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

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ALUMINUM CHEMISTRY OF SELECTED PODZOLSINSOUTHWESTERN BRITISH COLUMBIAbyGUODONG YUANB.Sc., Nanjing Agricultural University, China, 1984M.Sc., Chinese Academy of Sciences, 1987A THESIS SUBMITTED IN PARTIAL FULFILMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(Department of Soil Science)We accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAJune 1994©Guodong Yuan, 1994In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department of_____________________The University of British ColumbiaVancouver, CanadaDate ///7- / / / 1 / -DE-6 (2/88)iiABSTRACTThree related aspects of Al chemistry of selected HumoFerric Podzols in Southwestern British Columbia wereinvestigated: mechanisms of podzolization, acidity transferfrom soils to surface waters, and phosphate status inrelation to soil acidification.Distributions of Al and Fe in horizons and results ofcolumn leaching studies revealed that Al behaves differentlyfrom Fe in podzolization in terms of ease of eluviation fromthe top horizon and illuviation into underlying horizons.This may be thermodynamically explained by the solubilityproducts of Al-bearing minerals and stability constants ofAl-organic complexes. This result differs from thetraditional belief that Al and Fe behave similarly inpodzolizat ion.Both organic and inorganic mechanisms of podzolizationare proposed in the literature. Studies reported are insupport of either one or the other mechanism. Chemicalextraction results in this study showed that the content ofAl in proto-imogolite was significant in some Bf horizons.This may indicate the contribution of an inorganic mechanismin podzolization. The competition among Al-O-Si, Al-O-C, andAl-O-H bonds, which determined the proportion of inorganicand organic processes, was related to annual precipitationand pH, but not influenced directly by dissolved organic1 4r Icarbon content.Podzol formation is a natural process of soilacidification. This study suggested that the amorphousAl(A10) content in soil might be used as a capacity factorto characterize acidity transfer from soils to surfacewaters. Al activity in neutral salt extracts of soils, whichrepresents the amount of Al subject to transfer to surfacewaters in situations with little organic and mineral acidinput to soils, correlates significantly with Al0. This Alactivity can be described by an exchange model. A parameterin the model has an empirical relationship with organic-bound Al content. Al concentration in simulated leachates,indicating the amount of Al transferable to surface watersin situations where soils receive acidic inputs from naturaland anthropogenic sources, is much higher than that inneutral salt extracts and is related to Al0. Exposure of Bfhorizons to the land surface may contribute to acceleratingtransfer of acidity to surface waters.Reduction in bioavailability of phosphorus is aphenomenon during soil acidification. Phosphate sorptionparameters were strongly dependent on amorphous Al, Fe, andother constituents. Amorphous Al and Fe can be used topredict phosphate sorption capacity of the soils. TwoEuropean-derived models were shown to be applicable in theareas of this study. Modification was done to include nativesorbed phosphate in the sorption capacity of the models.TABLE OF CONTENTSAbstract iiTable of Contents iVList of Tables viiList of Figures V11Acknowledgements xIntroduction 1Chapter One Literature Review 4I. Fundamental Chemistry of Al in Soil andAssociated Environments 51. Solubility of Al minerals in soil 52. Aluminum speciation in soil solution andsurface waters 63. Precipitation and crystallization ofhydrolytic Al products 9II. Podzol and Podzolization 111. Concept of podzol 112. Allophane and imogolite in podzols 123. Hypotheses and theories of podzolization 15III. Aluminum Related Environmental Problems 181. Ecological effects of Al 192. Acidification of soil and surface water 21Chapter Two Materials and Methods 27I. Study Areas 27ooJpiddftftHHCDCDHHHhhHHH‘-Ii-CD0pHC)-co.-jouiWMp0ftCU•J-CD•-••CUH-CDCUCDtTHF-U)ZiC!)‘dZ00U)MH-‘dH-H-C)I—’CDH-H-01C!)CDtCUHC)bCU0HU)dH-U)0CDCUCUH-•••H-CDQCUH-U)CDftftC)NCl)U)U)U)C)HFH-H-00C)‘iJH-H-HH0hC)ft)JCUC)FHHCD0HCDH-CDftCUHCUCDk<CDH,CD0I-C)H-H,U)ct><CDftHU)ClCUCr)d0a)C)HHCDNCrU)U)CrH-ftQCDH-C)IQftftC)ftH-CD><CUH-FdH-hfthClCDCDH-CDH-H-H-H-C)a.hCrCU00CUk<CUHU)CD><Jftct0H,CU$0H-HHC)CD0ftHH-H-H-CfV0H,0NH-H-ftCUhfti-<0ftC)CDCUC)H-‘xjW0NH-C)H-UU)0CU0CD<(UHH-0ftH,C)CDU)H-ftH,Clfti0H-U)H-H-H-ftU)H,U)H-U)CU-CUN(Q00C)H0(1)<CUH-U)t-QCU0oCDH-H-H-ftC)HftftH-U)C)CD0H-CUCrCDU)H-C)H-<0‘dU)Cl><ft0‘dCUCDU)CDft‘1CU0H-doftII0••U)C)HCDCDClClH-CDU)H-H-U)I-H-N0HH0ftftH-CDoCtU)CUCDH,k<H-U)HU)0CDU)CU0CDCU<C)IIftU)HftftftCDH-•U)oCUPiU)0CUC!)HF-’-U)HClCDC)0CUH1xJ CDCUHC)ClC)H-H-CDCl U) --1—)oawwwwwwwwMWH0U,coooUWMJHcovi1. Constituents and factors affecting aciditytransfer 83a. Constituents contributing to aciditytransfer 83b. Intensity versus capacity factors 85c. The capacity of soils to transferacidity 872. Justification of Al0 as a capacity factor 90a. Aluminum activity vs. gibbsitesolubility 92b. Relationship among pAl3, pH and Al0 94c. An exchange model 96d. Acidic input and transferrable Al 98III. Phosphorus in Relation to Soil Acidification 1031. Natively sorbed P vs. P sorption maximum 1052. p sorption parameters in relation to soilproperties 1063. The applicability of two European models 108Chapter Five Conclusions 113Bibliography 117Appendix1. Soil Description 1322. Total Nitrogen Content and CuC12 Extractable Al 136I-HiHIHI‘-HIHi‘-HI‘-HIHIHIHi‘-HI‘-HIpicuuJP)JPJPiPiPiP)PiP.)P.)P.)P.)P.)PidbbHHHHHHHHHHHHHHHHHHCDCDCDCDCDCDCDCDCDCDCDCDCDCDCDCDCDCD‘dCl)I-i4<WWhWWWWWWWWMMCDH0IitIIIIII0IIIIIIIIUihWl\)HH‘-.0‘zICD<1CDUiWMHMHC)HCDP.)-0CD---•itHC)Hititfl()‘xjC!)itC)C)CDw0WH-C)0)00h0C)H-0C)H0HPipiCD0hP.)I—’H0CDCDH-C)CD‘1S5Cl)CI)hP.)‘dC)P.)0)Cl)I-hQC)5P.)it‘d5H‘1PiCDitHi0P.)H-H-HpiHP.)CDP-HH-H-IH-C)C)H-IHI—’H-P.)0H0)P.)C)CDC)P-P.)I—’PP.)HCl)itH-H-itH-CD‘xJHC)CD1QciCD0H-ciNCDCDith-CDHC)HtlH-.)00‘-<CDhitCD‘-<it0)H0C)HiCl)itP.)h-0)C)H-H-CDH-5Cl)0‘tIC)0I—’P.)H-01’i0NCl)50P.)I-hbhI-0H-itCDH-P.)C)I-C)tCD00‘-<dI-hNH-C)itIQit00CDçtCl)Q0)itH-0CDCD‘1CDP.,CDitCD0)HH-itH-C)P.)><H-Cl)H-I-hCDitC)P.)00CQititC)C)0)it0HiC)CDH-itI—’I-pJI-11ititpjpjH-0HhC)P.)P.)P.)P.)IIIIC)CDP.)H-dCD.)1C)citYH-P.)itH-C)Hi.)HitH-H15Cl)P.)CDCD‘-<PCDIIP.)P.)P.)P.’0CDCDCDIIHitC)C)bitit0P.)ititC)Cl)55H-H-itHCl)H-CDHi5CI)ciH-CD0itH-CDI—’hQCDP.)pjP.)P.)3it‘.<H--0IiCl)itlYitj1YCDCDH-I—’CDCDH-pI.H-IIl-0ciH“iCDP.)hit0CDHP.)Cl)I-h-HCDI—50)0PH-HCD—ciH-CDCl)ititCl)H-‘uJP.)H-CDZ3CDC)P.)CDC)CDZH-CDHC)Cl)P.)-,C)Cl)P.)P-‘-P.)Cl)00P.)itI—’0Cl)Cl)3H-H-CDCD0H-0H-0)itI—’1H-HH-0itP.)HP.)CDCl)C)CD‘]j0><H-0Cl®ititctH-0) it 0 I-h Hi P.) H CD 0)H 0 —:1H cD 0‘-.0-CDCDUiUiUiU]LOH‘-.0—JU]U]-,HCDHLA.)LA.)M‘-.00‘-.0H-H-ViijList of FiguresFigure 1-1. Schematic diagram illustrating two theoriesof podzolization 16Figure 3-1. Infrared spectra of clay size samples 63Figure 4-1. Index of movement for Al and Fe 66Figure 4-2. pAl3 and pH relationship 93Figure 4-3. Empirical relationship between PKapp andA1Figure 4-4. Comparison of Al0 and Al concentrations insoil leachate 101Figure 4-5. Comparison of measured and predicted Psorption capacity 110IXFrequently Used SymbolsA -- Mineral soil horizon formed at or near the surface inthe zone of leaching, or eluviation of materials insolution or suspension, or of maximum in situaccumulation of organic matter or bothAB -- Transitional horizon between A and BAe -- A horizon characterized by the eluviation of clay, Fe,Al or organic matter alone or in combinationBf-- B horizon enriched with amorphous material,principally Al and Fe combined with organic matterC -- Mineral horizon comparatively unaffected by thepedogenic processes operative in A and BL, F, and H -- Organic horizons that developed primarilyfrom the accumulation of leaves, twigs, and woodymaterials with or without a minor component of mossesCEC -- Cation exchange capacitynta -- Sodium nitrilotriacetate extractableo -- Acid ammonium oxalate extractablecbd Cd) -- Citrate-bicarbonate-dithionite extractabler -- Cation exchange resin extractableANC -- Acid neutralizing capacityP0 -- Natively sorbed phosphateXm -- Phosphate sorption maximumxACKNOWLEDGEMENTSI would like to express my sincere appreciation to Dr.L. M. Lavkulich for his guidance and encouragement throughthis project.I am very grateful to the members of my supervisorycommittee, Drs. T. M. Ballard, H. E. Schreier, and K. Klinkafor their willingness to help me at all times.Thanks are due to Mr. B. von Spindler, Ms. Sally Finoraand Ms. Susan Harper for their help in technical aspects.The number of friends and colleagues who helped in oneway or another is too large to list but none the less theyare gratefully acknowledged.I acknowledge Fletcher Challenge Canada Limited fortheir partial financial support.Last but not least, I would like to thank my wifeYibing, my son Matthew and my parents to whom I dedicatethis thesis.1INTRODUCTIONConcerns for surface water acidification and potentialinteractions between expected global warming and soildynamics and processes have prompted new interests in thestudy of soil, particularly the important podzol±c group ofsoils. In many Southwestern British Columbia regions,Podzolic soils are dominant in upland well-drainedpositions. Characteristically these soils lack Ae horizonsbut the Ae may be found under accumulations of decaying woodrather than the more characteristic LFH associated withaccumulation of a variety of forest plant litter.Understanding of Al chemistry of podzolic soils in thisecologically fragile zone may have great practicalsignificance for sustainable forestry and for the solutionof some environmental problems.The key chemical issue in podzolization is the verticalseparation of Si from Al and Fe. Both organic and inorganicmechanisms have been proposed, but most studies in podzolgenesis are pro one mechanism and con another one (Farmer,1982; Chesworth and Macias, 1985; Dahigren and Ugolini,1988) . Detailed investigations are still needed to betterunderstand the mechanisms and relative importance of organicacids vs. silicic acid in podzolization in a specific regionor pedon.Podzolic soils are more easily affected by acidic2deposition than other soils in terms of soil acidity. Thepotential relationship between acidic deposition andelevated Al concentrations in soil solutions and surfacewaters has received much attention during the past decade(Cronan and Schofield, 1990) because elevated Alconcentration is considered an environmental stress in bothterrestrial and aquatic systems. Most existing modelspredicting Al activity in soil solutions or surface watersare based on the solubility of a specific mineral. However,results of both under- and oversaturation with respect tothe mineral phase have been reported (Cronan et al., 1986;Driscoll and Schecher, 1988)Phosphorus is an important plant nutrient and ofconcern from the environmental point of view. The reactionsof phosphate with soil constituents have been extensivelystudied in many parts of the world and some models have beendeveloped for estimating phosphate sorption capacity (vander Zee and van Riemsdijk, 1988; Borggaard, 1990; Singh andGilkes, 1991), but the applicability of these models inwestern North America regions has not been examined.The aim of this thesis was to provide a betterunderstanding of soil genesis as a baseline to allow anunderstanding of the effects of forest management. Morespecifically, the study focused on an understanding of soilproperties and chemical processes of Podzol formation inthis ecologically important zone of the Pacific Northwest.ftQiMiMi.P3H-J000DrtCDMiftQhC)CDCDMiCDCDCl)CDHU)U)U)0IIH-H-ftftCl)P3ftCDP3CC)U)H-CDH1CDçtiftU)Fl00CtP3ZMift0H-C)P3F-1P3HiCrCDLJHH-QIU)CDftCDC)C)CDP3CDP3CDCfMirr<‘dP3HMiH-P3H-F-1P3CDC)HF-1‘-<C)IQCDC)H-H-H-CDU)ft3P3ftMiU)U)ct‘-<H-0ci.CD-.C)H-MioU)MiMiftL’J0Zft0—H-0U)hCDF-1FlH-CDoCDH-ftU)ftH-U)Fl0CDrtHftH-FlFlH-CDP3CDP3C)0U)HU)C)0F-1CDftçtH-H-iCDCDU)U)U)fthP30H-H-H-H-3MiftH-MiU)I1hH-H-CDC)00ftP3iP3MiFlftU)0CD0HH-P3oNC)CDCDp3QH-MiFlftIiHMift0oH-P3H-CDHNftC)CDCDWP3ftk<ftU)HU)ftH--U)H-MiH-C)Flft0‘-<0iH-Mi0MiP3P3ftP3C)CDP3FlftP3ftCD><ft0H-ftCDFlCDCDHU)FlP30CtCDP3Fl0U)HCDU)W4Chapter 1 LITERATURE REVIEWAluminum is the most abundant metallic element insoils, making up approximately of the solid matter inan average soil (Lindsay, 1979) . It occurs in a series ofcrystalline and amorphous (short-range ordered) Al-bearingminerals (e.g., feldspars, micas, chlorites, vermiculites,smectites, kaolinite, halloysite, gibbsite, allophanes, andimogolite). It also exists as exchangeable Al and hydroxy Alinterlayers.Aluminum was isolated by the Danish chemist Oersted in1825 and characterized by WOhier in 1827 (Sigel and Sigel,1988) . Analogous to carbon as a coordinator for organicmatter, Al ranks in abundance next to silicon as an oxygencoordinator in minerals in terrestrial and aquaticenvironments (Huang, 1988) . Aluminum may be released fromminerals to soil solutions and natural waters throughchemical and biochemical weathering reactions. Duringweathering, primary