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Aluminum chemistry of selected podzols in Southwestern British Columbia Yuan, Guodon 1994

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ALUMINUM CHEMISTRY OF SELECTED PODZOLS IN SOUTHWESTERN BRITISH COLUMBIA by GUODONG YUAN B.Sc., Nanjing Agricultural University, China, M.Sc., Chinese Academy of Sciences, 1987 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Soil Science) We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA June 1994 ©Guodong Yuan,  1994  1984  ___  In  presenting this thesis  in  partial  fulfilment of  the  requirements  for an  advanced  degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  (Signature)  Department of The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  ///7-  /  /  /  1  /  -  ii ABSTRACT  Three related aspects of Al chemistry of selected Humo Ferric Podzols in Southwestern British Columbia were investigated: mechanisms of podzolization, from soils to surface waters,  acidity transfer  and phosphate status in  relation to soil acidification. Distributions of Al and Fe in horizons and results of column leaching studies revealed that Al behaves differently from Fe in podzolization in terms of ease of eluviation from the top horizon and illuviation into underlying horizons. This may be thermodynamically explained by the solubility products of Al-bearing minerals and stability constants of Al-organic complexes.  This result differs from the  traditional belief that Al and Fe behave similarly in podzolizat ion. Both organic and inorganic mechanisms of podzolization are proposed in the literature.  Studies reported are in  support of either one or the other mechanism.  Chemical  extraction results in this study showed that the content of Al in proto-imogolite was significant in some Bf horizons. This may indicate the contribution of an inorganic mechanism in podzolization. The competition among Al-O-Si, Al-O-C,  and  Al-O-H bonds, which determined the proportion of inorganic and organic processes, was related to annual precipitation and pH,  but not influenced directly by dissolved organic  1 4r I  carbon content. Podzol formation is a natural process of soil acidification. ) 0 Al(A1  This study suggested that the amorphous  content in soil might be used as a capacity factor  to characterize acidity transfer from soils to surface waters. Al activity in neutral salt extracts of soils,  which  represents the amount of Al subject to transfer to surface waters in situations with little organic and mineral acid input to soils,  correlates significantly with Al . This Al 0  activity can be described by an exchange model. A parameter in the model has an empirical relationship with organicbound Al content. Al concentration in simulated leachates, indicating the amount of Al transferable to surface waters in situations where soils receive acidic inputs from natural and anthropogenic sources,  is much higher than that in  . 0 neutral salt extracts and is related to Al  Exposure of Bf  horizons to the land surface may contribute to accelerating transfer of acidity to surface waters. Reduction in bioavailability of phosphorus is a phenomenon during soil acidification.  Phosphate sorption  parameters were strongly dependent on amorphous Al,  Fe,  and  other constituents. Amorphous Al and Fe can be used to predict phosphate sorption capacity of the soils.  Two  European-derived models were shown to be applicable in the areas of this study. Modification was done to include native sorbed phosphate in the sorption capacity of the models.  TABLE OF CONTENTS  Abstract  ii  Table of Contents  iV  List of Tables  vii  List of Figures  V11  Acknowledgements  x  Introduction  1  Chapter One I.  Literature Review  Fundamental Chemistry of Al in Soil and Associated Environments 1.  Solubility of Al minerals in soil  2.  Aluminum speciation in soil solution and surface waters  3.  Podzol and Podzolization 1.  Concept of podzol  2. Allophane and imogolite in podzols 3.  Hypotheses and theories of podzolization  III. Aluminum Related Environmental Problems 1.  Ecological effects of Al  2. Acidification of soil and surface water Chapter Two I.  5 5  6  Precipitation and crystallization of hydrolytic Al products  II.  4  Materials and Methods  Study Areas  9 11 11 12 15 18 19 21 27 27  M  U)  M  U)  F-  H0  U)  H  CU C) CD  W  C) H-  H  H  --1  U)  Cl  F-’C)  CD  C!)  H  Pi  II  0  U)  CD II U)  <  Cl  CU  C) ft  CU  Ct  CD  CD U) H-  0 H,  CU  H-  0  —)  HC) CU ft H0  H,  ft H-  C)  Cr)  H-  C) ft H0  C)  H-  C)  H-  H  H-  CU  ‘iJ I-  CU  o  ft  U)  o  N  ft  Cl  o  CU  HC)  ft U)  H-  ‘d  o  H,  CD  ct  C)  H-  Hft  Cl 0  IQ CD  a)  CD  ft H-  C) 0  t  C) H-  H,  0  CD  CU  ft CD  p  H H  H  Cl  CU  U)  CD U)  CD  H  H-  0  U)  H-  ‘xj  H0 i U)  o  CD  V  Cf  CU  HC)  H  d a.  H  0  0  ft H-  CU  H CU  CD  HC)  CU  <  0  $  h  CD  •  •  H  b  C)  U,  H  •  U)  <  CD  ••  ft  CD  (1)  -  0  0 H,  ><  CD  H  •  CU  Cr H0  CU  0 H HN  N  0  ‘d  H-  CD  xJ 1  Cl  CU  H  H,  0  ‘1 U)  H0  <  CU  W (U  H  CU  Cr H-  CD  h  0  HN CU ft H-  H  N 0  Fd 0  H,  0  U)  U)  Cl)  H-  H  CU  J  H-  •  H  CD C)  H  -  a  0  U) U) H-  co  w  U)  ct  H  o  w  k<  ft  CU C) H-  ‘d  C) CU  (Q  H-  H HN  CU  h  Cr  CD  Q  HU) C)  C)  •  co  H-  CD U)  CD CD  d  -  0  -  h  h ‘-Ii  pi  d ft CD  d ft CD  o  J  o  o  w  0  H-  ft  U) 0 H  U) 0 HH  H-  k<  Hft  U  w  HCD U)  Cl  U) ft Cr  0  C) ft H-  CU  ft h  ><  CD  H-  CU C) ft H-  CD U)  Zi  o  I—’  .-j  ><  W  w  ft U)  CD  CD IH-  d  CD  t-Q  H-  C)  CU  H CD  Q  CD  ft  )J  H  H-  C!)  -  ui  M  w  U)  HCD  Cl  U) ft  ft H0  h  U) 0  CD  CU ft  U)  0  ‘d  •  J  w  0  H-  ft HH, HC) CU ft  CD  HCl  CU H  F  CD  H-  Z  •  W  H  w co  U) CD U)  < U C) ft H 0  i-  J  H  ><  CD  H-  ft  0  p  ft  CD  C) CU H  H-  CD  0  M  F  U)  0  ft  CD  k<  0  ft  1 CU  tT 0  CU  H H H  H CD U)  C!) CU  HH  0  H H  vi 1.  Constituents and factors affecting acidity transfer a.  83  Constituents contributing to acidity transfer  83  b.  Intensity versus capacity factors  85  c.  The capacity of soils to transfer acidity  2.  87  Justification of Al 0 as a capacity factor a. Aluminum activity vs.  gibbsite 92  solubility b.  , 3 Relationship among pAl  c.  An exchange model  pH and Al 0  Phosphorus in Relation to Soil Acidification 1.  Natively sorbed P vs.  2.  p sorption parameters in relation to soil  P sorption maximum  properties 3. Chapter Five  The applicability of two European models Conclusions  Bibliography  94 96  d. Acidic input and transferrable Al III.  90  98 103 105  106 108 113 117  Appendix 132  1.  Soil Description  2.  2 Extractable Al 136 Total Nitrogen Content and CuC1  P.)  Cl) <  —:1  H cD 0  0)  CD  P.) t  C)  0  HH  Cl) 0  CD CD Z  it  lY CD  it CI)  CD  C) H-  H-  Hi  CD I-h  0  C)  ci H0  P.)  HH  ‘-.0 Ui  H  N  P.)  ‘]j  H-  Cl)  H -,  CD P  I.  P.)  0) it  C) 0 3  U]  CD LO  CD H  Cl)  H-  it  II  CD  H3  5  i CD  H-  H  it P.) I—’  0)  ‘-<  h  C)  P.) H  H  H-  Cl) ci P.) 1Y  P  H ‘-< C)  P.)  it  C)  Q  0  ‘tI  CD  ci  ‘-<  0) H-  H H-  CD  it H-  H-  Cl)  0  Hi  0  0  I  H-  Ui ‘-.0  Cl)  l-  it CD  CD  5  II  .)  d  0  H-  it  d  I-  0  Cl)  P.) it CD  Ui —J  CD Cl)  it H-  CD  ‘zI  h 0  0 CD I-h  C)  CD  I  W  CD  H  U]  U] H  CD ><  itct  0  I—’  H-  3  H-  ci  H-  it H-  P.) C)  1  pJ  it  Hit ‘.<  P.) C)  .)  C)  CQ  it hP.) it H0  CD  C)  0  C)  H  -  CD  I  W  CD  H  Pi  ‘-  Cl) 0 H-  Z C)  I-h  0  P.)  it H0  CD H  h  I-  C) 0  0 I-h  it  it h P.) I—’ HN H-  CD  Q  H-  C)  <1  I  W  CD  H  Pi  HC) HCD  0 0)  ‘-.0  I  W  CD  HI  ‘-  Pi  H-  P.)  H  C)  Hi b  PJ  Hi  I—’  0  C!)  0  H  I  W  CD  H  b  J  HI  it  P.) C)  ‘xj h  H  I  CD  H  P)  ‘-  ®it  CD  0  CD  H-  Cl) 0  0 it  p  Cl)  j  H0  pj  H  CD  CD  çt  b CD  0  H-  P.) it  CD H  h  () 0  I  l\)  I  W  H  CD  H  uJ  HI  CD  cu  HI  it  P.)  it  C) CD  C) 0  H  I-h  0  0  Cl)  H-  -  P H CD .)  ‘d Pi  fl 0  -  I  P.)  0)  it h P.) C) it  H  h 0)  CD it CD  5  P.)  II  P.)  H0  it  Cl) 0 I-  tl  P  ‘1 CD  I—’  h  C) 0  Ui  i4 I  CI)  CD  CD H it H-  0  I-  ‘d  H  CD  H  Hi  CD  d  pi  I-  -  CD  H-  Cl)  1  P.)  CD  ‘uJ  H  H CD  P.’ b  it  I—’  CD  H  ‘1 P.) C) it P.) tY  it  1’i  H H ‘-<  P.)  C)  H-  5  CD  C)  W  ,  P.) it CD  P.) C)  CD  H  I  W  CD  H  HI P.)  H-  CD  P-  P.)  —  CD  “i  H--  Cl)  0  ci H-  P.)  11  P.) C)  it  I-  CD  C)  0  C)  CD  ‘xJ  H  -  I  W  CD  H  HI Pi  it  CD  CD 0) H-  h-  P-  P.)  C)  0  Ui  W  CD  H  HI P)  H  CD Cl)  H-  ci  I—  CD  0  h  CD  1  P.)  CD >< C)  it H0  C)  P.)  M  I  W  CD  H  Hi P.) ‘-  N  ‘-  0  C)  5  H  H  H  H  W  H  H  ‘-.0  LA.)  0  C)  0  ‘-  P.)  C)  0  ‘-.0  M  Cl) P.)  CD Q Ii  it  CD  5  P.)  II  pj  H-  it  H-  II  it  Cl  P.)  P.) I—’  CD  H-  5  I—’  Hi  0  it Cl)  pj  it  Cl)  0  C) it H  CD  CD  H  HI Pi  Cl)  CD  P.) it  5  C) H H-  I  pi  5 5  w  H  M  CD  H  P.)  H-  LA.)  HIQ  Cl)  CD  1Q  H H-  S  ‘d  pi  CD  •  M  I  M  CD  H  HI P.)  0)  P.,  CD  0) H-  CD  I—’  C)  it H-  Pi ‘1  -  H  I  W  CD  H  P.)  H CD 0)  Hi P.)  0 I-h  H0) it  H-  H-  Viij List of Figures  Figure 1-1.  Schematic diagram illustrating two theories of podzolization  16  Figure 3-1.  Infrared spectra of clay size samples  63  Figure 4-1.  Index of movement for Al and Fe  66  Figure 4-2.  3 and pH relationship pAl  93  Figure 4-3.  Empirical relationship between PKapp and  A1 Figure 4-4.  Comparison of Al 0 and Al concentrations in  soil leachate Figure 4-5.  101  Comparison of measured and predicted P  sorption capacity  110  IX  Frequently Used Symbols  A  Mineral soil horizon formed at or near the surface in  --  the zone of leaching, or eluviation of materials in solution or suspension,  or of maximum in situ  accumulation of organic matter or both AB  Transitional horizon between A and B  --  Ae  A horizon characterized by the eluviation of clay,  --  Fe,  Al or organic matter alone or in combination Bf  B horizon enriched with amorphous material,  --  principally Al and Fe combined with organic matter C  Mineral horizon comparatively unaffected by the  --  pedogenic processes operative in A and B L,  F,  and H  --  Organic horizons that developed primarily  from the accumulation of leaves,  twigs,  and woody  materials with or without a minor component of mosses CEC nta o  --  --  0 P Xm  Cd)  --  Citrate-bicarbonate-dithionite extractable  Cation exchange resin extractable  --  ANC  Sodium nitrilotriacetate extractable  Acid ammonium oxalate extractable  --  cbd r  Cation exchange capacity  --  --  --  Acid neutralizing capacity  Natively sorbed phosphate Phosphate sorption maximum  x  ACKNOWLEDGEMENTS I would like to express my sincere appreciation to Dr. L. M. Lavkulich for his guidance and encouragement through this project. I am very grateful to the members of my supervisory committee, Drs. T. M. Ballard, H. E. Schreier, and K. Klinka for their willingness to help me at all times. Thanks are due to Mr. B. von Spindler, Ms. Sally Finora and Ms. Susan Harper for their help in technical aspects. The number of friends and colleagues who helped in one way or another is too large to list but none the less they are gratefully acknowledged. I acknowledge Fletcher Challenge Canada Limited for their partial financial support. Last but not least, I would like to thank my wife Yibing, my son Matthew and my parents to whom I dedicate this thesis.  1 INTRODUCTION  Concerns for surface water acidification and potential interactions between expected global warming and soil dynamics and processes have prompted new interests in the study of soil, particularly the important podzol±c group of soils.  In many Southwestern British Columbia regions,  Podzolic soils are dominant in upland well-drained positions.  Characteristically these soils lack Ae horizons  but the Ae may be found under accumulations of decaying wood rather than the more characteristic LFH associated with accumulation of a variety of forest plant litter. Understanding of Al chemistry of podzolic soils in this ecologically fragile zone may have great practical significance for sustainable forestry and for the solution of some environmental problems. The key chemical issue in podzolization is the vertical separation of Si from Al and Fe. Both organic and inorganic mechanisms have been proposed, but most studies in podzol genesis are pro one mechanism and con another one Chesworth and Macias,  1982; 1988)  .  (Farmer,  1985; Dahigren and Ugolini,  Detailed investigations are still needed to better  understand the mechanisms and relative importance of organic acids vs.  silicic acid in podzolization in a specific region  or pedon. Podzolic soils are more easily affected by acidic  2 deposition than other soils in terms of soil acidity.  The  potential relationship between acidic deposition and elevated Al concentrations in soil solutions and surface waters has received much attention during the past decade (Cronan and Schofield,  1990)  because elevated Al  concentration is considered an environmental stress in both terrestrial and aquatic systems. Most existing models predicting Al activity in soil solutions or surface waters are based on the solubility of a specific mineral. However, results of both under- and oversaturation with respect to the mineral phase have been reported Driscoll and Schecher,  (Cronan et al.,  1986;  1988)  Phosphorus is an important plant nutrient and of concern from the environmental point of view. The reactions of phosphate with soil constituents have been extensively studied in many parts of the world and some models have been developed for estimating phosphate sorption capacity der Zee and van Riemsdijk, Gilkes,  1991),  1988; Borggaard,  1990;  (van  Singh and  but the applicability of these models in  western North America regions has not been examined. The aim of this thesis was to provide a better understanding of soil genesis as a baseline to allow an understanding of the effects of forest management. More specifically,  the study focused on an understanding of soil  properties and chemical processes of Podzol formation in this ecologically important zone of the Pacific Northwest.  U)  P3 rt CD  L’J  ft  0 i U)  C) P3 ft  H 0 Fl CD  ><  CD  C) CD  P3  ft 0  P3 ft  ft H0  P3  W  U)  0  0 Fl  P3  U)  Ct  HCD  Fl  ft  -  k<  Hft  Ii  ft HMi ‘-<  C) H-  P3  Mi  0  H HN  P3  P3  U)  ft CD h  Q  N  0  CD ft HMi  H-  U) 0 H1 FU)  H-  F1 ‘-<  CD  Z  0  CD U) CD  ft  0 Mi  CD Mi Mi CD C) ft U)  CD  ft  P3  CD U) çt  0 Fl ft  Z  P3 C) HMi HC)  ‘d  CD  Cr  0 Mi  MiMi 0 0 h Cl) CD U) U) ft ft CC) U)  p3  Fl Mi  U)  o  o  H-  Hft H-  HMi H-  H-  F1 CD U) 0 i  HFl  0  ft 0  CD HFl  —  -.  H1 FHft ‘-<  U) ft P3  1 F-  P3  CD Fl  H-  Q  i  P3 ct CD  H  C)  Mi 0 h CD U) ft  ci.  3  P3  <  CD  P3 i QI  J ft CD H HP3 1 H U)  P3 C) H-  HH  o  U)  Mi  o  ft U)  C)  P3 rr HC)  CD Mi Mi CD  ft C) H H-  Q HMi Mi CD II CD  0 ft CD i Ct HP3 H  CD  ft  Fl P3 H  P3 ft  Hi  CD Fl ft H CD U)  Fl 0  U) 0 HI1  CD Fl P3 H  H-  H-  IQ CD U)  P3  C)  CD  ft  çt  Cl)  0 C)  .  P3  P3 ft CD  C) H-  CD H  ft 0  H  h CD  3  CD U) HU)  rt  CD  ft  0 Mi  CD U)  CD C) Cf H  LJ  0  P3 H-  D CD  W  4 Chapter 1  LITERATURE REVIEW  Aluminum is the most abundant metallic element in soils, making up approximately an average soil  (Lindsay,  1979)  crystalline and amorphous minerals  (e.g.,  smectites,  of the solid matter in .  It occurs in a series of  (short-range ordered)  feldspars, micas,  chlorites, vermiculites,  kaolinite, halloysite, gibbsite,  imogolite).  Al-bearing  allophanes,  and  It also exists as exchangeable Al and hydroxy Al  interlayers. Aluminum was isolated by the Danish chemist Oersted in 1825 and characterized by WOhier in 1827 1988)  .  (Sigel and Sigel,  Analogous to carbon as a coordinator for organic  matter, Al ranks in abundance next to silicon as an oxygen coordinator in minerals in terrestrial and aquatic environments  (Huang,  1988)  .  Aluminum may be released from  minerals to soil solutions and natural waters through chemical and biochemical weathering reactions. During weathering,  primary aluminosilicates dissolve to form  secondary aluminosilicates and aluminum hydroxide precipitates. Both inorganic and organic ions are integral parts of the environment.  They are important weathering  agents of primary and secondary minerals.  The extent of Al  release from minerals to the environment has increased with time,  population growth,  industrialization (Huang,  intensification of agriculture, 1988)  .  The aluminum released to  and  5 soil solution and natural waters undergoes a series of reactions including hydrolysis, polymerization, complexation, precipitation,  and crystallization.  Understanding of these processes is an asset to the study of podzols and podzolizat±on,  since accumulation of amorphous  mixtures of organic matter and aluminum,  with or without  is the feature common to most Spodosols or Podzols  iron,  (Soil Survey Staff,  1975).  The recent  (last two decades)  flurry in aluminum research has focused on the effects of increased mobilization of aluminum from the edaphic to the aquatic environment by acidic deposition  (Lewis,  1989)  Podzols are an extremely important part of the debate relating to this environmental issue.  I.  Fimda.tnental Chemistry of Al in Soil and Associated Environments  There are several recent books and articles dealing with this subject 1989);  therefore,  (e.g.,  Sposito,  1989; Huang,  1988;  Lewis,  the following section will only highlight  some potentially important aspects of Al chemistry in relation to Podzols. 1.  Solubility of aluminum minerals in soil  The solubility of aluminum in soils is controlled initially by minerals present in significant amounts that have the highest solubility or are most easily weathered.  6 Weathering processes slowly remove the thermodynamically unstable minerals,  so that the more stable minerals  supporting the lowest activity of Al 3 ultimately control the solubility of aluminum  (Lindsay and Waithall,  1989).  Selective equilibrium constants for dissociation reactions of potentially important minerals and complexes in Podzols are listed in Table 1-1. For the most part, weathering is essentially a form of an incongruent reaction which may be summarized as reported by Maclas and Chesworth primary minerals  +  (1992) attacking solution secondary minerals  +  leachate  2. Alu.tninu.m speciation in soil solutions and surface waters a. Hydrolytic reactions of Al The Al 3 ion, which is released from Al-bearing minerals to soil solutions and surface waters,  is  octahedrally coordinated with six water molecules and exists as the 6 O) ion can 2 Al(H 3 O) ion. Hydrolysis of the 6 2 Al(H 3 proceed through monomeric and polymeric mechanisms Mesmer,  (Base and  1976)  3 hydrolysis: There are four monomeric species of Al , Al(OH) 2 AlOH , 0 3 , Al(OH) 2  and Al(OH) 4  (Table 1-1). Aluminum  hydrolysis in solution containing relatively low concentration of Al and low ligand number may be described by the monomeric hydrolysis mechanism. However,  hydrolysis  of Al in solutions of either higher Al concentrations or  (  0  0  M Cl)  +  +  H  H U]  H H—  W Cl)  +  +  I’ H  H O  0  H FJ  W  D  0  D  0) 0)  H  —  .-  0  H  Z Q0 L.J 0— I)  H  0)  ‘ 1Q  0  H  IJ  1  ?1  W  0  H W  +  0  H  +  +  +  +  +  “ +  H  H -J  +  H  H  +  H  H LD  M 0  W  0  H Cl)  r’J  Cl) 0  +  +  H  H  0 W  D  H  H  H tJ  0) Ui  C  H  o  1  ‘xj  w  +  +  H  H M  11-  ‘xj  +  +  H  H W  0) 0  J  H  +  H  1-  ‘xj  ij  +  +  H  H H  o 0)  0)  hij  H  11-  +  +  H  H 0  +  +  kO  —J  I  0  0  H 0)  )  I t’J  +  H W  -  I H 0  +  £\)  -  H  0  +  +  H  -  —S  H  0  +  “ +  H  + +  I.J  0  H  0  M  +  H  ‘.D  o .D  I  +  ‘  0  H  1  +  +  H  Ji  4 Ui  U]  0  0  H-  •Cl)  H + +  t\.)  ±  9  H  1  0  -...,  H-  Cl)  H  (ii  CD  H  0  H-  -  H  +  -  Ui  H H  0  +  Cl) H-  ..-  ++  H  +  0) M  —J  0  +  0  H  1’J  +  L,.I +  +  0  Q  cn  0  L  ‘  H-  CD  0  J H H  H-  c,  0  ‘  H  W  i-  0) 0)  Il)  rs,  w  +  H  4  +  Cl)  0  ‘d  S Q  0  H  M  “-  0  CX)  0  +  H  +  CD  r  Cl) H-  0  H  H  0  IQ  Q  H  H  C)  -  0  HQ  rt  C)  CD  H  H-  Cl)  HO Wrt  p.i  H- CD H  o  H Cl)—  H-J  -JctH  HCD Ci) IDJ0  HCD  P)rfF  rtH-M]  00) (DO  ‘-<O)rt  CDW  c1 H’PJ  Z  -.  OD Wh -H H-  COHtJ  )CDH H H I- H  CDH5W I ct H-  CD  Cl))O  H CD  I-]  8 higher ligand number is better described by the polymeric hydrolysis mechanism. Aveston  (1965)  in terms of the species Al 2 (OH) Mesmer  (1976)  interpreted his results  and 24 (OH) Baes and 4 O 13 Al . 7  conclude that the polynuclear species formed  by Al hydrolysis are 2 (OH) 4 Al , 4 (OH) 3 Al , 5  and 24 (OH) 4 O 13 Al . 7  b. Aluminum-organic/inorganic complexes The nature and concentration of inorganic ligands play an important role in influencing the hydrolysis and polymerization of Al  (Huang,  1988).  Inorganic ligands that  form soluble complexes with Al 3 include fluoride, and nitrate.  