l a r . Therefore, the l i t t e r f a l l measurement was assumed to be the best estimate of the forest f l o o r decomposition rate. Again, this estimate did not include the turnover of large woody mater-i a l . A-3 Standing Biomass Accumulation and Production A-3-1 Standing Biomass Accumulation To characterize the vegetation of the younger ecosystem, 4 tran-sects were run p a r a l l e l to the slope. A t o t a l of 45 prism pl o t s were measured; the trees within the prism's f i e l d were t a l l i e d by species, diameter and height. In addition, the understory vegetation biomass at each p l o t was su b j e c t i v e l y estimated on the a r b i t r a r y scale of 1-15. To co r r e l a t e the subjective understory estimates with actual biomass, 1 m2 p l o t s were clipped at 3 points. The range of the c l i p p l o t s was from 2-15 on the subjective scale. . Regression equations (based on diameter) from Gholz et a l . (1979) were used to obtain rough estimates of the standing vegetation biomass by species. These regressions were developed from measurements taken i n Oregon and Washington; they were 66 Table A-6. Species d i s t r i b u t i o n and biomass (kg h a " 1 ) . Species Stems*ha 1 Foliage Wood+Bark Total Younger Ecosystem-— B a s a l Area = 34.7 m2 h a - 1 Douglas-fir 1,160 4,610 55,433 60,043 Hemlock 250 555 3,480 4,035 Cedar 11 185 1,583 1,768 Subtotal 1,421 5,350 60,496 65,846 Alder 769 1,565 17,725 19,290 Vine maple 2,400 479 14,040 14,519 B i t t e r cherry 836 895 10,872 11,767 Bigleaf maple 142 105 1,901 2,006 Subtotal 4,147 3,044 44,538 47,582 Understory 0 2.000 5.000 7.000 TOTAL "57568 10,394 110,034 120,428 Older Ecosystem--Basal Area = 68.8 m2 ha 1 Hemlock 411 13,126 231,398 244,524 Douglas-fir 68 2,897 112,355 115,252 Cedar 157 5.604 58.915 64.519 TOTAL 636 21,627 402,668 424,295 3Based on regress ^ B i t t e r cherry es ion equations timates based from Gholz et a l . on equations for . (1979). pin cherry (Prunus pennsylvanica) from Ribe (1973). Understory biomass estimates assume a l l understory biomass i s 2.5 cm base diameter salmonberry for the purposes of foliage:woody d i v i s i o n ^Understory biomass was not estimated f o r older ecosystem. not evaluated f o r accuracy of p r e d i c t i o n i n the younger ecosystem study. Therefore, the estimates i n Table A-6 should be taken only as best estimates and not precise values. The values l i s t e d f o r the biomass of the major overstory species i n the older ecosystem were calculated by applying equations from Gholz et a l . (1979) to cruise data supplied by F e l l e r (1974). A-3-2 Biomass P r o d u c t i v i t y Estimates Rough estimates of aboveground net ecosystem production can be obtained by d i v i d i n g biomass accumulation by age. Aboveground net primary p r o d u c t i v i t y can be estimated by summing the net biomass i n -crement and the annual aboveground l i t t e r f a l l . Table A-7 presents my estimates of these values for both ecosystems. The f i n a l estimates are based on c a l c u l a t i o n s on rough estimates, therefore they are very approximate figur e s . The younger ecosystem appears to be about one-half to two-thirds more productive and to be accumulating about one-t h i r d more biomass. Table A-7. Aboveground net primary p r o d u c t i v i t y estimates. Component Younger Older Total Biomass: Wood+Bark F o l i a g e 3 Forest Floor Total (kg ha" 1) Annual Aboveground Net Ecosystem Production 0 Annual Aboveground L i t t e r f a l l ' (kg ha 1 • yr) d Estimated Annual Aboveground Net Primary P r o d u c t i v i t y : (kg h a - 1 yr) 110,000 4,200 20,000 135,200 7,500 7,800 15.300 403,000 18,000 35,000 456,000 5,700 3., 500 9JM These values represent only 4/5 of the coniferous f o l i a g e and none of the deciduous. It i s assumed that the differences be- , tween these l i s t e d values and those i n Table A-6 are included i n the annual l i t t e r f a l l f i g u r e . Obtained by d i v i d i n g the t o t a l s above by 18 years for the younger ecosystem and by 80 for the older. This estimate represents the lower l i m i t of the true aboveground NPP; biomass consumed by herbivores i s not considered. Not a f u l l year's l i t t e r f a l l f o r the younger ecosystem. Figure A-L Regional map of the study areas. Figure A-2. U.B.C. Research Forest, study area l o c a t i o n s . o 

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