aluminosilicates dissolve to formsecondary aluminosilicates and aluminum hydroxideprecipitates. Both inorganic and organic ions are integralparts of the environment. They are important weatheringagents of primary and secondary minerals. The extent of Alrelease from minerals to the environment has increased withtime, population growth, intensification of agriculture, andindustrialization (Huang, 1988) . The aluminum released to5soil solution and natural waters undergoes a series ofreactions including hydrolysis, polymerization,complexation, precipitation, and crystallization.Understanding of these processes is an asset to the study ofpodzols and podzolizat±on, since accumulation of amorphousmixtures of organic matter and aluminum, with or withoutiron, is the feature common to most Spodosols or Podzols(Soil Survey Staff, 1975). The recent (last two decades)flurry in aluminum research has focused on the effects ofincreased mobilization of aluminum from the edaphic to theaquatic environment by acidic deposition (Lewis, 1989)Podzols are an extremely important part of the debaterelating to this environmental issue.I. Fimda.tnental Chemistry of Al in Soil and AssociatedEnvironmentsThere are several recent books and articles dealingwith this subject (e.g., Sposito, 1989; Huang, 1988; Lewis,1989); therefore, the following section will only highlightsome potentially important aspects of Al chemistry inrelation to Podzols.1. Solubility of aluminum minerals in soilThe solubility of aluminum in soils is controlledinitially by minerals present in significant amounts thathave the highest solubility or are most easily weathered.6Weathering processes slowly remove the thermodynamicallyunstable minerals, so that the more stable mineralssupporting the lowest activity of Al3 ultimately controlthe solubility of aluminum (Lindsay and Waithall, 1989).Selective equilibrium constants for dissociation reactionsof potentially important minerals and complexes in Podzolsare listed in Table 1-1.For the most part, weathering is essentially a form ofan incongruent reaction which may be summarized as reportedby Maclas and Chesworth (1992)primary minerals + attacking solutionsecondary minerals + leachate2. Alu.tninu.m speciation in soil solutions and surface watersa. Hydrolytic reactions of AlThe Al3 ion, which is released from Al-bearingminerals to soil solutions and surface waters, isoctahedrally coordinated with six water molecules and existsas the Al(H2O)63 ion. Hydrolysis of the Al(H2O)63 ion canproceed through monomeric and polymeric mechanisms (Base andMesmer, 1976)There are four monomeric species of Al3 hydrolysis:AlOH2, Al(OH)2, Al(OH)30, and Al(OH)4 (Table 1-1). Aluminumhydrolysis in solution containing relatively lowconcentration of Al and low ligand number may be describedby the monomeric hydrolysis mechanism. However, hydrolysisof Al in solutions of either higher Al concentrations orI-]CD C)HrtCDHHHHHHHHHH‘.D-Ji(iiWMHH-Cl))OLD-JOU]WMH0QCDH-0HHHI’HHHHHHHHHHH-HJHHH-CDH5W“HH“‘H‘IctH-++++++++++++Cl)0HL00++H-++++++++++++-...,c,0cn)CDH++00H-H-HHI-H0WMCl)wijH0Q+WCl)0‘xj‘xj‘xjMCOHtJODWh10Cl)0r’J11-001CDCDS-HH-+?1IJ11-11-Q010i-‘dCl)H+H--.HHHhijHHHHtJHH0+0rH—S-HCD0HCl)o+‘ZH—000‘9Cl)1QQ0Zc1L.J0+±+++C)H’PJHCDW0—H‘-<O)rt.-I)I.J0—+00)(DO(+£\)L,.IrtH-M]H++t\.)4++++P)rfFH+HHCD++1’JH+..-H-Cl)+HCDCi)H-H+IDJ0•Cl)0wH- 0+“--JctHH-J+rs,000H0Cl)—oH-CDHp.iIIHOHHHHIt’JHIHWrtW0)0HHWDCJ0)—J)0U]H—JIl)CX)H-Q0WH0)M00)0)oHHo4Ui0)0)0IQDDFJ0)00WUi00)kO0)W.DUi-M0)Cl)08higher ligand number is better described by the polymerichydrolysis mechanism. Aveston (1965) interpreted his resultsin terms of the species Al2 (OH) and Al13O4(OH)247.Baes andMesmer (1976) conclude that the polynuclear species formedby Al hydrolysis are Al2(OH)4,Al3(OH)45, and Al13O4(OH)247.b. Aluminum-organic/inorganic complexesThe nature and concentration of inorganic ligands playan important role in influencing the hydrolysis andpolymerization of Al (Huang, 1988). Inorganic ligands thatform soluble complexes with Al3 include fluoride, sulfate,and nitrate. These complexes contribute to total solublealuminum in soils, particularly in acid soils.Essentially every aspect of the chemistry of aluminumin soils, sediments, and aquatic systems is influenced byinteractions involving organic substances. The interactionof Al with organic substances is of considerable importancein controlling soil solution levels of the highly toxic Al3ion in acid soils and natural waters. The effects of organicacids on Al behaviour occur through two distinctive modelsof action, namely, lowering of the pH value because ofionization of acidic functional groups (e.g., COOH COO- +H) and formation of chelate complexes (Stevenson and Vance,1989). The carboxyl and hydroxyl groups are the principalfunctional groups involved in the reactions of Al withorganic acids in soil solutions and natural waters. Thesefunctional groups are present in both the humic and nonhumic9fractions of soil organic components. The significance ofthe humic fraction, such as fulvic acids, in complexing withAl in solution has been extensively studied (Schnitzer andKodama, 1977) . The nonhumic fraction, such as the low-molecular-weight organic acids, have been recentlyconsidered important in controlling Al behaviour (Huang,1991) . The sources of low-molecular-weight organic acids insoil environments include root exudates, canopy drip, decayof plant and animal residues, and microbial metabolites.Considerable emphasis recently has been given to theimportance of oxalic acid as a chelator of Al in acid forestsoils. Many fungi are prolific producers of oxalic acid,including the vesicular-arbuscular mycorrhizal fungi(Stevenson and Vance, 1989). At the pH values found in manyPodzols, formation of soluble Al-organic complexes increasestotal soluble Al in soils and contributes to its mobility.The Podzol is often cited as a prime example of the role oforganic matter in the eluviation of Al during pedogenesis.3. Precipitation and crystallization of hydrolytic AlproductsMononuclear and polynuclear Al species can betransformed into colloidal or solid phases. Many of thecolloidal solid phases initially formed are of very fineparticulates that may not settle upon centrifugation and mayeasily pass membrane filters (Huang, 1988). Theprecipitation products of Al can be either short-range10ordered materials or crystalline Al hydroxides, depending onsolution composition and formation conditions.Three types of Al hydroxides and short-range orderedaluminosilicates have been identified in soils: crystallinehydroxides (e.g., gibbsite, boehmite), hydroxyaluminuminterlayers in vermiculites and smectites, andallophane/imogolite. Gibbsite is a common product oftropical and subtropical weathering. In temperate soils, Almobilized by acidic attack on soil minerals is believed tobe precipitated as allophane/imogolite, and trapped asexchangeable aluminum or hydroxyaluminum interlayers inexpanding layer silicates (Paterson et al., 1991).Allophane and imogolite, long known as major metastableweathering products in volcanic ash and pumice soils, haverecently been recognized as pedogenic components of the Bhorizons of many podzols and podzolized soils (Farmer, 1982;Wang et al., 1991). Generally they have been detected insubstantial amounts only in B horizons of pH(H20)>4.8(Parfitt and Kimble, 1989) . The stability of imogoliterelative to gibbs±te is determined by the concentration ofsilicic acid in solution, according to the equilibrium:(HO)3A12OSiOH + 3H20 2A1(OH)3 + S±(OM)4Podzols commonly contain chlorite-like l4A layersilicates (Ross, 1980) which appear to consist ofvermiculites with an incomplete aluminous interlayer, ratherthan the magnesium-iron hydroxide interlayer sheet of true11chlorites. These pseudo-chiorites are believed to form bythe leaching of interlayer potassium from micas, followed bythe entry between the layers of hydroxyaluminum polymericspecies. The aluminous interlayers of soil pseudo-chloritesare apparently more stable than gibbsite, allophane orimogolite. They appear to be best developed in A and Bhorizons of pH(H20) values of 4.4-5 (Barnhisel, 1977) andcan persist even at pH 4 (Karathanasis et al., 1983),whereas allophane and imogolite are seldom present in soilhorizons of pH(H20) below 4.8 (Parfitt and Kimble, 1989;Wada, 1989)II. Podzo]. and Podzolization1. Concept of podzolPodzols are a major class of soil developed in sandy toloamy materials occurring in cool, temperate, humid regionsof the world. Typically, they have four major horizons: adark-colored organic surface horizon; a bleached eluvialhorizon; a reddish, brownish or black illuvial horizonenriched in amorphous materials; and a sandy C horizon(McKeague et al., 1983)Dokuchaiev examined podzols as early as 1879(Ponomareva, 1969) . The origin of the name “podzol” is notentirely clear. In one interpretation it is assumed to haveoriginated from the preposition pod”, meaning under, andthe noun “zola”, meaning ashes, perhaps reflecting the fact12that the gray ashy layer is usually not at the soil surfacebut rather under a darker horizon, or perhaps indicatingthat the soil is under °ashes” thought to have been left byburning of the forest (Ponomareva, 1969)The meaning of podzol has changed with time. Theoriginal concept of podzol in Russia emphasized the ashygray eluvial horizon and the name was applied to soilshaving such a horizon regardless of the nature of theunderlying illuvial horizon. As the term was translated intoGerman and later into English it became associated withsoils having, in addition to a bleached layer, an underlyingreddish to dark-brownish or black illuvial horizon typicalof podzol. In Soil Taxonomy (Soil Survey Staff, 1975) andThe Canadian System of Soil Classification (AgricultureCanada Expert Committee on Soil Survey, 1987), the ashyhorizon (Ae or E) ceased to be a diagnostic horizon ofPodzols (Spodosols) for several reasons: 1) in many forestedareas, due to blowdown of trees and other disturbances, theAe (E) horizon of Podzols (Spodosols) is intermittent; 2)cultivation may completely destroy the Ae horizon; 3) many Bhorizons of Brown Podzolic soils (no Ae or E horizon) hadthe same properties of Bf horizons of Podzols with Aehorizons.In this thesis, Ae and E are used synonymously and onlyAe is used when dealing with Podzols.2. Allophane and imogolite in podzols13Allophane and imogolite, long known as major metastableweathering products in volcanic ash and pumice soils, haverecently been recognized as components of the B horizons ofmany Podzols and Spodosols (Farmer, 1982; Ugolini andDahlgren, 1991; Wang et al., 1986). Because of their largespecific 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 hydrousaluminosilicates with a hollow spherical morphology.Morphology, however, even for crystalline minerals, varieswith the condition of their formation (Huang, 1991)Therefore, Farmer et al. (1991) define allophane as anynoncrystalline hydrous aluminosilicates, and does not implya spherical morphology. Because of this difference in thedefinition of allophane, a soil fraction with the imogolitestructure that is soluble in citrate-dithionite-bicarbonateis 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 uniquetubular structure. It appears as threads consisting ofassemblies of a tube unit with inner and outer diameters ofl.O and ‘2.O-2.7 nm, respectively.Another often used term is proto-imogolite. Again,14there is variation in the definition. Hydroxyaluminumcations react with orthosilicic acid in dilute acid solution(pH<5) to form a hydroxyaluminum orthosilicate complex. Thiswater soluble complex is termed hydroxyaluminosilicate ionby Wada and Wada (1980) but termed proto-imogolite by Farmer(1982), as it could be readily converted to imogolite byheating the solution, and its infrared spectrum indicates aclose structural relationship to imogolite. Within thegeneral group of materials that have the chemical structureof imogolite, but have not developed a tubular morphology,Huang (1991) suggested making a distinction between protoimogolite sols (a dispersed phase) and proto-imogoliteallophane (a precipitate phase).The formation of short-range ordered aluminosilicates(allophane, imogolite, and analogous materials) isinfluenced significantly by organic and inorganic ligands,metallic cations, and expansible layer silicates. Chemicalcomposition, size, number, and nature of the functionalgroups, and concentrations of non-humified organic acidsplay a vital role in perturbing the formation of allophaneand imogolite (Inoue and Huang, 1984,1986). Humic substancesalso substantially perturb the interactions of hydroxy-Alions with orthosilicic acid and thus inhibit the formationof these aluminosilicates (Farmer, 1981; Inoue and Huang,1987, 1990) . The phosphate anion common in soil solution andother natural waters inhibits the formation of imogolite15(Henmi and Huang, 1987). Iron has a stronger inhibitingeffect than Mn on imogolite formation, resulting in theformation of poorly ordered mineral colloids (Henmi andHuang, 1985). Adsorption of hydroxy-aluminosilicate polymersin the interlayers of montmorillonite results in an expandedstructure. The transformation of hydroxy-aluminosilicateions to noncrystalline aluminosilicates can, therefore, beaffected by naturally occurring expansible layer silicates(Lou and Huang, 1990) . The perturbation effect of theseionic factors on the formation of short-range orderedaluminosilicates deserves close attention in the associatedchanges of physicochemical properties of podzols and theirrelated environments.3. Hypotheses and theories of podzolizationSeveral hypotheses and theories have been proposed toexplain the formation of Podzols or Spodosols (e.g., Deb,1949; Stobe and Wright, 1959; Ponomareva, 1969; Rode, 1970;De Conninck, 1980; Anderson et al., 1982; Duchaufour, 1982;McKeague et al.,1983; Chesworth and Macias, 1985; Ugoliniand Dahlgren, 1987). Currently two major contrastingtheories share the most attention: the fulvate theory andthe proto-imogolite theory. They are illustrated in Fig.l-l.The fulvate theory involves two stages which may occurconcomitantly. The first stage involves the formation ofwater soluble organic acids, predominantly fulvic acid,primarily from litter and root decomposition caused by fungi16FULVATE THEORYPROTO- IMOGOLITE THEORYSECOND STAGEDEC OM P0 SITONMIGRATIONFE AND ALSYNTHESISIMOGOLIJE ANDAL LO PH AN EMIGRATIONARRESTSECOND STAGEFORMATIONFAMIGRATIONARRESTFigure 1-1 Schematic Diagram Illustrating Two Theoriesof Podzolization ( Modified from Ugolini andFIRST STAGEFORMATIONSI LIC ATESOLS• ‘I:..