sulfate,  These complexes contribute to total soluble  aluminum in soils, particularly in acid soils. Essentially every aspect of the chemistry of aluminum in soils,  sediments,  and aquatic systems is influenced by  interactions involving organic substances. The interaction of Al with organic substances is of considerable importance 3 in controlling soil solution levels of the highly toxic Al ion in acid soils and natural waters. The effects of organic acids on Al behaviour occur through two distinctive models of action,  namely,  lowering of the pH value because of  ionization of acidic functional groups H)  and formation of chelate complexes  1989).  (e.g.,  COOH  COO-  +  (Stevenson and Vance,  The carboxyl and hydroxyl groups are the principal  functional groups involved in the reactions of Al with organic acids in soil solutions and natural waters.  These  functional groups are present in both the humic and nonhumic  9 fractions of soil organic components. the humic fraction,  The significance of  such as fulvic acids,  in complexing with  Al in solution has been extensively studied Kodama,  1977)  .  The nonhumic fraction,  molecular-weight organic acids,  (Schnitzer and  such as the low-  have been recently  considered important in controlling Al behaviour 1991)  .  (Huang,  The sources of low-molecular-weight organic acids in  soil environments include root exudates, of plant and animal residues,  canopy drip,  decay  and microbial metabolites.  Considerable emphasis recently has been given to the importance of oxalic acid as a chelator of Al in acid forest soils. Many fungi are prolific producers of oxalic acid, including the vesicular-arbuscular mycorrhizal fungi (Stevenson and Vance, Podzols,  1989). At the pH values found in many  formation of soluble Al-organic complexes increases  total soluble Al in soils and contributes to its mobility. The Podzol is often cited as a prime example of the role of organic matter in the eluviation of Al during pedogenesis. 3.  Precipitation and crystallization of hydrolytic Al products  Mononuclear and polynuclear Al species can be transformed into colloidal or solid phases. Many of the colloidal solid phases initially formed are of very fine particulates that may not settle upon centrifugation and may easily pass membrane filters  (Huang,  1988).  The  precipitation products of Al can be either short-range  10 ordered materials or crystalline Al hydroxides,  depending on  solution composition and formation conditions. Three types of Al hydroxides and short-range ordered aluminosilicates have been identified in soils: hydroxides  (e.g.,  gibbsite, boehmite),  hydroxyaluminum  interlayers in vermiculites and smectites, allophane/imogolite.  crystalline  and  Gibbsite is a common product of  tropical and subtropical weathering.  In temperate soils, Al  mobilized by acidic attack on soil minerals is believed to be precipitated as allophane/imogolite,  and trapped as  exchangeable aluminum or hydroxyaluminum interlayers in expanding layer silicates  (Paterson et al.,  Allophane and imogolite,  1991).  long known as major metastable  weathering products in volcanic ash and pumice soils,  have  recently been recognized as pedogenic components of the B horizons of many podzols and podzolized soils Wang et al.,  1991).  1982;  (Farmer,  Generally they have been detected in  0)>4.8 2 substantial amounts only in B horizons of pH(H (Parfitt and Kimble,  1989)  .  The stability of imogolite  relative to gibbs±te is determined by the concentration of silicic acid in solution, A (HO) S 3 O 2 iOH 1  +  according to the equilibrium: 0 2 3H  3 2A1(OH)  +  4 S±(OM)  Podzols commonly contain chlorite-like l4A layer silicates  (Ross,  1980)  which appear to consist of  vermiculites with an incomplete aluminous interlayer,  rather  than the magnesium-iron hydroxide interlayer sheet of true  11 chlorites.  These pseudo-chiorites are believed to form by followed by  the leaching of interlayer potassium from micas,  the entry between the layers of hydroxyaluminum polymeric species.  The aluminous interlayers of soil pseudo-chlorites  are apparently more stable than gibbsite, imogolite.  allophane or  They appear to be best developed in A and B values of 4.4-5  ) pH(H 0 horizons of 2  can persist even at pH 4  (Barnhisel,  (Karathanasis et al.,  1977)  and  1983),  whereas allophane and imogolite are seldom present in soil below 4.8  ) pH(H 0 horizons of 2 Wada,  (Parfitt and Kimble,  1989;  1989)  II. Podzo]. and Podzolization 1. Concept of podzol Podzols are a major class of soil developed in sandy to loamy materials occurring in cool, of the world.  Typically,  temperate,  humid regions  they have four major horizons: a  dark-colored organic surface horizon; a bleached eluvial horizon;  a reddish,  brownish or black illuvial horizon  enriched in amorphous materials; and a sandy C horizon (McKeague et al.,  1983)  Dokuchaiev examined podzols as early as 1879 (Ponomareva,  1969)  entirely clear.  .  The origin of the name “podzol” is not  In one interpretation it is assumed to have  originated from the preposition pod”,  meaning under,  and  the noun “zola”, meaning ashes, perhaps reflecting the fact  12 that the gray ashy layer is usually not at the soil surface but rather under a darker horizon,  or perhaps indicating  that the soil is under °ashes” thought to have been left by burning of the forest  (Ponomareva,  1969)  The meaning of podzol has changed with time.  The  original concept of podzol in Russia emphasized the ashy gray eluvial horizon and the name was applied to soils having such a horizon regardless of the nature of the underlying illuvial horizon. As the term was translated into German and later into English it became associated with soils having,  in addition to a bleached layer,  an underlying  reddish to dark-brownish or black illuvial horizon typical of podzol.  In Soil Taxonomy  (Soil Survey Staff,  The Canadian System of Soil Classification Canada Expert Committee on Soil Survey,  1975)  and  (Agriculture  1987),  the ashy  ceased to be a diagnostic horizon of  horizon  (Ae or E)  Podzols  (Spodosols)  for several reasons:  1)  in many forested  areas,  due to blowdown of trees and other disturbances,  Ae  horizon of Podzols  (E)  (Spodosols)  is intermittent;  cultivation may completely destroy the Ae horizon; horizons of Brown Podzolic soils  3)  (no Ae or E horizon)  the 2)  many B had  the same properties of Bf horizons of Podzols with Ae horizons. In this thesis, Ae and E are used synonymously and only Ae is used when dealing with Podzols. 2. Allophane and imogolite in podzols  13 Allophane and imogolite,  long known as major metastable  weathering products in volcanic ash and pumice soils,  have  recently been recognized as components of the B horizons of many Podzols and Spodosols Dahlgren,  (Farmer,  1991; Wang et al.,  1986).  1982; Ugolini and Because of their large  specific surfaces and high chemical reactivity  (Wada,  1989),  these minerals have significant effects on the physical, chemical,  and biological properties of soils.  There are differences in the definition of allophane. Wada  (1989)  limited the term allophane to hydrous  aluminosilicates with a hollow spherical morphology. Morphology,  however,  even for crystalline minerals, varies  with the condition of their formation Therefore,  Farmer et al. (1991)  (Huang,  1991)  define allophane as any  noncrystalline hydrous aluminosilicates,  and does not imply  a spherical morphology. Because of this difference in the definition of allophane,  a soil fraction with the imogolite  structure that is soluble in citrate-dithionite-bicarbonate is termed “proto-imogolite” allophane by Farmer et al. (1983)  but “allophane-like constituents” by Wada  (1989),  since he is uncertain of its morphology. Imogolite is a hydrous aluminosilicate with a unique tubular structure.  It appears as threads consisting of  assemblies of a tube unit with inner and outer diameters of l.O and ‘2.O-2.7 nm,  respectively.  Another often used term is proto-imogolite. Again,  14 there is variation in the definition. Hydroxyaluminum cations react with orthosilicic acid in dilute acid solution (pH<5)  to form a hydroxyaluminum orthosilicate complex. This  water soluble complex is termed hydroxyaluminosilicate ion by Wada and Wada (1982),  (1980)  but termed proto-imogolite by Farmer  as it could be readily converted to imogolite by  heating the solution,  and its infrared spectrum indicates a  close structural relationship to imogolite. Within the general group of materials that have the chemical structure of imogolite, but have not developed a tubular morphology, Huang  suggested making a distinction between proto  (1991)  imogolite sols allophane  (a dispersed phase)  and proto-imogolite  (a precipitate phase).  The formation of short-range ordered aluminosilicates (allophane,  imogolite,  and analogous materials)  is  influenced significantly by organic and inorganic ligands, metallic cations, composition, groups,  size,  and expansible layer silicates. number,  Chemical  and nature of the functional  and concentrations of non-humified organic acids  play a vital role in perturbing the formation of allophane and imogolite  (Inoue and Huang,  1984,1986). Humic substances  also substantially perturb the interactions of hydroxy-Al ions with orthosilicic acid and thus inhibit the formation of these aluminosilicates 1987,  1990)  .  (Farmer,  1981;  Inoue and Huang,  The phosphate anion common in soil solution and  other natural waters inhibits the formation of imogolite  15 (Henmi and Huang,  1987).  Iron has a stronger inhibiting  effect than Mn on imogolite formation,  resulting in the  formation of poorly ordered mineral colloids Huang,  (Henmi and  1985). Adsorption of hydroxy-aluminosilicate polymers  in the interlayers of montmorillonite results in an expanded structure.  The transformation of hydroxy-aluminosilicate  ions to noncrystalline aluminosilicates can,  therefore,  be  affected by naturally occurring expansible layer silicates (Lou and Huang,  1990)  .  The perturbation effect of these  ionic factors on the formation of short-range ordered aluminosilicates deserves close attention in the associated changes of physicochemical properties of podzols and their related environments. 3. Hypotheses and theories of podzolization Several hypotheses and theories have been proposed to explain the formation of Podzols or Spodosols 1949;  Stobe and Wright,  De Conninck,  1959;  1970;  1982; Duchauf our,  1982;  McKeague et al.,1983; Chesworth and Macias, and Dahlgren,  1987).  Deb,  1969; Rode,  Ponomareva,  1980; Anderson et al.,  (e.g.,  1985; Ugolini  Currently two major contrasting  theories share the most attention: the fulvate theory and the proto-imogolite theory. They are illustrated in Fig.l-l. The fulvate theory involves two stages which may occur concomitantly.  The first stage involves the formation of  water soluble organic acids, predominantly fulvic acid, primarily from litter and root decomposition caused by fungi  16 FULVATE THEORY  SECOND STAGE  DEC OM P0 SITON MIGRATION FE AND AL  SYNTHESIS IMOGOLIJE AND AL LO PH AN E  PROTO- IMOGOLITE THEORY  FIRST STAGE SECOND STAGE  FORMATION FA  FORMATION  MIGRATION  SI LIC ATE SOLS MIGRATION ARREST  •  ‘I:.  C...  .  .•  !..  ARREST  —------•. -  ,.  ‘S  Figure 1-1 Schematic Diagram Illustrating Two Theories of Podzolization ( Modified from Ugolini and Dahigren, 1987)  17 and other floral and faunal attack.  Fulvic acid chelates Fe  and Al in the Ae horizon and subsequently migrates through the Ae and Bhf to the top of the Bf horizons where arrest occurs, when the ratio of Al and Fe to organic C become sufficiently high or when the organo-metal complex is adsorbed by Al and Fe hydroxides.  In the second stage,  these  organo—metal complexes decompose and liberate the Fe and Al which migrate as free metals into the Bf horizon.  Synthesis  of imogolite/allophane may occur when the Fe and Al react with percolating silica. The proto-imogolite theory proposed by Farmer and co workers similarly occurs in two successive stages al.,1980;  Farmer,  1981,  1982).  (Farmer et  The first stage involves the  formation of the Bf horizon enriched in imogolite-type materials and iron oxides. The imogolite-type materials can be deposited from solution containing a positively charged hydroxyaluminum silicate sol. This positively charged sol can form in the Ae horizon from Al and Fe brought into solution by non-complexing organic and inorganic acids, by readily biodegradable small complexing organic acids. can migrate through the Ae and Bhf horizons,  or It  and becomes  arrested in the Bf horizons in response to an increase in pH or adsorption by negatively charged surfaces or anions. is transported by a similar mechanism.  The second stage  involves the formation of fulvic acid and its migration through the Ae and Bhf horizons.  Fulvic acid is then  Iron  18 precipitated on the imogolite surface of the Bf horizon. Based on soil solution studies, Ugolini et al. 1990)  (1987,  provide an alternative explanation of podzol formation  in two stages. minerals,  In the first stage,  carbonic acid attacks  leaving an Al-rich amorphous residue.  Synthesis of  imogolite/allophane then occurs in situ as silica combines with the Al.  In the second stage,  fulvic acid produced in  the forest floor forms organo-metal complexes with Fe and Al in the Ae and Bhf horizons.  These organo-metal complexes  migrate through the Ae and Bhf horizons and are arrested by interaction with the amorphous materials of the Bf horizon. There is little corroborative research to comment on this explanation at present. In the discussion above,  processes that promote  podzolization and differentiation of parent material into horizons are emphasized.  However,  a variety of processes,  such as mixing of materials by soil fauna, vegetation blowdown or management practice, may retard horizon differentiation  (Simonson,  1976)  III. Aluminum Related Environmental Problems  The chemistry of Al is quite complex, charge and small effective ionic radius fold coordination)  its high ionic  (0.054 nm in six  combine to yield a level of reactivity  unmatched by other soluble metals found in soil solutions  ft H0  CD  H-  P1  CD  CD  P1  Hft ‘-<  H  ii CD  CD  ft  -  CD 0 HH CD  C)  >< H-  oft o  ft  P1  H  P1 C)  0 H,  H-  H-  ft  HCi) ft h  S  CD  S  0 H  LJ  P1  5  P1  CD  H-  H  CD  Cl  P1  H  H  CD  ft  P1  C) CD  H-  b  H  CD  CD 0 H  k<  -) 0  CD  Ci) 0  CD CD  P1 Ci)  ft  H-  LQ  0  H ft  CD P1 h CD  P1 ft  ft  CD  H P1 ft  ft  0 CD  d  ‘-Q  C)  I0  ft  HICi)  H,  CD  ft  H Pi  ft 0  H D H  CD -  5  5  Hft P1 ft H0  CD  H-  Ci)  o  CD  P1  CD  ft  CD CD  CD ft  -  —  O  H D CD  -  H -  P1  ft  CD  HCi) C) 0 H H  h  H0 ft P1  b  HP1  HC)  ft 0  CD  C)  H-  H-  P1 C) CD  C) h CD P1 CD CD CD  H-  HC)  ft  -  0  b  I-  C) P1  C)  H-  P1  C-Q  0 h  Q  P1  CD  CD  H P1 ft  ft HC)  P)  HCD  H,  0  <  HH Hft  CD ft P1  P1 H  5  CD  ft  CD  ft  CD Ci)  C)  CD P  h  3 Q  P1  C)  <  P1 h CD  Ci)  p1  ft h  C)  CD  CD  ‘d  HC)  P1  Q  h  0  H-  H,  0  ‘<  Hft  C)  H  ><  ft 0  H  ft  0 ft CD  d  Q  P1  -  CD Ci)  H 1  ft  P1  .Q  P1  P1  < CD 1Q CD ft P1 ft H0 3  H,  0  H P1 ft H0  C) 0 P1 1  W  —  0  Y  C) P1 I  C)  H-  P1 3  II  0  CD  <  H  0  HCD Ci)  Q  Q  P1 3  CI)  II  0  0 Ci) d J  frj  •  (  CD •  CD  CD  H  C)  <  C)  CD 3 ft  5  H CD  CD  Hft HC) P1 H  C)  Hft  CD ‘1 P1 C) ft H0  ft  H  F\)  d  H  0  ft  <  P1 H Hft  .Q  P1 ft CD II  CD  C)  CD  H  H,  H-  -<  5  P1  Ci)  -  0  (Q  ft H-  CD h H-  H, H,  CI) 0 H  P1 H  ft  P1  H-  H  H,  0  P1 ft H0  I  ft  CD  C)  C) 0  P  CD  P1  <1  H CD  Li  •  0  IP1 ft H-  ft  C) CD 3  C) 0  CD  P1  CI) H H  P1 CD  HP1 ft H0  C)  CT)  CD  Hft CD  H,  0  C) ft H0  H,  P1  P1 ICD  Ci)  CD  ft  P1  CD  H P1 C)  Ci)  P1  H0  ft  CD 0 H  CD 0 HH  H-  H  H,  0  CD C) ft Ci)  H,  CD H,  H  HC) P1  0  H  C) 0  CD  CD  H  H  ‘  H  0  (t D2  0  HM CD  CD  U H  Q  I-’•  0  H  0  fl  •  0)  •  W  -J  W •  •  ft  H  H  p  +  -  CD  ‘xJ  S  0  h  H,  3 CI)  0  ‘0 ft 0 3 P1 ft H-  Q CD  P1 3.  °i -  0  —  -  -  M  0 H,  CD CI)  < P1 H  I‘  0  H,  H3 1Q  0  Ci)  ‘d  CD  C) 0  CD  ft  -  P1 Cfl ft  ft  0  C)  i—i  •  CD  (Q  P1  0  P1  HCD  ft  ft 0  CD H P1 ft CD  F  <  ft HP1 H H  P1  HCi)  H  H,  0  0  H-  <  P1  j  CD -  P1 H  H-  0  H0  H,  0  H CD  S  C) 0  CD  o  H D  Ift H-  P1  M  Q  P1  0  CD  -  ,  CD  CD  H  P1  <  H-  Hft  ‘-Q  H 0  CD  0  p1  ft  H CD CD CD  H,  0  CD  (Q  h P1  I  -  P1  ‘<  P1 H H  CD  0  ft  H-  CD CD N CD  CD  CD  i-  P1  .—  C)  H  Q  HCD H  k<  ft 0  ,.  H  0  H,  CD  P1 ft H0  0  g -  d  CD  CD  <  Ci) H-  CD  CD  C)  C)  Ci)  1  0  H,  CD  CD C) HCD CD  Ci)  C)  ft H-  -<  0 H  <  CD h P1 H  <  CD CD  ft 0  ‘1 HCD CD  Q  H3  <  H-  Q  -  CD  H  -  P1 Hft HCD  CD  0 ft  Q  p1  Hft CD  H,  0  Ci) CD  P1  CD C)  Li  CD h CD  ft  P1  p1 C) CD  H,  I-  Ci)  p1  I-  ft CD H H  P1  <  H  ft 1 0  CD  +  I—’  -  CD  H-  0-’  P1  HC)  H0  <CD CD S 1 P1 H < H  H CD CD  CD C)  0 H  5  ft CD  P1  P..  CD  ft  < P1  CI) 0 H  CD  CD  HN  -  0 H P1  F—’  5  CI)  0 13  CD  H13  Cl) F-  H  13  Cl)  CD  TI  0 13  Cl) CD 0  CD  13  -  Cl)  HCD  0  13  CD  Cl)  F-’  H0  >4  Ft 0  H,  0  0 13  Ft H-  Cli  1-4  Ft  CD 13  H-  Cl)  1-4  13  0  0 0  CD  13  Ft  CD  C)  Q  CT)  h  k<  J  5  H  H  C)  Cl) Ft H-  Ft  HCl  H-  CD  Ft  13 0  o  0  13 CD  Ft  -  CI)  CD  CD  13  Ft  0  CI)  H,  Ft  0  02  Ci) Cli H  CD  13  CD  N  H  5  0  13  H  -  H  C) H  H-  0 1-4  C) )i  02  H,  0  CQ  -  13  HFt H0  CD  —S  ICI)  Cli  TI  Cli  CD  Ft  Cl)  H-  H  13  (-Q Cl)  F1 H-  Ft  13  CD Ft  13  H,  H0 Cl)  Ft  H-  Ii  Cl)  H-  j-  CD  02  13  H0  13  —  1-4  CD  Ft Ft  Cl)  5  o  l 3 H-  0 1-4  CD -  TI  H-  -4  0  H  H,  -  CD  Cli Ft  0 CI)  13  -‘  13  Cl)  0  H-  F-  >< <  0  I-I  Q,  k<  -  -  CD  —  Cl)  TI  Cl) 13  F-’ HIQ  13  CQ  H-  >4  H CD  5  0 0  I  H  H,  0  0 13  HFt H-  TI TI  Cl)  CD  13  Ft  HCI)  Ft  CI)  h  H-  H,  <  H-  CD  ‘—3  CI)  CD  -4 CD  3  -  HCl)  TI  b CD  Cl) CI)  Cl)  S  CD  13  Ft  CD  0  Ft  HFt ‘-<  0  CD Ci)  H-  >4  Ft  Cl) Ft  1Q  Ft  H  H,  0  0 13  Ft H-  1-4  0  CD H H-  5  HO  Cl) 0  CI)  Cli 1-4 H0  <  H,  13  HFt H0  TI  Cl)  HCli  TI  13  CD  CD  5  j  Ft  0  I  CQ  Ct)  Ft  Ft  -<  0  TI  0 Cli  1-4  0  Ft  Ft 0  13  H-  CD TI  TI  H  <1  H-  TI  CD  Cl) ‘-<  5  3 Ft CI)  5 CD  Q  CD  I-  CD Cli Ft  Ft  T)J 0 H(1)  CD  D  H,  0  13  0  Ft H-  Cl  H-  0  CD  C!)  CD  Ft  Pi  1-4  0  0  Cl)  TI  13  Cl)  Ft CD  CD  H  z5  5  0 0  13  H-  02  F1 Ft HCD  H H0  1-i,  H-  TI  Q  Ft  CD  H  CD  Ft  ‘-4  i  d  13  H-  ‘<  )  5  Ft  H0)  >4  CD  CI)  HCD  <  IQ  13  H H0 Ft H-  H,  13  0 0  CD CI) CD  13  Ft  Cli Ft  13  -  —  Cli  CD  D  -  -  H  i  CD Ft  CD 1-4  1-1  ‘d Ci  --  CD  H  w  -‘  0  CD  13  P1  1  TI  Cl) 3  Cli  5  Cl)  Ft  Cli IQ Cl)  H0  <  0  Ft  ‘<  H  (.Q 13  H-  CD  13  0 Cl)  HCD U)  CD 0  02  U) CD  CD  Ft  P1 Ft  13  Ft  CD TI  CI) Ft  CD  CQ IQ  Ci)  CD  <  Cli  13’  h$ Ft CI)  h CD  H  Cl)  h  CD  <  CD  0)  J  ><  Ft  5  -  H0  0 >4  Ft  13 0 13  Cl Ci)  TI  CD  HCD  13  CD CD  b  Cli H F-’ ‘-<  h4  CD  13  CD  Q  Cl) W  F-  I  k<  I0  <  CD Cl) 1-4  H  0  13  H ‘<  ‘d 0  -  —  CD  H  ‘.o  -  -  Cl) F-’  Ft  CD  1-4  CD  1-4  Cl)  —S  0)  CD  CD 0 H-  Ci)  0 1 FCD Cli  3  0  5 0 13  H H  pi  H,  Ft  r.  Q  H  0  Cj  Ft  ‘  F-  >  0  Ft  CD TI  Cl) Cl) 0 1-4 H-  3  CD  CD  CI) H  HCD  -  -4  H0  Cli  <  Cl) CI)  k<  HC) HFt  0 ><  Ft  Ft  H  H-  Ft  0  Cl  pi  CD  CD  >  CD  0)  CD  -  Ft  Ft  i  -  —  0  —..  1 F-  H  -  Cl)  0)  CD  1-4  Ft  Ci)  H  H,  0  CD  5  CD Cli CI)  k<  Cli 1-4  5  1-4 H-  ‘d  CD  13  Ft  Cli CI)  CI) CD  HCI)  t Cl) Ft H0  H  CT) 0 13  Ft  0  -4  CD H13  CD 1-4  13  CI)  CD  I.Q  H-  13  13  Ft CD 0  1-4 CD  H Ft  0  13  0  Ft H-  CI) 0 H  IQ  13  H-  02  t Cli Ft 0 I‘-<  0  ICl)  CD  Ft  13  H-  CD  H-  TI  Ft  CI)  13  CD  Ft  H,  0  HCl)  H0 HFt ‘-<  >4  Ft 0 Ft 0  13 <  1 F-  —  Ft 1 F—  13  CD  CD  .Q  13 0)  0  C)  -  Ft Cl)  13  CD  Ft 1-4 H-  13  TI  13  Cli  Cl) Ft CD 1-4  TI  CD  TI  13 CD CD  h4  I-h  0  H1 F-  0  CI)  CD  13  Ft  ICD  F1 0  ><  CD  Ft 0  ‘<  Ft  H-  HH  Cli  -  Ft Cl)  13  H Cl)  CD  Ft  HFt Cl)  5  H H-  F-’ ‘-<  IQ 1-4 CD Ii Ft  5  Cl) Ft CD  k<  Ci)  II 0 0 Ft  CD  13  Ft  H  0  13  13  Ft H-  Ft  Cl)  H I—’  Cl  CD 1-4  0  13 CD  -  S—  CD  H  -  0  Ixj  —  TI  HCI) 0 0 H 0 1-4 CD  Q  13  )  -  TI  0 II Ft CD  Ft  H0)  -  <  b  Ft  Cl)  1-4 Ft  0  CI)  CD  1-4  Cli  Ft CI)  13  Cli  d H  TI  Ft CD  Cli H, H, CD 0  H  H,  0  II 0 0 Ft Cl)  --  13  0  F-  H  CD  1-4  CD  Cli  CI)  0 5  Z Ft  5  ‘<  CI)  13 CD  Ft  -  <1  CD  CI) H-  CD H  CI)  13  Cl) H-  5  -4 CD  k<  Ft  H-  HC)  >4  Ft 0  1 F-  I-  0  I-h  Cl) CI) HCI)  1-4  H  Cl)  0  CD  5  0 H  Ft  Cl) 0  >4  CD  CD  13  Ft  CD  H  H  13  0  CD 1-4 CI) Ft 0  13 TI  <  F  1 F-  H,  0 Ft  13  H H F  Ft  CI)  ) 0  21 of toxic Al are not reduced,  but activities are.  Calcium  amelioration may also result from direct physiological effects  (Parker et al.,  1989b).  Although much information on the terrestrial effects of Al dates back to the early part of this century, research in aquatic ecosystems is contemporary.  