• !...—------•.C... - ,.‘SDahigren, 1987)17and other floral and faunal attack. Fulvic acid chelates Feand Al in the Ae horizon and subsequently migrates throughthe Ae and Bhf to the top of the Bf horizons where arrestoccurs, when the ratio of Al and Fe to organic C becomesufficiently high or when the organo-metal complex isadsorbed by Al and Fe hydroxides. In the second stage, theseorgano—metal complexes decompose and liberate the Fe and Alwhich migrate as free metals into the Bf horizon. Synthesisof imogolite/allophane may occur when the Fe and Al reactwith percolating silica.The proto-imogolite theory proposed by Farmer and coworkers similarly occurs in two successive stages (Farmer etal.,1980; Farmer, 1981, 1982). The first stage involves theformation of the Bf horizon enriched in imogolite-typematerials and iron oxides. The imogolite-type materials canbe deposited from solution containing a positively chargedhydroxyaluminum silicate sol. This positively charged solcan form in the Ae horizon from Al and Fe brought intosolution by non-complexing organic and inorganic acids, orby readily biodegradable small complexing organic acids. Itcan migrate through the Ae and Bhf horizons, and becomesarrested in the Bf horizons in response to an increase in pHor adsorption by negatively charged surfaces or anions. Ironis transported by a similar mechanism. The second stageinvolves the formation of fulvic acid and its migrationthrough the Ae and Bhf horizons. Fulvic acid is then18precipitated on the imogolite surface of the Bf horizon.Based on soil solution studies, Ugolini et al. (1987,1990) provide an alternative explanation of podzol formationin two stages. In the first stage, carbonic acid attacksminerals, leaving an Al-rich amorphous residue. Synthesis ofimogolite/allophane then occurs in situ as silica combineswith the Al. In the second stage, fulvic acid produced inthe forest floor forms organo-metal complexes with Fe and Alin the Ae and Bhf horizons. These organo-metal complexesmigrate through the Ae and Bhf horizons and are arrested byinteraction with the amorphous materials of the Bf horizon.There is little corroborative research to comment on thisexplanation at present.In the discussion above, processes that promotepodzolization and differentiation of parent material intohorizons are emphasized. However, a variety of processes,such as mixing of materials by soil fauna, vegetationblowdown or management practice, may retard horizondifferentiation (Simonson, 1976)III. Aluminum Related Environmental ProblemsThe chemistry of Al is quite complex, its high ioniccharge and small effective ionic radius (0.054 nm in sixfold coordination) combine to yield a level of reactivityunmatched by other soluble metals found in soil solutions<HftCI)C)Ci)H<QhftCi)p1p1CDH-CDCD1hP)00•P1CDP1CDP100ft551Qp10H,HHj0CDQHH-CDCDftCi)H,C)H‘-(QP1-(Qk<C)P1CDftCDftCi)Ci)H-dCDftCDP1flCD0CD<CDH-H--Ci)CDP1-P1-C)JhH-3C)0CI)ft•H-P1CDCD0H-ftHftP10H-0ftCDH000HCDftNI-H-ftH-P1hHIII-CD003i—iQH,QCDCDH,ft0H0CDP1(QCi)P1H,P1CDp1D03QftCI)-ftP1CDI-’•ftHP1C)CDHC)CD5H-ftC)QMH-C)0CDHH-CI)CDftCDLQP1<CDP1F\)P10CD0U-00H,MCDCDft0P103-<HH-J3CDC)H-HP1P1QH•Ci)0-CI)ftH,H-d3H-CDHftIH,CD<P1.—0-P1ftCDHH-ftP10QQQftLiP1H-H-WH,P1P1ftCDoPiI-.QftH-CDH,HI-C)M•hCflH-I-p11HCDhCi)CDh0CD‘1HCDCDP1CD0)0ftCi)ftP1P..CDCDCi)ftftP1P1CDhCi)P1<1H0—S-H-i-Ci)Ci)ftftPC-Q0C)CDP1P1(t0CDC)‘-QdH-H-P1HftCDD20‘xJftP1C)P1LiI-0C)P1C)<H-C)CDH,H,CDCDCDC)-ftCDCD0CDCDHCDH-CD0CDPH,0°i-CDftHCDCDC)SftCDbCi)C)CDH-H-DHCDQP1H-ftH-ftC)C)C)C)P1o0CDCi)H-Ci)H00ftC)0P10ftft‘P10H‘-QCDH-<5Ci)ftP1Ci)ft><P1IIH-ftH-Ci)H3.I-HN<H-0CDhH-ft0P1HCDI-ftCDC)0‘<CDCD3HCDSC)bP1IICD0+CDQCD0C)H,CDH-ft03H,Ci)FH-0P1ftH-C).Qft0•‘dCDftH-CD‘1H,C)ft-)h‘<CD-C)frjIH,Wp0HCDdH-HH-H-0H-H-P1P1H•P1ft-CDCDftP1Ci)05C)ftHftH-ftC)H-Hftk<C)H,P1P1H-H-H-ftH-H-CD00gCDCDCDCDCD0HH-IC)ft0CD3S0ft<CDP10CDP1HH-C)YP1<1Q0CDSH-0hHCD0HCDCDftHP11P1HHCD0ftft00HH,0CDftCD<HCDCDhP1H-—CDH,CT)H-0H-CDH-bCDftQHC)Hft0<CDHH-P1H-C)CD0H-0<CDCDftH-ftCDP1HhW5HP1CDH-H,P1CDh10ftC)HH-H-CDCDft0CDHP1P10oCDCD-C)ftP1C)3H-H-HHH,HH-ftH-<CD0ft0H-CDHC)P10CD‘<0HoiiCDCDP1Hft><CDH-P1H‘d0CD1C)H-H-HCDDCDH,<P1P100,<<P1C)P1ftCDC)ftHC)dftCDH0P10-’H-ftP1OH-P1P1HftH--H0H-HP1ftH-CD—CDC)CDftCDP1‘-<05H-CDH-H-CDP1CI)P1-<I-CDP1H0HHHftft-P1CDLJftH-HH-CD0P10C)CD,.C)HCDH-H0•P1-HI—’ClH,(CDCD•CD+F—’02CDH-5H,T)JFtH0)J5FtCT)I-C)CD0I-hCI)H-Cl)Cl)Jk<H-D0DH-CD<0F-10HCl)0><HH-0Ftj-k<Q,hCDCt)CDCD(.Q<13—..><0130)0I-HIiFtFtI-ICI)H-13CDI-00H-1300)F-1FtFtH-13h0FtFt(1)CQFtCliHh03C)ttCD013013H FH,CDCT)><I-<IQ—‘<Cl)><—H-Cl)Cli.QI-CDII--F-1H-5Q<H-CDCD0-Hk<0FtFtFtCDFt130CDCliF-CI)CliQTIFtIF-1-k<H-0CDIICDIIFt0Cl)FtTIC)FtFtH-0hCD0I-13Ft0TI00Ft13CliCDH-Ft5j1-i,13<CDF-Clii‘-<Ft130-0>4FtI-H-013CD-<HCliH-Cl)F—1CDFtFtH-H,CI)H-)Cl)C)CI)FtFt13CD35H-Ft0CI)02—CI)Ci)13H-F-1F-1H-13Cl)FtFtCD0h$Cl)Ci)H-—S0CD-‘Cl)CI)13TIFtFtWFt<H-0k<Q0FtF(-QCD13TICDH-F-113CI)CDCli13H-Cl)H,k<<Cl)-0TI5CliFtCDCliQ0-4CI)IQF-1F-1Ft13CQ0013H-Cl)Cl)H-CI)IQ13’CDH-FtH-CDCDH--4H,130Ft‘-<CDCDCl)Cli13CD-0CI)I-h5CI)HCD130CI)H-TI02Ft<CD0)CD013005TIH02CD0H-50Cl)CDh4CI)CliH<h4IQ0CliCl)CD0C)H-1313CDFtCDH-0Cli—S0)HCI)Ft1-4HH,H-1-41-4)i5FtCliH-H13135Ci)HFt013CD0H,13CI)FtH-FtCDIi1-4CDCI)FtC)1-4Ft0TI0H-H,CliF-’Cl)HHCliCDH,H-1300HCQ‘-<1-41300CDFtCD001-40H-Cl)IQCDCD13>4TIF-’TIFtCD0HNCDFt-<1503CDbCDCDCDH-CD‘-<CDH-H-HCi)0H,HTIH,Ftz5FtTICI)CD1-4>3‘d00TI—TIHCli13HICDH-HH-FtCD1-4H-HIxjCI)13H0TI<0CD131CD13CDCl)H-HFtH-0dH-000Cli13FtIQP1TIFtCDCl)5Ft‘-<Cl)5H<113CD02H,-45H-1-4CD130CliFtH--CliCDHH-13H-0<CDFtH-Cl)1-41-41-4H-CDFt13-H00FtTIHFt0H,Cl)H-13CDF-’CDH-k<CDCl)1-4Cl)HFtCD13H,0CDCD013CD0P1-CI)Ft>4->4CI)TI-‘FtCD-CD5Ft0CliFtCD13Ft0FtH-H-FtHCI)TIpiTICDCDH,13CliCD13Ft130013Cl)Cl)HFtHCli0FtTICDS—1-4CDCI)CD1-4CQ0CDCD0Ft0CDwCl‘.oFtCI)13CD-CDCI)HO0>4CDCDCi)CD0131313‘<CDH-HCI)5>4CI)C)F-’lF-’>4H-U)ClI.QCI)FtCl)13ZCl)-H3H-1-4FtH-1-40)--CD130>CDCl)H-IQ0CD0PiFt0—FtF-Ft1-413CD0Ft0FtH-oCl)CliCi)H-Ft‘d0213-H-‘0CDH-Ft1-40Ft13HCD13TIFtCD5CiFt-H,CI)TICDCl)0Ft5CDH-05TIFt‘-<)1-1CD0‘dHH-13-CI)513H-Cl)Cl)00C!)‘<0>40FtFtCDFtCD00H-CDCDFtCl)CDH-H-HH-0H13Cl)Cli1-4Cl)CliHoClCl)Ft—FtFtCl)CD1-4CD0‘<CDCD-ClFt1-4CD13Cl)-CDCDCD13CI)0H-U)-13CjCi)1-4H-H-HCD00131-41QCDH-13CDHFtCD13HI—’bFtbClFt050Q1-4H-H-H13—--4SCDFtdCl)HCD13FtFtCl)<CDCl)FtCl)CD-H-Cl)CDH-ii13FtCDH,r.0)‘<Ft-H1-41-4HCDTI30‘-4HCl)Cl)-4CDF-Cl)Cl)13CI)H-13Ft-1-4pi-0Ft13FtCl)CDH-Cl)-CDHFt0FtCl)FtH-CI)H-F-00-0HH13H-0H-013‘—3H,131313CDCI))CI)CDTICD021of toxic Al are not reduced, but activities are. Calciumamelioration may also result from direct physiologicaleffects (Parker et al., 1989b).Although much information on the terrestrial effects ofAl dates back to the early part of this century, most of theresearch in aquatic ecosystems is contemporary. Concern overthe effects of elevated Al concentration in surface watershas focused primarily on fish because of the clear economicand sociological importance of some species. The principalmechanism of fish response to Al is established as analteration in the influx and efflux of sodium and chlorideions across the gill membrane. Al ion species interfere withNa-K ATPase in gills and thus regulation of plasma sodiumand chloride (Harvey, 1989).The implication of Al in several human disorders suchas Alzheimer’s disease and Osteomalacia has been of publicconcern and scientific controversy in recent years. MostAmericans probably consume 2-25 mg Al daily, with 1-10 mgfrom natural sources including food and water, 0-20 mg fromadditives, and 1-2 mg from contaminations from pans andutensils (Greger, 1992)2. Acidification of soils and surface watersSoil acidification refers to a complex set of processesthat result in formation of a soil more acidic than theparent material. Soil acidification, therefore, in thebroadest sense, can be considered as the summation of22natural and anthropogenic processes that lower measured soilpH (Krung and Frink, 1983) or reduce base storage. In forestecosystems, natural acidifying processes include base cationuptake (by plants or microbes); natural leaching bycarbonic, organic, or nitric acid; and humus formation(Ulrich, 1980) . Anthropogenic acidifying processes includebiomass harvesting which remove base cations, land useconversion, fertilization, as well as acidic deposition.Attempts to measure soil and surface wateracidification often center on attempting to detect changesin pH values. Though this approach seems intuitivelyobvious, practical considerations ranging from suitableanalytical methodology, spatial variability, anddetermination of soil horizonation to changes in land usepatterns often severely limit the usefulness of this rathersimple approach (Robarge and Johnson, 1992). A morequantitative measure of soil and surface water acidificationcan be obtained by defining it as a decrease in the acidneutralizing capacity (ANC) (van Breemen, 1991; Reuss,1991) . ANC is equal to the quantities of basic componentsminus those of acidic components. What is ilacididfl or“basic” depends on the reference pH chosen.The transport of Al is an important aspect of thedevelopment of soils in northern temperate regions. In areaswith precipitation surplus, dissolution, downward transportand subsequent precipitation of Al is a natural process.QFtC)HMiCD0-5H—..C)H-CDCDDCDI-J‘.D0-0iCD-CD0C)0JCD‘dCD0Ft—JhH-H-]MiHC)I-LOI-JIICl)Q.H-<C)ooC)H-LDCDCDHCDCl)AMiIW0CDH-HCDCDCDHCDCD0—CDC)CD0I-WCl)cxUCD1QCDC)CDH-0H-CDFt0H-J-3>H-)J—bFtFtFtCDHHHOH-JC)FtCDHH-QH-CDHH-CDHH-CDH-—CD5H-H-CD‘-<oi0CDCDH0Ft•-N--SCI)CI))-FtCICDH-CI)CDHIIHCl)FtC)CDHHHFtCDCDH-“iCI)Q(-Q0H-H-frj-D0CDLDCl)H-i4H-—CDI-iCDFtCI)35CI)H-0H--I—’H-FtH-1Cl)CDhCDC)FtCDFt00CI)3CDHH-FtIC))FtCD1oH-CQCI)<-.PC)CDIC)HFtCDI-CDCD53CDH-H-HUiiI-0CD0CI)<CI)MiMiCDCI)CI)C)QC)H-FtCI)H-MiCDI-h<Ft0CDCDoH-<3HH-0CD—CDC)HH-CD1DMiCDQWk<Ft0C)FthCDCDCDCDHCDH-IIC)CI)I-0)CDHZH-CDLo05CDQCT)H-H0—SIWCDPCD03H-FtC)0)Ft0IQIQI-‘dCDI-CDMi><HtY—.-CDHIICDWCl)Mi05MiH-DHFtQ0CD—.H-<J0110H-H-CDSLoMiZFtHC)‘‘ooFtHH-CI)hNCD3CDHCI)HMiH-U)CI)CI)(QH-I-hH-H-CDI-0H-(HFt—CD—2FtCDH-CI)HCI)CI)NFt52HFt5—SCDCQU)Ft55CDH-HCI)CDH-H-CI)MiHH-CT)--IIH-Cl)CI)HHFtI-FtC)0C)dH-CDH-H-CDh1QC)C)W‘-<H-H0H-HCD1FtH-CDH-I-I-()U)C)CI)552MiUiFtCDCDI-C)SI—’CDCDb3CY)H0dH-FtMiHCD5FtbFt‘-<CI)0HCI)CDCDWtIC)0CD0CI)CDCDCDCI)CD50——0IFtC)CI)H-CD520CI)Ft0HCDCI)CI)Mi-.C)520)(QJHI—’MiCDSH-52MihH0CI)CD-•CDCDCI)52CI)Ft52I-CDMit’.)0U)H52‘CI1”.)CD-ii0FtCDH-CDCDH0)0H0CDMiH-52MiH-HFtC)CI)UiIQ‘-<CDI-A-0CDH‘d5JCD0h’lC)FtCI)5))‘-<H-CDC)H5U)0CDhQ5))CDtC)5))FtFt-C)5))HCDU)0CI)FtCDFt5YFtH52CDC)CI)CI)-MiH-CI)MCI)I-00MiH3HCD-CDdMi0j—Ftb0--FtCDCI)0-5FtH5252CI)CD52-H-0H-C)0CI)0CDC)C)H-Mi0CD<C)03C)hCI)C)H-CDH-0HCDCDI—iCl)CDH-FtH-CD5))IiCI)LQh1QHH-HFt52C)5))U)Ft5))C)52CD0FtI-0CI)H52CDCDH-C)I-C)0)CDFtCI)52552CDCDCD—H-hC)CDCDH-b0CD0HCI)5CDH-CDH-C)t3-CI)Cl—‘-<H-52MiH0C)H-C)bMiCDC)HCI)FtCDH---HH-052CDCDt-’MiI-U)52CDLrJCDI-CDC)CI)CT)Ft520CI)MiCDCDCI)U)CDCI)5))525)C)5))H—Mi1-50CDC)0dC)1-5FtH-CD52FtCDCDH-FtH-—00ClH525252CD-CI)MibCD1-5H52CDCI)‘Ck<0CDH-C)CDMiCDCI)CDCI)H-CDWC)H-CDMi-HFt1Q-CD-5—52C)Mi-52H-CDCDH-FtCD—052L’JCDC)CD-5-W24of podzolization (David and Driscoll, 1984; Rutherford etal.,1985)During precipitation events, acidic deposition enteringthe soil is unlikely to reach equilibrium between liquid andsolid phases as water rapidly infiltrates and percolatesthrough the profile (Hooper and Shoemaker, 1985). Residencetime of water flowing through soil will be the crucialfactor when assessing effects of acidic deposition on Almovement. Lateral water flow may further reduce contact timeof leaching waters with some soil mineral horizons (Dahlgrenet al., 1989). When significant lateral flow occurs,organically complexed Al may be transferred to surfacewaters (Driscoll and Newton, 1985) rather than undergoingprecipitation in soil mineral horizons. Humic material mayact as solid-phase adsorbent controlling solution Al underconditions of lateral flow through organic surface soilhorizons (Cronan et al., 1986).Temporal fluctuations in total and free monomeric Al insoil solutions and surface waters under conditions of highflow will not be adequately explained by models that assumethermodynamic equilibrium between infiltration water andsoil mineral phases (Hooper and Shoemaker, 1985). In welldrained soils in which percolating soil water makesprolonged contact with the soil mineral phase, Al activityin soil solution should be controlled by dissolution!precipitation of a discrete mineral phase. Models treatingCDJC)5CDa)HCDHitIJJC)HH)Ja)I-H-<1C)HH-CDH-itCl)><LO1DPi00CDH0JC)H-itl)JH-H-itH,a)‘dCDH-CDQiHI-IDH-itHHQ5itCDIDH,H-CDa)Qa)“C)HCDPH-IDa)CDI-HH-Q,h--.ititH--itIDC)itH-hID-C)CDH-IDIDIDH-Ha)a)C)itCDa)itH-H-50itHH-0QHCDCDPa)CDLJCDC)CD0CDCDititC)3CDHCDCDSHCD0a)H-+Ui$1CDCD3H-CDa)a).Ditit‘d<ID0ita)dWJJH,0a)0itIDCDita)CDHHH,-H-0itI-ja)itHH-a)CDitH-0CDH00IDa)0H-IDH-H,CD—05it<-CQoCDa)H‘-‘I5it30CDH-IDHHa)itIDIDH-iH-H-IDa)itIDHH-oCDIHHit0IDCDHIDID.0it+H50IDC)Q,H-a)H-CD-I-CDitCDH-ita)a)CDH-(1)(1)CDiCDC)H-H-C)IID‘10QCDk<000itp)a)b’0a)H-ID-C)H-H-X00‘--5HHita)H-H-()03IDC)itH,I-H-HH-QCDçuQ-S‘H-hCDH-CDPJIDk<HIDa)CD5505it0H-0itH-C)-a)3H-H-itIDH-a)ID0H3a)QH,CDH-IDitit0H><HCD‘ti0IQhl0H-CDCDHCDbita)‘<5H-C)CDit‘1Qa)Q1-H,hCl)H-0+QH-0k<CDH-CDH-CDID-05IDCDCDa)IDUI0a)IIa)0C)QHa)itCDC)><witC)H,itit00H,IDIDHC).CDIDH-•C)H-ititH-a)CDCDCD-+H-CDHa)0a)CDHa)CDH-H00CDH‘dCDitF-’H0H,0a)0II0H-H-I-iUiC)Ha)C)CDH-H H-IDH-H-a)H,Ha)HH-—IDCD‘<CDa)CDC)HH•01N•a)IDCDClH-H0itCD0H-00CDC)a)0H+IDIDIDa)SH-QHH,C)it0+--CD3H,itoC)ID0a)Sa)0H-H-ID0H,H-IDa)CDitIQ0HClH5+I-0ClC)itI-H-H--H-IDH-a)H,IDH-C!)SitH-H-CDCD0CDH-WS<itCDk<WCDH,5H,3F-’H-itH-0H-C0CDH-H-0a)H-I-LQ0tritHiHC)C)C)hH-1H-0C)HH-H,CDCD-itIDIDCDitIDCDIDHCDitH-SCDHI-itIDitHH-05H-it0a)CDC)Clita)IIa)çbH0‘d0itH-ClID0H-CDH-CDbHCDS<CDa)IDitH-IDH,ititQja)a)I-itHCDH-H-H—‘-0CDCDitH,H-IDa)‘<ClitCDIDCDIDCQH-i-.QCDitIDitCDClitCDitCDCDI-H-1JH,itC)QQH-Q3CDH,CDa)0itHHJCDa)C)H-0ID0HH-a)0H,(.QitCDSHHCD0CDC)hIDhitCDH-itH-CDCDIDa)-QCDita)ja)it0a)ClC)IDitH-itit0itCD0IDHa)H,CD3‘-<a)U]26of northern Europe and eastern North America that currentlyreceive acidic inputs have undergone substantial changes inland use and consequent vegetation succession during thepast two centuries (Brand et al., 1986). As many of theseforest are now aggrading, the natural soil acidificationthat accompanies such regrowth cannot be attributed toacidic deposition (Krung and Frink, 1983).Acidification of soil and water is, like most recentenvironmental problems, a consequence of change in thenatural cycles of elements. It has been recognized as afairly complex process involving many mechanisms. Ourcurrent understanding about the processes of soil and wateracidification is still limited and more research is needed.27Chapter 2 MATERIALS AND METHODSI. Study AreasTo address the issue of soil genesis under forestconditions in the Pacific Northwest, the study focused ontwo areas: Cowichan and Vancouver. As shown in Table 2-1,the climatic characteristics of the areas reflect conditionsfound within southwestern coastal British Columbia. TheCowichan Lake Research Station (48°50’N, 124°8’W) is locatedin south central Vancouver Island, about 63 km northwest ofVictoria. The area is a part of the mountain range whichmakes up Vancouver Island, and is characterized by a largeglacially scoured valley which drains to the southeast. Theclimate in the area is characterized by mild, wet wintersand relatively dry, moderate summers. The forest regeneratednaturally after logging and burning which occurred in 1908.The forest is dominated by coniferous species, such asDouglas-fir (Pseudotsuga menziesii Mirb. Franco) , westernhemlock (Tsuga heterophylla Raf. Sarg.) and western redcedar(Thuja plicata Donn.). The dominant soils are classified asOrthic Humo-Ferric Podzols and recognized as the Rumsley andShawnigan soil series (Jungen et al., 1989). They aredeveloped from glacial till. The bedrock is chiefly Mesozoicvolcanic and sedimentary rock (Holland, 1964)The second area is at Pacific Spirit Park in VancouverHP35H-FtCDU)P3CDCtC)0‘dDH.5U)00H-P3h’<t0CDDp1CDH-ctClC)CDCDCDp15HoHCDFtfrCrNHO0C)H-CDU)CDU)Ctp1P3ftQ03’Cl]<Cl]P3C)U)HC)Ft5HC)rrCDH-0CDCl)05P3CDH-H,H-CDH-CDU)ZI-’-5CDH-ctH-CDCrH,çt0HFH-HH-HHCDI-0CDCDHp1P3CDCDC)H,H-C)H-CDCDFtFH-U)-H-:iHP3H-CDU)DFtCDClp1j1)HP3P3CDC)CDU]CD0w1CD505-0C)ftCD-5P3Cl0CD3ClCDCDCDH-HHCDHdH-HCDU)—SCDCDH-HC)0‘<P3P3CDCDNCDCD0CDP3CD5b‘o0H-P3D2HIIU)i0CDH-hp1H-FtCDCDDCQHCD‘-<ftp13(PctH,0ClHCDFtHCDH-CDH-P3CD0Fth—H-HCDCD<-CDCl)U)<P30NPJU)HCDH,II-IH-(QCDP3-C)CDI-‘dtCDHCDHU]5(PtF-ClCDCDHP3•CDCDCDCDCDCDC)H-C)P3bC)U]CDFt‘FtP3H-(PCDP3C)H-H,Cl)FtH-I-QClC)‘1CDCDP3U)CDU)HCDFtH-1H-H000CDI-Ft-ct0‘•dP3Ci)CD0CDHF’-Cl)CDCDH-CDHC1CD0p1p1H,CDHp1CDP30U)IQhCl)H-U)C)P35H-U)(QCDCl)H-3FtH-p1FtCliH-(QFt‘-<H,C)gCDP3CDCDCDI-P3P3HP3CDftWH-H0Ft<CDU)II00CDHCl)ClU]ClH-—p1H-CDH,5Cl)p1p1i0C)P3hH,HP3Ft<ftCDP3CDCDCD-U]H-hCDCDU)CDp1FtFtP3CDCl‘CI0WHH-00CDCDP3Cl]dCDClft5CDH,0FtH-CD10CDH-0H,CDHH-H-p10H,H-0CD0CDFt<P3II(P00CDP3ICD5P3HCl]ftHCDPI-<C)tOCDFtH-0CDP3p1CD0•ft5FtH-C)H-5H-Cl)P3p1H,U)0ClU)CDCD0Cl]5C)IHICDftCDh’CDH,H,HFtFtCD0H,C)p1HFt<(PhH-Ft0p1H,CDP3CD‘1CDH-CDHCDFtCD0F<C)CDC)P3hP3CD5HFtIIH-P3FthC)00P3CDCDCDH-‘-<hCD‘-<P3H-H-ICD0P3CDC)(PH-CDClhP3HClCl)H-C)(P<CDHCDJHC)(PH-1D0P3Cl]hk<Ft0CD05P3HH,CDIICDCl]Cl]h(P0CDU)C)H-HhCH-U)H-P3P3ClH-p10U)CDP3U)H-C)FtC)5H-0-0-Cl<CDCDH-P3ClH-H-Cl)HtOH(P-0C)P3CDFtCDHU)CDC)C)P3—CD—CDrtCDCDHqCiP3CDP3hP3P3H-HCDCDCDC-tC)C)P3P3CD-CDU)CDP3H-P3C)rtMH-IIH-I-iidrtHP3iH-CDC)HH-CDitct1U)(CD1YCDP3P3P3H-Cl)-IfrjHçtHU)-hCDH-ititHCDCDC)P3•o°U)coHCDCD.ijI-—C)oP3P3HftctHCDCDQU)1C)P3CDrrCt)CDCDQçtItO)U)H-P3.CDH-C)c-iHP3C)H-C)000--—1C)P3P3cxWH-P3C)C)C!)L P3CDP3ftU)ciCDCDU)H-I-CU)C)CD0P3‘1H-CDciCU)CDP3CDP3C) H-Cl)I-hC)HHf10)it‘0Hft...C)CDctP3Cl)P3 ftH-H-IICDCH-P3itU)30Table 2-2 Sampling DesigntStudy Area Dominant Soil Decaying Pedon#(mean annual tree moisture woodprecipitation) species regimeWestern Sightly + V-ihemlock dry - V-2Vancouver1258 mm Douglas Wetter + V-3fir - V-4Douglas Moderately + C-ifir dry - C-2Western Slightly + C-3hemlock dry - C-4Cowichan2076 mm Douglas Slightly + C-Sfir dry - C-6Western Moist + C-7hemlock - C-8Sites were selected by Professor K. Kl±nka, Forest SciencesDepartment, University of British Columbia.31Details of the following methods and procedures may befound in Methods of Soil Analysis (Page, 1982), page numberis given in parenthesis.pH(H20), pH(CaC12), and pH(NaF) were measured insupernatant solutions of soil in distilled water, 0.01MCaC12, and 1M NaF (Wada,1986), respectively. Total carboncontent was determined by a LECO analyzer. Total nitrogencontent was analyzed by Kjeldahl digestion method (p.610).Particle size analysis was done by pipette method afteroxidizing organic matter and removing free sesquioxides(Klute, 1986, p.399)Cation exchange capacity was determined by measuringsorbed NH4 after replacing cations by 1M neutral ammoniumacetate method (p.160) . Effective cation exchange capacity(Juo et al., 1976) was calculated by adding KC1 exchangeableAl and ammonium acetate exchangeable Ca, Mg, K, Na.Exchangeable Al (Alexch) was displaced with lM KC1 anddetermined by titration (p.164).2. Chemical extractionsReactive aluminum was extracted by 0.5M CuC12 solution(Juo and Kamporath, 1979). Organic-bound Al (Alnta) and Fe(Fenta) were estimated by 0.lM sodium nitrilotriacetatemethod (Yuan et al., 1993). Amorphous Al (Al0) and Fe (Fe0)were assessed by extraction with acid ammonium oxalatesolution for 4 h (Ross and Wang, 1993) . Free (nonsilicate)sesquioxides were extracted by citrate-bicarbonate-32dithionite (CBD) solution at 80°C (Mehra and Jackson, 1960)Aluminum and Fe contents in the above extracts weredetermined by atomic absorption spectrometry (AAS).3. Mineral identificationClay samples (< 2 tim) for X-Ray Diffraction analysiswere separated by sedimentation after oxidizing organicmatter by hydrogen peroxide and removing sesquioxides byCBD. Magnesium and K-saturated slides were prepared and runat 20=3-33°. Their glycerol-solvated or heated (300°, then550°C) slides were run at 20=3-16°.For identification of amorphous minerals by infraredspectra, soil samples were treated with H20 to destroyorganic matter, then dispersed by ultrasonic treatment withdilute HC1 (pH 4) . Clay-size samples were separated bysedimentation. Synthetic imogolite was synthesized by themethod of Farmer et al. (1977) . The infrared spectra of thesoil samples and synthetic imogolite were recorded on aPerkin Elmer infrared spectrometer using a KBr disk.Detailed procedures for mineral identification may befound in Methods of Soil Analysis (Klute, 1986)4. Phosphate sorption studiesSeven 1-2 g samples of each soil were shaken for 24 hat 25°C with 30 mL 0.002 M CaC12 containing between 0 and3.5 mM KH2PO4. Since P sorption is pH dependent (Barrow,1984) , sorption experiments were conducted at the originalpH (CaCl2) values of the soils. After shaking, the33suspensions were centrifuged at 13800 x g for 10 mm. andthe phosphate concentrations in the clear supernatants weredetermined by the method of Murphy and Riley (1962). Thedifference between phosphate concentrations before and aftershaking with soil samples was used to calculate the quantityof phosphate sorbed by the soil samples. The sorption datawere fitted to the linear form of the Langmuir equation(correlation coefficients >0.98) and the sorption maximum(X) was calculated for each sample (Barrow, 1978)Natively sorbed phosphate (P0) was assessed byextracting soils with acid ammonium oxalate solution for 4 h(Sheldrick, 1984) . In the extracts, P was measured by acolorimetric method (Wolf and Baker, 1990). The sum of P0and Xm is taken as total P sorption capacity.5. Simulated leaching experiments:Soil column leaching experiments were carried out asfollows: for each of three soil samples (V-4-AB, C-4-AB, C7-Bf 1), 25.0 g soil was gently packed into a 50 mL plastictube with a small hole (Dl mm) at the bottom. A piece ofWhatman 42 filter paper was placed below the soil in eachcolumn to prevent loss of particles during leaching. Eachcolumn was leached with 150 mL leaching solution at the rateof 25 mLh1 at room temperature. The leaching solutioncontained 1.0 mM of each of the following: salicylic acid,oxalic acid, malic acid, citric acid, sulphuric acid, andnitric acid. The pH of the solution was adjusted to 4.034using NaOH (pH values of LFH and decaying wood in this studyare close to 4) . These organic acids are commonly found inforest litter (Tam and McColl, 1991) and sulphuric andnitric acids are components of acid precipitation. Vacuumwas applied to the columns when necessary. The leachate wascentrifuged at 25900 x g for 15 mm. A portion of thesupernatant was saved for determination of Al and Fe, theremainder was used as leaching solution for soil samples V—4-Bfl, C-4-Bfl, and C-7-Bf2 (the leachate from sample V-4-ABwas used as the leaching solution for sample V-4-Bf 1; C-4-ABfor C-4-Bf 1; C-7-Bf 1 for C-7-Bf2). This time, the leachingexperiment was conducted at the same soil/solution ratio asmentioned above, but at a slower rate: 15.0 g soil wasleached with 90 mL solution at the rate of 8 mLh1. It wasassumed that water moves slower in Ef horizon than in Ahorizon under field conditions. The leachate was centrifugedas above and saved for determination of Al and Fe. Eachcolumn leaching experiment was duplicated.For determination of Al and Fe, 20 mL of thesupernatant were digested with HNO3 and H20 with heatinguntil colourless, to oxidize organic matter. At the end ofdigestion, the solution was heated to dryness and theresidue was dissolved with dilute HC1 (pH2). The content ofAl was measured by the chrome azurol S method (Close andPowell, 1989) and Fe by o-phenanthroline method (Olson andEllis, 1982) . All measurements were duplicated.356. Resin extraction experiments:The procedure of the resin extraction used is similarto that of Sakagami et al. (1993). The <2 mm sample wasground to pass 100 mesh sieve. Two g of 100 mesh sample and10 g of H-saturated cation-exchange resin, Rexyn 101(H)R203 (active group RS03), were placed in a 100 mLpolyethylene tube, and 20 mL distilled water were added. Thetube was shaken for 20 mm and the pH of the suspension wasadjusted to the pH(H20) value of each sample with NaOH. Thisstep was repeated for a total of three times. Afterwards,the tube was shaken for 48 h at room temperature. At the endof this extraction, the tube was centrifuged at 23300 g for10 mm and the dissolved total carbon (TC) and dissolvedinorganic carbon (IC) contents in the supernatant weredetermined by a Shimadzu total carbon analyzer (Model TOC500) . Dissolved organic carbon (DOC) content was calculatedfrom (TOC-IC) and expressed as cmol/Kg soil. The resin wasseparated from the soil sample by sieving the suspensionthrough a 60 mesh sieve. The separated resin was shaken withfive 50 mL aliquots of distilled water. This should removeany soluble Si. After this, the resin was extracted by acidammonium oxalate solution for 4 h. The content of dissolvedAl (Alr) and Fe (Fer) was determined by atomic absorptionspectrometry; Si (Sir) was analyzed colorimetrically by themolybdate-blue method (Smith, 1984) . Thus, Si in crystallineminerals