most of the Concern over  the effects of elevated Al concentration in surface waters has focused primarily on fish because of the clear economic and sociological importance of some species.  The principal  mechanism of fish response to Al is established as an alteration in the influx and efflux of sodium and chloride ions across the gill membrane. Al ion species interfere with Na-K ATPase in gills and thus regulation of plasma sodium and chloride  (Harvey,  1989).  The implication of Al in several human disorders such as Alzheimer’s disease and Osteomalacia has been of public concern and scientific controversy in recent years. Most Americans probably consume 2-25 mg Al daily,  with 1-10 mg  from natural sources including food and water, additives, utensils  0-20 mg from  and 1-2 mg from contaminations from pans and  (Greger,  1992)  2. Acidification of soils and surface waters  Soil acidification refers to a complex set of processes that result in formation of a soil more acidic than the parent material. broadest sense,  Soil acidification,  therefore,  in the  can be considered as the summation of  22 natural and anthropogenic processes that lower measured soil pH  (Krung and Frink,  1983)  or reduce base storage.  In forest  ecosystems, natural acidifying processes include base cation uptake  (by plants or microbes); natural leaching by  carbonic, (Ulrich,  organic, 1980)  .  or nitric acid; and humus formation  Anthropogenic acidifying processes include  biomass harvesting which remove base cations, conversion,  land use  fertilization, as well as acidic deposition.  Attempts to measure soil and surface water acidification often center on attempting to detect changes in pH values.  Though this approach seems intuitively  obvious, practical considerations ranging from suitable analytical methodology,  spatial variability,  and  determination of soil horizonation to changes in land use patterns often severely limit the usefulness of this rather simple approach  (Robarge and Johnson,  1992). A more  quantitative measure of soil and surface water acidification can be obtained by defining it as a decrease in the acid neutralizing capacity 1991)  .  (ANC)  (van Breemen,  1991; Reuss,  ANC is equal to the quantities of basic components  minus those of acidic components. What is ilacididfl or “basic” depends on the reference pH chosen. The transport of Al is an important aspect of the development of soils in northern temperate regions. with precipitation surplus,  dissolution,  In areas  downward transport  and subsequent precipitation of Al is a natural process.  Q  5252  W —  -5  CD CD  CD  52  HC)  H-  C)  5)  52  CI)  b  ‘-<  —  H--C)  CD  Cl  CD Ft  0  5  Ft CD 52  C)  CD  CI)  I-  H U) 0)  -  -  H  5))  CD  Ft  CI) Mi Mi  CD  b  Ft HCI) H H ‘-<  Ft Cl)  0  CD CD  5))  C)  5  CI)  W ICD CD  CI)  —.  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() 3  HH HN CI) Ft H-  0  5  Q  CI) 3  CQ  H-  CD CI C)  H  0  Ft H-  C) J  CD  CD Mi Mi CD C) Ft CD  52  Ft Ft  CD  C)  52  H-  0  H-  HFt  0 CD  CD  52  HC)  52  CI) C) H-  H3 (  I-  C) CT)  C) 0  H HN CI) Ft H0 3 CD  J  Cl) I-  CD  0 CD  5  C) Ft CD  Mi CD  5)) Mi  H ‘-<  CI)  0  I  d  0 CD HFt H0  CD  Q  HC)  Q  CI) C) H-  H  •-  CD 0 HH CD  0 i  CD  5  CD 0  52  CD Ft CI)  CD I-  52  Ft 0  H  Mi  CD H  HCD  H HCD Ft  HCD  -  ] A W  -  -5  Mi Mi CD  b  0  t-’  H-  52  5))  -  j—  M  -  A  ‘CI  -  Mi Mi CD  5  H-  5  CI) H  —  Ui  I  H  -  i4  —  Cl)  Mi Mi  CD  CI)  C)  CD  Ii  Ft H0  CI)  C)  -  1”.)  •  0)  I  0  Ui  —S  Mi CD H  Mi  i Ft CD  C)  CD HI—’ H-  -  O  -  cx  I  H  -  S  1-5  Mi CD  Mi  b  Ft CD  CI)  b 0  C) 5)) I-  CD  CD  (Q  H CI)  d  CI) Ft CD  >< HS  0  I-  CI)  HFt  CD  U 3 HCD  5 CD C)  1-5  CD  Mi  Mi  LQ  H3  0  H H  0  Mi  J CD  Ft  H HCD Ft CD  —  H  Lo  H D  —S  HC)  I-  H  H CD —  5  J  >  CD  I-  0  -  HH CD  CD 0  H-  I-  C) C)  0  CD  5  HCD  CI)  CD C)  5  1  H-  Mi CD  Mi  tY  I  0 Mi  HCD Ft  II  CI)  LO W  H  —  -  CI) H  Ft  CD  I-  CD  h 0 CD CD  --  H U) U) 0  -  CI) H  CD Ft  CT) CD  Z  0) W —.  H  “i IH-  1  I-  —..  CD  52  C) H-  CI)  HC)  0  52  CI)  H U) U) 0 —  —  CI) H H  H Ft h 1Q CI)  CI) Mi  CI) i 52  CD CD  CD  --  H U) —2 U)  -  P  0 I-h HCD H  Cl) C)  Q  CI)  )J  0  II  C)  0  ‘d  i  52  HI—’  b  H-  CQ  H Ft H-  h CD CD  CD CD  I  H CI) i 1  H-  Q  J  C)  52  0  -  CD  1Q  CI)  C)  t3  CI) CD  CD  HH  0  CD  CD CD CD  Ft  0 Mi  ‘-<  I-  Ft  HCD  5  CD  C)  H  CD  1D  Ft  Ft  )  Ft  Ft H-  CD  1-5  LrJ  h  CD  CD Ft  CD  Ft  h  0  52  CI)  CI)  0 ‘C -  CI) H-  ‘  Q  3  H-  CD CD I< CD  0  CD CD  b  CD  <  J  k<  Cl  CI)  CD  -  HC)  52  H-  C)  CI)  5  Mi h’l Q  I-  Ft CD  CI)  Cl) CI) h 1Q H-CD C)  5  Ft  II  Z 0  0 Mi  h Ft CD  CI)  H-  —  H-CD 0 HQ. HH C) CD  HFt H-  d 0 CD  CD  52  HC)  52  C) H-  CI)  3  5J 0 Ft  Ft 0  52  CD  Ft  H-  II  CI) Ft Ft  CD CD  CI) < CD  CD CD  (-Q  )  C)  CD CD  Cl)  3  I-  CD  0  Ft H  5))  Ft  C) CD  0  C)  H  HC)  CD  S  0  S  0  H C)  CI)  ‘  (Q  0  H-  C) 1 CD CI) CD CD  H-  -  Ft H ‘-<  C) CD  CD  L’J W  24 of podzolization  (David and Driscoll,  1984; Rutherford et  al.,1985) During precipitation events,  acidic deposition entering  the soil is unlikely to reach equilibrium between liquid and solid phases as water rapidly infiltrates and percolates through the profile  (Hooper and Shoemaker,  1985).  Residence  time of water flowing through soil will be the crucial factor when assessing effects of acidic deposition on Al movement.  Lateral water flow may further reduce contact time  of leaching waters with some soil mineral horizons  (Dahlgren  1989). When significant lateral flow occurs,  et al.,  organically complexed Al may be transferred to surface waters  (Driscoll and Newton,  1985)  rather than undergoing  precipitation in soil mineral horizons. Humic material may act as solid-phase adsorbent controlling solution Al under conditions of lateral flow through organic surface soil horizons  (Cronan et al.,  1986).  Temporal fluctuations in total and free monomeric Al in soil solutions and surface waters under conditions of high flow will not be adequately explained by models that assume thermodynamic equilibrium between infiltration water and soil mineral phases  (Hooper and Shoemaker,  1985).  In well  drained soils in which percolating soil water makes prolonged contact with the soil mineral phase, Al activity in soil solution should be controlled by dissolution! precipitation of a discrete mineral phase. Models treating  CD  3  H  CD W  ID  Cl  a)  a)  it  CD  h  it  C)  ID  h  3 it CD  (.Q  H,  0  H-  I-  CD  1J  H  ‘<  a)  0  ID  C)  H,  0  it a) CD  ID it  H  0  Cl  H CD  CD  Q  H-  Hit  <  S  1  H-  CD  CD Q a)  ID it CD II a)  ID  HH a)  0  a)  H-  a) CD  ID  0 it H-Cl  F-’  it H0  H  0  a)  H,  0  0  HID it H-  0 C)  I-  ID H  CD  5  H-  -  -  k<  a) a)  ID  a) it HH,  LJ  h  CD  it  CD it  CD  S  CD C)  it CD  HCl  S  H-  3  H0  it  ID  S  0  H,  HH  0  a)  H, H,  CD  CD  it  CD  h  H,  5 0  CD  CD I-  •  a)  a)  C) CD  0  II  -  HCD hl  HIQ  H  ID I-  CD  it  H H-  CD  Q,  H-  0 H  a)  CD  Hit  a)  H-  i  0  it H-  CD  S  a)  k<  HH,  Q  C) H-  ID  3  ID  a)  H-  a)  ID it CD  5  C) H H-  CD  a) it  a)  HH  0  a)  it  a)  1 CD  0  H,  ID  0  0  a) Hit H-  0  P  CD  C)  H-  Q  C) H-  J  it  ‘d  H-  C)  C)  ID it H0  H-  H-  ID C)  0  H,  0  it  PJ 3 Q ‘ti Q H-  it  a)  CD  it  5  H-  H,  H-  Cl  H-  ID C)  HH  0  a)  H,  0  C) CD a) a) CD a)  ‘1 0  ID H  ‘-‘I  0  I-j  H,  H  it CD  ID  I-  CD  5  it CD  CD  it  oH,  ID  •  CD UI  H  -  H-  ID  b’  it ID  ID  ID  ID it CD  it  -  JJ it  l)J  it  <1  H-  CD  H-  I-  CD it CD  ID  a)  ID  CD  it  H-  a)  H-  IQ  H  0  0  it H-  ID  C)  it HH, H-  CD  H-  CD  .D CD CD —  H  -  -  ID H  CD it  ID  —  0  H  it  H-  S  H-  1  HH H-  Q  CD  it CD  ID  5  H-  X  0  ID  0  it  it  CD  H-  C)  H, H-  H,  a)  H  ‘-  CD  ID  a)  I-  0  W  -  0  H,  0  a) 0 HH  H  ID  CD  H-  5  Hit  a)  CD  5  H-  it  C) CD  CD  Q,  H-  Cl) a)  3  it H0  a) 0 H  ID it  it  HC) ID it CD  H-  a)  0  I-i HN  0  a)  H  0  a)  0  Q  0  (1)  Hit  it a)  CD  5  H-  h-  CD  ><  CD  ‘d  CQ  H-  C)  CD ID  I H  S  H  0  C)  •  —  H CD CD Ui  -  CD h  ID  5  CD  0  (1)  ID  CD  0 0  ‘d  -.  H LO CD  -  C) 0 H H  H-  ID  Cl  ID  H-  <  ID  CD  C) ID a)  CD  it  Cl)  b  0  it  ‘-  CD p)  ID  it  0  a)  0 CD  a)  H-  1D  it  -  -  H H  ID  ID H it  Q  i  J  a)  CD  Q it  i-  0  H,  it  Hit  H-  C) it  ID  H  0  H-  it  0 H  ‘-<  j  Q H  CD  it  a) H-  LQ H-  a)  Cl  a)  CD  CD  0 5  a)  3  -  H .0 ID H-CD CD i a)  H  <  CD  <  ID it CD H  Q  IJ  P CD  ID  a)  CD  H  0  H,  0  CD  H ‘<  çu  -  -o  0  CQ  -  it  a) it ID  0 i  C)  o  H-  HH H-  CD .Q  CD  it  H,  0  CD  H  ID  CD Cl  CD  ‘d  C) C)  ID  H ‘<  5  C)  H  +  “  H  ID  a)  J  CD  it it  H-  II  CD  W  +  +  H  +  w  +  H  tr  k<  5  0  a) a) H-  CD  -  ><  CD  5  H-  H  H-  CD  CD  C)  H-  I-  H  0  H  --  +  it  H-  CD  Q  H-  ><  0  ‘  Q  it IH-  I  H  H,  0  it H0 3  ID C)  CD  CD  it  H,  Q  a)  CD  it  H-  CD  H  C)  CD  .  H-  it  H-  C) it H-  +  H  -  Ui  CD  H  )J H  CD it  Q a)  j  CD  ç  H  -  a)  0 H  it  C) 0  Hit CD  a)  b b  H-  Hi  I-  0  H,  CD  H-  F-’  H  it ID  a)  k<  ‘1  C)  S CD  a) 0  CD  5  a) a)  ID  $1 a)  CD  a)  it CD  J  S C!) CD H-C  ID 3  CD  CD  it 0  H-  h  -  ()  H  0  it H-  Q H  a)  HH  0  a)  ID  a)  H  H  0  H  0  0  H-  ID it  H HC)  H  ID C) H-  Q  CD  C)  I  H3  0  it H  H  a)  CD d 0  C)  H-  P  C) H  U]  26 of northern Europe and eastern North America that currently receive acidic inputs have undergone substantial changes in land use and consequent vegetation succession during the past two centuries  (Brand et al.,  forest are now aggrading,  1986). As many of these  the natural soil acidification  that accompanies such regrowth cannot be attributed to acidic deposition  (Krung and Frink,  1983).  Acidification of soil and water is, environmental problems,  like most recent  a consequence of change in the  natural cycles of elements.  It has been recognized as a  fairly complex process involving many mechanisms. Our current understanding about the processes of soil and water acidification is still limited and more research is needed.  27 Chapter 2 MATERIALS AND METHODS  I.  Study Areas  To address the issue of soil genesis under forest conditions in the Pacific Northwest,  the study focused on  Cowichan and Vancouver. As shown in Table 2-1,  two areas:  the climatic characteristics of the areas reflect conditions found within southwestern coastal British Columbia. The Cowichan Lake Research Station  (48°50’N,  in south central Vancouver Island, Victoria.  124°8’W)  is located  about 63 km northwest of  The area is a part of the mountain range which  makes up Vancouver Island,  and is characterized by a large  glacially scoured valley which drains to the southeast. The wet winters  climate in the area is characterized by mild, and relatively dry, moderate summers.  The forest regenerated  naturally after logging and burning which occurred in 1908. The forest is dominated by coniferous species, Douglas-fir hemlock  (Pseudotsuga menziesii Mirb.  (Tsuga heterophylla Raf.  Sarg.)  such as  Franco)  ,  western  and western redcedar  (Thuja plicata Donn.). The dominant soils are classified as Orthic Humo-Ferric Podzols and recognized as the Rumsley and Shawnigan soil series  (Jungen et al.,  1989).  They are  developed from glacial till. The bedrock is chiefly Mesozoic volcanic and sedimentary rock  (Holland,  1964)  The second area is at Pacific Spirit Park in Vancouver  H ‘< D2 CD  1) 1  CD  H  P  0  CD  i  g  0  H  H  CD  -  H 0  CD  Ft CD p1  Cl)  H H-  CD  CD  H ‘-< CD  P3  P3  HC) P3 H  5  C)  rr I-’-  p1  P3  0  .  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H-  .  H-  .  U)  P3  CD  f1  Cl) HH  CD P3 C)  ft  P3  CDct  ft  I-hC)  CD P3  ci  HC  ci  P3  C!)  C)  H-CD CU)  it  —1  C)  çt H-  P3  H  C) H  P3  Cl)  H  M  CD  H  P3  0 ‘1  H 0)  W  C)  H-  C) Q  C)  rt H  P3  H-  C) H  C)CD P3  U)  U)  C)C)  H-  00  P3  CD  1 CD  ct  P3  CD  it CD  H  P3  H-  d  H-  CD C)  h  P3. c-i H-C) -  CD  1Y  i  ct  i  P3  P3  CD P3  I-i  CD  CD  rt  U)  Ct)  it  CD frj  H-  CD P3  I  Ci CD C)  —  ItO)  CDCD QU) CDrr  ft  I-  CD  CD  I  CD  o  H  -  U)  CD  P3  .ij  coH  •o  -  U)  (  I  HH-  CD  CD-  C-t  q  —  30 Table 2-2 Sampling Designt  Study Area (mean annual precipitation)  Dominant tree  Soil  Decaying  moisture  wood  species  regime  Western  Sightly  hemlock  dry  Douglas  Wetter  +  -  Pedon#  V-i V-2  Vancouver 1258 mm  fir  +  -  Douglas  Moderately  fir  dry  Western  Slightly  hemlock  dry  Douglas  Slightly  fir  dry  Western  Moist  +  -  +  -  V-3 V-4  C-i C-2  C-3 C-4  Cowichan 2076 mm  hemlock  +  -  +  -  Sites were selected by Professor K. Kl±nka, Department, University of British Columbia.  C-S C-6  C-7 C-8  Forest Sciences  31 Details of the following methods and procedures may be found in Methods of Soil Analysis  (Page,  1982),  page number  is given in parenthesis. 0), 2 pH(H  ), 2 pH(CaC1  and pH(NaF)  were measured in  supernatant solutions of soil in distilled water, , 2 CaC1  and 1M NaF  (Wada,1986),  respectively.  content was determined by a LECO analyzer.  0.01M  Total carbon  Total nitrogen  content was analyzed by Kjeldahl digestion method  (p.610).  Particle size analysis was done by pipette method after oxidizing organic matter and removing free sesquioxides (Klute,  p.399)  1986,  Cation exchange capacity was determined by measuring 4 after replacing cations by 1M neutral ammonium sorbed NH acetate method (Juo et al.,  (p.160)  1976)  .  Effective cation exchange capacity  was calculated by adding KC1 exchangeable  Al and ammonium acetate exchangeable Ca, Exchangeable Al  (Alexch)  determined by titration 2.  Mg,  K,  Na.  was displaced with lM KC1 and (p.164).  Chemical extractions 2 solution Reactive aluminum was extracted by 0.5M CuC1  (Juo and Kamporath, (Fenta) method  1979).  Organic-bound Al  (Alnta)  and Fe  were estimated by 0.lM sodium nitrilotriacetate (Yuan et al.,  1993). Amorphous Al  ) 0 (Al  and Fe  ) 0 (Fe  were assessed by extraction with acid ammonium oxalate solution for 4 h  (Ross and Wang,  1993)  .  Free  (nonsilicate)  sesquioxides were extracted by citrate-bicarbonate-  32  dithionite  solution at 80°C  (CBD)  (Mehra and Jackson,  1960)  Aluminum and Fe contents in the above extracts were determined by atomic absorption spectrometry 3.  (AAS).  Mineral identification  Clay samples  (< 2 tim)  for X-Ray Diffraction analysis  were separated by sedimentation after oxidizing organic matter by hydrogen peroxide and removing sesquioxides by CBD.  Magnesium and K-saturated slides were prepared and run  at 20=3-33°.  Their glycerol-solvated or heated  (300°,  then  slides were run at 20=3-16°.  550°C)  For identification of amorphous minerals by infrared spectra,  0 to destroy 2 soil samples were treated with H  organic matter, dilute HC1  then dispersed by ultrasonic treatment with  (pH 4)  sedimentation.  .  Clay-size samples were separated by  Synthetic imogolite was synthesized by the  method of Farmer et al. (1977)  .  The infrared spectra of the  soil samples and synthetic imogolite were recorded on a Perkin Elmer infrared spectrometer using a KBr disk. Detailed procedures for mineral identification may be found in Methods of Soil Analysis 4.  (Klute,  1986)  Phosphate sorption studies  Seven 1-2 g samples of each soil were shaken for 24 h 2 containing between 0 and at 25°C with 30 mL 0.002 M CaC1 PO 2 KH . 3.5 mM 4 1984) pH  ,  Since P sorption is pH dependent  (Barrow,  sorption experiments were conducted at the original  ) 2 (CaCl  values of the soils. After shaking,  the  33 suspensions were centrifuged at 13800 x g for 10 mm.  and  the phosphate concentrations in the clear supernatants were determined by the method of Murphy and Riley  (1962).  The  difference between phosphate concentrations before and after shaking with soil samples was used to calculate the quantity of phosphate sorbed by the soil samples.  The sorption data  were fitted to the linear form of the Langmuir equation (correlation coefficients >0.98) (X)  and the sorption maximum  was calculated for each sample  (Barrow,  Natively sorbed phosphate  was assessed by  ) 0 (P  1978)  extracting soils with acid ammonium oxalate solution for 4 h (Sheldrick,  1984)  .  colorimetric method  In the extracts,  P was measured by a  (Wolf and Baker,  1990).  0 The sum of P  and Xm is taken as total P sorption capacity. 5.  Simulated leaching experiments:  Soil column leaching experiments were carried out as follows: 7-Bf 1),  for each of three soil samples  (V-4-AB,  C-4-AB,  C  25.0 g soil was gently packed into a 50 mL plastic  tube with a small hole  (Dl mm)  at the bottom. A piece of  Whatman 42 filter paper was placed below the soil in each column to prevent loss of particles during leaching.  Each  column was leached with 150 mL leaching solution at the rate 1 at room temperature. The leaching solution of 25 mLh contained 1.0 mM of each of the following: citric acid,  salicylic acid,  sulphuric acid,  and  oxalic acid,  malic acid,  nitric acid.  The pH of the solution was adjusted to 4.0  34 (pH values of LFH and decaying wood in this study  using NaOH  are close to 4) forest litter  These organic acids are commonly found in  .  (Tam and McColl,  1991)  and sulphuric and  nitric acids are components of acid precipitation. Vacuum was applied to the columns when necessary.  The leachate was  centrifuged at 25900 x g for 15 mm. A portion of the supernatant was saved for determination of Al and Fe,  the  remainder was used as leaching solution for soil samples V— 4-Bfl,  C-4-Bfl,  and C-7-Bf2  (the leachate from sample V-4-AB  was used as the leaching solution for sample V-4-Bf 1; for C-4-Bf 1;  C-7-Bf 1 for C-7-Bf2).  This time,  C-4-AB  the leaching  experiment was conducted at the same soil/solution ratio as mentioned above,  but at a slower rate:  15.0 g soil was  . 1 leached with 90 mL solution at the rate of 8 mLh  It was  assumed that water moves slower in Ef horizon than in A horizon under field conditions.  The leachate was centrifuged  as above and saved for determination of Al and Fe.  Each  column leaching experiment was duplicated. For determination of Al and Fe,  20 mL of the  supernatant were digested with HNO 3 and H 0 with heating 2 until colourless, digestion,  to oxidize organic matter. At the end of  the solution was heated to dryness and the  residue was dissolved with dilute HC1  (pH2).  Al was measured by the chrome azurol S method Powell, Ellis,  1989) 1982)  .  The content of (Close and  and Fe by o-phenanthroline method All measurements were duplicated.  (Olson and  35 6.  Resin extraction experiments:  The procedure of the resin extraction used is similar to that of Sakagami et al.  (1993). The <2 mm sample was  ground to pass 100 mesh sieve.  Two g of 100 mesh sample and Rexyn 101(H)  10 g of H-saturated cation-exchange resin,  ), were placed in a 100 mL 3 (active group RS0  R203  polyethylene tube,  and 20 mL distilled water were added. The  tube was shaken for 20 mm ) pH(H 0 adjusted to the 2  and the pH of the suspension was  value of each sample with NaOH. This  step was repeated for a total of three times. Afterwards, the tube was shaken for 48 h at room temperature. At the end of this extraction, 10 mm  the tube was centrifuged at 23300 g for  and the dissolved total carbon  inorganic carbon  (IC)  (TC)  and dissolved  contents in the supernatant were  determined by a Shimadzu total carbon analyzer 500) from  .  Dissolved organic carbon (TOC-IC)  (DOC)  (Model TOC  content was calculated  and expressed as cmol/Kg soil.  The resin was  separated from the soil sample by sieving the suspension through a 60 mesh sieve. The separated resin was shaken with five 50 mL aliquots of distilled water. any soluble Si. After this,  the resin was extracted by acid  ammonium oxalate solution for 4 h. Al  (Alr)  and Fe  spectrometry; Si  (Fer) (Sir)  molybdate-blue method  This should remove  The content of dissolved  was determined by atomic absorption was analyzed colorimetrically by the (Smith,  1984)  .  Thus,  minerals should not be included in Sr•  Si in crystalline  36 7. Al activity in soil extract Soil samples were shaken with 0.01 M CaC1 2 solution for at 1:2 soil/solution ratio.  30 mm  This extraction time is  enough for the solution to approach equilibrium with Al (OH) 3 having a solubility constant of gibbsite 1989).  (Dahigren et al.,  The suspensions were passed through Whatman 41  filters,  then centrifuged at 27000 x g for 15 mm.  The pH  values and dissolved organic carbon contents of the supernatants were measured. Al concentrations were analyzed by the chrome azurol S 1989).  method  (CAS)  , 3 CAS reacts rapidly with A1  Al (OH) (aq) 3  ,  Al (OH) , 4  (Close and Powell, , 2 AlOH  (OH) and 4 A1 4 2 (OH) 3 Al . 