should not be included in Sr•367. Al activity in soil extractSoil samples were shaken with 0.01 M CaC12 solution for30 mm at 1:2 soil/solution ratio. This extraction time isenough for the solution to approach equilibrium with Al (OH)3having a solubility constant of gibbsite (Dahigren et al.,1989). The suspensions were passed through Whatman 41filters, then centrifuged at 27000 x g for 15 mm. The pHvalues and dissolved organic carbon contents of thesupernatants were measured. Al concentrations were analyzedby the chrome azurol S (CAS) method (Close and Powell,1989). CAS reacts rapidly with A13, AlOH2, Al(OH)2,Al (OH)3aq , Al (OH)4, A12(OH)4 and Al3(OH)45. It isunreactive toward the polymer A113(OH)327, colloidal Al (OH)3and the hydroxy-aluminosilicates, imogolite and allophane(Kennedy and Powell, 1986). Although aluminum bound tofluoride is soluble in 0.01 M CaC12 (Moore and Ritchie,1988) , no correction was made for fluoride complexes sincethese complexes are not included in the CAS reaction (Closeand Powell, 1989)8. Acid neutralizing capacity (ANC)Soil acidity may be described in two aspects: intensityfactor and capacity factor. The pH of a soil describes theintensity factor of acidity. The ability to resist changesis a capacity factor. The resistance to pH change as H isadded is called acid neutralizing capacity, or titratablealkalinity (Binkley et al., 1989).37Compared with the determination of ANC of watersamples, measurement of ANC of soil samples is much morecomplicated and there is no standard method to follow,unlike the case of water samples (Gran plot method) . Theprocedure described here is similar to that of Binkley(1986) . Three g of soil sample were shaken 30 mm with 30 mL0.01 M CaC12 solution. The mixture was allowed to settle for30 mm before the pH was measured with a combinationelectrode in the supernatant. This is the initial pH value.Incremental amounts of 0.1 M HC1 were added to thesuspension. After the suspension was shaken for >3 h andallowed to settle for 30 mm, the pH value in thesupernatant was measured. This step was repeated till the pHvalue reached 3.5. The amount of H consumption wascalculated and taken as the acid neutralizing capacity to pH3.5.38Chapter 3 RESULTS1. Soil texture and carbon contentThe most frequent soil texture class (Table 3-1) isSandy Loam (21 horizons), followed by Loam (16 horizons),Silt Loam (5 horizons) and Loamy Sand (2 horizons). TheCowichan pedons have lower sand and higher clay contentsthan the Vancouver pedons. Carbon content varies from 0.53to 5.15. The higher C% in the Ae horizons of V-i and V-3may be a result of incomplete removal of fiber-like organicresidue from mineral part by pick-up and sieving.2. Reaction and cation exchange characteristicsSoil reactions are acidic in all horizons for both theVancouver and Cowichan pedons (Table 3-2). Virtually all pHvalues fall within the ranges 3.87-5.83 (H20) and 3.14-5.11(CaC12) . The lowest values in the mineral soil always occurin the Ae (when present) or AB horizons.In these acidic soils, rich in amorphous materials,raising the pH to 7.0 artificially creates additional chargeon the surface of soil constituents. The cation exchangecapacity as determined by neutral ammonium acetate (CEC7)necessarily includes a large component of pH-dependentcharge. For variable-charge soils, effective cation exchangecapacity (ECEC), proposed by Kamprath (1970) and Juo et al.(1976), undoubtedly gives values closer to the actualcapacity of soils to retain cations under field conditionsC)C)IIIIIICDpWH0QHII0CDH-WWLJlWWWWWWWWNwH,H,H,H,H,H,H,JjHH,CDC)HiH,C)H,H,Cl)0IMHMHWL’)HFOHHMHMHH I- r1 Huio-aia-..j.jaiIDa-oWWUiH-.J00iai00H-•CDW‘J00M0DW0L\)Ui0CD—..]0CDWL\)(1) H- N CDWi4Wii4WL\)MWpMHHMHMWMHPMHCD0WWi4CDH4.0-CD0‘S.DHDHUi‘-H-(1)•••••••••PCtCDJWM.oo-..i0coHW-.JOOUi‘oMUiCD0CtH Cto\0H 0HHHHHHHC)HWWWWCDO—JCDHoowui--j‘o—:1.oiH•••.•••••••.•..••••••pipiHW0PMtJCD—IHCDH‘—]i1.HUiUiOC) pi 0HHHtOWWPWWtOHUi0HtOHHtOtOW••..••.-••••...•.••••(_)0CDOCD-W-JCDCDHCDWUitOWWH0C)CD0CDCDIØ00tOiCDUiWPtOtOil‘.D0 rt CD CrwHIC)C)C)IIIUiWH CDwIiiWWWWWWWWWWWWWWMiMiMiHi-hHiC)MiI—hMiMiIIC)MiMiWC)MiMiC)IWMHIjJMHMHMHtJHNiHH C-) 0 CI4U]WWi4U]U]U]W-JWFIUiWGi4U]i4HL,DHU]NiU]UiWWH-JWLDW0i4C101D0W-JU]oUiH0—.]0)‘DNi00Ji00HJi0W0)0)CDWUiU]WWWU]NiNiU]WiWU]NiI.JWU]U]0NikD0‘O—JJiCOHNi0)—aCoJiNi0)HHHHHHHHHHHHHWHOOJiW0)H-JOHHH—J-JHOHM0)0Ji‘-0HJiCoW—JCONi0)0)WU]Cx)NiH0HHHHHMHHOMOHNiOHHHOHHOHWWLoW00H0)WCOH‘0—1HCoU]NiU]0)0HNi0Co0NiWCoLx)HU]0)WNiH1WNiNiWi041Table 3-2 pH and Cation Exchange PropertiesV-l AeBf 1Bf 2BmBCV-2 BflBt2BCV-3 AeBhfBf 1Bf 2V-4 ABBf 1Bf 2Bf 3C-l BflBf 2BmC-2 Bfl3.87 3.145.34 4.555.83 5.115.57 4.914.88 4.154.51 4.194.75 4.565.39 4.933.95 3.314.79 4.304.87 4.495.06 4.614.23 3.525.18 4.505.50 4.914.84 4.654.08 3.524.37 3.814.68 4.084.66 4.130.050.060.070.060 .100.060. 030. 020. 050 . 020.030 . 030 . 040.040.030. 030.060. 040.030. 043.24 1.16 3.890.39 0.01 2.470.06 0.02 2.400.12 0.00 1.552.07 0.34 3.201.59 0.08 1.870.42 0.04 0.620.09 0.02 0.623.09 1.31 4.920.93 0.20 1.120.51 0.06 0.820.30 0.04 0.732.52 0.96 4.030.42 0.11 1.810.18 0.01 1.240.36 0.11 0.573.54 0.52 3.872.79 0.25 3.031.71 0.17 1.911.35 0.14 1.73Pedon# pH pH CEC7 Exchangeable ECECand (H20) (CaC12) Ca Mg K Na Al HHorizon cmol (+) kg112.54 0.40 0.15 0.0520.89 1.77 0.20 0.0522.19 1.98 0.23 0.0617.96 1.13 0.18 0.0718.21 0.74 0.17 0.1214.45 0.12 0.04 0.0613.60 0.10 0.02 0.0511.35 0.39 0.06 0.0530.04 1.42 0.29 0.0729.56 0.10 0.04 0.0315.08 0.20 0.03 0.0528.26 0.31 0.05 0.0414.74 1.23 0.17 0.0718.62 1.15 0.13 0.0719.88 0.86 0.40 0.0718.13 0.12 0.02 0.0427.65 0.01 0.14 0.1230.48 0.01 0.09 0.1018.02 0.01 0.06 0.1020.80 0.07 0.12 0.1542Table 3-2 (Continued)Bf2 5.06 4.49 16.24 0.09 0.11 0.10 0.03 0.51 0.00 0.84Bm 5.06 4.41 13.90 0.08 0.10 0.13 0.04 0.69 0.05 1.04BC 4.97 4.31 14.59 0.05 0.11 0.11 0.04 0.78 0.09 1.09C-3 Bfl 4.80 4.23 15.68 0.16 0.10 0.10 0.04 0.93 0.11 1.33Bf2 5.10 4.35 16.07 0.24 0.18 0.10 0.05 0.60 0.13 1.16BC 5.15 4.54 11.69 0.10 0.10 0.07 0.03 0.48 0.11 0.78C-4 AB 4.28 3.84 18.08 0.07 0.24 0.16 0.07 4.17 0.38 4.71Bfl 4.89 4.25 20.52 0.21 0.19 0.15 0.05 1.11 0.12 1.70Bf2 4.94 4.21 15.43 0.11 0.12 0.08 0.04 1.14 0.09 1.49BC 5.09 4.35 18.20 0.17 0.13 0.09 0.04 1.14 0.00 1.57C-5 AB 4.53 3.75 25.19 1.02 0.49 0.15 0.06 4.68 0.79 6.40Bfl 5.16 4.56 24.40 0.60 0.19 0.11 0.04 0.72 0.07 1.66Bf2 5.27 4.64 17.25 0.20 0.07 0.09 0.03 0.36 0.08 0.75C-6 AB 4.81 4.00 24.66 1.78 0.47 0.14 0.06 1.89 0.28 4.34Bfl 5.04 4.80 17.95 0.06 0.03 0.10 0.03 0.30 0.02 0.52Bf2 5.03 4.52 17.68 0.06 0.04 0.12 0.03 0.45 0.05 0.70BC 4.80 4.40 16.27 0.05 0.04 0.06 0.03 0.69 0.05 0.87C-7 Bfl 4.89 4.21 29.24 0.71 0.22 0.19 0.05 1.50 0.20 2.67Bf2 5.07 4.23 16.65 1.81 0.49 0.12 0.05 1.38 0.04 3.85Bf3 5.21 4.45 25.08 0.94 0.27 0.10 0.05 0.75 0.14 2.11C-8 Bfl 5.12 4.39 19.38 0.79 0.21 0.10 0.06 0.93 0.16 2.09Bf2 5.04 4.53 17.69 0.57 0.15 0.08 0.04 0.51 0.13 1.35Bf3 5.20 4.51 18.45 0.58 0.17 0.07 0.04 0.60 0.09 1.4743(Uehara and Giliman, 1981). ECEC was calculated by the sum ofexchangeable base cations and exchangeable Al, the value isabout one order of magnitude lower than CEC7. Amongexchangeable base cations, calcium (sometimes Mg) isdominant, while potassium and sodium exist only in traceamounts.3. Chemically extractable Fe, Al, and SiInterpretations of these data (Table 3-3) are based onthe following assumptions about the three extraction methods(McKeague et al., 1971; Parfitt and Childs, 1988):(1) Sodium nitrilotriacetate (NTA) is used instead ofsodium pyrophosphate to estimate organic-bound Al and Fe(Yuan and Lavkulich, 1993). The commonly used sodiumpyrophosphate method yields somewhat ambiguous results due tothe peptizing effect of pyrophosphate on soil particles(Schuppli et al., 1983; Loveland and Digby, 1984) and isinconvenient if an ultracentrifuge is not available in thelaboratory. NTA extracts the same amounts of Al and Fe asdoes pyrophosphate, while the dissolution effects on standardmineral samples are kept at a minimum. NTA has the advantagesof not requiring ultracentrifugation, ultrafiltration, or theaddition of a flocculating agent as is the case for thepyrophosphate method.(2) Oxalate extracts both organic-complexed andinorganic amorphous forms of Fe and Al. The inorganicamorphous Al, as estimated by (AloAlnta). and Si0 aren ICDCUMHWMH0 M0HWWWWWWWWH-CDHiHiHiHiHiHiHiWHiHiCDC)HiHiC)HiHiCDN3MHt’JHWk)HHHiMHL\JH0Wp3I w C-)MMHWHMMWMU]HMMpMWWa]U]LDHWU]IDHa]MC)MHa]U]a]U]CDHHa]MM1)iHWC)C)U]MU]a]a]‘—]C)a]IDa]H-U]a]a]W-Ja]WC)HkDDWC)C)U]U]D1.DU]WC) CU HWMW‘JU]U]‘OW—JHU]U]Wt’JU]-.3a]HoMU]—JW—.3Wa]W—.3—3HWHa]U]C)U]—.3—.3—.3C)WC)WHWiTi4CO—.3C)a]C)U]i4H0--.3Wa]a]U]M—.3C)C)C)WW‘..O.OOD1.01.0H1.0X rtHHHHHHHHMHW—.3C)HHHHHMW1.0i4iTU]WMWHPMC)HWM3••••••••••••H•••••C)MW—-.3U]MC)U]C)—.3[‘.3WPHU]4[‘.3C)C)WU](-IWa]1.0H—.1M—.3[‘.3H4W1.0W1.01.0[‘.3i11.03C)HW[‘.3PW[‘.3H[‘.3H[‘.3H[‘.3HH[‘.3[‘.3P[‘.3WCDPC)-.3C)[‘.31.0U][‘.3[‘.3[‘.3WH-a]HW—1HWa]0•••••••••••••HH1.0ci[‘.3a]1.0-.3[-.3H[‘0C)1.0[‘0H[‘0WU]a]WC)[‘.3[‘0HCX)U]1.0a]C)C)C)WU]H-oWC)C)-..3PC)0PHHHHHHHa]U]1.0—3Wa]a]1.0WW—.3H—3C)(0(0i1-—.30W‘-xl•CDP‘.0U]U]U]i1‘-.0a]H(0—3HWC)i4iTiIU]‘.0W1.0oH[‘.3HWC)WW(0a]a],ia](0(0C)[‘0[‘.3[‘.3WU][‘.3a]—3[‘0PW[‘0WWU]C)HW[‘0H[‘0WF-’•••••••.•.•••••••••.•HH(0MU]W-[‘.3U](0C)W(0(0-.3[‘.3P.3U]U]C)CD(0a]WWC)W(0[‘.3Pi4C)HC)1.010U]1.0HC)-P3HHHWHHHHH10H(0WH1.0-.3[‘.3C)C)C)—.3H(0a]C)‘.0C)C)cr3•••••••••H-H-PH1.0U]10C)HC)a]a]U]—31.0‘-0U]‘-0U]C)H H C)WU]a][‘0101010101010[‘.3[‘0[‘3[‘0[‘0ç-t0••ZZH-Hr’C)10HW10a]W—3[‘0U]QC)HC)10W-.3C)[‘0U]a]C)-1+(2(27Ci)IU,WHH-OWWWtiIiiWLxiWWWWWlxiWWlxiLxiCDOC)1hHiHiHiHiHi(2I-hHiWHiI-hW(2HiMiW(2HiHi()SllWtOHWtOHtoHtoHtoHtoHW wHCto-tototOtoHtoHtoWHtoWHHtoW‘-oHtotoHtoC)toUiW-JtoD-CDUiCDCDCDCDWWU,CDU,CD0H•HIIto-DH-Dto—JCDtoWCDCDCDU,HU,U,CD—jWCDLDCDCDCDtoCDCDtoCDto‘DWHCDtoU,4WtoWWtoWHWtoi4U,HWHtotoi4HtoWWHWCDoH-toWU,U,HCD—JU,Hi4totoHCDHWCDHHcito-o...CDCDCDtoCDD‘S.DtoHDCDCDCDWtoCDWCDtociHZH-toCDHU,CDCDCDtoU,toCDHOCD‘OI-DtotoWlI(DHHHHHHHHHtoHHHHHiWCDciCDHU,CDtoH-‘.OCDCDCDHHDH0.....rtQCDtoWHtoHCDWHWiWWCDCDU,toCDU,4IICDCDWCDHCDHtototoWU,CDHDCDLOHJoHtoi4WWtoHtoWWHtototoWWtoHWtoHWHHOciHHWCD-DWWU,CDCDU,HHCDto‘D-JH0r1toU,WCDCDCDHWtoCDCDCDHCDtociCDU,-ciCD—.))CDH‘.-DCDWCDtototoCDWWU,CDLDCDHCDCDCD‘0WHH CDHHHHHHHHHHHHHtoHHHHCtCD—]toU,LO—.Jo—]totoCDIDCDciCDCDIIHLOU,WWU,CDWH.CDWCDU,toCDtoCDU,U,toCDHtotoCDU,WLOCDCDLOHLOCDHU]CDH rtU,CDtoWWU,toCDCDtoi4U,WtoWtoU)H-HtoHtoLOU,CDCDCDHCDciU)toCDCDU,CDU)CDU)H0U)LDCDLOU)<1CDCDCDCDLOCDCDLDCDtoLOU,Cr H-HHCDU,toCDHU)U,CDHCDciCDCDtotoCDCDU,U)U,C).....CDU)CDH4CDciU)ciciCDU)—IHU)citoCDtoU,U,ct La)46attributed to allophane and imogolite components;(3) Citrate-bicarbonate-dithionite extracts all formsof free Fe and Al (hydro)oxides.Imogolite is a hydrated aluminosilicate with a molarAl/Si ratio of 2.0. The ratio of inorganic amorphousAl/Si0=2 can be used as an evidence of the presence ofimogolite (Parfitt and Kimble, 1989) . The ratios of (Al0-Alnta)/SIo for the Bf horizons of pedon V-i, V-2, and V-3 areclose to 2. This indicates the possible presence ofimogolite in these pedons (see clay mineralogy)4. Results of simulated column leaching experimentsIron and aluminum contents in leachates are listed inTable 3-4. Aluminum concentrations in the leachates arehigher than iron, the molar ratio of Al/Fe varies from 2.46to 8.85. The Al and Fe captured by Ef horizons werecalculated from the differences between AB and Bf 1 (for V-4and C-4) or Bf 1 and Bf 2 (C-7). Much more Al than Fe wascaptured by the Bf horizon for the same pedon.5. DOC and resin extractable Al, Fe and SiA Cation-exchange resin can extract positively chargedcations under certain conditions. The contents of resinextractable Al, 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 smallexcept in Ae and AB horizons. Most of the Alr in Bf horizonsexists in forms other than exchangeable Al. Alr content may‘-d‘-CDoph0HH-CDNMiHiMiWHiW0wJHHHI I4 H 0HHHHHHH-C)••••••0CXHi4HMCX)DUiUiCX)HC)oLOU)M0)MCDCDC)Cr IIHp)oo0000CrCr5••••••CDH-HFOMW‘ij..—.QoHU)0—]CDSU)WHMHM5 C) oo HC) CD0)WUiM)H••••••—..rrCD0D00MUi-..JM0)HCl)) CtCrHH-oo000•••C)HHPiHU][‘3HU)UiCrCD p)oo05CDC)•••IJoo0CDPi0H0CrHH‘-<CD wHHHMioL’.)[‘3xJUiUiCDC)C)C)C)C)H]IIIIIII0CDUWMHWHH-0HNCDwwwwwwiwwwwwww0H,WHHH,H,H,H,H,H,WH,H,JCDH,H,H,H,CDWHOHMHMHt)HMHH,1”)HMHU] 0 C)HHHHHHHHHHHHHHHCD0CD00000.DH0-.-JH0H-.J0000--JMHU]U]HCDHIDHHDMW-JMCDHHHW-JH—J[‘3[‘JH-JCD-TWU]—.3[‘3U]U)CDCD Ci) H[‘3HMHHHHH[‘3HU)HU)HH[‘3HU].DU)HLØU]1.0.-.JU)-.31.0HWCD0U]CD[.3U]•-•HoU)0CD1.01.0[‘3CD—31.0CD0CDCD[‘3U)1.0U)U)CDH0CDH—.1-.3CD-3CDHi4U)F1U]—3i4CD—JHCDC) Ct000H0[‘3000[‘300U)[‘30[‘30i[‘30•-•Cl)HH00[‘00H0CD0U]00CDU)H0H—30H-CD[‘3U)HCDU]CDHi1-.30U)0[‘0HCD[‘3i1.0U)H0C)H0-HI-IloHH0000HH000000H0H0H0(.QCD••-••••.•-•-•••••--••-xJ1.00HU)-U]1.0HU)HCDU)aCDaU)CDCDU)U]00a—JCDCD1.0CD1.0U)U]U]CDU]‘.0Cl) H-HH[‘3H[‘-3[‘3U]HH[-3-J0CDU]‘.00CDU)CD-JCD-JHCDU]CDU)0••---•••.