5  unreactive toward the polymer A1 , 7 32 (OH) 13 and the hydroxy-aluminosilicates, (Kennedy and Powell,  ,  It is  colloidal Al (OH) 3  imogolite and allophane  1986). Although aluminum bound to  2 fluoride is soluble in 0.01 M CaC1 1988)  , 2 Al(OH)  (Moore and Ritchie,  no correction was made for fluoride complexes since  these complexes are not included in the CAS reaction and Powell,  1989)  8. Acid neutralizing capacity  (ANC)  Soil acidity may be described in two aspects: factor and capacity factor. intensity factor of acidity. is a capacity factor.  intensity  The pH of a soil describes the The ability to resist changes  The resistance to pH change as H is  added is called acid neutralizing capacity, alkalinity  (Close  (Binkley et al.,  1989).  or titratable  37 Compared with the determination of ANC of water samples, measurement of ANC of soil samples is much more complicated and there is no standard method to follow, unlike the case of water samples  (Gran plot method)  .  The  procedure described here is similar to that of Binkley (1986)  .  Three g of soil sample were shaken 30 mm  0.01 M CaC1 2 solution. 30 mm  with 30 mL  The mixture was allowed to settle for  before the pH was measured with a combination  electrode in the supernatant.  This is the initial pH value.  Incremental amounts of 0.1 M HC1 were added to the suspension. After the suspension was shaken for >3 h and allowed to settle for 30 mm,  the pH value in the  supernatant was measured. This step was repeated till the pH value reached 3.5.  The amount of H consumption was  calculated and taken as the acid neutralizing capacity to pH 3.5.  38 Chapter 3 RESULTS  1.  Soil texture and carbon content  The most frequent soil texture class Sandy Loam Silt Loam  followed by Loam  (21 horizons), (5 horizons)  and Loamy Sand  (Table 3-1)  is  (16 horizons),  (2 horizons).  The  Cowichan pedons have lower sand and higher clay contents than the Vancouver pedons.  Carbon content varies from 0.53  The higher C% in the Ae horizons of V-i and V-3  to 5.15.  may be a result of incomplete removal of fiber-like organic residue from mineral part by pick-up and sieving. 2.  Reaction and cation exchange characteristics  Soil reactions are acidic in all horizons for both the Vancouver and Cowichan pedons  (Table 3-2). Virtually all pH  values fall within the ranges 3.87-5.83 ) 2 (CaC1  .  0) 2 (H  and 3.14-5.11  The lowest values in the mineral soil always occur  in the Ae  (when present)  or AB horizons.  In these acidic soils,  rich in amorphous materials,  raising the pH to 7.0 artificially creates additional charge on the surface of soil constituents. The cation exchange capacity as determined by neutral ammonium acetate  ) 7 (CEC  necessarily includes a large component of pH-dependent charge. capacity (1976),  For variable-charge soils, (ECEC),  effective cation exchange  proposed by Kamprath  (1970)  and Juo et al.  undoubtedly gives values closer to the actual  capacity of soils to retain cations under field conditions  i4  0  CD  CD 0  0 CD  W  W  •  tO  H  •  H  M  P  0  W  CD  .  H  O CD  .  IØ  CD  •  0  •  •  CD  H  •  H W  .  H W  •  •  H W  H W  •  o  W  H H  .o  W  W  M  i4  i  -  .  P  •  O  -..i  i4  L\)  oUi  ui  M  L’)  H,  W  H,  l  J  W  W  0  W  H  H,  LJ  p  I  C)  CD  •  W  0  W  ‘J  W  o  a-  ID  -  M  H  H,  W  M  W  H,  H,  I  C)  W 0  -  W  •  —J  0  CD  M  0  ai  H  H,  tO  •  W  tJ  •  CD  co  H  W  D  a H  Jj  I  -J  •  tO  CD  •  H H  H  4.  p  W  FO  H  W  i  CD  •  H  —I  •  o  W  0  M  0  -.J  H  H,  W  CD CD  •  H  .  o  -.J  -  H  L\)  H  W  H Ui  .  Ui  CD  •  w  O  •  CD  H  Ui  CD  I W  CD  .  0  H  .  ui  O  M 0  0  -..j  C)  W W  .  H  ‘—]  .  --j  Ui  •  H ‘S.D  CD  Ui P  •  tO  i1.  •  ‘o  •  M H  •  0  tO tO  .  H  H  •  H  M  •  W D  —..]  0i  C)  H  H,  Hi  M  W  W  W  I  W  •  H  Ui  •  ‘o  Ui  •  M  0  ai  W  W tO  •  tO  Ui  •  —:1  •  H H  CD  0  M  H,  H il  •  tO  O  •  .o  CD  •  P Ui  W  .j  H  H,  W  I  0 ‘.D  •  W  •  i  0  •  ‘-  M  L\)  0  ai  Cl)  H  o\0  0  HN  II  0  (_)  pi  C) H  HP Ct  Q 0  CD H  Cr  CD  rt  0  C)  0  pi  C)  pi  0  H  Ct  H  H (1) Ct  CD  HN  (1)  CD  H  H  Ir1  H  I  w  CD  w  o  Ui  U]  W  -J  0  0)  Hi  kD  U]  Ui  0  H  i4  W U]  W Hi H  W -h M  ‘O  W  0  Ui  U]  W C)  Ji ‘-0 H  H H H H WHOOJi  Ni  Ni  IjJ  Ji  W  0)  W  U]  H  I—h  W  CO  U]  ‘D  W  Ji  Co  W  H W0)H  —J  W  —.]  W  U]  Mi M  —J  -J  H  Ni  Ni  -J H  M  Mi  W  CO  Ni  Ni  0  -J  H  Mi  W  W  Ji  LD  C)  Ni  0)  H H OH  0)  U]  0  W W  II  —a  W  0  Ui 0  H  Mi  W  0)  W  H H HH  i  0  W  FI  tJ  Mi  W  U]  —J  U]  H  i4  W  W  Cx)  -J  Ni  Ji  C  G  W C)  Ni  H H  Co  I.J  0  i4 10  Ni  Mi  Ni  W  0)  0  U]  C)  W  0)  0)  W  i4  W  H  0  H H H OHM  Ji  W  1D  H  Mi  W  W H  W Ni  0  Lo  W Co 0 0 0 Ni H W  0) Co  W Lx)  CO H  H U]  ‘0 0)  —1 W  H Ni  Co H  1  U] W  Ni Ni  U] Ni  0) W  i  0  HHHHHMHHOMOHNiOHHHOHHOH  U]  U] 0  W U]  U] H  L,D  4  H  Mi  M  W  Mi  W  Iii  W  Ui  Mi  w  I  I  I  C)  C)  C)  CD  CI H  0  C-)  H  I  W  CD  H  HI  0  41 Table 3-2 pH and Cation Exchange Properties  Pedon# and  pH 0) 2 (H  pH  7 CEC  Exchangeable Ca  ) 2 (CaC1  Mg  K  Na  ECEC Al  H  cmol (+) kg 1  Horizon  3.87 3.14  12.54  Bf 1  5.34 4.55  20.89 1.77 0.20 0.05  0.06  0.39 0.01 2.47  Bf 2  5.83  5.11  22.19 1.98  0.23  0.06  0.07  0.06  0.02 2.40  Bm  5.57 4.91  17.96 1.13  0.18  0.07 0.06  0.12  0.00 1.55  BC  4.88 4.15  18.21 0.74  0.17 0.12  0 .10 2.07 0.34 3.20  V-2 Bfl  4.51 4.19  14.45 0.12  0.04  0.06  0.06 1.59  0.08  1.87  Bt2  4.75 4.56  13.60  0.10  0.02  0.05  0. 03  0.42  0.04  0.62  BC  5.39 4.93  11.35  0.39  0.06  0.05  0. 02  0.09  0.02  0.62  V-3 Ae  3.95 3.31  30.04  1.42  0.29  0.07 0. 05 3.09  Bhf  4.79 4.30  29.56 0.10  0.04  0.03  Bf 1  4.87 4.49  15.08  0.20  0.03  0.05 0.03  0.51 0.06  0.82  Bf 2  5.06 4.61  28.26  0.31 0.05  0.04  0.30 0.04  0.73  4.23  14.74 1.23  V-l Ae  V-4 AB  3.52  0.40  0.15 0.05  0.05 3.24  0  .  02  0.93  0  .  03  0.17 0.07 0  .  04 2.52  1.16 3.89  1.31 4.92 0.20 1.12  0.96 4.03  0.07 0.04  0.42  0.11 1.81  0.86  0.40 0.07 0.03  0.18  0.01 1.24  18.13  0.12  0.02  0.04  0. 03  0.36 0.11 0.57  4.08 3.52  27.65  0.01 0.14  0.12  0.06 3.54  Bf 2  4.37 3.81  30.48  0.01 0.09 0.10  0. 04 2.79 0.25 3.03  Bm  4.68 4.08  18.02  0.01 0.06 0.10  0.03  4.66 4.13  20.80  0.07 0.12  Bf 1  5.18 4.50  18.62 1.15 0.13  Bf 2  5.50 4.91  19.88  Bf 3  4.84 4.65  C-l Bfl  C-2 Bfl  0.15  0.52 3.87  1.71 0.17 1.91  0. 04 1.35  0.14 1.73  42 Table 3-2  (Continued)  Bf2  5.06 4.49  16.24  0.09  0.11 0.10  0.03  0.51 0.00 0.84  Bm  5.06 4.41  13.90  0.08  0.10  0.04  0.69 0.05 1.04  BC  4.97 4.31  14.59  0.05  0.11 0.11 0.04  0.78  0.09 1.09  C-3 Bfl  4.80 4.23  15.68  0.16  0.10  0.10  0.04  0.93  0.11 1.33  Bf2  5.10 4.35  16.07 0.24  0.18  0.10  0.05 0.60  BC  5.15 4.54  11.69  0.10  0.10  0.07 0.03  C-4 AB  4.28 3.84  18.08  0.07 0.24  0.16  0.07 4.17 0.38 4.71  Bfl  4.89 4.25  20.52  0.21 0.19  0.15  0.05 1.11 0.12  Bf2  4.94 4.21  15.43  0.11 0.12  0.08  0.04  1.14  0.09 1.49  BC  5.09 4.35  18.20  0.17 0.13  0.09 0.04  1.14  0.00 1.57  4.53  25.19 1.02  0.49  0.15 0.06 4.68 0.79 6.40 0.11 0.04  C-5 AB  3.75  0.13  0.48  1.16  0.11 0.78  1.70  Bfl  5.16 4.56  24.40  0.60  0.19  Bf2  5.27 4.64  17.25  0.20  0.07 0.09 0.03  4.81 4.00  24.66 1.78  0.47 0.14  0.06 1.89  0.28 4.34  Bfl  5.04 4.80  17.95 0.06  0.03  0.10  0.03  0.30  0.02  Bf2  5.03 4.52  17.68  0.06  0.04  0.12  0.03  0.45  0.05 0.70  BC  4.80 4.40  16.27 0.05  0.04  0.06 0.03  0.69  0.05 0.87  C-7 Bfl  4.89 4.21  29.24  0.19 0.05 1.50  0.20 2.67  Bf2  5.07 4.23  16.65 1.81 0.49  0.12  0.05 1.38  0.04 3.85  Bf3  5.21 4.45  25.08  0.94  0.27 0.10 0.05 0.75  0.14 2.11  C-8 Bfl  5.12 4.39  19.38  0.79 0.21 0.10 0.06 0.93  0.16 2.09  Bf2  5.04 4.53  17.69  0.57 0.15  Bf3  5.20 4.51  18.45  0.58  C-6 AB  0.71 0.22  0.72  0.13  0.07 1.66  0.36 0.08  0.08 0.04 0.51 0.13  0.17 0.07 0.04 0.60  0.75  0.52  1.35  0.09 1.47  43 (Uehara and Giliman,  1981).  ECEC was calculated by the sum of  exchangeable base cations and exchangeable Al,  the value is  about one order of magnitude lower than CEC . Among 7 exchangeable base cations,  calcium  (sometimes Mg)  is  dominant, while potassium and sodium exist only in trace amounts. 3.  Chemically extractable Fe, Al,  Interpretations of these data  and Si  (Table 3-3)  are based on  the following assumptions about the three extraction methods (McKeague et al., (1)  1971;  Parfitt and Childs,  Sodium nitrilotriacetate  (NTA)  1988):  is used instead of  sodium pyrophosphate to estimate organic-bound Al and Fe (Yuan and Lavkulich,  1993). The commonly used sodium  pyrophosphate method yields somewhat ambiguous results due to the peptizing effect of pyrophosphate on soil particles (Schuppli et al.,  1983; Loveland and Digby,  1984)  and is  inconvenient if an ultracentrifuge is not available in the laboratory. NTA extracts the same amounts of Al and Fe as does pyrophosphate, while the dissolution effects on standard mineral samples are kept at a minimum. NTA has the advantages of not requiring ultracentrifugation,  ultrafiltration, or the  addition of a flocculating agent as is the case for the pyrophosphate method. (2)  Oxalate extracts both organic-complexed and  inorganic amorphous forms of Fe and Al. amorphous Al,  as estimated by  (AloAlnta).  The inorganic and Si 0 are  H iT  W U] H i4  C)  H 1.0  —.3 W  o  --.3  •  W  a]  [‘.3 C)  •  ci  [‘0  H U]  U] [‘.3  U]  •  •  M  W  W P  •  1.0  [‘.3  P a] •  ‘.0  W  •  W C)  P  [‘0  C)  10  W • H  C)  •  r’  1.0  C) H  U]  U]  C)  a] 10  [‘0  H -.3  H 1.0  •  H  • H  W  • P  (0  H  10  -  (0  W  W  W W  U] C)  M  (0  H  a]  H  •  •  •  C)  W —3  a] W  ‘-.0  a]  a]  -.3  H U]  U] —.3  •  •  a]  U] H  a]  1.0  1.0  M  C)  •  H U]  a]  i  i1  H W  H  —3  U]  CX)  1.0  [‘.3 [‘.3  U] H  a]  M —.1  •  C) M  1)  M ID  •  [‘.3  U]  1.0  H  [‘.3  •  P -.3  1.0  —-.3  •  H W  —.3 a]  (0  H  H  H M  —.3  •  W —.3  ‘J W  W —J  W M MU]  a]  U] U] —.3W  M -J  M W  M U]  a] a]  H a]  H U]  LD  H W  M U]  M a]  Hi k)  W H  Hi H  Hi M  H  Hi W  W Hi H  H  Hi t’J  M  nI  10  10  H  H [‘.3  [‘.3 [‘.3  .  W  H W  1.0  Z  C)  C)  U] P  •  [‘0  —3  (0  W W  10  a]  W C)  (0 i4  .  W  (0  H W  W  C)  [‘0  C)  •  [‘.3 [‘.3  [‘.3  10 -.3  10  a]  H C)  C)  •  W  H a]  —.3  W  •  H W  W 4  •  H W  M M •  W  a] C)  10  H —.3  W C)  •  a]  H H  C) U]  •  [‘.3 H  P W  •  W H  CO  W  —J —3  U] D  U] C)  Hi  W  i4  W —.3  C) kD  M  Hi H  W  C)  iT  ‘O W  C) H  M  Hi  [-.3 C) H  H [‘.3  H  —.3  •  W  W C)  a]  W C)  a]  W  •  [‘.3 [‘.3  [‘.3  C)  •  H  H C)  H W  W H  Hi H  W  H  (0 H  •  U]  W ,i  —3  H  1.0  •  H -  H  —.3  ‘..O  H H  M W  H M  CD  W  W  10  H (0 • U]  (0 C)  •  C)  C) a]  C)  -o  [‘0  H a]  U]  H  C)  —.3  U] W  C)  U]  M H  C)  W  [‘0  [‘.3  —3  H a]  -.3 1.0  •  H  (0  i4  (0  W  H  [‘.3 H  4 1.0  H P  .O  C)  U] H  C)  a]  M a]  Hi M  W  —3 U]  [‘0  1.0  C)  [‘.3 10  •  W  (0  iT  (0  C)  [‘0  [‘.3 W  [‘.3 W  •  H M  O  a]  W a]  a] U]  Hi H  W  M  • ‘-0  P U]  •  [‘0  C)  iI  i1-  W  •  —1  1.0  C)  •  C)  D  C)  t’J  U]  ‘—]  p U]  W C)  [‘0 a]  [‘3  H ‘.0 • U]  .3 1.0  •  H  U] [‘0  —.3  U] C)  •  P  1.0  •  H H  1.0  U]  U] U]  C) D  M  C)  [‘0  ‘-0  •  10  U] H  •  [‘0  ‘.0 [‘.3  H 0  a] -..3  •  [‘.3 H  [‘.3  C)  •  H  1.0  i4  -.3  a] .D 1  W a]  Hi L\J  U]  [‘0  H C) • U]  U] C)  .  W  W [‘.3  H  W P  •  W W  i1  W  H W  H  a] C)  U]  ID  W U]  Hi H  Z  C) • C)  C) -  •  F-’  1.0  W  C) C)  •  a]  1.0  U]  •  M  1.0  H  U]  W  a]  CD  H  H  0  C)  0  HN  0 M  CD  ‘-xl  -1+  Q  H-  ç-t  H-  CD  o  0  p3  3  0  CD  C) 0  HH H  cr3  P3  P  0  H  H CD  3  (-I  C)  3  rt  X  H H  CU  C)  H-  CD  C-)  I  w  W  H CD  CU  H-  II  H  HCt  La)  ct  C) CD  H-  Cr  0  HH  H rt  II  Ct  CD  H  ) CD  0r1  HH  Jo  U)  CD  to U)  CD  H  CD H  to  CD  LD  U,  to  .  CD  LO  LO  W to  U, U, U,  —]  H  CD W  4  H  U, U)  W CD  to  H  CD CD  W W  W H  .  to CD  CD  H  LO U,  H  H  W CD  U,  to H  H  i4 H  to ci  H O  ‘.-D  W CD  CD  II  to  CD  rtQ  ci  H W  CD  W  i  0  H  H  H  H  lI(D  CD  CD  to U,  ZH-  H  CD  CD  CD  H H  W U,  to  to U,  W W  CD  CD  W to  H  D  H to  LD  to -J  -  tO W  CD  to Ui  tO  Hi  to  to to  W  Hi  ti  CD  -o  o  o  tO  W  OC) H  Hi  Hi  1h  ll  W  W  W  H-O  7Ci)  CD  .  U)  CD <1  CD  U, H  H U,  to  CD  to CD  H H  .  CD  H  D CD  W CD  CD  -D  to  H  Hi  Iii  ci  U,  CD CD  to  CD to  LO  to  H  H  CD CD  H  H  ‘S.D CD  to —J  to  U)  H CD  CD  W  W to  —.J  H  to  W  to -D  W H  H  to  to  i4 U,  CD  —J  -  to  to  D  to  I-h  Lxi  H  W (2  ci  H H  H CD  W  H CD  H  CD  to  W W  H to  H U,  U,  H  U, H  CD CD  W CD  H  Hi  W  ci  .  CD  CD CD  U,  .  H  W  CD  W W  W to  CD  D  H i4  to  to  •  H Ui  W  CD  .  ci  ci CD  to  U,  o  W  CD  H U,  i  H to  CD to  .  W to  W CD  to CD  to  Hi  W  U)  CD  U) LO  CD  CD W  —]  H  U,  CD  to CD  W to  to H  CD CD  CD to  CD  W  H  I-h  W  —I  CD  to  CD  W LO  H to  CD  H  to CD  W  -  CD H  H to  CD ‘D  H CD  W  to  CD CD  to  CD  H to  LD  CD  to U,  W U,  ‘.O  O  W  to H  CD W  H CD  (2  H  .  to  CD  i4  CD CD  H  CD  to  W H  CD  H CD  to  .  to CD  U, H  to W  to  Hi  U)  CD  U, CD  U,  U, LO  to CD  ci H  W  CD  H  CD  CD  i4 H  H CD  W W  H  Mi  W  ci  CD  LD  CD  W  H  ID  CD CD  to H  CD H  .  CD  ‘O  .  H W  U,  H  ‘-o  W  to  U,  CD  U)  to  LO  CD  H  U, CD  H CD  D  U,  .  CD  I-D  W  to CD  U, to  U,  H  lxi (2  CD  U)  CD  CD  ci  H  CD  -  W to  CD  to  .  H H  CD to  W H  CD U,  to CD  to  Hi  W  to  to  W  H  to  H  ‘0  ci  ‘D  to  CD  H H  to  W H  4  U,  to  H  Hi  W  U,  W  (2 I W  (2  U,  U,  U) LO  to  CD U]  CD  W  CD  -J  H  U, LO  D  ci to  H ci  W  —j  CD  H  lxi ()  U,  H U,  U)  to CD  CD  H  H  —.)  W H  H  4  H H  H W  W to  W to  to  Lxi S  CD  C) 0  -  w  W  H CD  46 attributed to allophane and imogolite components; (3)  Citrate-bicarbonate-dithionite extracts all forms  of free Fe and Al  (hydro)oxides.  Imogolite is a hydrated aluminosilicate with a molar Al/Si ratio of 2.0.  The ratio of inorganic amorphous  =2 can be used as an evidence of the presence of 0 Al/Si imogolite  (Parfitt and Kimble,  1989)  .  The ratios of  Alnta)/SIo for the Bf horizons of pedon V-i, close to 2.  and V-3 are  This indicates the possible presence of  imogolite in these pedons 4.  V-2,  0 (Al  (see clay mineralogy)  Results of simulated column leaching experiments Iron and aluminum contents in leachates are listed in  Table 3-4. Aluminum concentrations in the leachates are higher than iron, to 8.85.  the molar ratio of Al/Fe varies from 2.46  The Al and Fe captured by Ef horizons were  calculated from the differences between AB and Bf 1 and C-4)  or Bf 1 and Bf 2  (C-7).  (for V-4  Much more Al than Fe was  captured by the Bf horizon for the same pedon. 5. DOC and resin extractable Al,  Fe and Si  A Cation-exchange resin can extract positively charged cations under certain conditions. extractable Al,  The contents of resin  Fe and Si are listed in Table 3-5.  Air is much greater than Fer and SIr of the same sample.  The potential contribution of Alexch to Alr seems quite small except in Ae and AB horizons.  Most of the Alr in Bf horizons  exists in forms other than exchangeable Al. Alr content may  0)  H  M  Ui M  0 M  Ui  D U)  U) H  W  o •  M H W  0)  o •  FO  0  0D  Ui  CD  M  U] Ui H U)  L’.) Ui  o Ui  H  H H  •  0  o  •  o o  •  •  o  0  0  -..J  •  •  W  •  0  •  U)  o  H Ui  i4  H  CX CX) LO  M  0  •  •  0  H [‘3  CD  xJ  H  CD 0 H  0  H  CD  ‘ij  H  IJ  H  •  )  —] M  •  0  M  M CX)  •  H  W  •  0  H [‘3  •  0  0)  •  •  0  •  H  o  •  H  •  •  H  H  H  Hi H  •  W  H  J  Mi H  Hi  Mi  H-  5  Cl)  —..  H  S  Mi  ‘-<  CD  Cr  C) Pi  w  Pi Cr CD  C)  p)  CD  H  o  H-  o  Cr  H  rr  CD  C)  o  C)  5  H  5  H  0  H  I I4  w  CD  H  ‘-  Ct  )  H  o  Q  Cr ..—.  CD  Cr II  C) CD  0  C)  0  p  ‘-d CD  Cr  p)  C)  CD  H-  0  N  H-  oh  H  0  CD  0  H  1.0  [‘-3  -  H 0  H  1.0  -J  •  [-3  H  -  U)  •  H  0  1.0  CD  H  •  o  H  U)  [‘3  •  0  0  -  0  0 0  H  •  U)  o  •  U)  H  [‘3  .D  -J  W  H  U]  CD  W  LØ  U]  [‘3  -  U) U)  •  0  [‘0 CD  H  1.0  -  CD  U]  •  0  0 U]  0  1.0 H  U]  H  M H  CD CD  H  H —J  CD  0  •  U]  U] 0  •  0  CD  H  [‘3  1.0 —.1  U]  M H  0  H  0  H  0  H  H, M  CD  CD  •  ‘.0  1.0 0  •  0  0 H  0  -.3  -  1.0  H  U] [‘3  0  H  H, H  0  [‘3  CD  .  H CD  [‘3 0 •  —J  U)  •  H  0 -.3  0  a  H  .  H  CD i1  0  CD -3  U)  .-.J [‘3 CD  H  CD H  .D  H, H  H  [‘J  H  0  H  H, M  w w  H H  w  H O  w  I  H  I  I  I  0  H  H, H  C)  C) M  C) W  C)  CD  U  I  C)  U]  —3  •  U)  H CD  -  0  U] 0  [‘3  —3 CD  -.3  [‘3  H -J  H  H  w  H, t)  U] CD  -  CD  CD  •  0  0 U)  0  1.0 H  1.0  H  ID CD  0  H  H, H  w  U)  [‘-3  •  -J  [‘-3  CD 1.0  -  0  0 0  0  CD i4  H  H -T  -.-J  i W  CD  0  •  CD  U)  •  0  CD [‘0  U)  0 U)  W  U)  H W  H  H  H, M  w  0  •  -J  CD  •  0  U) H  [‘3  1 F  CD  CD  H  D  0  H  H, H  w J  CD  1.0  •  H  [‘3  1.0  •  0  H CD  CD U]  0  U)  M U]  H  H  H,  w  CD CD  -  CD  U]  U)  a  •  H  0 [‘3  0  [‘3 —3  U]  —.3  W  -.J  CD  W  0 CD  •  U]  CD U]  •  0  i  H  [‘3  i4  H  [‘3  -J  0  H  H, 1”)  w  U] —3  •  H  U]  a  -  H  1.0  —3  0  U) CD  CD  H  U]  M  0  H  H, H  w  I  [‘-3  .  CD  U) CD  -  0  U)  i  1.0 —J  [.3  [‘3  U)  CD  0  H  H, M  w  H U]  .  H U)  U]  •  H  H  [‘3  U) H  U]  H  H  0  H  H, H  w  I  U) 0  .  0  ‘.0  •  0  0 0  •  0  U) CD  •  CD  H  --J  CD  H  -  (.Q  0 H  C)  0  HN  0  C)  0  xJ CD  H-  Cl)  H  0  CD  H-  Cl)  CD  I-Il  -  H  CD  H  Ct  C)  H  CD Ci)  0 C)  U]  W  CD  H  H]  49 Table 3-5  Bfl C-6  C-7  C-S  (Continued)  11.00  28.88  0.18  1.84  7.24  8.58  3.00  0.03  0.81  14.40  Bfl  10.71  22.97  0.00  0.22  4.25  Bfl  10.58  11.81  0.81  1.80  7.66  Bf2  9.37  1.86  0.01  0.52  5.00  Bfl  10.58  11.38  0.54  0.19  7.08  Bf2  10.93  18.16  0.00  0.40  7.83  AB  DOC= dissolved organic carbon  50 be higher or lower than Ainta  this and the high  (Table 3-4),  DOC content imply partial or total organic-bound Al may be extracted by the cation exchange resin. 6. Al activity in soil extract The pH values,  DOC,  and Al concentrations in the  extracts are shown in Table 3-6.  To calculate Al 3 activity,  the following equilibrium equations for the hydrolysis of 3 were considered Al Mesmer,  (Lindsay and Walthall,  1989;  1976) LogK°  Equations 3 Al  +  0 2 H  2 AlOH  +  3 Al  +  0 2 2H  Al (OH)  2  3 Al  +  0 2 4H  4 Al(OH)  3 2Al  +  0 2 2H  2 (OH) Al  3 3Al  +  0 2 4H  3 (OH) Al 5 4  ‘  H  -4.99  [3-1]  +  2H  -10.13  [3-2]  +  4H  -23.33  [3-3]  2’  +  2H  -7.69  [3-4]  +  4H  -13.94  [3-5]  Since all pH values of the extracts were 3-6), 4])  Baes and  the activities of Al(OH) 4  and 4 (OH) 3 Al 5  activity.  and Powell,  1989).  (Eq[3-  5 M) (1X1O  However,  weakly bound  when CAS and Al  (Al-salicylate)  concentrations  (Close  the DOC concentration in the  final solution for absorbance measurement divided by a dilution factor, magnitude higher than CAS  (Table  (Eq[3-3]), 2 (OH) Al 4  CAS may react with freshly prepared,  salicylate have the same  4.2  3 are negligible compared with Al  (Eq[3-5])  organic-Al complexes  <  25-100)  M), 5 (1xl0  (DOC in Table 3-6  is about one order of  thus,  neglecting the  reaction of CAS with Al-salicylate should not bring  W  ci (3  0)  CO  [-3  H  H  -  CD  CO  H (3  U]  (3  C)  H  [‘3  U]  U]  U]  C)  CO  U] CO  CO U]  [3  CO  H CO CO  -  (3  [‘3  H  0  0) —3  [‘3 (3  CO (3  0)  ci C)  ci  CO ci  [3  [3  (3  U]  M  ci  C)  CO  CO  (3 U]  CO  H  (0 M  U] M  H  CO (3  CO C)  (0 CO  ci  (3  [3  CO  H C)  [‘3 U]  H  C) (0  L\)  W  W  H,  W  H  W  U]  W  H  J  CO  W  H,  W  H,  W  W  H  M  5  W  W  H,  W  H  M  H,  W  I  I  W  S  C)  0  [‘3  1.0  CO  C)  iT  CO [‘3  [‘3  CO U]  W  H  H  W  CX)  (0 0)  ci  ci  [‘3  H  0)  C)  ci  (3  (0 (3  H  H H U] CO  C) CO  H, J  Ui  M CO  W  Ui  Ui  C)  H ci  H  CO  -3  H  CO CO  (3  H  H,  U]  U] H  CO  C)  [3 (3  -  U]  (3  (0 H  (3  H,  Ui  -  H (3 C)  CO  1.0  U] U]  z  H ci  (3  CD  w  I  i4  C)  ci  H  (0 (3  0  C) ci  Ui C)  Ui  (0  (0  CO  iT  CO H  H  [3 —3 [3  CO  C)  CO  [‘3  H C)  .  U] (0  H  H (0  5  Ui  H H 0)  —1 (0  (3  H  H,  Ui  •  C) [‘3  [‘3  H,  CO  C)  U]  (3  C)  (3  [‘3  ) C)  [‘3  H,  Ui  H  CO  ci  [-3 ci  (3  H  (3  C) U]  F  H  H,  Ui  CO  H ci H  [‘3  ci  -3  -+  [‘3 (0  (3  CD  i  I  HN  Cr  H  <  C) Ct H-  Pi  5  H  0 C)  -3 03  0  0  0  CD  Ct  C)  P)  rt  Ui  H H  C’) 0  H  H  H-  C•)  0  H-  Ct  C-) CD  0  C)  H  CO  I  W  H-’ CD  I-1  U] H  CD  -)  H-  CD  rf  -I. z I:)  U,  —J -  NJ  CD  —J  W  W CD  W  CD  Ui CD  H H  W  -  W  •  NJ  •  NJ  CD  •  NJ  W  •  •  NJ  H  H  ‘.D H  W .  W  H, M  .  Hi W  —J CD  U,  -.J Lxi  o  W  w Hi H  W  W  W  eti Hi t’J  CD  w Hi W  cxi  I  C)  0  H  H  CD  CD  CD  .  H  CD  W  C)  CD W  LO  .  U,  .  W  H, H  NJ  NJ  H  H  —1  .  H  0 H  Hi M  NJ  Lxi  -  •  H  ‘.D H  W  H, H  0  NJ  Lxi  CD  0  •  W  .  W  W  w H, NJ w Hi H  W  H CD  0  .  H  Lxi  CD  W  U,  NJ  U,  Lxi  .  H  D W  W  I  I  U)  —.J  NJ  NJ  w  Lxi  H  •  U, U,  W  W  ‘  U,  C)  C)  w  NJ  H  U,  —J  CD  •  H  cxi  W  C)  0  NJ  Lxi H  Lxi  •  NJ  Lxi  -..  .  W  w Hi NJ  U,  H  --J 0  0 CD  .  CD  CD  W  w Hi H  H  Lxi  0  0  Lxi  i  W  U)  CD  H  0  .  H  Lxi NJ  W  C)  U,  W  NJ  NJ CD  NJ  cxi CD  .  W  NJ  w  Hi  U)  H  0  CD  0 NJ  --J  CD  .  W  w Hi H  W  I  C)  Lxi  0  W Lxi  NJ  CD  —J  W  C)  iii  CD  H-  CD  w I  H  I-  NJ  U,  53 significant error to the following calculation.  