•-••••-••...0U)1.0[‘30CDCD—3U][‘-3001.0CD0U][‘-3HU)C)[‘-31.0HU]1.0CDCD0[‘3U]CDU)CDCDCDCD—3U]049Table 3-5 (Continued)Bfl 11.00 28.88 0.18 1.84 7.24C-6 AB 8.58 3.00 0.03 0.81 14.40Bfl 10.71 22.97 0.00 0.22 4.25C-7 Bfl 10.58 11.81 0.81 1.80 7.66Bf2 9.37 1.86 0.01 0.52 5.00C-S Bfl 10.58 11.38 0.54 0.19 7.08Bf2 10.93 18.16 0.00 0.40 7.83DOC= dissolved organic carbon50be higher or lower than Ainta (Table 3-4), this and the highDOC content imply partial or total organic-bound Al may beextracted by the cation exchange resin.6. Al activity in soil extractThe pH values, DOC, and Al concentrations in theextracts are shown in Table 3-6. To calculate Al3 activity,the following equilibrium equations for the hydrolysis ofAl3 were considered (Lindsay and Walthall, 1989; Baes andMesmer, 1976)Equations LogK°Al3 + H20 ‘ AlOH2 + H -4.99 [3-1]Al3 + 2H0 Al (OH) 2 + 2H -10.13 [3-2]Al3 + 4H20 Al(OH)4 + 4H -23.33 [3-3]2Al3 + 2H0 Al2 (OH) 2’ + 2H -7.69 [3-4]3Al + 4H20 Al3 (OH)45 + 4H -13.94 [3-5]Since all pH values of the extracts were < 4.2 (Table3-6), the activities of Al(OH)4 (Eq[3-3]), Al2(OH)4 (Eq[3-4]) and Al3(OH)45 (Eq[3-5]) are negligible compared with Al3activity. CAS may react with freshly prepared, weakly boundorganic-Al complexes (Al-salicylate) when CAS and Alsalicylate have the same (1X1O5 M) concentrations (Closeand Powell, 1989). However, the DOC concentration in thefinal solution for absorbance measurement (DOC in Table 3-6divided by a dilution factor, 25-100) is about one order ofmagnitude higher than CAS (1xl05M), thus, neglecting thereaction of CAS with Al-salicylate should not bringI-10C)IIII0CDMHwH-’H-0CDN 0WWWWWWWWWUiUiUiUiUiUiUiUiUiiISH,H,5H,H,HH,HUiH,H,CDC)H,H,5H,H,CDCOMHJHWL\)HJHH,[‘3H[‘3HH C) 0WWWWWWWWW(3(3(3(3F(3C-)CO(0COciCOU](0C)COMC)CO(0HC)C)—1H)C)[‘3CDU]COC)(3MM(0U]COCOCOHcici[‘3(0(0C)U](0-3 03CtH- 0HHMU](3ci0)HH[‘3HHH(30HH[‘3(3z•.50ci[3[3COciCO[‘3COU](0U](0U]HH(3HC)HCOHciC)(3COU][‘3CO(3-(3(00)C)C)(3-+C•) Ct H-H[-3COci[3U][3-3[‘3H[‘30)(3(3HiT[‘3(3-3(3U]—3[-3H(3(3—300)U]C)C)ciciCOC)1.0H[3[‘3(3ciciU]U][‘3(3-COCOCOCOciC)HCOCOciCOHCOU]ci[‘3H C’)Pi0HHHHC)H[3COCO(0HU](3COciCtHU](3-U]U]COCO[31.00)0)ciHC)C)(0HC)C)COHH-H<UiU]C)CDC)COCOC)(3[‘3CX)HC)U]-i4(0iTCOCOHCOH Crrt P) C)U] H-I.I-zC)C)C)C)I:)IIIIcxiU,WHrfwwetiwww‘wwwwwiiiIHiHiHiHiH,H,C)HiH,WH,HiWC)HiHiC)HiHiC)CDWt’JHWMHMHNJHNJHNJHCD H--)WWWWWWWWWWWWWWWWWWWWH-CD.......CD-.J—J‘.DCD0‘.DCDDU,cxi-..CDiLxicxiCD—JoLxiCDHCDHHWLxiWU,LxiCDLxiNJCD--JCDCDHHNJNJNJU,HHHHHHNJHNJNJ•••••...••..•••..HUiCDLO—100LxiHCD00NJ0WW-HCDCDH-U,Lxi—JLxiCDCDNJLxiwWNJWWWCDHCDHNJNJU,Lxi--J0HNJCDWU,NJWCDWCDNJLxiLxiCDNJH00CDW00HHNJ—.JHNJHLxiH—JU,-—JCDCD0NJNJ0WU,U)NJ0U,HU)U,U)LxiU,NJ53significant error to the following calculation. If there isan error, the result will be an over-estimation of Al3activity. This will make the conclusions based on Al3 moresolid. Making an approximation, the CAS-reactive Al is equalto the sum of Al3, AlOH2 and Al (OH) 2•[Al] = [Al3] + [AlOH2] + [Al (OH) 2 [3-6](Al3) = y3[Al] [3-7](AlOH2) = y2[AlOH] [3-8](Al(OH)2) =1[A1(0H) [3-9]Combination of Eqs[3-1], [3-2] and [3-6]-[3-9] yields:(Al3)= [Al]/{l/Y3 + K10/y2(Hi + K2°/y1(H) } [3-10]where the parentheses denote activity, the bracketsconcentration, and y represents the activity coefficientfor ions with valence i, as calculated from the ionicstrength of the 0.01 M CaC12 solution using the Davies formof the Debye-Hückel equation (Lindsay, 1979). The K1° and K2°are the equilibrium constants for the hydrolysis of Al3 toform AlOH2 and Al(OH)2, and are taken as i0 and 10-10.13,respectively. The calculated Al3 activities in the extractsare listed in Table 3-6.7. Acid neutralizing capacityAs shown in Table 3-7, ANC to pH 3.5 varies from 0.1 to14.2 cmol(H)/Kg. As it is generally recognized that thevalues of ANC are highly dependent on the analyticalconditions, such as concentration of supportingelectrolytes, rate of acid addition (Kinniburgh, 1986;C)C)‘-IIICDHWtJH0QhQHH-CDN*wwwwwwuiwwwwww0wC)SH,H,5H,H,H,H,H,WH,H,C)HH,C)5H,H,MHHW1’JHHH,MHHu-IC)‘-3III(71WH CDwwwwwwwwtElWWtiWH,H,H,H,H,HC)H,H,tElH,H,C)H,H,C)H,H,WliHW1’JHL’JHMHMHL’JHC) 0 rt HFFIFFI4WFICDU]U]U]WWU]—J0)HOU](0WMHaU]W‘oa-,0WU,W0U]Cr,0W—.JU]—JU]o‘.oHHHHLD(00)0U]ca—JHM0-,(00L\)-0(00(J(0COWHU]0HHCOCOW,(0(0WMU] U]56Valentine and Binkley, 1992; Funakawa et al., 1993), directcomparison of the data presented here with those in theliterature may be inappropriate.Table 3-8 shows the correlation between ANC and otherchemical properties (in logarithm scale). This Log scale mayreflect a characteristic of ANC, since the measurement ofANC is directly related to the change of pH (-log(H))values during titration. ANC correlates well with organic-bound Al (Ainta) and amorphous Al (Al0). In contrast to Al,organic bound Fe and amorphous Fe have no significant effecton ANC at pH 3.5. The negative correlation between ANC andAlexch indicates exchangeable Al is a storage of acidiccomponent rather than basic component, whereas theinsignificant relationship between ANC and exchangeablebases reflects the fact that the percentage of exchangeablebases in the total basic components is very small. Theimplication of Al0 and Alnta in acidity transfer will bediscussed in Chap. 4, section II.8. Phosphate sorption characteristicsThe sorption maximum (Xm) is calculated from theLangmuir 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 havingdifferent initial P concentrations, and X= phosphate(_)Ob’1+CDCDU)HC)11HictwiIH-II’,CDCOw2U)C.)Hç.0 CDH-I—iH-HiCDHi(.QJ<H-HF—iCDC)H,CDHQU)CDH-HU)CDOoLxiIw0HIC)Hi0I•ICD-C)0I0IQQHICD0HiHiHCD0HUirt H-00U)•I-CDII1:-IH1+0pjc(Q-00IHiwwCDI>I‘xjC)C,I ICD-dI°H-°IIr\)rt-0I0ICD0UiIrrHiL%)CD0IUi58sorbed corresponding to each C.Native sorbed phosphate (P0) was assessed by acidammonium oxalate extraction. The ratio of P0 to totalphosphate sorption capacity (Po+Xm) was calculated and shownin Table 3-9,. This value varies from pedon to pedon and fromhorizon to horizon. It is lowest in Ae horizons and muchhigher in Bf horizons.9. Clay mineralogyInterpretative results of XRD spectra are given inTable 3-10. Chlorite is absent from Ae horizons, whilesmectite and vermiculite are dominant minerals. The majormineral in Bf horizons is chlorite, sometimes with mica andvermiculite. Trace kaolinite may exist in the top mineralhorizon of some pedons. Quartz appears in every pedon in atrace amount.Chemical extraction indicates the potential presence ofimogolite in pedons V-i, V-2, and V-3 since the (AloAlnta)/Si0 ratios are close to 2 (Table 3-3) . The existence of atrace amount of imogolite is suggested by the infraredspectra. Fig.3-1 shows the spectra of the synthetic imogolite and clay-size samples. There is a weak absorption peakat 350-360 cm1, which is the key criterion for IR identification of imogolite. The intensity of the peak is reducedafter heating the samples to 350°C. For identification ofimogoiite, transmission electron microscope (TEM) is anessential tool; the result is subject to verification by TEM.C)CDII HWMH0H CD wwwwwwwwIt)iWWIH,H,H,H,H,H,HiHiHiCDC)HiH,C)HiHiCl)CD[‘3HL\)HW[‘3H[‘3HH,[‘3H[‘3Ho H-0NCl)ort CD CD 0HU,UiUiWO—.J[‘30WWJ0U,WHCDCDCD0CD[‘3UiHCDCD-JCDCDUi—JCD—JCDCDUiWi4WH-CDCDCDHCDHCD[‘3-JHH0WCDCD—3[‘3HCDJ00 SU,UiUiUiOUi[‘3-UiciWUiUiUiUiOUiUiHCD CiWCD0WCD—3—.1H00CDHUiGUiHCDCDO’i—3CDCDUiCD0WHU]HCDUiciWOUiCDUi0CDCD0Cl) C)I-tiS0Q Hoo00000000000CD00000000•--IQUiUiiiWUiUiWHOi[HUiUi[‘3UiUiH+H0ciciW0[‘3CDOCDCD0iHHciUiCDW-JUiCDI-00IIIU]U)H CD U)WWLiiLiiLiiLiiLiiIiii’WLiiLiiWWWLiiIH,H,H,H,HiHi()H,H,WH,HiC)H,H,WC)HH,C)CDU)L\iHU)MHMHMHl’JHMH(-) 0 H CDHFICDCDHaCDL’JMJHMWJU)0)U)0CD00CDH0UiU]U)a0M0-a-UiCDHo—.]CD)U]U]U)0))OUia-CD0)0CDCDGiUiU]U]0)U)U]U]0)U]U]U]U)U)U]U]U)U)CDU)H0)CDU]0UiU)U]U]CDU]U]U]U)000000????00000??????U)U)L\)LiM0)0)H0)0)U)U)MU]U)U)U)U)0U)CDU)—]U)HCDH[\J.jU]COU]00CD0)CD0) 0Table 3-10 Clay-size Crystalline MineralsPedon# and Smec.* Verm.* Chl.* Mica Kaoi.* Q Feld.HorizonV-i Ae + + trace tr. tr.Bfl + +Bf2 + + tr.Bm + tr. tr.BC + + tr.IIC + + tr.V-2 Bfl + + tr. tr. tr.Bf2 +BC + tr. tr.V-3 Ae + + tr. tr. tr.Bhf + +Bfl + + tr.Bf2 + + tr. tr.V-4 AB + + tr. tr. tr. tr.Bfl + + tr.Bf2 + tr. tr. tr.Bf3 + tr.C-i Bf2 + tr.C-2 Bf2 + tr.C-3 Bfi + tr.C-4 Bfi + tr.6162Table 3-10 (Continued)C-5 AB + + + tr.C-6 AB tr. + + tr. tr.Bfl + + tr.C-7 Bfl + + tr.C-8 Bfl + + tr. tr. tr.* discrete or interlayered. Smec=Smectite, VermVermicu1ite,Chl=Chlorite, Kaol=Kaolinite, Q=Quartz, Feld=FeldsparFigure 3-1 Infrared Spectra of Clay-size Samples1 = synthetic imogolite (105°C)2 = V13f2 (105°C) 3 = V13f2 (350°C)4 = V2Bf3 (105°C) 5 = V2Bf3 (350°C)6 = V3Bf1 (105°C) 7 = V3Bf1 (350°C)636730C)ci.01-40‘I,251100 900 700 500 300 cny’64Chapter 4 DISCUSSIONI. Mechanisms of PodzolizationVarious theories and hypotheses of podzol±zation havebeen discussed in Chapter 1. In summary, the discussionconcerning the pros and cons of the theories andhypotheses of podzolization may be grouped into twofundamental questions: 1) which one is more important in thetranslocation of Al and Fe in podzol formation, silicic acidor organic acid? and 2) do Al and Fe behave in the samemanner in podzol formation?1. Differential behaviour of Al and Fe in podzolizationMany studies on Podzols during the last decadeconcentrated on short-range-order minerals and their rolesin podzolization (Farmer, 1982; Ugolini and Dahlgren, 1991;Wang et al., 1991). While the traditional fulvate theoryemphasizes the importance of the sesquioxide-organic mattercomplex in podzolization (McKeague et al., 1983; Duchaufour,1982), the proto-imogolite theory advocates the formation,transportation and precipitation of anFe203-A1Si0Hsol as the principal mechanism in podzolization (Farmer etal., 1985; Fraser and Farmer, 1982). Regardless of themechanism in podzol formation, it is generally accepted thatFe and Al behave in a similar way (McKeague et al., 1983;65Farmer and Fraser, 1982) . This assumption is reflected inthe chemical criteria of Podzolic B (Spodic) horizons ofvarious classification systems (Soil Survey Staff, 1992;Agriculture Canada Expert Committee on Soil Survey, 1987).However, little solid support has been provided for thisassumption, except that the two are often extracted bysimilar procedures. Therefore, more quantitative studies onFe and Al eluviation and illuviation in podzols in variousenvironments are still needed.This section presents the differential distribution ofAl and Fe in podzols, examines the possible mechanismsresponsible for this distribution, interprets thedistribution using thermodynamic data and discusses theimplications of these results for podzol genesis andidentification.a. Index of movement: Fe vs. AlDuchaufour (1982) used an index of movement of Fe andAl to characterize their differential mobility in podzols.The index can be calculated from contents of amorphous ironand aluminum hydroxides and oxides using the followingformulae:FeifldexFeQ(Bf horizon) /Fe0(A or AB horizon)A1.d=Al(Bf horizon) /A10( e or AB horizon)From the Fe0 and Al0 data in Table 3-3, Alindex and Feindex werecalculated and shown in Fig.4-1. The Alindex ±5 1.34-5.18times as large as the Feindex. This result can be6612T10 -I A18-•64,•-S‘SL1Fe2t .. —.o——cIDfl•0• I I I I I I I I IIn C N 00 C ‘, •SAMPLEFigure 4-1 Index of Movement for Fe and Al1=V1Bf1 6=V4Bf1 11=CSBf12=V1Bf2 7=V4Bf2 12=CSBf23=V3Bhf 8=V4Bf3 13=C6Bf14=V33f1 9=C4Bf1 14=CEBf25=V3Bf2 10=C4Bf267caused by either one or both of the following processeswithin a pedon: (1) Al eluviates faster from Ae or ABhorizons than does Fe; (2) Al illuviates more to Bf horizonthan does Fe.Data from the column leaching experiments indicate bothprocesses occur. In Table 3-4, molar ratios of Al/Fe in theleachates of sample V-4-AE, C-4-AB and C-7-Bfl are greaterthan 1.0. From this, one can infer that Al is leachedpreferentially compared with Fe from AB horizons or evenfrom Bf horizon, if the Bf horizon exists on the surface ofthe pedon. When these primary leachates (containing more Althan Fe) pass through the lower Bf horizons (sample V-4-Bf 1,C-4-Bfl and C-7--Bf2, respectively), the molar ratios ofAl/Fe in secondary leachates decrease, indicating partialremoval of Al and Fe in the primary leachate. The amounts ofFe and Al removed by the Bf horizons can be calculated fromthe differences of Fe and Al contents in the primaryleachates and the secondary leachates. The calculatedresults show that these Bf horizons capture much more Althan 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 upperhorizons and the ease of illuviation in Bf horizon for Alresult in the Alindex >Fejfldex in the same pedon.b. A thermodynamic explanation of Aljx>FejexRegardless of the relative importance of inorganic and68organic mechanisms in podzolization in various environments,these two mechanisms no doubt coexist in some podzols. In aparticular pedon, Fe encounters the same pH conditions,species and concentrations of organic acids as Al does.Therefore, two chemical parameters can be used to compare Feand Al behaviour in podzolization: solubility products ofminerals and stability constants of organo-metal complexes.Table 4-1 lists the solubility products of someminerals potentially occurring in Podzols and stabilityconstants of Fe and Al with some organic acids. A generalequation (Eq[4-3]) dombining solubility and complexationreactions can be derived from Eqs[4-l] and [4-2]:M(OH)3(s) + 30H (M=Fe or Al, K) [4-1]M3 + (ML)3’ (L=ligands, Kf) [4-21M(OH)3(s) + L (ML)3” + 30H [4-3]K= [(ML) 3] [OW] / [L] =KSPKfIn a specific pedon, Fe encounters the same pH and ligandsas does Al, therefore, the concentration of mobile (ML)3’only depends on K. Since the differences between K-Fe andK-Al are much greater than the differences between Kf-Feand Kf-A1 (Table 4-1), the overall effect is (KSPKf) -Al>>(KSPKf)-Fe. This explains why Al is eluviated from A horizonsmuch more than Fe. When the solution containing ML3 movesdown to the Bf horizons, the increasing Al(or Fe)/ligandratio makes the ML less mobile (McKeague et al., 1983), andmore AlL deposits in Bf horizons than does FeL, since AlL iso4oaiH-0cOa)N4J(THa)n3a)H(ThoC)-i-)(ClCl)G)‘4-)a)lHcO01:14iZIHNOLoiHHH-Ii4)-HH(Cl-H4-)U)LflmmHCO‘Cl4)0comNCl)UU)rC)-H-HC)C)H-HC)C)>i4-HC)-HC)ClC)-HH-H4)4-)-H4)H(ClH-H(Cl<(Cl(Cl(Cl(ClU0Cl)El4-)1U)00oNa)>0(Cl-I-’E—H-Ha)0o’>HC)(ClHCO(ClO-H-iI)a)GU)Na)HZ(ClClClHOH(Cl(Cl0El—H4)Cl)C)-H—Cl4-)Cl)Cl)i-ia)r-I-)(ClC))rtC)00m0-H.‘-HCl)f]0OmCONomU)om-‘-i>iHa)..II0ImCmpin-HQQmmmI-Hm0C’.)C’.)04)-H++-I-H.QmNC’.)COCOHmmm-HH00.-Q0QP1Cl)iimHoa)a)Cl)4J4..)-H-HH1-iQ)rda)a)IU)a)4-)a)a)4.)H4..)>-i-H4-)-I-),(Cl(Cl‘H(Cl-H$-H-H—.1—iHa)-Ha)-IiU)4-)40Ha)4)-I(Cl.-Q0U)0t5)a)bE.Q-‘H0(Cl-H0a)(Cla)-HH0HEElZ(!)r14‘-470not as stable as FeL (Kf-A1L << Kf-FeL). This explains whymore Al is captured in Bf horizons than Fe.a. Implications in soil genesis and classificationIn many Southwestern British Columbia regions, Podzolslack an Ae horizon. Bf horizons are found directlyunderlying LFH with or without decaying wood. How these Bfhorizons change when they continually receive organic acidsfrom the decomposition of LFH and decaying wood is ofinterest. As an example, when sample C-7-Bfl (top mineralhorizon in that pedon) was leached with the simulationsolution, significant amounts of Al and Fe were released tosolution (Table 3-4). Thus once a Bf horizon is brought tothe land surface by whatever means, the illuviated Al and Fein the Bf will be subject to leaching by organic acids. Ifthe leachate does not move out of the solum, part of the Aland Fe in the leachate may be captured by the underlyinghorizons (e.g. C-7-Bf2 in Table 3-4). Eventually, the upperboundary of the Bf horizon will move downward and thehorizon may lose the characteristics required by a PodzolicB (Spodic) horizon. However, if the leachate moves out ofthe solum and subsequently reaches nearby rivers or lakes,it may have an effect on surface water quality as discussedin section 11-2.The Podzolic B horizon is defined by morphological andchemical properties (Agriculture Canada Expert Committee on71Soil Survey 1987). Although both Fe and Al are incorporatedin the chemical criteria, the morphological features (mainlycolour) do not reflect Al illuviation, since Al-containingminerals contribute little to the red to brown colour. Thismay not be a problem for well developed undisturbed Podzols,but for Podzols in which Al is the only or dominant elementin illuviation, the chemical criteria may disagree with themorphological features. In these cases, field identificationof podzols may be difficult.In conclusion, for the soils studied, Fe and Al behavedifferently, at least in quantitatively, duringpodzolization. Al is more easily removed from the topmineral horizon and deposited in the underlying Bf horizonthan Fe within a pedon. This may be explained by thedifferential solubility products of Fe-bearing and Al-bearing minerals in soils and the differential stabilityconstants of Fe and Al with organic acids. A Bf horizonexposed at the surface may be subject to leaching of Al andFe, this makes the upper boundary of the Bf horizon movedownward and begins to destroy the original Bf horizon.Whether the greater leaching of Al is associated withsurface water acidification merits attention. The definitionof Podzolic B horizon sets a arbitrary limit for Al and Feilluviation. It is not surprising if chemical criteria andmorphological features do not agree with each other.2. Silicic acid and pH versus organic acids in podzolization72The recognition of the widespread occurrence ofimogolite/allophane in Spodic horizons (Farmer et al. 1985;Ugolini and Dahigren 1991; Wang et al. 1986) has stimulatednew interest in podzolization. Farmer and co-workers suggestthat H4SiO rather than organic acids plays an importantrole as a complexing agent and the soluble hydroxyaluminumorthosilicate complex (proto-imogolite) is responsible forthe translocation of Al (Farmer, 1982). Therefore,quantification of Al in proto-imogolite would be helpful todetermine if the inorganic mechanism exists in Podzolformation at a particular site. While chemical extractionmethods (acid ammonium oxalate, tiron, pyrophosphate) areoften used to estimate the amount of imogolite/allophane insoils when the existence of the minerals is confirmed byinfrared spectra and electron micrographs (Parfitt, 1990;Wang et al., 1991), these extraction techniques are muchless useful in distinguishing proto-imogolite, which isquite reactive in podzolization, from other amorphouscomponents. Proto-imogolite may occur as complexes withhumus and clay minerals, as well as water soluble components(Wada and Wada, 1980) . In acidic conditions, proto-imogolitehas a positive charge (Farmer, 1981) and can be incorporatedinto cation-exchange resins (Wada and Wada, 1980) . Thisproperty has been used to separate proto-imogolite fromterrestrial waters (Inoue and Yoshida, 1990) and soilsolutions (Ugolini and Dahlgren, 1991). Recently, this resin73extraction method has been used to extract proto-imogolitefrom soil samples (Sakagami et al., 1993).Both pH and organic acids may influence the formationof imogolite/allophane. Statistical studies indicated that apH (H20) >4.7 was required for allophane to precipitate insoils (Parfitt and Kimble, 1989). The formation of imogoliteand allophane is favoured in horizons with pH (H20) values>5.0 (Shoji et al., 1982; Shoji and Fujiwara, 1984).Laboratory studies (Inoue and Huang , 1986; 1990) revealedthat even a small amount of organic ligands stronglyperturbs the formation of allophane and imogolite. However,there is a gap between the laboratory studies and thestatistical studies. In the laboratory studies, theperturbation effects of organic ligands were observed at pHvalues of 2.9-3.4 for imogolite and at pH values 5-7 (excepttannic acid) for allophane. These pH values do not cover thewhole pH range in which Podzols may occur. Thus, moreempirical studies are needed to better understand theeffects of pH, organic ligands, and other factors onpodzolization in Podzols with more moderate acidity (e.g. pH4.5-5)This section shows the Al content in proto-imogolite,the contribution of an inorganic mechanism to podzolization,and the pedogenic implications of pH, atmosphericprecipitation versus dissolved organic carbon.a. Fractions of resin extractable Al (Al,.) constituents74As shown in Table 4-2, Air is less than Al0. The molarratio of Air/Al0 varies between 0.16 and 0.84. Thus onlypart of the amorphous Al components exists in positive-charged forms. Air may include partial or total organic-bound Al, as explained in Chap. 3, section 5. It ispostulated that Al3, hydroxy-Al ions, and hydroxyaluminosilicate(s), combined with or without organicligands, are the components of Alr• Because of the diversityof Air constituents, it is difficult to calculate the Al inproto-imogolite directly from Alr• Nevertheless, it ispossible to estimate the Al in proto-imogolite indirectlyfrom S±r Since pK1=9.71 (Lindsay 1979) for the followingdissociation equation:H4SiO H + H3SiO4 [4-4]H4S±0 behaves as a neutral species in an acidic environmentand should not be extracted by a cation-exchange resin.Thus, the Si extracted with the resin (Sir) must be relatedto the Si incorporated in positively charged proto-imogolite(Sakagami et al., 1993). If the smallest structural unit ofproto-imogolite is [Si(OH)20A1(O (OH2)6] (Farmer, 1981)with a molar ratio of Al/Si =2, then the Al content inproto-imogolite can be calculated and is equal to 2Sr•Therefore, Alr2Sr represents the positive-charged Al thatexists in forms other than proto-imogolite (Al-O-Si),such as Al-c-H groups and Al-c-C groups. All these groups(Al-c-H, Al-c-C, and Al-O-Si) are highly reactive, as75Table 4-2 Fraction of Positively Charged Al, Si and FePedon4* and Alr/Alo Fer/Feo 2Sir/(Alr2SIr)tHorizonV-i Ae 0.84 0.12 0.00Bfl 0.25 0.10 0.46Bf2 0.31 0.03 0.63V-2 Bfl 0.50 0.11 0.09Bf2 0.28 0.07 0.42V-3 Ae 0.46 0.14 0.01Bhf 0.39 0.04 0.37Bfl 0.45 0.06 0.38Bf2 0.35 0.02 0.28V-4 AB 0.29 0.18 0.00Bfl 0.45 0.05 0.00Bf2 0.52 0.03 0.22C-i Bfl 0.59 0.10 0.01Bf2 0.47 0.07 0.11C-2 Bfl 0.59 0.06 0.00Bf2 0.39 0.03 0.38C-3 Bfl 0.63 0.05 0.01Bf2 0.71 0.02 0.13C-4 AB 0.96 0.12 0.00Bfl 0.70 0.05 0.00C-S AB 0.42 0.08 0.0576Table 4-2 (Continued)Bfl 0.64 0.10 0.01C-6 AB 0.20 0.06 0.02Bfl 0.45 0.01 0.00C-7 Bfl 0.38 0.12 0.163f2 0.16 0.04 0.01C-8 Btl 0.44 0.01 0.10Bf2 0.55 0.03 0.00t 2S±r/(Alr_2Sr) = molar ratio of (Al in proto-imogolite)/(Al in A1-O-H and Al-O-C groups).H-bct‘-ciPiF-C)CDftH-H-C)QçtH-Ci)JCD—H-5I-3•I—’J-a)a)0H-CCDiH1H-hI-’oCDCDPH-l)HH-a)C)-‘Cl)CDC)h’Ci)hCDCl).Qç-tC)CDCuUiH-oCDC)H-ft0oi-i’H-CD3C)HCu‘dHC)CDFtH-Cua)Cua)oft((I)fta)CCDCl)CT)ftH-0l-CDHa)0a)H-CD‘-<CuC)0fta)a)HCDc-tftCCDSCDCuCDH-‘-‘ISCDH-0CuCIICDCDCD*CD10tCua)CD‘-ciCQHftH-,H-X-5I-’-H,H-a)CDpJS0H-CDN1ftIICuftfl0CD0CuIICuH-HH-H-0CDIICDk<H-ftH,CDC)CDH<H0a)ftrtftCuCuOI-’.a)Q><HH-H-a)a)CDC)C)Mç-tCDHCDH-C)iqCDCul-ftftCDCDCDdCu‘lCDH‘CuCl)H-H-HCDH-CDI-’a)CC‘-xiCD‘Cii3H-HC)><‘-ciH-a)HH-QfttCDCt0ftCDI-IQCDCDCCQC)I-’•0CDHCuCDCiHFt—3a)hHCCD‘Cucii-CF—aCu0)HI-I+CDk<ftCi)C)ftk<ftC)I-rta)CDI-IH-QH,H-CDC)H-CDhH-H-OHC)CC3a)CDCftuHHI-çCi)CCtCua)CuCD13’C)F-1H-0a)‘-ci—CuCDFt0bftCDC)CDCtI-flCtCuI-Ha)ftC).C)CtIICDQI<101i-<FtH-Cu0‘-‘ICD0CDCDH-CDwCC)H-HH-QI.jCDCuCD-,CDftCDH‘-ci‘-HCD5CD,-,CuHH,H-S—.--i—hCtHI-ho-H.CDH-CftH,H-Cu-CuCDIftH‘-U‘--<‘-<H-05I-fthCD-CDHHH.Oa)k<SCHHCDQIHHOC)30“H-0QQftH-II-QCDC)NH-CDCDOVCD,..CD‘ciiCO+i-0oH-CuH-0CtCDCD‘-ci° i-,,a)Ti)ftH-‘-C)Ctft3HjCtC)0H-CD—N+‘-ciftCuC)H-LQH-)a)*CDCO0CDH-HCH,a)H-ft0CH-FC‘-ciCIQCD3ftC+CDCDHIiJI-FftCQCuCQIHa)——.CDh5CDCDHI-hSC-a)><CiiCuCu<CDCDl)COH,CuIQC)LQFta)CuC)CDhC)COCD‘-U—hH-CHCDCDCCDJJQftCDCi)a)5-H,CuCuCDo‘-ciH‘-ciH-H5CCDCDC)—Cl)IQba)I-h130H-CDCDft—CDa)H—3‘a)CDC.Cu-‘HCDCftZ—SCDCu‘-ciCDi4ftCC‘-‘<I0CDCDI-CH,-l)CDi-ilCDH-jftCD‘-‘1Hftk<0-UiCD11CWa)CDC‘-cia)0CDFt‘-cia)oIH-CD0CuQIH)I-5Ia)i-CftCuCDa)Z(.QHCDCCH-—ftCDCui-QIfl—H- C)a)H-<a)<Cl)‘-ljCu‘-xJHfta)H-CDH-‘-‘aCDH-S—’CDCDQIHH-‘-HCD0-S78reactive component of Al0. Thus the value of 2S±r/(Alr_2Sir)iwhich represents the ratio of (Al in Al-O-Si)/(Al in Al-O-Cand Al-O-H), may be used to approximately evaluate therelative importance of the inorganic process and the organicprocess in podzolization. This ratio varies between 0 and0.63 as shown in Table 4-2. For Ae and AB horizons, thevalue is zero or close to zero. Based on this ratio, one caninfer that the inorganic (proto-imogolite) mechanism isalmost absent from pedons C-4, C-5, and C-6 (2S±r/Alr2S±r<5%) and insignificant in pedons C-i, C-3, C-7, and C-8 (theratio <16%) . While in pedons V-l, V-2, V-3, V-4, and C-2, atleast one Bf horizon in each pedon has a value between 22-63%, suggesting that the inorganic process does exist andplays a role in the podzoiization of these pedons, althoughthe organic process may play a major (the ratio <1.0) role.The coexistence of organic and inorganic processes requiresrethinking of the chemical criteria of Podzolic B horizon,i.e. pyrophosphate extractable Al+Fe, which is based on theorganic process only.The difference between Vancouver pedons and Cowichanpedons merits attention. All Cowichan pedons except C-2 arelow in 2S±r/ r_2r) while the ratios in Vancouver pedonsare much higher. This difference may be related to the muchhigher annual precipitation (2076 mm) at the Cowichan sitethan that (1258 mm) at the Vancouver site (Table 2-1)Intensive leaching, a result of higher precipitation, may79lower Si concentration in soil solution and thus hamper thereaction of hydroxyaluminum with silicic acid to form protoimogolite. The finer textures of the Cowichan soils mayfurther increase the effect of the higher precipitation onlowering Si concentration. The relative abundances of protoimogolite and Al-organic acid complexes largely depend onthe competition between silicic acid and organic acid toreact 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 thatcontrol the competition. considering the difference inprecipitation of the Vancouver area and the Cowichan area,one may separate the Vancouver soils from the cowichan soilsto evaluate the effects of pH and organic acids onpodzolization.The hydrolysis reaction of Al3 ion can be written as:Al3 + H2C A1CH2 + HpIC=4.99 (Table 1-1). The amount of hydroxy-Al decreasesmarkedly with decreasing pH below 4.9. Therefore, aluminumis hindered in its reaction with Si to form Al-C-Si, buttends to form a stable complex with organic acids (Shoji andFujiwara, 1984), i.e. Al-C-c. Intensive leaching may enhancethis effect of pH by lowering Si concentration in soilsolution. Cn the other hand, hydroxy Al increases markedlywith the rise in pH above 5.0, promoting coprecipitation ofAl and Si, if Si exists in soil solution. The significant80correlation between pH(H20) and either Al content in protoimogolite (2S±r) or the ratio of 2S±r/(Alr_2S±r) (r=0.70** and0.71**, respectively, n=12) for the Vancouver soils providessupport