If there is  an error,  the result will be an over-estimation of Al 3  activity.  3 more This will make the conclusions based on Al  solid. Making an approximation, to the sum of Al , 3 [Al] ) 3 (Al  =  ) 2 (AlOH  2 and Al (OH) AlOH  ] 3 [Al  =  +  +  [Al (OH)  =  [AlOH y ] 2 =  [3-8]  [A1(0H) 1 y ] 2  3 [Al]/{l/Y  +  [3-2]  [3-9] and  / 0 1 K ( 2 Hi y  yields:  [3-6]-[3-9] +  ° K ( 1 2 H) /y  where the parentheses denote activity, concentration,  [3-6]  2  [3-7]  Combination of Eqs[3-1], =  ] 2 [AlOH  2•  [Al y ] 3  ) 2 (Al(OH)  ) 3 (Al  the CAS-reactive Al is equal  }  [3-10]  the brackets  and y represents the activity coefficient  for ions with valence i,  as calculated from the ionic  2 solution using the Davies form strength of the 0.01 M CaC1 of the Debye-Hückel equation  (Lindsay,  1979).  The K ° and K 1 ° 2  3 to are the equilibrium constants for the hydrolysis of Al form AlOH 2 and Al(OH) , 2  and are taken as i0 and 10-10.13,  3 activities in the extracts respectively. The calculated Al are listed in Table 3-6. 7. Acid neutralizing capacity As shown in Table 3-7,  ANC to pH 3.5 varies from 0.1 to  14.2 cmol(H)/Kg. As it is generally recognized that the values of ANC are highly dependent on the analytical conditions,  such as concentration of supporting  electrolytes,  rate of acid addition  (Kinniburgh,  1986;  C)  w  S  w  H,  H  H,  M  5 H,  I  I  H  H,  w  H  C)  C)  H,  W 1’J  H,  H  H,  w  W H,  w H  H,  w H,  ui  W  C)  w M  H  w H  H,  w  tJ  C)  w  5 H,  w H  H,  w  H  I  *  Q  Q  HN 0  h  0  CD  w  CD  H  ‘-  u-I  0)  ‘o  (0 (0  LD (J CO  a-,  U]  W  H 0  0  U]  H  U]  W W  U]  ca  W U,  F  F  U]  H  H  1’J  W  w  H,  H,  H  w  H,  w  H, li  w  H, W  0  —J  U]  w  C)  H  H H  —J W  I  L’J  H,  w  H  H M  0) 0  F  H  H,  w  CO  0-,  H U]  F  tEl  I  CO  (0  O Cr,  I4  M  H,  W  H 0  U] 0  H  H,  w  ,  (0  -  —.J  L\)  W  W  F  C)  (0  W  I (71  (0  0  U]  M  I  M  H,  tEl  W  (0  H —J  H  H,  W  M  0  U]  a  C)  U] o  L’J  H,  W  W ‘.o  H  H,  ti  I W  C)  CD  H  rt  0  C)  W  CD  H  ‘-3  U] U]  56  Valentine and Binkley,  1992; Funakawa et al.,  1993),  direct  comparison of the data presented here with those in the literature may be inappropriate. Table 3-8 shows the correlation between ANC and other (in logarithm scale).  chemical properties  reflect a characteristic of ANC,  This Log scale may  since the measurement of  ANC is directly related to the change of pH  (-log(H))  values during titration. ANC correlates well with organicbound Al  (Ainta)  and amorphous Al  ). 0 (Al  In contrast to Al,  organic bound Fe and amorphous Fe have no significant effect on ANC at pH 3.5.  The negative correlation between ANC and  Alexch indicates exchangeable Al is a storage of acidic  component rather than basic component, whereas the insignificant relationship between ANC and exchangeable bases reflects the fact that the percentage of exchangeable bases in the total basic components is very small.  The  implication of Al 0 and Alnta in acidity transfer will be discussed in Chap. 8.  4,  section II.  Phosphate sorption characteristics  The sorption maximum  (Xm)  is calculated from the  Langmuir one-surface equation: X/X  =  KC/(l÷KC)  [3-11)  which can be transferred to a linear form: C/X  =  C/Xm  +  l/KXm  [3-12]  where C= final phosphate concentrations in solutions having different initial P concentrations, and X= phosphate  w  I I I  I I I  2  H  Hi  -  °  -  C, >  CD  pjc  CD  U)  CD  IQQ  CDO  H,CD QU)  F—i  (.QJ  H-  0  Hi  0 Ui  II 0  d  -  L%)  r\)  w  0  0  I  II  I  I  I  I  I  I  I  (Q  1+  I 1:-I  •  0  Ui  0  H  o  II  0  Hi  H  •0  0  HU)  CD  <  CD  I—i  CD  w  H  H  H-  H-  Lxi  °  CD  ‘xj CD  w  H  -  C)  U)  CD  rr  0  rt  H-  C)  Hi  0  -  0  H-  rt  H  CD  0  C)  Hi  0  CD  H C)  Hi  Hi  CD  0  C.)  H-I CDCO  Hç.  ctw I’,  I  i  CDCD  Hi 11  H  Ob’  C)  U)  (_) 1+  Ui  58  sorbed corresponding to each C. Native sorbed phosphate  ) 0 (P  was assessed by acid  ammonium oxalate extraction. The ratio of P 0 to total phosphate sorption capacity in Table 3-9,.  (Po+Xm)  was calculated and shown  This value varies from pedon to pedon and from  horizon to horizon.  It is lowest in Ae horizons and much  higher in Bf horizons. 9.  Clay mineralogy  Interpretative results of XRD spectra are given in Table 3-10.  Chlorite is absent from Ae horizons, while  smectite and vermiculite are dominant minerals. The major mineral in Bf horizons is chlorite,  sometimes with mica and  vermiculite. Trace kaolinite may exist in the top mineral horizon of some pedons.  Quartz appears in every pedon in a  trace amount. Chemical extraction indicates the potential presence of imogolite in pedons V-i, V-2, 0 ratios are close to 2 Si  and V-3 since the  (Table 3-3)  .  (AloAlnta)/  The existence of a  trace amount of imogolite is suggested by the infrared spectra.  Fig.3-1 shows the spectra of the synthetic imogo  lite and clay-size samples. There is a weak absorption peak , 1 at 350-360 cm  which is the key criterion for IR identifi  cation of imogolite. The intensity of the peak is reduced after heating the samples to 350°C. imogoiite,  For identification of  transmission electron microscope  (TEM)  is an  essential tool; the result is subject to verification by TEM.  ii  ci  o  -  Ui  0  •  Ui H  ci  0  0  0 W W  0  0  Ui  0  U]  W H  CD  W  o  CD  H  0  CD Ui  W CD  CD  H CD  Ui  -  0  H  —3  O  CD CD  —.J  [‘3  W  O  H,  w  H,  w  W  H, H  w  [‘3  W  0  CD  —.1  Ui  -J [‘3  [‘3  H  Hi  w  CD  H  0  H  [‘3  -J  0  O O  0  0  -  CD H  W  H  [‘3  Hi  i[  0  Ui  0  CD  0  ci  CD  ci  0  Ui  Ui  H  J  H,  CD  W  H  Hi  CD  H  CD  W  H  W  W  —J  0  CD  0i  Ui  0  O  Ui  Ui  CD  I C)  H  Ui  0  Ui  G  Ui  CD  —J  U,  [‘3  Hi  t)i  H  0  CD  Ui  Ui  CD  CD  W  H  H,  ci  [‘3  0  Ui  H  Ui  —3  CD  H  C)  W  Ui  Ui  0  0  CD  O  [‘3  Ui  CD  W  CD  Ui  0  CD  CD  Ui  H  W  CD  [‘3  Hi  W  0  CD  O’i  Ui  i4 CD  CD  H  Hi  H -J  0  0  —3  H  W J  0  Cl)  0  0  +  I-ti  o  HN  o  0  H  CD M  I H W  C)  0  Ui  Ui  Ui  H  Ui  Ui  H, L\)  w  U,  [‘3  w  CD  H, H  CD  CD  Ui  H, [‘3  CD  U,  w  I  IQ  H  Q  S  C)  Cl)  CD  Ci  CD  S  0  H-  CD 0  CD  rt  Cl)  0  CD  I  w  H CD  CD  Ui  —.]  U]  U)  U] U)  0) o  Ui  U)  Lii  U)  0)  CD  H, U)  H  U)  CD )  Hi M  Lii Lii () H, M  Lii  0)  U]  0 U]  CD  0 U]  U]  U]  CD U)  FICD  Hi H  Lii  0)  H 0)  CD  H  H, H  Iii  0 )  H  W  i’ Hi H  0  Ui O  Ui  U]  U] Ui  aCD  H, M  W  U)  U)  U]  a a-  L’J  H, H  W W  W C)  U]  U]  CD  0  CD  U]  M  U]  U)  0)  0-  U]  U)  a0  MJHM  H, l’J  H  H,  W  U]  U]  Ui CD  U]  CD CD  WJ  H M  U)  U]  Lii  I  I  Lii C)  0  0  U)  Gi  H  U)  Lii C)  U)  U) 0  L\) U)  Li CD  M U)  —]  0) U)  0) H  H CD  0) H  0) [\J  .j  U)  U) U]  M CO  U] U]  U) 0  0  U) CD  U) 0)  U) CD  000000????00000??????  CD  0  H, L\i  H, U)  H, H  W  W  I  CD  H  (-) 0  CD  I  U)  CD  H  I-  0) 0  61 Table 3-10 Clay-size Crystalline Minerals  Pedon# and  Smec.*  Verm.*  Chl.* Mica  Kaoi.*  Q  trace  tr.  Feld.  Horizon  V-i  Ae  +  Bfl  V-2  V-3  + +  tr.  +  Bm  +  tr.  +  BC  +  +  tr.  IIC  +  +  tr.  Bfl  +  +  Bf2  +  BC  + +  Bhf  +  tr.  AB  +  Bfl  +  tr.  tr.  tr.  tr.  tr.  tr.  tr.  + +  Bf2  tr.  +  Bfl  V-4  +  Bf2  Ae  tr.  +  +  +  tr.  tr.  +  tr.  tr.  tr.  tr.  tr.  tr.  +  tr.  tr.  Bf2  +  Bf3  +  tr.  C-i  Bf2  +  tr.  C-2  Bf2  +  tr.  C-3  Bfi  +  tr.  C-4  Bfi  +  tr.  tr.  62 Table 3-10  *  (Continued)  C-5  AB  +  +  +  tr.  C-6  AB  tr.  +  +  tr.  Bfl  +  +  tr.  C-7  Bfl  +  +  tr.  C-8  Bfl  +  +  tr.  tr.  tr.  tr.  discrete or interlayered. Smec=Smectite, VermVermicu1ite, Chl=Chlorite, Kaol=Kaolinite, Q=Quartz, Feld=Feldspar  63 6  7  3  0 C) ci .0 1-4  0  2 ‘I,  5  1100  900  700  500  300 cny’  Figure 3-1 Infrared Spectra of Clay-size Samples 1 = synthetic imogolite (105°C) 3 = V13f2 (350°C) 2 = V13f2 (105°C) 5 = V2Bf3 (350°C) 4 = V2Bf3 (105°C) (105°C) 7 = V3Bf1 (350°C) 6 = V3Bf1  64 Chapter 4 DISCUSSION  I. Mechanisms of Podzolization  Various theories and hypotheses of podzol±zation have been discussed in Chapter 1.  In summary,  the discussion  concerning the pros and cons of the theories and hypotheses of podzolization may be grouped into two fundamental questions:  1)  which one is more important in the  translocation of Al and Fe in podzol formation, or organic acid?  and 2)  silicic acid  do Al and Fe behave in the same  manner in podzol formation?  1.  Differential behaviour of Al and Fe in podzolization Many studies on Podzols during the last decade  concentrated on short-range-order minerals and their roles in podzolization Wang et al.,  (Farmer,  1982; Ugolini and Dahlgren,  1991;  1991). While the traditional fulvate theory  emphasizes the importance of the sesquioxide-organic matter complex in podzolization 1982),  (McKeague et al.,  1983;  Duchauf our,  the proto-imogolite theory advocates the formation,  -Si0 Fe 3 0 A1 H transportation and precipitation of an 2 sol as the principal mechanism in podzolization al.,  1985;  Fraser and Farmer,  mechanism in podzol formation,  1982).  (Farmer et  Regardless of the  it is generally accepted that  Fe and Al behave in a similar way  (McKeague et al.,  1983;  65  Farmer and Fraser,  1982)  .  This assumption is reflected in  the chemical criteria of Podzolic B various classification systems  (Spodic)  horizons of  (Soil Survey Staff,  1992;  Agriculture Canada Expert Committee on Soil Survey, However,  1987).  little solid support has been provided for this  assumption,  except that the two are often extracted by  similar procedures.  Therefore,  more quantitative studies on  Fe and Al eluviation and illuviation in podzols in various environments are still needed. This section presents the differential distribution of Al and Fe in podzols,  examines the possible mechanisms  responsible for this distribution,  interprets the  distribution using thermodynamic data and discusses the implications of these results for podzol genesis and identification. a.  Index of movement:  Duchaufour  (1982)  Fe vs. Al  used an index of movement of Fe and  Al to characterize their differential mobility in podzols. The index can be calculated from contents of amorphous iron and aluminum hydroxides and oxides using the following formulae: (Ae or AB horizon) 0 FeifldexFeQ(Bf horizon) /Fe (Ae or AB horizon) 0 A1.d=Al(Bf horizon) /A1 From the Fe 0 and Al 0 data in Table 3-3, Alindex and Feindex were calculated and shown in Fig.4-1. times as large as the Feindex.  The Alindex  ±5  1.34-5.18  This result can be  66  T 12  10  -  A1  I  8•  6  4 ,•  ‘S  L1Fe  2t  —  ..  .o——cI  D  fl•  0•  I  I  I  I  I  I  In  C  N  00  I  I  I C  ‘  ,  •  SAMPLE Figure 4-1 Index of Movement for Fe and Al 11=CSBf1 1=V1Bf1 6=V4Bf1 12=CSBf2 7=V4Bf2 2=V1Bf2 13=C6Bf1 8=V4Bf3 3=V3Bhf 14=CEBf2 4=V33f1 9=C4Bf1 10=C4Bf2 5=V3Bf2  -  S  67 caused by either one or both of the following processes within a pedon:  (1)  Al eluviates faster from Ae or AB  horizons than does Fe;  (2) Al illuviates more to Bf horizon  than does Fe. Data from the column leaching experiments indicate both processes occur.  In Table 3-4,  leachates of sample V-4-AE, than 1.0.  From this,  molar ratios of Al/Fe in the  C-4-AB and C-7-Bfl are greater  one can infer that Al is leached  preferentially compared with Fe from AB horizons or even from Bf horizon,  if the Bf horizon exists on the surface of  the pedon. When these primary leachates than Fe)  (containing more Al  pass through the lower Bf horizons  C-4-Bfl and C-7--Bf2,  respectively),  (sample V-4-Bf 1,  the molar ratios of  Al/Fe in secondary leachates decrease,  indicating partial  removal of Al and Fe in the primary leachate. The amounts of Fe and Al removed by the Bf horizons can be calculated from the differences of Fe and Al contents in the primary leachates and the secondary leachates. The calculated results show that these Bf horizons capture much more Al than Fe,  since the captured Al/Fe ratios far exceed unity.  This indicates Al is more subject to illuviation than Fe. The overall effects of the ease of eluviation from upper horizons and the ease of illuviation in Bf horizon for Al result in the Alindex >Fejfldex in the same pedon. b. A thermodynamic explanation of Aljx>Fejex  Regardless of the relative importance of inorganic and  68  organic mechanisms in podzolization in various environments, these two mechanisms no doubt coexist in some podzols. particular pedon,  In a  Fe encounters the same pH conditions,  species and concentrations of organic acids as Al does. two chemical parameters can be used to compare Fe  Therefore,  and Al behaviour in podzolization:  solubility products of  minerals and stability constants of organo-metal complexes. Table 4-1 lists the solubility products of some minerals potentially occurring in Podzols and stability constants of Fe and Al with some organic acids. A general equation  (Eq[4-3])  dombining solubility and complexation  reactions can be derived from Eqs[4-l] (s) 3 M(OH) 3 M  ’ 3 (ML)  +  (s) 3 M(OH) K= [(ML)  L  +  3]  In a specific pedon, as does Al,  30H  +  [OW]  (L=ligands, +  [4-1]  K)  Kf)  [4-21  30H  [4-3]  [L] =KSPKf  Fe encounters the same pH and ligands  therefore,  only depends on K.  [4-2]:  (M=Fe or Al,  ” 3 (ML)  /  and  the concentration of mobile  ’ 3 (ML)  Since the differences between K-Fe and  K-Al are much greater than the differences between Kf-Fe and Kf-A1 (KSPKf)-Fe.  (Table 4-1),  the overall effect is  (KSPKf)  -Al>>  This explains why Al is eluviated from A horizons  3 moves much more than Fe. When the solution containing ML down to the Bf horizons,  the increasing Al(or Fe)/ligand  ratio makes the ML less mobile  (McKeague et al.,  more AlL deposits in Bf horizons than does FeL,  1983),  and  since AlL is  4-)  0  (Cl 4-) U)  o >  -I-’ -H H -H  (Cl 4) Cl) r  (Cl ) C)  o  ‘-i  4)  .-Q  -H H -H  o  H Cl) I  H  a) H (Cl El  o a)  o Cl)  -Ii -H H -H  ‘Cl 4) Cl)  o 4  0 a)  H  n3 (Cl  ai  -i-) G)  cO  H  C)  H O  (T  l  N  m  ‘4-  ) 0 iZI 4)  a)  H  m N  4J  Lfl  m  (Th  (Cl 4-) U)  co  a) 1:14  0  U  C)  N  cO  -  H  H  CO  iH H  Lo  H  C) >i  C) -H 4 Cl  O N O H  m  —  o  m  ,  C  .  m m  CO  -H i-i  >  4)  o’  C’.)  I  m  m  —  G H  CO  —  C)  < 0  0  H  U)  Cl  m  0  El  I  C’.)  (Cl U)  -H  C)  U)  -H H  C) 4)  (Cl  -H -H U  (Cl  E Cl  -H H (Cl  r  (Cl a) C) Cl)  0  0  I  N  m  a)  .Q  -H  H  -‘  0  —.  N .  m m  0  (Cl 1—i 4-) U)  rd  -H  a)  a)  -I-)  4..)  4-)  a)  -H -Ii  (Cl  E a)  .-Q  -H U)  4J  Q) 4-) -H  -H 1-i >-i  -I  (Cl  b  a) 4)  a) r14  $ -H a) 0 (!)  a) 4..) -H  m  m  O  (Cl El  -H H  C) -H  (Cl 1  0 0 C) (Cl  I)  a) -i  Q  H (Cl Cl)  -H C)  a)  Q  0 P1 m  +  0 Q ii  +  H  0  .‘  Z  0 Cl)  -I-) C) rt  0 f] >i  -H H -H  .Q H 0 Cl)  U) H (Cl a) -H Z  N a)  a) H  4-)  H (Cl  H  Cl  -H Cl)  m  0 I CO  -  in  a)  0 -  -H  p I C’.) -  m  CO  a)  ‘-4  E  0  t5)  0  a) 4.) ‘H H (Cl 4  0 H H  70  not as stable as FeL  (Kf-A1L  <<  Kf-FeL).  This explains why  more Al is captured in Bf horizons than Fe.  a.  Implications in soil genesis and classification  In many Southwestern British Columbia regions,  Podzols  lack an Ae horizon. Bf horizons are found directly underlying LFH with or without decaying wood. How these Bf horizons change when they continually receive organic acids from the decomposition of LFH and decaying wood is of interest. As an example, when sample C-7-Bfl horizon in that pedon) solution, solution  (top mineral  was leached with the simulation  significant amounts of Al and Fe were released to (Table 3-4).  Thus once a Bf horizon is brought to  the land surface by whatever means,  the illuviated Al and Fe  in the Bf will be subject to leaching by organic acids.  If  the leachate does not move out of the solum, part of the Al and Fe in the leachate may be captured by the underlying horizons  (e.g.  C-7-Bf2 in Table 3-4). Eventually,  the upper  boundary of the Bf horizon will move downward and the horizon may lose the characteristics required by a Podzolic B  (Spodic)  horizon. However,  if the leachate moves out of  the solum and subsequently reaches nearby rivers or lakes, it may have an effect on surface water quality as discussed in section 11-2. The Podzolic B horizon is defined by morphological and chemical properties  (Agriculture Canada Expert Committee on  71 Soil Survey 1987). Although both Fe and Al are incorporated in the chemical criteria, colour)  the morphological features  do not reflect Al illuviation,  (mainly  since Al-containing  minerals contribute little to the red to brown colour.  This  may not be a problem for well developed undisturbed Podzols, but for Podzols in which Al is the only or dominant element in illuviation,  the chemical criteria may disagree with the  morphological features.  In these cases,  field identification  of podzols may be difficult. In conclusion, differently,  for the soils studied,  at least in quantitatively,  Fe and Al behave  during  podzolization. Al is more easily removed from the top mineral horizon and deposited in the underlying Bf horizon than Fe within a pedon. This may be explained by the differential solubility products of Fe-bearing and Albearing minerals in soils and the differential stability constants of Fe and Al with organic acids. A Bf horizon exposed at the surface may be subject to leaching of Al and Fe,  this makes the upper boundary of the Bf horizon move  downward and begins to destroy the original Bf horizon. Whether the greater leaching of Al is associated with surface water acidification merits attention. The definition of Podzolic B horizon sets a arbitrary limit for Al and Fe illuviation.  It is not surprising if chemical criteria and  morphological features do not agree with each other. 2.  Silicic acid and pH versus organic acids in podzolization  72 The recognition of the widespread occurrence of imogolite/allophane in Spodic horizons  (Farmer et al.  Ugolini and Dahigren 1991; Wang et al.  1986)  1985;  has stimulated  new interest in podzolization. Farmer and co-workers suggest that 4 SiO rather than organic acids plays an important H role as a complexing agent and the soluble hydroxyaluminum orthosilicate complex  (proto-imogolite)  the translocation of Al  (Farmer,  1982).  is responsible for Therefore,  quantification of Al in proto-imogolite would be helpful to determine if the inorganic mechanism exists in Podzol formation at a particular site. While chemical extraction methods  tiron, pyrophosphate)  (acid ammonium oxalate,  are  often used to estimate the amount of imogolite/allophane in soils when the existence of the minerals is confirmed by infrared spectra and electron micrographs Wang et al.,  1991),  (Parfitt,  these extraction techniques are much  less useful in distinguishing proto-imogolite, quite reactive in podzolization, components.  1990;  which is  from other amorphous  Proto-imogolite may occur as complexes with  humus and clay minerals, (Wada and Wada,  1980)  has a positive charge  .  as well as water soluble components  In acidic conditions, proto-imogolite (Farmer,  into cation-exchange resins  1981)  and can be incorporated  (Wada and Wada,  1980)  .  This  property has been used to separate proto-imogolite from terrestrial waters solutions  (Inoue and Yoshida,  (Ugolini and Dahlgren,  1990)  and soil  1991). Recently,  this resin  73  extraction method has been used to extract proto-imogolite from soil samples  (Sakagami et al.,  1993).  Both pH and organic acids may influence the formation of imogolite/allophane. pH  0) 2 (H  soils  Statistical studies indicated that a  >4.7 was required for allophane to precipitate in  (Parfitt and Kimble,  1989).  The formation of imogolite  and allophane is favoured in horizons with pH >5.0  1982;  (Shoji et al.,  Laboratory studies  Shoji and Fujiwara,  (Inoue and Huang  ,  1986;  values  0) 2 (H 1984).  1990)  revealed  that even a small amount of organic ligands strongly perturbs the formation of allophane and imogolite. However, there is a gap between the laboratory studies and the statistical studies.  In the laboratory studies,  the  perturbation effects of organic ligands were observed at pH values of 2.9-3.4 for imogolite and at pH values 5-7 tannic acid)  for allophane.  (except  These pH values do not cover the  whole pH range in which Podzols may occur.  Thus,  more  empirical studies are needed to better understand the effects of pH,  organic ligands,  and other factors on  podzolization in Podzols with more moderate acidity  (e.g. pH  4.5-5) This section shows the Al content in proto-imogolite, the contribution of an inorganic mechanism to podzolization, and the pedogenic implications of pH,  atmospheric  precipitation versus dissolved organic carbon. a.  Fractions of resin extractable Al  (Al,.)  constituents  74  . 0 As shown in Table 4-2, Air is less than Al ratio of Air/Al 0 varies between 0.16 and 0.84. part of the amorphous Al components exists in  The molar  Thus only positive-  charged forms. Air may include partial or total organicas explained in Chap.  bound Al,  , 3 postulated that Al aluminosilicate(s), ligands,  3,  hydroxy-Al ions,  It is  and hydroxy  combined with or without organic  are the components of Alr•  of Air constituents,  section 5.  Because of the diversity  it is difficult to calculate the Al in  proto-imogolite directly from Alr• Nevertheless,  it is  possible to estimate the Al in proto-imogolite indirectly =9.71 1 Since pK  from S±r  (Lindsay 1979)  for the following  dissociation equation: SiO H 4  H  +  SiO 3 H 4  [4-4]  S±0 behaves as a neutral species in an acidic environment H 4 and should not be extracted by a cation-exchange resin. Thus,  the Si extracted with the resin  (Sir)  must be related  to the Si incorporated in positively charged proto-imogolite (Sakagami et al.,  1993).  proto-imogolite is  If the smallest structural unit of  ] 6 ) 2 A 0 [Si(OH) 0 2 (OH) 1 (OH  with a molar ratio of Al/Si =2,  (Farmer,  1981)  then the Al content in  proto-imogolite can be calculated and is equal to 2Sr• Therefore,  Alr2Sr represents the positive-charged Al that  exists in forms other than proto-imogolite such as Al-c-H groups and Al-c-C groups. (Al-c-H,  Al-c-C,  and Al-O-Si)  (Al-O-Si),  All these groups  are highly reactive,  as  75 Table 4-2 Fraction of Positively Charged Al,  Pedon4* and  Alr/Alo  Fer/Feo  Si and Fe  t 2Sir/(Alr2SIr)  Horizon  V-i  V-2  V-3  V-4  C-i  C-2  C-3  C-4  C-S  Ae  0.84  0.12  0.00  Bfl  0.25  0.10  0.46  Bf2  0.31  0.03  0.63  Bfl  0.50  0.11  0.09  Bf2  0.28  0.07  0.42  Ae  0.46  0.14  0.01  Bhf  0.39  0.04  0.37  Bfl  0.45  0.06  0.38  Bf2  0.35  0.02  0.28  AB  0.29  0.18  0.00  Bfl  0.45  0.05  0.00  Bf2  0.52  0.03  0.22  Bfl  0.59  0.10  0.01  Bf2  0.47  0.07  0.11  Bfl  0.59  0.06  0.00  Bf2  0.39  0.03  0.38  Bfl  0.63  0.05  0.01  Bf2  0.71  0.02  0.13  AB  0.96  0.12  0.00  Bfl  0.70  0.05  0.00  AB  0.42  0.08  0.05  76 Table 4-2  C-6  C-7  C-8  t  (Continued)  Bfl  0.64  0.10  0.01  AB  0.20  0.06  0.02  Bfl  0.45  0.01  0.00  Bfl  0.38  0.12  0.16  3f2  0.16  0.04  0.01  Btl  0.44  0.01  0.10  Bf2  0.55  0.03  0.00  2S±r/(Alr_2Sr) = molar ratio of (Al in proto-imogolite)/ (Al in A1-O-H and Al-O-C groups).  0  fl  I-  l)  QI S  C  0  0  —  V  CD  HN  CD  k<  I  0  Ft  0  ‘-ci  a)  H-  Cu a)  -  CD  CD  H  CD  H-  <  C  i-  QI  ‘<  C  5  CD  C a) ft  H  a)  CD  o  Cu H  Ct  —  I-I I-I H  H-  ‘-  5  CD —  ‘-xi  H  Q  CD Cu a) CD  CD  ft  Pi 3  0 ‘-ci  <1  ‘-ci  CD  Ft  CC  Cu  a)  H0  t  Cu  Hft  ‘d  CD C) H-  I-  ‘-ci  Q  -  CD  H-  QI  Ft  a)  a) 0 H H a)  CD  ft  H,  0  a) (I)  Cu  C)  CD  ct  J  I-h  C  ft  CD  ft  O  CD  ft  CD  0) rt  Ci  Cu IH H-  I-’•  I-’  d  I-’.  fl  I-’-  1  CD  0  CD  CD  ft HO  CD  S  CC  a)  H-  J  Cu  CO Ti) H-  S  O  I-h h  CD  F1 Cu Ct  C) Cu F—a C)  CD  k<  Cu  5  CD  H H ft  (  CD  o o  a)  b  5  H-  i4 I Ui  .  +  +  ,  +  ‘-  1  0  +  CD  ‘l  ..  H  i-<  H-  ‘  CD  0 H,  ‘-< a) Ha)  H  0  h’  P  CD  ft  C  H,  CO  ‘-ci  i-  CD  C  H  CD  Ft  Q  H Cii H 3 CD  ><  CD  CD  Cu  C)  HCi)  F-  -  CD  a)  CD  <  H-  ft  C  CD  H-  o  i  H  .  C a)  0  ç  H  Ht  CD  pJ II  S ‘-ci  C) C  CD  H  •  CD  ‘-ci  11  0  Cu  CD  H,  C  ft HC  ‘-  ‘ci 0  H H  5  Cu  O I-  H,  3 ft a)  Cu C)  CD  ‘-‘I  CD  h  l)  C)  H  o  CD  CD  ft  CD  a)  CD  H-  Cu  0  CD  -  -,CD  H-  ‘  CD  H H  CD  I—’  ,  H-  Cu  CD  CD Cu C) ft  a)  CD  H  C)  H.  ‘-‘I  Ci)  H CD h  H-  <  Cu  S  CD  0  ft JHCl)  S  ‘-‘a  QI  Cl)  I  W  CD  H  Cl)  — ‘-U  — —  IQ  H —.  C  C)  CD  H  I  H CD  0  Ct  ft CD  C) 0  H-  H 0  CT)  ft  H-  .Q  Ha)  Cu  -‘  —  F  Ct  H-  QI  CD  CD H Cu  I-  C  C)  k<  Ct H  HH HC) Cu  CQ  Cl) H-  Ft  o  Ha)  ><  CD  ‘-lj  —  a) H-  CD  I-  IQ CD  Ci)  C)  CD  I  C  H-  ft  Cu  C)  Hft  H CD  b  Ci) C) CC Cu  ft  ><  Cl)  HH 0  ft  a)  Cu  ç-t  0  C)  çt  ‘-U  H-  C) CD a) a) CD a)  C  I-  ‘-ci  CD  ft  CD  Cu ft  Cu H  H  a)  Cii  LQ h  h  iJ  ‘-ci  LQ  3  H-  5  CD  HH  CD ft Cu  CD  -j  C  Ft H-  Cu  I-  C  H,  0 H  N  HO Q Q  H  C  H,  CD  ft  H3  CD  H-  iq  Ha)  0  H-  a)  a)  H-C a) CD C)  Q  H  a) CD  C  ft  CD  H  b  Cu  Cu a) C  CD  F  a)  H-  Ct  H-  Hft ‘--<  h CD Cu C) ft H-  IQ  H-  a)  rt  H-  H-,  C  a) CD  Cu  CD C)  -  S—’  ‘-xJ  Cu  Z  ‘-ci  H,  C  CD a)  Cu H  <  H-  IQ  CD  ft  ‘-<  C) CD QI  CD  H-  CD  Ha)  a)  N 0  H-  II  0  i-i’  Ui  i  H-  .j  w  .  ‘  Cu H H CD  H-  1 H  ‘-  i-  (.Q  CD  CD a)  -  ft  I-h  o  CD  C)  j  CD  S—.--  -‘  0  H  QI  )  ‘-‘1  l)  Z  1 —  ‘-ci  CD CD  ft  CD  Ct  CD  C) H-  H, H-  C) C CD i—h  Cu ft HC  H-  CD l-  ft  CD  1  CD  c-t  CD  Ci) H-  H  fl—  0  H  —S  3  H  a)  CD  h  CQ CD  ) 3  C)  CD  I  3  0  C) Cu Ct H-  CD  ft  k<  ci  Q  C) ft CD  C)  H-  ft  CD  3  0  ‘-ci  5  C) C  H  a)  0  ‘-ci  I-  0  5  Cu  CD  Ct H-  i-  C  ICD  k<  CD  ‘  -  CD  CO  *  CO  i-,,  °  “  I-  -  -,  *  M CD  -  I-’  —  13’  u  ft  CD  C) ft H-  Cu  Cu  II  II CD  CD  l-  C  CD  CD  ft  X  CD  ft  o  3  h Cl)  J  H  i-il  Cu  CD  ft  CD  a)  Q  CD H Cu ft H-  II  C)  CQ C  CD  ç-t  CD  HC)  H-  78 reactive component of Al . 0  Thus the value of 2S±r/(Alr_2Sir)i  which represents the ratio of and Al-O-H),  (Al in Al-O-Si)/(Al in Al-O-C  may be used to approximately evaluate the  relative importance of the inorganic process and the organic process in podzolization.  This ratio varies between 0 and  0.63 as shown in Table 4-2.  For Ae and AB horizons,  value is zero or close to zero. infer that the inorganic  <5%)  Based on this ratio,  (proto-imogolite)  almost absent from pedons C-4,  C-5,  .  C-3,  While in pedons V-l, V-2,  one can  mechanism is  and C-6  and insignificant in pedons C-i,  ratio <16%)  the  (2S±r/Alr2S±r C-7,  V-3,  V-4,  and C-8  (the  and C-2,  at  least one Bf horizon in each pedon has a value between 2263%,  suggesting that the inorganic process does exist and  plays a role in the podzoiization of these pedons, the organic process may play a major  although  (the ratio <1.0)  role.  The coexistence of organic and inorganic processes requires rethinking of the chemical criteria of Podzolic B horizon, i.e.  pyrophosphate extractable Al+Fe,  which is based on the  organic process only. The difference between Vancouver pedons and Cowichan pedons merits attention. All Cowichan pedons except C-2 are low in 2S±r/ r_2r) while the ratios in Vancouver pedons are much higher.  This difference may be related to the much  higher annual precipitation than that  (1258 mm)  Intensive leaching,  (2076 mm)  at the Cowichan site  at the Vancouver site  (Table 2-1)  a result of higher precipitation,  may  79 lower Si concentration in soil solution and thus hamper the reaction of hydroxyaluminum with silicic acid to form proto imogolite.  The finer textures of the Cowichan soils may  further increase the effect of the higher precipitation on lowering Si concentration. The relative abundances of proto imogolite and Al-organic acid complexes largely depend on the competition between silicic acid and organic acid to react with  Al-C-H to form Al-C-Si and Al-C-c bonds,  respectively. Therefore,  Si concentration, H activity (pH),  and quantity of organic acids are the major factors that control the competition.  considering the difference in  precipitation of the Vancouver area and the Cowichan area, one may separate the Vancouver soils from the cowichan soils to evaluate the effects of pH and organic acids on podzolization. The hydrolysis reaction of Al 3 ion can be written as: 3 Al pIC=4.99  (Table 1-1).  +  C 2 H  2 A1CH  +  H  The amount of hydroxy-Al decreases  markedly with decreasing pH below 4.9.  Therefore,  aluminum  is hindered in its reaction with Si to form Al-C-Si, tends to form a stable complex with organic acids Fujiwara,  1984),  but  (Shoji and  Intensive leaching may enhance  i.e. Al-C-c.  this effect of pH by lowering Si concentration in soil solution. Cn the other hand,  hydroxy Al increases markedly  with the rise in pH above 5.0, Al and Si,  promoting coprecipitation of  if Si exists in soil solution. The significant  80  ) pH(H 0 correlation between 2 imogolite 0.71**,  and either Al content in proto  or the ratio of 2S±r/(Alr_2S±r)  S±r) 2 (  respectively,  for the Vancouver soils provides  n=12)  i.e.  support for the above statements,  or 2Si/(Al-2Si)  soils.  (1.120)  (r=0.23,  higher pH values  In contrast,  favour Al-0-Si over Al-O-C. correlation between pH  (r=0.70** and  no significant  and either 2S±r  n=16)  (r=0.24,  n=16)  was found for the Cowichan  This may be related to the higher precipitation in  the Cowichan area,  which makes Si concentration rather than  pH the limiting factor.  The effect of pH on  organic/inorganic mechanisms in podzolization is also evidenced by the ratio of  (AloAl,.ta)/Alnta• Alnta as an  estimation of organic-bound Al  (Yuan and Lavkulich,  1993)  and AloAlnta approximates the Al in inorganic amorphous constituents. (r=0.80**,  (AloAlnta) /Alnta significantly correlates  n=12)  with pH  (1.120)  not in the Cowichan soils  in the Vancouver soils,  (r=0.45,  but  n=16)  It is well known that organic acids inhibit the formation of imogolite/allophane in well controlled laboratory conditions 1991)  .  (Inoue and Huang 1986,  1990; Huang,  Organic ligands with strong affinity for Al  significantly modify the nature of the soluble products which range from proto-imogolite sol complexed with organic acids to hydroxy-Al-organic complexes 1986)  .  However,  (Inoue and Huang,  whether conclusions from the laboratory  studies can be unconditionally extrapolated to soils with pH  81 values different from those in the laboratory studies is under question. Moreover, perturbation effects of organic ligands on imogolite/allophane formation may not necessarily exclude the role of the inorganic mechanism in podzolization.  It is suggested that in the soils examined  atmospheric precipitation and pH are the key factors controlling proto-imogolite formation and subsequently its role in podzol±zation.  The direct effects of organic ligands  on proto-imogolite and on the relative importance of inorganic-organic mechanisms in podzolization may not be unequivocal,  since no statistically significant relationship  between 2Sr  [or 2S±r/(Alr_2S±r)]  and DOC  (or total carbon)  can be found for both the Vancouver soils and the Cowichan soils. DOC and total carbon are significantly correlated (r=O.60**, n=28)  .  The disagreement between this  investigation and above-mentioned studies may be the result of the difference in pH values between the laboratory conditions and field soils.  Significant perturbation effects  of organic acids on imogolite formation were observed at pH values of 2.9-4.3 in laboratory conditions 1986)  .  (Inoue and Huang,  These pH values are lower than those of the soils  studied.  In conclusion, positive-charged Al accounts for a variable portion of the amorphous Al constituents.  This  positive-charged Al is highly reactive in Podzols.  The Si  82  extracted by the cation-exchange resin is used to estimate the content of Al in proto-imogolite.  The ratio of Al in  proto-imogolite to Al in Al-O-C and Al-O-H may be used to assess the relative importance of inorganic vs.  organic  processes in podzolization. The results indicate these two processes may co-exist in some pedons.  Higher atmospheric  precipitation may be responsible for the low contents of Al in proto-imogolite in the Cowichan pedons, while higher pH may contribute to the formation of Al-O-Si over Al-O-C bond. The direct correlation between organic matter and the competition of Al-O-Si, Al-O-H and Al-O--C was not found.  II.  Transfer of Acidity from Podzols to Surface Waters  Soil acidification affects aquatic systems as well as  forest ecosystems. The processes involved in the transfer of acidity  (mainly Al)  from soils to surface waters has  recently drawn considerable attention, due to the elevated Al concentration in lakes and streams in areas receiving acidic deposition. The topic lies between the domains of the soil chemist and the water chemist, that it is poorly understood by both  and it seems fair to say (Reuss.  1991).  In this  section an evaluation of the commonly used intensity and capacity factors that relate to acidity transfer is  83  examined,  a new capacity factor is proposed,  and  finally  the use of extraction and column leaching experiments to test the suitability of the new factor is discussed. 1.  Constituents and factors affecting acidity transfer  a.  Constituents contributing to acidity transfer  Aluminum is a strongly hydrolyzing metal and is relatively insoluble in the neutral pH ranges. Under acidic conditions and/or in the presence of complexing ligands,  the  solubility of aluminum is enhanced, making it more available for biogeochemical transformation. Constituents affecting acidity transfer in the absence of strong acid inputs may include organic acids, and carbonic acid.  acid,  2 may have an important role in CO  the solubilization and transport of Al 1985)  .  silicic  (Reuss and Johnson,  Mobilization of Al by CO 2 is most significant at  values of ANC near zero  (pH near 5.0)  (Driscoll and Schecher,  increasing partial pressure of CO 2 1988). At low values of ANC and pH, concentration of Al is available, Al (OH) 3 solubility. However,  and increased with  significant  due to pH-dependent  acidic conditions restrict the  , 3 2 to H and HC0 hydration/dissociation of CO decreasing HC0 3 mobilization. increases,  thereby  to serve as the counterion in Al  3 Conversely at high ANC and pH values, HCO  but Al concentration decreases,  resulting in a  decrease in Al mobilization. The role of silicic acid in acidity transfer may be explained by the formation and  84 mobilization of proto-imogolite sol.  Complexation of Al by  organic acids and subsequent movement of organic-Al complexes is a common feature in Podzols.  This organic-Al  movement is important not only in Podzol formation, but also This transfer  in the transfer of acidity to surface waters.  of acidity to surface waters can occur if the organic anions are not broken down by microbial processes or not precipitated by sesquioxides. The amounts of organic acids added to soil may be affected by the characteristics of the forest and various management practices. Thus, of acidity depends on natural processes, anthropogenic factors  the transfer  as well as  (acidic deposition and management of  forest) Superimposed on the natural process of acidity transfer is the introduction of strong acids from acidic deposition. Anthropogenic inputs of sulphur or nitrogen may increase the concentration of the sulphate and/or the nitrate anions several-fold.  Charge balance principles  (Seip,  1980)  dictate  that they be accompanied by an equivalent amount of cations in the soil solution.  If the ion-exchange complex is well  supplied with base cations,  the major effect will be an  , 2 , Mg 2 increase in the rate of removal of Ca salts of S042  K,  or N0 . As these are neutral salts, 3  no acidity transport will take place. cations is limited,  and Na as little or  If the supply of base  as is the case in the soils studied,  3 species, deficit will be made up by H and Al  so that  the  85 acidity will be transported from soil to the drainage water. b.  Intensity factor versus capacity factors  Hydrogen ion activity (the intensity factor)  or pH is  one of the most commonly measured soil and water parameters. To the nonspecialist it is often the parameter of most interest.  It may be measured in a variety of ways,  each of  which has certain advantages and limitations. However,  this  parameter is not well suited for measuring acidity transfer. The following explains the reason in a simple fraction only)  (mineral  way:  For dissolution of Al(OH) 3 minerals: Al (OH) 3  +  3H  “  3 Al  +  0 2 3H  3 and H may be the equilibrium relationship between Al written as: ] 3 [Al  =  In the soil environment, (gibbsite)  to 9.66  3 K0[H+]  [4—61  the value of logK° varies from 8.04  (amorphous aluminum hydroxide).  By  rearranging Eq. [4-6], we get, [H] [H]  =  ] 3 [Al  1/3/  (K°)  1/3  is proportional to 1/3 power of  [4] ] 3 [Al  .  Thus a  3 in soil solution can occur before significant change of Al the change in pH value can be detected confidently. This is particularly true when K° is relatively large aluminum hydroxides).  If the soil solution moves out of the  solum and becomes surface water, to water.  (amorphous  acidity transfers from soil  86 While the intensity factor is not well suited for indicating acidity transfer; the capacity factor, neutralizing capacity  (ANC),  soil acid  is often believed to be  responsible for acidity transfer from soil to surface water (Reuss,  1991)  .  ANC is a concept from water chemistry.  it is introduced to soil chemistry,  When  its definition and  measurement become vague. The ANC of soil material is made up of contributions by mineral solids, aqueous phases  (Bruggenwert et al.,  organic solids,  1991).  and  The mineral solid  phase contribution to ANC is equal to the quantities of basic components minus those of acidic components. Which is “acidic” or “basic” depends on the reference pH chosen. example, when titrating a soil to pH 5, FeO are basic components  CaO, MgO,  0, Na 2 K 0, 2  (proton acceptors), while SO , 3  and HC1 are acidic components  (proton donors)  .  For  , 5 0 2 P  Aqueous ANC  is ascribed to alkalinity due to carbonate plus organic anions, minus free mineral acidity  (van Breemen,  1991)  .  The  composition of the organic solid ANC is not given by van Breemen  (1991).  Soil ANC may be determined by titration of  soil with mineral acid, but it is strongly operationally dependent  (Kinniburgh,  Funakawa et al.  1993)  .  1986; Valentine and Binkley,  The measured values vary with the  concentration of supporting acid addition.  1992;  electrolytes and the rate of  This makes it difficult to compare the ANC  values from different researchers. It is worthwhile to point out the differences between  87 water samples and soil samples in terms of buffering capacity. Water samples are usually low in buffering capacity to acids or bases and the acid/base reactions in solution are much faster than those in solid samples. Therefore,  The ANC or BNC  (base neutralizing capacity)  of  water samples can be conveniently determined by a titration method. However,  soil samples have much greater buffering  capacity and contain a wide variety of weak acid and base surface functional groups of varying acidity or alkalinity, consequently tending to give rather featureless titration curves  (Kinniburgh,  1986).  They commonly lack identifiable  acid or base endpoints in the pH range of 3-10.  Furthermore,  the slower acid/base reactions imply that continuous titration curves are inevitably nonequilibrium curves. Since both the intensity factor factor  (ANC)  have their limitations,  (pH)  and capacity  it is necessary to seek  new criteria to characterize a soil’s  (potential)  capacity  to transfer acidity to surface waters. c. The capacity to transfer mineral acidity  To fully understand acidity transfer from soil to surface waters,  the following issues must be addressed:  The amount of acidic inputs  (natural+anthropogenic);  The capacity of soil as the proton sink; The rate at which soil can take up protons; The hydrological pathway of the watershed.  and  88 To the best knowledge of the author,  accurate data of  acidic inputs at the sampling sites are not available. As an estimation, van Breemen et al.  (1984)  listed the order of  magnitude of various groups of processes in terms of their contributions to acidic inputs  (kmol(H)  acidic deposition  0.1-6  organic acids  0.1-1  nitrification  0-10  yr’) 1 ha  (Spodosols) (clear-cut watershed)  a few assumptions are made:  For simplicity of discussion,  ; 1 yearly input of H is 3 kmol h& thickness of soil solum is 1 meter  (seldom exceeds 1 m  in the study areas); ; 3 the bulk density of the whole solum is 1500 kg/rn fine earth  (<2 mm)  and  is 10% by weight of the total materials.  Thus 3 krnol/ha H input is equivalent to: *l m*0.l*lSOOkg/m 2 ) 3 (3*1000 molH*100 cmol/mol)/(l0000 m 0.2 cmol H/Kg  (fine earth).  i.e.  If we compare this number with  the exchangeable base cations  (sum of Ca, Mg, Na,  K)  in  Table 3-2, we reach the conclusion that the storage of exchangeable base cations is only enough to neutralize acidic inputs for a few years. This estimation is compatible with the results in other regions 1991)  .  (Bruggenwert et al.,  After the base cations are depleted by acidic inputs,  exchangeable Al may be subject to leaching from exchange sites to soil solution which may become surface water.  p3  p3  CD  CD  H,  k<  P3  8  it  +  U)  CD  H,  0  3  CD  ii  3  0  H-  0  H HN  P3  P3 it  H0  it  -  IQ  Q  +  i-N  —  H-  U)  ._1  CD  0  ,4  L  I  H-  CD CU C) it  o  it P3 it H-  H-  ‘  —  .-  tl)  U) Hit  H-  C)  CD  II  H  it  5  P3  I  it H0  U) 0 H  HU)  CD  +  P3  C)  0  ,  0  H,  it  HU)  it  H  it  P3  U)  U)  1  U) CD  U)  U)  CD  Zi  CX)  H  -  H-  P3 i i  -  it  H-  tT  U)  CD  —-  Ui  W  LU  H  -  0  CD  <  ‘ti  Cl)  CD  C) P3  1  P3  —  0  LU  H  -  -  H  P3  it  CD  it CD  H-  --  it H,  3  U)  0  C  —S  0  H  —  P3 H H  it H0  H  0  LU  0  0  H-  it  P3  H-  F 1 it  3  HU) U)  Q  CD U)  +  J  +  C  C) 0  P3  P3  h  —  it CD  H-  it  H  CD it  I  0  H  H-  ‘°  b ‘<  CD  h H-  it  H,  0  <  H  0  CD  -  CD  p3  C)  ‘—3  h CD H CD CU U) CD  ft  CD  I-I  0  C)  H-  1D ‘<  U)  CD CD  C)  0  ‘  CD  <  CD  0  -  H U)  U) 0 H-  H-  U)  P3 H  CD  H-  5  it CD  P3  U) HH HC)  H,  0  H-  CD  it  CD  -  U)  -  H  H,  CD P3 U) CD  H  CD  h’  CD  it  H,  0  Cl)  U)  P3  C)  CD  h CD P3 C) it H0  +  H-  N  H-  it  CD  °  H-  it  -  CD  U)  C) 0  it it CD  U)  P3  ICD P3 C) it H0  Cl)  +  CD  U’  H  Z3  -  o  it  0  H,  CD  U)  U)  ‘d  ‘  Cl  P3  H,  Q  CD  CD  H-  P3 it  H-  C) 0  CD  5  U) 0  -  r  CD  o  Z  -  ,  •  -  C) P3  HU)  CD 1 CD  I  o  H-  +  +  F-’  +  +  +  +  0  H-  H Cl)  U)  P3  Cl  CD  it  I—i CD U) CD  ‘d  h’ CD  CD  C)  H  P3  CD  H-  S  CD  C) P3 it  U) HH H-  ‘<  I-  CU  H-  ‘-d  P3  H,  0  0  H-  it  H  U) U) 0  H-  it  CD  t.Q I-j  0  C)  CD  J  —3  -  it  ‘-d  H-  C)  H-  C) H-  P3  it  it CD  U)  0 U)  CD  p3  H,  0  C) CD  P3  CD U) HU)  5  II  CD  it  I  0  H  CD  it  CD C) it  H, H,  P3  U) 0  I—’  P3  HH F-’  Cl  P3  5  U) it CI)  k<  0 U)  CD C)  CD U) it  I-  0  H,  P3  H,  0  CD  P3 ct  it  U)  I-  P3 H  S  CD  C)  CD  it  0  CD  C)  CD  H  H,  H-  it  C) P3  H-  H,  H-  U) H(  P3  CD  P3  3  P3  C)  1Q  H,  0  CD  it  CD  it  CD  -  P3  +  H  P3  H-  5  P3  P3 U)  C)  U)  -  H  0 H-  U) CD  CD  it  H,  0  U)  0  0 I it H-  CD I-  it  0  C)  P3  H  CD  H H  H-  H3 tQ  CD  H-  h  P3 it  CD  CD  P3 it  CD  S  0  H,  U)  HQ  it  p3  C)  CD  P3 U)  Y  H,  it H0  H-  Cl  P3 Cl  ‘-<  P3  -  H CD  H-  U)  h  CD  <  CD  I-  ‘<  H H  H-,  HU)  Cl  C) H-  P3  it  H-  k<  b  U)  0  H-  C) P3 it  CD  t3 P3  (Q CD P3 b H CD  P3  C)  X  CD  H,  0  it  CD  5  H P3 C) CD  M CD  CD  ‘-3  -  II  P3 C) it 0  H,  it ‘-<  H-  C) P3 ‘d P3 C)  P3  P3 U)  Q  CD  U)  CD  b  it Q  F1 CD  b  P3  H-  U)  HU)  H  -  0  3 U)  H-  C) P3 it  b P3 U) CD  CD  H  P3  CD  Q  < C)  CD  CD  Hit  CD  k<  U) H  0  H-  b <  0  it U)  H3  H-  H-  P3 C)  P3 U)  CD  p  ii-  H-  IQ  p3  H,  CD  CD  U) P3  CD  it  H-  U)  H-  1Q  —  +  Q 1 F—  5  C)  P3  U) it 0  CD  it  ><  H  -  H  II  Cl)  P3 H  CD P3  S  H  ‘  CD  H  IQ CD P3  P3  C)  CD  H,  0  Q CD  -  CD  CD  0  90 mineral solid phase. However,  the weatherable primary  mineral content is usually low in podzols,  especially in the  eluvial horizon and the rate of cation release from weathering is lower than the rate of base leaching at the Podzol stage of soil development. is inevitable.  Therefore,  leaching of Al  Since the storage of exchangeable Al is too  small to be considered as a capacity factor controlling acidity transfer from soils to surface waters, we have to choose other parameters, capacity  such as Al , 0  (in the longer term)  to indicate the soiPs  to supply Al which may be  transferred to surface waters.  2. Justification of Al 0 as a capacity factor The following text will explain the rationale of selecting 0 Al as a capacity factor through statistical and experimental approaches. 0 and Ainta correlate As shown in Table 3-8, both Al Q73**, respectively) This well with ANC (r=0.92** and .  suggests the importance of organic-bound Al and amorphous Al (organic  +  as acid buffering constituents.  inorganic)  The  possible mechanisms may be explained by the reactions of inorganic Al monomerization complex dissociation  (Eq. [4-10])  (Eq. [4-11])  and organic-Al  at low pH conditions  (e.g.  pH 3.5): Al (OH) ° 3  +  H  Al (OH) 4 1  The logK values for Eq. [4-10]  +  0 2 H  [4-10]  can be derived from reactions  91 No.  2,  6,  for X=l,  and 7 in Table 1-1 and are 4.99, 2,  and 3,  Al-Org  +  and -0.47  respectively. H  AlHOrg  [4-111  naturally occurring organic anion)  (Org  The LogK value of Eq. [4-11] No.  5.14,  can be calculated from reactions  18-19 in Table 1-1 and is 4.70.  Since Al 0 is supposed to  include both organic-bound Al and inorganic amorphous Al, 0 is responsible for both Eq. [4-101 Al  and Eq. [4-11]  .  Thus,  0 may be used as a capacity factor from the aboveAl mentioned statistical evidence. Results of two experiments will be used to demonstrate 0 as a capacity factor. the suitability of Al experiment was done with little acidic input.  The first 0.01 M CaC1 2  solution, which is often used to approximate ionic strength of soil solution,  is assumed to simulate this condition.  . Al 2 This solution may also include the role of CO 2 extract represent the Al concentration or activity in CaCl subjected to transfer to surface water under conditions of low acid inputs from acidic deposition and organic acids. the second experiment, mineral acids  In  a pre-set amount of organic acids and  H 0 4 + 3 (HNO S 2 )  is added to a soil column, Al  concentration in the leachate are used to represent the amount of Al that may be transferred under the conditions of having acidic inputs from both natural and anthropogenic sources. 2 In the first experiment, Al concentration in the CaC1  CD  çt  CD U)  CU H-  CU  CD  -  U)  O  U)  ft  Hft  5  HF-’ F-’-  CD i.Q  ft  CD  CU  k<  0-.  U) ft  ft  1_I CD C) CD  CU  Ui  CU  ‘d  H .D 0)  CU ft  CD h CU H  H-  S  0 Hi  ft H0 3  HU) U) 0 H  CD  ft  0  O CD  S  U)  ft  r  H ft U)  CD U)  D CD  CU ICD  C) CU U) CD U)  CU ft H0  I—  IU) CU ft  0-. 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CD  ‘d  CU  —‘  p  i  w  -  Lii  Q  +  I—’  >  F-’  CU  C) ft  H M  a  I  Q)  w  II  ‘‘  H  0  •  +  H  •,  0 IQ  H  II  0 10  0  -‘,  w  +  +  H  1  +  +  CD  H  g  -  0  -  --  —J D  H  -  CU  Q  U)  H-  -  o-i  CU  ,  U) CD  1 CD  >  CD  HU)  0  ft H-  0 H  U)  0.  pi 3  H-  H-  p C)  H  3  CD  CD  CD ft  H-  U)  II CD F-’ CU ft H0  CD  HI  -  Ui  0)  H ‘O  CU H  CD ft  I  CD  h  HI  --  LO  H D  -  H-  CD  U) ft  Q.  0 H  Q  Hft U)  U)  CD  H-  0 ><  h  k<  0-.  CU  CU  1) ‘ 0  CU ft CD h U)  CD  CU C)  Hi  I  U)  0-’  CU  U)  ft H0  0 F-’  ‘‘  H  CU ft CD  5  CD U) ft H-  ft 0  0.  U) CD  CD  Cr  0 Hi  U)  H-  Hft ‘-<  H  H-  b  U) 0 HU) HO H U)  H3  U)  Hft HCD  <  H-  Cr  C)  5  H-  S  CU H  ft  CD II U) HU) ft CD  ft  U)  5 0  CD  ft  Hi  0  CD  0  U)  H-  Cl)  U) Hft  b  IQ H-  C) CD  C/) H-  1  F’-  ‘<  ct  F’H F’-  H  0  U)  CD  In F’-  b  F’  (Q  •  U)  <  1<  rt  <  F’-  fl  P1  c  F’-  H  I  •  CD H  S  0  CD  ft  H-  II  CD ft CD  5  )J  CU 1  -  CD  ft  ft  o  ft H0  U) 0 H  CU H  C)  F-’  ‘  H  S 0 3  CU  H-  U)  H0  ft  fCD F-’ CU  CU  IQ  U) H-  ‘‘  H  CD  b  H-  CD U) C)  0  -  H-o  5  ‘ti H-  CD  CU  CD  H--  CD  Cl  CU Z Q  CD F-’  0  S  3 t-Q CD  CU  C)  >  CD  ft  CD  H-  S  pi  ><  CD  HH H  .—  C)  I  —S  ft  CD  ft  H-  Hi 0 H H 0  CD  W  CU  b’-)  -  CU  C)  H CU ft CD  C) CU H C)  H  -<  Hft  ft H-  CU  C)  CD  ft  Cl  CU  CD Cl  5 CD CU U)  HU)  U C) ft U)  ft  CD  L’J  93  7 A  6 A A  AA&  5 4  AA  A  AA  A  A  A  A  A  A  A  A  A  3 2 1 0 3  3.2  3.4  3.6  3.8  4  4.2  pH  Figure 4-2 pAl 3 and pH Relationship in Soil Extract (Gibbsite Solubility Line is Shown)  94 respect to Al (OH) 3 is readily obtained from both conditions of undersaturation and oversaturation within 0.3 hours,  3 in soil solution may be regulated by and the Al  hydroxy-Al interlayer of expansible 2:1 layer silicates instead of gibbsite which is seldom found in Podzols 1980)  .  Other studies suggest that these waters may actually  be in equilibrium with a solid phase humic adsorbent et al.,  (Ross,  1986; Mulder et al.,  1989)  (Cronan  and contribute the  undersaturation cases to the complexation of Al with organic matter  (Bloom,  et al,  1979; Prosser et al.,1993)  It is  .  clear that the justification has not been fully demonstrated for applying the geochemical model solubility alone)  (which relies on  to soils in which both mineral and organic  components may exert influences on Al behaviour.  Therefore,  a general model for predicting aqueous aluminum chemistry must incorporate organic solid phase reaction to account for the undersaturation cases b.  , 3 Relationship among A1  (Cronan et al.,  1986)  0 pH and Al  3 and other soil properties The correlation between pAl was shown in Table 4-3. The property best correlated with 3 is pH, pAl  followed by DOC,  total carbon,  , whereas 0 and Al  3 clay content has no significant relationship with Al activity.  This implies crystalline minerals have little  . 3 effect on actual Al  Since both pH and organic matter  3 activity, content correlate significantly with Al  they  should be taken into account in a model predicting Al  95  Table 4-3.  Correlation between pAl 3 and other Properties  PHextract  3 pAl  0.83  DOC  -0.74  Total C  -0.60  0 Al  Clay  0.52  -0.04  for p=O.Ol and =±O. 40 for p=O.O5 ) 2 ra( 304 Sample size n=39 for DOC  96 This applies to soil solution and surface water  activity.  because both of them dynamically exchange with soil or sediments. a. An exchange nodel Cronan et al.  use the modified mass action  (1986)  expression derived by Langmuir  +  A1X  ‘  3 to describe Al  Given the exchange reaction,  activity in natural waters. 3H  (1981)  HX  +  3 Al  [4-13]  the empirical exchange function would be: X/AlX] 3 )/(H)] [H 3 [(Al  Kex  [4-14]  where the parentheses denote activities of the ions,  and AlX  and H X are their mole fractions on organic sorbent X. 3 X/A1X] 3 [H acidity  can be estimated from organic-bound Al/titratable (Cronan et al.,  nature of sorbent X, soil.  However,  soil.  Thus,  they should be constants for a specific  the values of Kex and n vary from soil to  direct application of Eq. [4-14]  activity is inconvenient, i.e.  Kexi  Kex and n depend on the  1986).  (H),  , 3 H  A1X,  negative logarithms,  to predict Al 3  because five items in the model,  and n,  have to be determined. becomes  Eq. [4-14]  Taking  (Mulder et al.,  1989) -3pH 3 pAl  =  ] -nLog[A1X/H X PKex 3  The calculated values of PKapp  -3pH) 3 (pAl  to -7.44 for the soils studied.  PKapp  [4-15]  varies from -5.63  Plots of this PI<app with  show a good correlation between them  organic-bound Al  (Alnta)  (r=_O.61**,  Figure 4-3)  n=42,  =  .  The significances of this  97  8  a  a  a aa  -i  a aa a aa  a a a aa  a  6  5 0  a  I  I  I  I  5  10  15  20  25  30  35  Ainta (cmol/Kg)  Figure 4-3 Empirical Relationship between (PKap) and Alnta (Gibbsite Solubility line is Shown  98  correlation are double. varies with Alnta•  Firstly, PKapp is not a constant,  it  This is different from the geochemical  model in which pK is taken as a constant. Hence,  the  exchange model can not be used universally with a fixed parameter.  Instead,  the parameter, PKappi  should be  determined for different regions or soils.  Secondly, PKapp  may be calculated from the empirical relationship  (Fig.  4-3)  for soils with similar nature of the sorbent X. Once PKapp calculated, pAl 3 can be predicted from pH.  Since the Al in  the extract represents the transferrabie Al in situations without significant acidic input, with Al 0  (Table 4-3),  and it is correlated well  the rationale for selecting Al 0 as a  capacity factor is shown for these situations. d.  acidic input and transferrable Al  In the second experiment  (Chap.2),  the soil columns  were leached by solutions containing both organic acids (oxalic acid,  citric acid,  and mineral acids  salicylic acid,  and malic acid)  (nitric acid and sulphuric acid).  , 0 similar trend of Al in leachates and Al  The  as shown in Figure  0 as a capacity factor 4-4, provides support for selecting Al in situations where soils receive both natural and anthropogenic acidic inputs. The fact that samples V-4-AB.  C-4-AB,  and C-7-Bfl have  Fed higher than or approximately equal to Aid but have more Al than Fe in the leachate attention.  (Table 3-3)  (Table 3-4)  merits  In southwestern British Columbia logging and  99 surface water acidification have received some attention, but no attempt has been made to relate these two issues. Although there are no studies known to the author about this relationship in British Columbia, (Likens et al.,  1970)  studies in other regions  suggest the relationship exists. The  elevated Al concentration in surface waters is often ascribed to acid precipitation. This may be an oversimplified explanation,  since the pH values of the  precipitation in British Columbia are much higher than that in eastern United States and some European countries (Science Council of Canada 1988). The main components of acid precipitation,  i.e.  ability to complex Al  sulphate and nitrate,  (reaction no.  14-17,  have little  Table 1-1)  the amount of dissolved Al in weakly acid water  Therefore,  is quite small if no organic ligands exist in the solution. Table 4-4 shows the differences of Al concentrations in 0.01 M CaC1 2 solutions  (no acidic input)  and in simulated leaching  (natural+anthropogenic acidic inputs)  .  Al  concentrations in leachates are much higher than those in 2 extracts CaCl  (3-23 times),  especially in the Bf horizon.  (Considering the solution/soil ratio in the leaching experiment  (6.0)  experiment  (2.0),  Table 4-4).  2 extracting is larger than that in the CaCl this Al ratio will be greater than that in  This ratio means,  once acidic input to soil is  increased, Al in soil leachate will increase as well. soil leachate moves out of the solum,  the amount of Al  If the  100  Table 4-4 Al Concentrations in Soil Extracts and Leachates  Sample#  Al in 0.O1M CaC1 (A) 2 mM  Al  in leachate(B) mM  Ratio of B/A  V4AB  0.43  1.28  3.0  C4AB  0.40  1.45  3.6  C7Bf1  0.08  1.89  23.0  101  2 :7-Bf 1  1.75 0  a,  ‘I  a,  .  a, -I  1.5  E 1.25  1-0  10  20  30  40  Alo (cmol/Kg) 0 and Al Concentrations Figure 4-4 Comparison of Al in Soil Leachates  J  Ft  ft  CD  H-  Ft  o o  H-  H  ‘-C  o  Ft  C)) C)  Hi  H3  I-  CD  Ft  Ci QI  02  C)  C))  CD  CD  d  I-  Q  Ft  Hi C)) C)  ‘<  0) HFt  Ft CD  H-  CD  Hi 0 I-C  1 F-  0 Ci (Q  C)  Ft 0  (I)  F-’-  Hi  1 H  0  (I)  0 C) CD (12  C))  I-C  C)) (1) Ft  ‘d  Ft  C))  0 (Q CD Ci HC)  I0  Ft  C))  S ‘-<  Ci  H-  CD 0) CD I-C  Cl) C)) Ft CD I-C  I-  F-  CD°  (P  I-C  H 1 C))  C))  0)  H-  3  0  F1 HN C)) Ft H-  0  N  Q  Q  C)  C))  Hi  C))  C))  C)) Ft Ii I-C C)) 1 H  I-C  0 Hi  (12  3  Ft J  Ft 0  0  Ft  HH  (1) 0  5  0  I-C  Hi  0  Hi 0 ‘-C  0)  Ci  H0  C)) Ft  Ft  H-  5  H H-  CD HI-C  Ft  CD  <  —  ()  P-  CD HFt H-  (1  N  C))  H-  I-C -  CD  CD 02  C)) I-C  0  Ft  H-  Ft  Ft  C))  HtQ I-C  HH-C 3 Hi  0 Q  CD I-C H-  ‘d  Ft  S  0)  0  C) 0  0) 0 H1 H  5  C)) C)  Hi  Ft ‘-<  H-  -  C)) Ft CD  C) CD  I-C Hi C))  0)  o  Ft  02  HH  5  0  Hi I-’  l-  02 Hi CD  C)) i  hj  Ft  HFt ‘-<  C)  HFt  C)  ‘d  C))  C)  C))  H-  C)  C))  d  C))  o  I  HN °  °  Hi  Ci  H-  H C))  1 F-  CD  Ft  CD  C)  (1) H-  (1) CD  0  F-’  C)  HFt  5  CD  I-C 0)  CD  Ft  C))  CD  C)  I-C Hi C))  0)  Ft 0  F1 (Cl  H-  0) C  5  0  I-  Hi  H  0 Hi  h  0 -  0) Hi CD  3  Ft IC))  Ft H-  t Ft CC)  QI  (I) CD  I-C CD C))  Ci  F-’-  3 Ft  CD  CD  Q  tY (12  (I)  QI  (U 3  0 3  C)) Ft H-  I-C  CD I-C Ft  I—a  H-  0  U)  Hi  0  02  Ft  C)  Cl) Hi Hi CD  HC)) 1 H  Ft  Ci  d 0 Ft CD  CD  Ft  -  5  C)  A [O  C)) F-’ I—’ ‘-<  (1)  -  CD  ‘  Ft Z5 H-  C))  Cl)  <  C))  I-  0  0  I-’ HN  0  CD  Ci  C)J  H  C)) C)  Ci CD I-C  HFt  CD  H (I)  0  N  0 QI  -  HC))  S b  0 1 F-  0  HFt H(12  I-C  Lii  (1) h  CD  (1) Ft  Ft  0  tO  I-I  •  C)) Ft CD I-C (I)  C) CD  IHi C))  0)  C)  CD C))  I-C  QI  C))  5  H  0  0)  CD  Ft  Hi  -  Ft CD (I)  C))  C)  CD C))  1 H  HHi  Ft CD 1-C 0)  C))  C) CD  C))  I-C Hi  0)  H-  0  Ft H-  C))  Ft I-C  CD  C)  0  C)  1 F-  P  Ft 0  Ft CD  C))  <1  Cl) 1 FCD  0  CD  <.  5 0  3  CD  Ft  0  Ft  Ft CD  H-  Ci Ft I-C  0  C)  0  F-’ 0)  C))  <  C))  S  -  (Q  I-’-  C)) C)  H CD  C)) C) H-  HC)  C))  tQ  I-C  0  Ft  CD  I.Q  CD  w  b  (Cl  0  Ft  C)  Ft  5 C))  Ci  Ci H-  -  Ci (P  (I) Ft H-  CD  <1  I-C  C))  Ft I-C CD CD  0 1 H CD  I-C  0  F-’-  C) Ft  CD  LJ  0)  QI  C))  CD  C)  I-C Hi C))  (1)  CD  Ft  0  Ft  0  1C  HN  H-  I-C  C)  I-C  C))  CD  C) 1 F-  -  0  I-  Ft Ft  0  Hi  W  Cl)  Ft  tQ  H-  Ft  -  I  QI  H-  Ft I-C CD CD  (1)  Ci C))  C)  (1)  U)  0  H-  Ft  C))  I-C  IFt  CD  0  1 F-  Z3 C))  Ft  CD  Ft  C))  Ft  (I)  0  Ci  C))  C)  CD  0  H0)  Ft  5  Q  I-C  ‘xJ  -  0)  H  H-  0)  Ft C  CD  (U  ‘-C CD  C))  Q, (I)  H-  C)  i C))  C))  Hi  C))  i—a  C) C))  H-  C))  C)  5  CD  Ci  1 F-  I-C  C))  CD  H-  QI  C)) Ci  HC)  I-  (P C)) Ci  0  CD  CD  Ft  C))  C)  H CD C))  H1 H  0  0)  H-  (1)  H0) Ft  ><  CD  1 F-  (D  H  5 0  CD  Ft  Ci  CD  Ft  1 H  CD  Ft  I-C  CD  H(P  CD  Ft  N CD —  H-  0)  H CD  5  0) C))  F1 H  5  (U  (1]  CD  ft  0  Ft  I  CD  S  CD Q  Hi  CD  Ft  3  C))  H0)  (1)  H  C))  C))  C)) 1 H  C)  (I) Ft H-  H-  Ft  Ft C))  (I)  t  0  Ft  1 F-  C))  -  -  ‘rj H-  Ci  H-  Ci  H  H-  Hi  CD  °  1 H  0  Ft  Q  CD  Ft  H 1 C))  I-C  CD  (12  H-  Ft 0) -  H3  F-’-  QI  0  I-C I-C CD 02  0  C)  1 H  H-  QI  C) H  C))  -  C)) (I) CD  CD  I-C  Ci C)  H-  C))  0  Ft  (P  -  Hi  0  1  3 I)) Hi CD  1  Ft  CD QI  C)) 0)  ‘-C CD  Ci  H-  H02  F-  -  0) CD 02  C)-I  CD  C) I-C  H-  0  (I)  H  C))  0)  CD  (U Ft  CD  C)  Hi C))  (I)  0  Ft  CD  I-C  ‘1  (1) Hi CD  C))  Ft I-C  H 0  103 further at other sites. The rationale can be shown from statistical correlation with ANC and from the relationships 3 in soil extracts and Al concentration between Al 0 and pAl 2 extracts 3 activities in 0.01 M CaC1 in soil leachates. Al are much lower than the predicted values from gibbsite solubility.  3 The exchange model may be used to predict Al  activity if the parameter determined.  pp) 9 (PK  in the model can be  The empirical relationship between PKapp and Alnta  provides a potential solution to calculate P app for soils 1 having a similar sorbent as the soils studied.  III.  Phosphorus in Relation to Soil Acidification  In addition to the changes of pH values and Al solubility,  other changes in soils that may occur during  soil acidification include loss of nutrients due to leaching,  and loss or reduction in the availability of  certain plant nutrients  (such as phosphorus and molybdenum,  which are more strongly retained in acid soils)  .  This  section will discuss the phosphorus issue in podzols and Lavkulich,  (Yuan  1994).  Phosphorus is an important plant nutrient and of concern from the environmental point of view.  The reactions  of phosphate with soil components have been extensively studied from the point of view of soil fertility,  soil  104 chemistry, 1991;  and environmental concerns  Parfitt,  1978)  .  (Sanyal and De Datta,  In many acid soils,  the oxides,  hydroxides and oxyhydroxides of iron and aluminum are the components that predominantly influence phosphate sorption (Parfitt,  1989; Borggaard,  Riemsdijk,  1986)  .  1990; van der Zee and van  For soils from various parts of the world,  sorption of phosphate has been variously related to different forms of Fe and Al and other soil properties and Torrent, al.,  1987).  1990; Wada and Gunjigake, Singh and Gilkes  (1991)  1979;  (Pena  Loganatham et  reported phosphorus  sorption capacity in Australian soils was predictable by measurements of citrate-bicarbonate-dithionite  (CBD)  extractable Fe and Al,  and clay  oxalate extractable Al,  content. Borggaard et al. (1990)  found that the P sorption  maximum was significantly correlated with poorly crystalline Fe and Al oxides and well-crystallized Fe oxides.  The  relationship was fitted into a linear model. Another model, which was proposed by van der Zee and van Riemsdijk  (1988),  described P sorption capacity as a function of amorphous Fe and Al  ÷Al Fe ) , in non-calcareous soils, that initially ( 0  contain little phosphorus. A coefficient  could be  defined to express the relationship between P sorption +A1 Fe . capacity measured and the content of 0 (1992)  Freese et al.  further demonstrated that oxalate extractable  1 ) 0 (p  which represents the phosphate originally sorbed by amorphous Fe and Al  (hydr)oxides in acid soils,  should be  105 taken into account in P sorption models. The idea of including originally sorbed P in P sorption models can be traced to Mead  (1981)  and Holford et al. (1974)  These kinds of models are very useful in monitoring soil and environmental quality for sustainable development, but the applicability of these models outside the model origin regions is still to be verified. This part of the study investigated the effects of different forms of Fe and Al oxides on P sorption capacity of Podzols.  The  applicability of two European derived models was also assessed. ) 0 (P  versus P sorption maximum (Xm)  Oxalate extractable  1 which represents the P ) 0 (p  1. Natively sorbed P  originally sorbed by amorphous Fe and Al acid soils  (Freese et al.,  1992),  (hydr)oxides in  has the lowest values in  Ae horizons and the highest in Ef horizons  (Table 3-10).  This is not difficult to understand if the sorption competition between phosphate and other anions is considered (Violante et al.,  1991).  Since oxalate is a common low—  molecular-weight organic anion in most forest soils Comerford,  1992),  (Fox and  its continuous addition to soils from  litter and decaying wood will increase P in solution by replacing P sorbed at metal-hydroxide surfaces through ligand-exchange reactions, by dissolving metal-oxides surfaces that sorb P or by complexing metals in solution and thus preventing precipitation of metal phosphates  (Fox et  I  H  --  it  ‘-<  U)  2  CD  0  CD  ci  0 >4 CU  H,  it  i  CU C)  H,  CU  H-  H  1Q  0  H it  H0  U) HCl CD  0  CD  ‘-<  CU  5  CD  -  H, 0  CD  F  II  H  U)  —‘  C-o  0  •  0  CD Cl  CD  U) H-  0  ,  ci  ,<  H-  CD  CD  CD  Hn 0  U)  U)  C)  HU)  IH-CD :i Q ci  d 0  it 0  HH CD  it  I  0  HU)  Hit  H  0  CU Cli CD  S  H CD  H  CU  CD  it  it H0 3  H CJ it  H-  ct IPi C)  >4  CD  I-  0  U)  ‘  H-  Z  H  —  H  ,  CD  CU  CD CU n  CD Cl  I-  CU  C) 0  H  CU  U)  H-  H  H,  S  0  -  it  Q  S  p  CD  it  it  -  H,  k<  b  P-  CD  0  H H  0  -  H  Cl  CU  CD  ‘i  H,  0  5  U)  CD  it  HU)  U)  i-  CD  it  CU  CU  0  it  U) 0 I-  ‘d  CD  it  Hit  Ho  H  S  H  CU  H-  IQ  0  H-L 0 •  0  U)  Hit  CD H H  CU it CD U)  CD H  I-  C) Q  0  CU H U)  H H°  CD  H  CU  -  U)  CD  C-Q  CU  C)  1X1 >4  CD  it  S CD  h  IQ  CD  U)  Q  C) it H  PJ  H, I-  H  t  CD  Ct  0  çt  H-  CD H CU it CD Cl  t—  -  C) 0  CD U)  k<  it  t-  0 d CD  t  U) 0 HH  CD  it  CU it  it  U)  0  U)  C-fl  I  CD  H  b  CU  •  —S  H  H C-o  U)  CD  Q HH  Cl  Q  H-  (I)  -•  H ‘-0  -  •  H  CD it  CD CD U) CD  -  ‘-xJ  --  0  H LD  Cl  -  CU  CU  (Q  0  W  CD H U)  0 it  ‘  5  0  -  H,  i-  CD  H, H,  H-  p  it  HU)  H-  HQ  U) C  3  Q  CD  °-  J CD  H  0  H, H, CD C) it  CD  CD  ‘--a  -  CD  H-  Cl  it  H U)  U) 0  CD  it  H0  ‘d  0 ‘-‘i  ‘-  CD  CD  H H  H-  k<  ct H  CU  ICD  Q  it  3 0  0  0  Cl  it  it CD  C) 0  ‘  J CD  Cl  u  H-  U)  0  it H-  CU II  it  CU  it  it CD U)  CU  C)  H-  H  U)  H-  0  CU  H0  0  CD  it  CU  CD  CU  0  0  CD  ‘-iJ  CD  ‘-xi  CD CD  CD it  CD  U) CD  0  U)  H-  ICD H CU ci H0  it  HC) U  H,  H-  Q  H-  0  •  Ui  I  CD  H  CU  H-  CD  <  H  CD  U)  C  CD it CD  S  CU  I-  ‘d CU  it H0  ‘-  U) 0  CD  it  Cl  CU  t HCD U)  CD ‘1  ‘i3  0  h  ‘d  HH  0  U)  CD  CD  CD it  H-  U)  CD H CU it H0  I-  h  CD CU  H H-  CD  it  h  0  H,  3 it U)  HCD  C)  H, H, H-  C) 0 CD  H CU it HQ  CD  h  C) II  C)  c-’)  II  m  CD  Ii ci-  CD  d  0  Ij  d  H  •  0  W  0  Cr  o  I-’  I-’ ) Cr  ii CD  I-’  rr CD 11  CD  1j  d  0  rr I-’-  0  o  tJ  •  •  it CD  CU  H  HU) C) ii U) U) CD  CU U)  0 Cl CD H U)  S  C-t H0 :i  d  0  U)  0 H,  it  CD  5  CD  it  CD  -  0  -  CD  it  H Cl  U)  it  H-  + ‘-d  it ‘-<  uJ C)  CU  C)  it H0  I-  0  CD U) U)  U)  )J  U) U)  °  H  it CU  it  it  ,  it  $  -  CD  °‘  H  H, 0  U)  C)  o CD  (I) H-  °  i  •  it CD  C) 0  CD  C)  CD Cl  5  H  CU  CD  S  H CD  U) H-  CD  U)  CD  çt  H  H  o  H LO  H  a  ()  H  (1) a) a)  0 —1  o  Ci)  U) a) 4)  a)  o  -H Cl)  a)  a)  U)  a) -H C) -H 4-I a)  o  U  o  -H  H a)  o  U LA  a) H  -c ci  H  U  H  a)c  c  -D  a) i  0  o  a)  a) + H  H  o  a)  U  N  0  LA  0  ‘O  0  LA  j1  0  .D  0  LA  H  0  N  0  1  LA  0  H  O  H  (N  0  ii  0  0  CO  0  m  0  HOD  0 0  (Y)  0  CO  0c  0  •  CO  Oc N  0  0  CO  N  0  0  H O  0  •  •  m a)  0  CO •  0  •  CO 0  0  0  E  0c 0  H H  0  •  m  H 0  0  m  0  m  .  N ‘D H  •  ‘D  +  0  •  0  0  O 0  E  m 0  +1 II  H 0  II  0  CD  4-1 LA 0  U) -H  H (Ii 4J  H  C) -H -H  tT) ())  -H  -I-  N 0 H  108 humus complexes are very reactive toward phosphate (Gunjigake and Wada,  1981;  Parf±tt,  The significant  1989).  relationship between Alnta and P sorption parameters may be important from the point of view of soil management. and Swift  Haynes  showed that Al-organic matter associations  (1989)  had a significant phosphate sorption capacity; Gerke and Hermann  (1992)  similarly,  reported that the molar ratio of  P(sorbed) :Fe was nearly 1 for Fe freshly complexed to humic substances,  whereas the ratio for amorphous Fe-oxides was  tenfold lower. complexed Al  For soils in this study,  (Alnta)i  not Fenta,  organically  correlates well with P  sorption parameters and the mean value of the molar ratio of (Po+Xm) :Alnta is 0.80.  Since organically complexed Al  accounts for a significant portion of Al 0 0.64),  (Alnta/Alo  (Alnta) =  0.15-  any change in organic matter dynamics resulting from  either environmental factors or management practices  (acid-rain,  slashburning,  liming,  fertilization)  will affect Alnta and consequently the P sorption capacity, as long as the relationships between Alnta and P sorption parameters remain. 3.  The applicability of two European models Both van der Zee et al.  (1988)  and Borggaard  (1990)  proposed models relating P sorption capacity to oxides of Fe and Al.  These kinds of models are useful since they allow  prediction of P sorption capacity from routine analysis data (Freese et al.,  1992). Whether these European-derived models  0  +  it CD  H  C)  H  C)  CD  CD  CD  S  CD CD  CD it  0  CD  H  0 S  C)  ‘xj  D  CD  J  CD  °  Cu  CD  iJ  o  H  0  i-  Hi  CD  .  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CD  HCD  P  C)  H-  H-  Cu it  0 CD d  0 Hi  C)  0  it H-  u  it  C) CD  C) 0  0  H ‘—  0  H  CD o +  ij  ,,  -  C)  ii  o  < +  --  CD  Cu  CD CD CD CD  CD  HCD  CD H  S  CD  -  N CD CD  I-  CD  < CD  H  0 Q. CD  0  0  it  z CD  0 Hi  CD  S  CD  CD CD  CD  CD  çu  CD  it  Z  H-  CD  Cu H 0  0 Hi  CD Cu  it  CD  H-  CD CD  CD  H-  +  ><  0  H-  ) Cu  H-  0  CD  Cu H  it  H HCD  CD Cu  CD  H-  CD  Cu  ‘i  --  CD  0  CD  H  H  Cu  H-  I-  0  H  HCu  p  i-i-  CD  b  CD  H-  Cu  it  0  k<  CD it  HCD  H-  H  CD Q H-  CD  it  C) CD  H-  Cl)  I-  -  CD CD it  CD  it  3  H-  Hi  0  HCD  i-i  L’J Cu  CD  it  Hi  CD  CD (C H0  I  CD  Cl-  it 0  CD  H  HC) Cu  H  ti 1  CD  h  U  0  H  110  25  4 ,  20 -1-  -1-  A  -k +  +  +  10  -  A A4  A  ++  0 0  5  10  15  20  25  MEASURED (cmollkg) Figure 4-5 Comparison of Measured P Sorption Capacity with Calculated Values from van der Zee’s Model (A) and Borggaard’s Model (+), 1:1 Line is Shown  111 shows good agreement  Fig.4-5)  2 >0.85, Cr  .  This implies both  models are applicable to the soils in this study.  They may  also be applicable to soils in other regions. When using van der Zee’s model,  the coefficient,  o,  should be determined  empirically if the P sorption capacity of concern differs from that in the model,  since P sorption capacity is  dependent on experimental conditions. inclusion of study,  Fed-FeO  In Borggaard’s model,  is unnecessary for the soils in this  since it has no significant correlation with P  sorption parameters  (Table 4-5)  .  In fact,  Borggaard’s model  predicts P sorption capacity better if Fed-FeO is omitted (data not shown in Fig.4-4). Fed-FeO  The contribution to Po+Xm from  0 and Fe 0 is much smaller than that from Al  0.120 or 0.223)  .  However,  (0.04<<  in the general case Fed-FeO may be  kept in the model. In conclusion,  0 should be included in sorption P  capacity in assessment of P sorption models. correlate better with Po+Xm than with X. studied in this thesis, amorphous Fe and Al,  0 0 and Al Fe  For the soils  the most important P sorbents are  especially Al. Although total C content  was found not to have a significant effect on P sorption capacity,  the fraction of Al that complexed with organic  matter has a close relationship with P sorption parameters. This fact may be important for environmental and forest management since organically complexed Al may be relatively easily changed by management practices.  P sorption capacity  0-  Pi  Hi Ft  o  N  I-  P  S  QCD I—’ U)  CD U) Ft  CD Fl  Hi  H-  CD  Fl  H-  Ft  -  Fl  CD  0  Li  H-  HU)  0  ‘d CD Ft  z o  CD  CL) H 0 Ft  H0  Hi  CD  U) H-  H-  o  i Ft  I—’  H-  CD  C) ‘d pi  0  CD  Hi H-  S  0  Ft  Ft  Hi  CD  0  C)  k<  FCD  tT  Pi  Ft  C)  H-  CD  I-  H U)  CD  H-  U)  CD  0 ‘tI  o  Ft  CD  o  Ft  Ft  S  U)  H-  U.  CD  I-i  d  J  M  H H  113 Chapter 5 CONCLUSIONS  Chemical criteria of Podzolic B  (Spodic)  horizons are  associated with a generally accepted assumption that Fe and Al behave in a similar way in podzolization. showed that Al and Fe behave differently, quantity,  This study  at least in  based on extraction data and column leaching  experiments. During podzolization,  more Al is leached from  the top mineral horizon and deposited in the underlying Bf horizon than is Fe.  This may be explained by the combination  of the solubility products of Al- and Fe-bearing minerals and the stability constants of Fe and Al with organic acids. Mechanical and faunal perturbations, which bring Bf horizon material to the land surface, boundary of the Bf horizon.  can lower the apparent upper  Since illuviation of Al in the  Bf horizon produces no visually observable morphological features required for Podzolic B horizons,  the disagreement  of morphological criteria with chemical criteria may bring difficulties in the identification of some Podzols in the field,  when Al accounts for a great portion of the  illuviated Fe and Al. The widespread occurrence of imogolite in Podzolic B (Spodic)  horizons has prompted the recognition of proto  imogolite’s role in podzolization. Extraction of soils with a cation-exchange resin shows that 16-84% of amorphous Al  114  constituents are composed of positive-charged Al. Aluminum content in proto-imogolite, calculated by resin extractable Si,  is negligible in Ae or AB horizons but significant in  some Bf horizons.  The competition among Al-O-Si, A1-O-C,  and  Al-O-H bonds, which determines the proportion of inorganic and organic processes, and pH,  is related to annual precipitation  but not significantly influenced by dissolved  organic carbon or total carbon content. a result of higher precipitation,  Intensive leaching,  hampered the formation of  Al-O-Si by lowering Si concentration, while higher pH favoured Al-O-Si by increasing hydroxy—Al content. The disagreement between this study and some frequently cited papers on the effects of organic matter on noncrystalline Al constituents may be explained by the different pH environments. Two global environmental awakenings are now occurring: the greenhouse effect on global warming and the acidification of ecosystems. While the former remains largely hypothetical, regions.  the latter is a reality in many  There has been much discussion concerning the  ability of soil to transfer acidity to surface waters. Both the intensive factor  (pH)  and the capacity factor  (ANC)  have  their limitations in characterizing acidity transfer. A new capacity factor  ) 0 (Al  was proposed.  Its rationale can be  explained by the statistical correlation with ANC and the by the relationships with Al activity in soil extract and Al  115 concentration in soil leachate. Al activity concentration)  (or  in 0.01 M CaC1 2 extracts of soils indicates  the amount of transferable acidity in situations with little acid input to soils. exchange model  This activity can be described by an  : pAl 3 -3pH  =  PKappi  but the parameter  (PKapp)  may vary from soil to soil. An empirical relationship between the parameter and Alnta has been established.  It may  be applicable to soils with a similar sorbent as the soils studied. When a soil column was leached by organic and mineral acids, Al concentration in the soil leachate indicated the amount of transferable Al in situations where soils receive acidic inputs from natural and anthropogenic sources.  This  2 Al concentration is much higher than Al activity in CaC1 extracts and is related to amorphous Al soils.  ) 0 (Al  contents in  Compared with other parameters characterizing soil’s  ability to transfer acidity, capacity,  such as acid neutralizing  0 is more distinct in concept and easier in Al  measurement. Numerous studies on the relationship between P sorption characteristics and other soil properties have been done, however, sorbed P  most of these studies do not include originally ) 0 (P  .  Since P 0 accounts for 17-66 percent of the  total sorption capacity  (Po+Xm)  in the soils studied,  it  should not be ignored in P sorption models. 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U1CDM  -O  H-  qCDd -d  -0 O  CD-  LII  -5-  0) WC))  IH,  t-O  --  Cr -)U)  0  ‘-<CD  O-  Cl)H-i  (CD M OCD H, 5H,  S  Cl)’ OCUC)) H-H •  ‘—]  X>’  -  <-  HH  C/)F-’U)  PCl) 0  HH(I) P  00  OCrH-’-<Q  CDfWOP ulH-— P U)H-Lil  OO MF—’PJ  H H-,Cflcl-  15JJ  O H-i  5X  CDH--  0) 0 •H-H’ij j  W’d-  0-  Cl) Cl) WJH—Jo  CD  CDCD  CDO  CDCl) CtC  0M  H-,Li  CD  Qs  H” Ct H--  0 CD  1( CD(D  ti-  0  ‘d  CDCD  -  Cr-  0  •  0  P-  H--O CrL’I C))Cr CD i H-  Cr HCI)H-  OH M MCDCrM MOCD - CDCDC)) 0-0  H-HOOH ‘-<  0  Cl)  COO  CDCDH--  -Cl)  • (DOCD MCDPI-1 F-’WU)H CUCi)- --LD LO tQCD—  <O—’F-’  H-Ct CD H-d’tH 0CUHCr tQ I CD M’tiCDWP) I hj H  ‘dLj MCD-•  CDH-X  CnQ-O-  •  QH-’tj  QF—(l)  H-H-CDOC)  Cr0  CDCD-  H---M 1Q 0  hhCDO-  Cl) Cl) JOOH-C) H-F-iH-q 1- QHbH-0  CD  Cr-  Ui  00)  00 H-HH H0  ‘<H,  bO  WCFO PCDCt -MCi)  IS) H, (3H, I C))CD  H O “H,L’I  •  lCrP HH-LD  iOOCD  <PJCH-OO MHOC1 H-Cl) i-hO H-  L’ICD-  •  C  •Q  Oa)CD  H-CD  CtU)-  QC 00CDCDO H-Cl)-  Cl) Cl) I’Tj— CDM  CD  OPJ  -  i  —  -  CO  CD  MC)) 0  —CD  CDH,  M  0  Ct  5  -  Lii  -P  XH-  0  OH, WM CD 0 I-CD5 Pi H-U)  QMM - H-  P)I-CD  CDCl) M HH,  HCr IQH’< CD M.• c-t I M <UiCU  H--  M0)Q  I  W  COMO ‘tiHH-  •  HH CL0 H--o CrMH ‘<0-  I—CDMO WC)•  H-CtC-  Ci) Cl) Cl)-  CD  ‘ti  LX1CD  C))  <  0  C)  Cr5 H-  Q-C) -  PH-’-< 0 CU  <C))(D CDCrM  H-H-  Cr  00<  ‘Z3H, MH-  H-d 5H--  •O H--  ‘  c-tCDHUi OH IC))H-H [‘JHCD U1CI  )W  Z  PMOCD --CDH,H  WWU) 0Hi  CDH-•  ic-rM  ‘tiCU  HC000P OCUOCD H-P5O) P’<ti-  -  C  M-  Cl)LDctQoC • CDW-  $  CDH-Q -CD-  M5CD-  H-F--1  Cl) Cl) ‘dCDCCD pii-- M CD  ctScf)  ‘d  0  ‘tIS  o F-i  Mi  ‘tiS  C1H-  H-fl  LDH, Ui 0 - C)JC)) OH  U1OCD  I  U1CDH, LD0 PCtCt  •-i-iO  L’JH  HCDD)  OHKDMO CU PJCrCr HH• CDO  -hP  0  iU)<ct H-CDHI MS$  LxJI<w  Cl)0)  IQ CDp  CDCDO i-  0>  H-0q  Cl) Cl) U)CD-  CD 0  CD  C))  -  CD  WP 0  -C))  CDCl) SM  U)-  C)) PHI  MO  CCt CDH-  H-N 00 H Cl)H- N  Ct  F—ad CDO  H, Cl)  CUO  M  ,-<  M  CD  N  H-  P  H  “ICr CDCD M Cr  C))  -  U)  W  00  IQ H-J  M(Q CD  i  H-  CUct  CDO  CU1 H-  MM MCD  CDd  c-t  -  M  CD  5  Cl)  CD MX H H-Lii  W  (-Q -C))  C))  HO  MH  <P  CDM  CD ‘1  I-Q  H--  I-i  H--  ‘d-t Q0  Cl)  -  H-I CrP ‘-<IS)  1-.J  H-.D  CDi 0.  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Plant Anal. 24:1333-1343.  Yuan,  G., and L.M. Lavkulich. 1994. Phosphate sorption capacity of Spodosol in relation to extractable Al and Fe. Soil Sci. Soc. Am. J. 58:343-346.  132 Appendix 1  Soil Description  Pedon: Vancouver 1, dominated by Western hemlock with some Douglas fir, having decaying wood Classification: Orthic Humo-Ferric Podzol Horizon Depth(cm) Description LFH+Decaying 20-0 Slightly, medium to well wood decomposed needle litter over reddish brown decaying wood (2.5YR 4/4) ; plentiful fine roots; pH 3 52. 0-2 Ae Light brownish gray (1OYR 6/2); sandy loam; structureless; loose; few fine roots; pH 3.87. 2-10 Strong brown (7.5YR 5/6); sandy Bf 1 loam; weak fine subangular blocky; friable; few fine roots; pH 5.34. Strong brown (7.5YR 5/6); sandy Bf2 10-30 loam; weak medium subangular blocky; friable; few medium roots; pH 5.83. Bm 30-60 Strong brown (7.5YR 5/6); sandy loam; weak medium subangular blocky; friable; few medium roots; pH 5.57. Light yellowish brown (1OYR 6/4); BC 60-73 loam; weak medium subangular blocky; friable; few medium roots; pH 4.88. IIC 73+ Pale brown (1OYR 6/3) with brow (7.5YR 4/4) mottles; sandy loam; strong medium block; firm; no root. .  Pedon: Vancouver 2, dominated by Western hemlock with some Douglas fir, having no decaying wood Classification: Orthic Humo-Ferric Podzol Depth(cm) Description Horizon Needle litter with various degree LFH 5-0 of decomposition; plentiful medium roots; pH 3.84. Strong brown (7.5YR 5/6); sandy 0-10 Bf 1 loam; weak fine subangular blocky; friable; plentiful fine roots; pH 4.51. Strong brown (7.5YR 5/6); sandy 10-30 Bf 2 loam; weak medium subangular blocky; friable; few medium roots; pH 4.75. Reddish yellow (7.5YR 6/8); sandy 30-60 Bf3 loam; weak to medium coarse subangular blocky; friable; few  133 fine roots; pH 5.39 Pedon: Vancouver 3, dominated by Douglas fir with some Western hemlock, having decaying wood Classification: Orthic Humo-Ferric Podzol Horizon Deth(cm) Description LFH 24-15 Needle litter with various degree of decomposition; few fine roots; pH 3.70. Decaying 15-0 few fine roots; pH 3.72. Ae 0-2 Yellowish brown (1OYR 5/4); loamy sandy; weak very fine subangular blocky; very friable; few fine roots; pH 3.95. 2-10 Strong brown (7.5YR 5/6); sandy Bhf loam; weak to moderate fine subangular blocky; friable; plentiful medium roots; pH 4.79. 10-30 Reddish brown (7.5YR 6/8); sandy Bfl loam; weak to moderate medium subangular blocky; friable; plentiful medium roots; pH 4.87. Bf2 30-60 Light brown (7.5YR 6/4); sandy loam; weak to moderate medium subangular blocky; friable; few coarse roots; pH 5.06. Pedon: Vancouver 4, dominated by Douglas fir with some Western hemlock, having no decaying wood Classification: Orthic Humo-Ferric Podzol Horizon Depth(cm) Description 6-0 Needle litter with various LFH degree of decomposition; pH 4.41. Yellowish brownish (1OYR 5/4); AB 0-10 sandy loam; weak fine subangular blocky; very friable; few medium roots; pH 4.23. Strong brown (7.5YR 5/6); sandy Bf 1 10-30 loam; weak to moderate medium subangular blocky; friable; few medium roots; pH 5.18. Reddish brown (7.5YR 6/8); sandy Bf2 30-60 loam; weak to moderate medium subangular blocky; friable; few medium roots; pH 5.50. 60-75 Very pale brown (1OYR 7/4) with BC light brown (7.5YR 6/4) mottles; sandy loam; moderate medium subangular blocky; firm; few fine roots; pH 4.84. IIC 75+  134 Cowichan 1, dominated by Douglas fir, having decaying wood Classification: Orthic Humo-Ferric Podzol Horizon Description Depth(cm) Variously decomposed needle litter 25-15 LFH 15-0 Decaying wood Yellowish brown (1OYR 5/4); loam; 0-10 Bfl field descriptions of structure, consistence, root distribution hereon were not made due to time limitation. pH 4.08. Brown (7.5YR 5/4) with dark 10-35 Bf2 reddish brown (5YR 3/2) coating; loam; pH 4.37. Light yellowish brown (1OYR 6/4) 35-55 Bm with yellowish red (5YR 5/6) coating; loam; pH 4.68. Pedon:  Cowichan 2, dominated by Douglas fir, having no decaying wood Classification: Orthic Humo-Ferric Podzol Horizon Description Depth(cm) 5-0 LFH Yellowish red (5YR 5/6) ; loam; 0-20 Bfl pH 4.66. Yellowish red (5YR 5/6) ; loam; 20-40 Bf2 pH 5.06. 40-70 Strong brown (7.5YR 5/6); loam; Bm pH 5.06. 70-80 Pale brown (1OYR 6/3) ; loam; BC pH 4.97.  pedon:  Cowichan 3, dominated by Western hemlock with decaying wood Classification: Orthic Humo-Ferric Podzol Depth(cm) Horizon Description Slightly, medium to well 20-0 LFH+Decaying decomposed needle litter wood Reddish yellow (7.5YR 6/6); loam; 0-15 Bfl pH 4.80. 15-35 Reddish yellow (7.5YR 6/6); loam; Bf2 pH 5.10. 35-65 Very pale brown (1OYR 7/3); sandy BC loam; pH 5.15. pedon: Cowichan 4, dominated by Western hemlock without decaying wood Classification: Orthic Humo-Ferric Podzol Depth(cm) Description Horizon 20-0 LFH Light gray (1OYR 6/1); silty loam; 0-2 AB pH 4.28. Brown (7.5YR 5/4); loam; pH 4.89. 2-15 Bf 1 Pedon:  ro  o  Ui  o  C)  Ui  •  H-  U)  —‘  U,  I-<  0  H  M 00  U, • ty  rcn.  -<  Cl-  Cl) HH  H 0 PJ  5 -  —.  —.  U,  —.  —.  U,  I-<  I-<  H0  Cl-  U,  U,  (DO U)1  .  -  “  ,-  -  b U,U, 0• 0  dd  -.  S  P 0 Pi  ..  —.  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U, —) —.  j  OUi  -  1J-J  dOQ  -<U,O  b  rl  U, U,  QW  U,U, I I  WH  M  flH,  WW  CD PdCiW rt  H  5  0  -  Ui  pi  J0 rtPH H0  I0Icth  H  CD 0  H-EQ 000  lCD oplrJQ  Q  H-  k<  J  QH,  WNW CDOH-  -.c-t---.Q P ti h-  ‘iOF— +H-W  k<5U,5H  0  I  Ui  P  H  H,  W  0H-0CD OP)l—’ bPJ1Q  CD  Cl-  H-  5  —) 0  0  I  0  M  H,  —3PC1  10 HIS 0  Id”-Q  OH-  H--< 0  lCD oWrJQo I IIrt0M0lct0  --H--0-0 U) ‘CI  ‘<  CD Q 0  H-fl OCDO JO rtPJH-  H,  OH-  WiNW  I H-  dd (DO Cl) ON  çt  I U, U,  I-J  fl OH IiH-O)  JCD0CDOCD0CD JP)F-P)F--  CJ)’d  —.  —5  ii  U,H —. 0  -  I-<  UiM  -J  0i  —J tY•  0  0)  I  +  U,  )  H  H,  W  1W<HiHF<PF<  CD  Cl-  Hii  5  Q 0  Ui Ui  M  H,  W  CX) 0  W C)  CD  I  0  z  ool— 10 HIS 0  0  U,15p H---H-i MCfl Cl) Hd—  ON 0 H- P  •  -] U,  4E1CDOCDh PP)P0  r-  ;-  I—,  .  -  I  1Jrt  0iolrrF-  I  MI  -1  h h H0  J CD  I  0  5  10 H15 0  CDP 1Mj  0  U,  •  b  Cl)  5PU,P5  lCD  M0iQ  i  0  0  H-  Id..  lCD  --  0  CD  H-fl 000 PJO rtQH-  Iti--(Q’  IQ  H-  “<  U  QH,  MHCDOH-  H,H,NW  WW+H-D  0  W  H,  W  “JOH  H-’< . OH-  i iIctO MoIrrO  0  ‘  0CD  0UitJQ  0CDCDOCD PJF— PP  —J o  HQH-  M  W  I  H,’JNU)  H,  H,  H-1  WH-U  tn  OH  U,  W  CD  Z  II  CD  çt  CD  0  II  *  1’JH  I  I  I  WL’JHWJH  fl  C)  1)  MH JH MH  (_) I  C)  1’JHWbJH  H  .JHH  W  L’JH  M H  •  ZZ’ZZZ’ZZZ’ZZ’ZOQQHHOHHOcDocoooo  1’JH  I  () W  (:2  I  (71  C)  H  (Q  H  H CD  ‘ç)  HO rt  o)  0  N  H-  I-jo  ]CD  H  C)  C)  (-I  CD  0  C)  CD  Q  H  HC-I• CDJ H  0•  <H  ErI  CD  H w  Biographical Information  1963  Born,  1984  B.Sc. Nanjing Agricultural University,  1984  M.Sc.  Chinese Academy of Sciences  1991-  Ph.D.  candidate,  1994  P.  R.  China China  Department of Soil Science,  University of British Columbia  

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