for the above statements, i.e. higher pH valuesfavour Al-0-Si over Al-O-C. In contrast, no significantcorrelation between pH (1.120) and either 2S±r (r=0.24, n=16)or 2Si/(Al-2Si) (r=0.23, n=16) was found for the Cowichansoils. This may be related to the higher precipitation inthe Cowichan area, which makes Si concentration rather thanpH the limiting factor. The effect of pH onorganic/inorganic mechanisms in podzolization is alsoevidenced by the ratio of (AloAl,.ta)/Alnta• Alnta as anestimation of organic-bound Al (Yuan and Lavkulich, 1993)and AloAlnta approximates the Al in inorganic amorphousconstituents. (AloAlnta) /Alnta significantly correlates(r=0.80**, n=12) with pH (1.120) in the Vancouver soils, butnot in the Cowichan soils (r=0.45, n=16)It is well known that organic acids inhibit theformation of imogolite/allophane in well controlledlaboratory conditions (Inoue and Huang 1986, 1990; Huang,1991) . Organic ligands with strong affinity for Alsignificantly modify the nature of the soluble productswhich range from proto-imogolite sol complexed with organicacids to hydroxy-Al-organic complexes (Inoue and Huang,1986) . However, whether conclusions from the laboratorystudies can be unconditionally extrapolated to soils with pH81values different from those in the laboratory studies isunder question. Moreover, perturbation effects of organicligands on imogolite/allophane formation may not necessarilyexclude the role of the inorganic mechanism inpodzolization. It is suggested that in the soils examinedatmospheric precipitation and pH are the key factorscontrolling proto-imogolite formation and subsequently itsrole in podzol±zation. The direct effects of organic ligandson proto-imogolite and on the relative importance ofinorganic-organic mechanisms in podzolization may not beunequivocal, since no statistically significant relationshipbetween 2Sr [or 2S±r/(Alr_2S±r)] and DOC (or total carbon)can be found for both the Vancouver soils and the Cowichansoils. DOC and total carbon are significantly correlated(r=O.60**, n=28) . The disagreement between thisinvestigation and above-mentioned studies may be the resultof the difference in pH values between the laboratoryconditions and field soils. Significant perturbation effectsof organic acids on imogolite formation were observed at pHvalues of 2.9-4.3 in laboratory conditions (Inoue and Huang,1986) . These pH values are lower than those of the soilsstudied.In conclusion, positive-charged Al accounts for avariable portion of the amorphous Al constituents. Thispositive-charged Al is highly reactive in Podzols. The Si82extracted by the cation-exchange resin is used to estimatethe content of Al in proto-imogolite. The ratio of Al inproto-imogolite to Al in Al-O-C and Al-O-H may be used toassess the relative importance of inorganic vs. organicprocesses in podzolization. The results indicate these twoprocesses may co-exist in some pedons. Higher atmosphericprecipitation may be responsible for the low contents of Alin proto-imogolite in the Cowichan pedons, while higher pHmay contribute to the formation of Al-O-Si over Al-O-C bond.The direct correlation between organic matter and thecompetition of Al-O-Si, Al-O-H and Al-O--C was not found.II. Transfer of Acidity from Podzols to Surface WatersSoil acidification affects aquatic systems as well asforest ecosystems. The processes involved in the transfer ofacidity (mainly Al) from soils to surface waters hasrecently drawn considerable attention, due to the elevatedAl concentration in lakes and streams in areas receivingacidic deposition. The topic lies between the domains of thesoil chemist and the water chemist, and it seems fair to saythat it is poorly understood by both (Reuss. 1991). In thissection an evaluation of the commonly used intensity andcapacity factors that relate to acidity transfer is83examined, a new capacity factor is proposed, and finallythe use of extraction and column leaching experiments totest the suitability of the new factor is discussed.1. Constituents and factors affecting acidity transfera. Constituents contributing to acidity transferAluminum is a strongly hydrolyzing metal and isrelatively insoluble in the neutral pH ranges. Under acidicconditions and/or in the presence of complexing ligands, thesolubility of aluminum is enhanced, making it more availablefor biogeochemical transformation.Constituents affecting acidity transfer in the absenceof strong acid inputs may include organic acids, silicicacid, and carbonic acid. CO2 may have an important role inthe solubilization and transport of Al (Reuss and Johnson,1985) . Mobilization of Al by CO2 is most significant atvalues of ANC near zero (pH near 5.0) and increased withincreasing partial pressure of CO2 (Driscoll and Schecher,1988). At low values of ANC and pH, significantconcentration of Al is available, due to pH-dependentAl (OH)3 solubility. However, acidic conditions restrict thehydration/dissociation of CO2 to H and HC03, therebydecreasing HC03 to serve as the counterion in Almobilization. Conversely at high ANC and pH values, HCO3increases, but Al concentration decreases, resulting in adecrease in Al mobilization. The role of silicic acid inacidity transfer may be explained by the formation and84mobilization of proto-imogolite sol. Complexation of Al byorganic acids and subsequent movement of organic-Alcomplexes is a common feature in Podzols. This organic-Almovement is important not only in Podzol formation, but alsoin the transfer of acidity to surface waters. This transferof acidity to surface waters can occur if the organic anionsare not broken down by microbial processes or notprecipitated by sesquioxides. The amounts of organic acidsadded to soil may be affected by the characteristics of theforest and various management practices. Thus, the transferof acidity depends on natural processes, as well asanthropogenic factors (acidic deposition and management offorest)Superimposed on the natural process of acidity transferis the introduction of strong acids from acidic deposition.Anthropogenic inputs of sulphur or nitrogen may increase theconcentration of the sulphate and/or the nitrate anionsseveral-fold. Charge balance principles (Seip, 1980) dictatethat they be accompanied by an equivalent amount of cationsin the soil solution. If the ion-exchange complex is wellsupplied with base cations, the major effect will be anincrease in the rate of removal of Ca2, Mg2, K, and Na assalts of S042 or N03. As these are neutral salts, little orno acidity transport will take place. If the supply of basecations is limited, as is the case in the soils studied, thedeficit will be made up by H and Al3 species, so that85acidity will be transported from soil to the drainage water.b. Intensity factor versus capacity factorsHydrogen ion activity (the intensity factor) or pH isone of the most commonly measured soil and water parameters.To the nonspecialist it is often the parameter of mostinterest. It may be measured in a variety of ways, each ofwhich has certain advantages and limitations. However, thisparameter is not well suited for measuring acidity transfer.The following explains the reason in a simple (mineralfraction only) way:For dissolution of Al(OH)3 minerals:Al (OH)3 + 3H “ Al3 + 3H20the equilibrium relationship between Al3 and H may bewritten as:[Al3] = K0[H+]3 [4—61In the soil environment, the value of logK° varies from 8.04(gibbsite) to 9.66 (amorphous aluminum hydroxide). Byrearranging Eq. [4-6], we get,[H] = [Al3]1/3/ (K°) 1/3 [4][H] is proportional to 1/3 power of [Al3] . Thus asignificant change of Al3 in soil solution can occur beforethe change in pH value can be detected confidently. This isparticularly true when K° is relatively large (amorphousaluminum hydroxides). If the soil solution moves out of thesolum and becomes surface water, acidity transfers from soilto water.86While the intensity factor is not well suited forindicating acidity transfer; the capacity factor, soil acidneutralizing capacity (ANC), is often believed to beresponsible for acidity transfer from soil to surface water(Reuss, 1991) . ANC is a concept from water chemistry. Whenit is introduced to soil chemistry, its definition andmeasurement become vague. The ANC of soil material is madeup of contributions by mineral solids, organic solids, andaqueous phases (Bruggenwert et al., 1991). The mineral solidphase contribution to ANC is equal to the quantities ofbasic components minus those of acidic components. Which is“acidic” or “basic” depends on the reference pH chosen. Forexample, when titrating a soil to pH 5, CaO, MgO, K20, Na20,FeO are basic components (proton acceptors), while SO3, P205,and HC1 are acidic components (proton donors) . Aqueous ANCis ascribed to alkalinity due to carbonate plus organicanions, minus free mineral acidity (van Breemen, 1991) . Thecomposition of the organic solid ANC is not given by vanBreemen (1991). Soil ANC may be determined by titration ofsoil with mineral acid, but it is strongly operationallydependent (Kinniburgh, 1986; Valentine and Binkley, 1992;Funakawa et al. 1993) . The measured values vary with theconcentration of supporting electrolytes and the rate ofacid addition. This makes it difficult to compare the ANCvalues from different researchers.It is worthwhile to point out the differences between87water samples and soil samples in terms of bufferingcapacity. Water samples are usually low in bufferingcapacity to acids or bases and the acid/base reactions insolution are much faster than those in solid samples.Therefore, The ANC or BNC (base neutralizing capacity) ofwater samples can be conveniently determined by a titrationmethod. However, soil samples have much greater bufferingcapacity and contain a wide variety of weak acid and basesurface functional groups of varying acidity or alkalinity,consequently tending to give rather featureless titrationcurves (Kinniburgh, 1986). They commonly lack identifiableacid or base endpoints in the pH range of 3-10. Furthermore,the slower acid/base reactions imply that continuoustitration curves are inevitably nonequilibrium curves.Since both the intensity factor (pH) and capacityfactor (ANC) have their limitations, it is necessary to seeknew criteria to characterize a soil’s (potential) capacityto transfer acidity to surface waters.c. The capacity to transfer mineral acidityTo fully understand acidity transfer from soil tosurface 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; andThe hydrological pathway of the watershed.88To the best knowledge of the author, accurate data ofacidic inputs at the sampling sites are not available. As anestimation, van Breemen et al. (1984) listed the order ofmagnitude of various groups of processes in terms of theircontributions to acidic inputs (kmol(H) ha1yr’)acidic deposition 0.1-6organic acids 0.1-1 (Spodosols)nitrification 0-10 (clear-cut watershed)For simplicity of discussion, a few assumptions are made:yearly input of H is 3 kmol h&1;thickness of soil solum is 1 meter (seldom exceeds 1 min the study areas);the bulk density of the whole solum is 1500 kg/rn3; andfine earth (<2 mm) is 10% by weight of the totalmaterials.Thus 3 krnol/ha H input is equivalent to:(3*1000 molH*100 cmol/mol)/(l0000 m2*l m*0.l*lSOOkg/m3)i.e.0.2 cmol H/Kg (fine earth). If we compare this number withthe exchangeable base cations (sum of Ca, Mg, Na, K) inTable 3-2, we reach the conclusion that the storage ofexchangeable base cations is only enough to neutralizeacidic inputs for a few years. This estimation is compatiblewith the results in other regions (Bruggenwert et al.,1991) . After the base cations are depleted by acidic inputs,exchangeable Al may be subject to leaching from exchangesites to soil solution which may become surface water.h‘—3C)bP3QU)hI-P3h’C)itU)0P3H-H-C)CDp3‘<H-H-CDCDCD0CDitCDCDitC)U)350HCD-U)HP3P3ClCD‘dIIP3P3P3H-QCDP3U)H-C)C)1I—it.Q5ctititCDClU)F—1CDCU0H0C)ititCDCDI-jCDI-itU)<‘°C)3HP3H-H-+U)CDCDH-‘-3H-U)+CDCDCDp30F1it00CDCDCD0hI-U)—H-ititCD‘HU)H,H-H-0CDP3-0p30H-Cl)H-Cl)ititH-3IH-,b01QH,HICH-P305P3‘dU)H-CDU)P31QtQitMF-1bitHitHH-CDU)0ClH-HCDCD<P3HC)C)H-P3H,C)0HH-CDH-+it——SCDP3P3+P3U)0P3‘<Hit0H-itCDitH-C-U)U)C)I-3H-U)P3QU)U)hitCDJ0H0P3U)0CDCDHI-C)U)itH-—HCl)it•CDhLU3U)itU),HU)H0CDCDbHH-0+0itP3H,<5CDk<-itH,CDCDP3CD+00U)0CDH-CDCDCDithitQitU)H,--0H-H,U)0p3C)U)itU)CDH-itC)U)0P3HCDH-CDCDCDit,H-U)0U)P30QH-0P30U)H-H0CDZ+0CDk<U)C)U)HH,itU)H,H-U)itLUH-+H,U)H-CD0CDP3P3U)0CDWHh’0it(H--CDU)CDCDHUiU)CDCDoP3U)CI)HXCD><ititC)CD—--HCDF-’5H-+-P3C)P3C)P3ititCDU)H,‘-dU)H,CDCDCDH-P3+itP3H-U)‘-<P3C)<P30P3CD0U)CD+H-CDC)P3C)H,+HU)CD+0CDI-tTCD-ClP3P3C)P3(Q‘dCDIQr-H-<0CUClCDP3CD5itIIitCDH,it-I-ititClP3C)P3P3HCDH-o‘<H--P3H-bH-QU)H-HH-U)itHitCDH,Hit0oU)P3F-’H-CD‘-<P3CDitP3C)H-H-QH-LUP3H5H-C)H,00H-IQ‘0i‘H-CDHH-P3Ht3H,Hp3‘NH-—H-—i--H-I—’P3P3CDIQHP3i-Nit0C)C)H-U)CDCDC)0itP3P3C)°Z3itC)0P3ii-SH,H-U)+itCD0P3C)0P3H,CDitbH-0H-H-1H-CDU)CDH-P3CDYC)IIU)CD3iiito-H-H,P3P3-CDpP3tl)C)-U)S‘-dH,05U)itCD30P3P3H-CDitH-CDH-C)CDH,H1DCDititC)0P3P3CDH-CD-ititC)itU)P3.-CD‘<HCDp3U)H-HCUititU)+C)CDCX)H-P3—3itCDP3itP3CDitCDHJHH-b3C)Cl)Qk<U)H-8it—H-Cl)C)U’CDCDC),40<Zi0H-IC)itIII‘tiCDH-CDHCDCDU)H-H-N0S0HLU)CD0H,--P3._1CDU)I-IU)U)0QH,H-CDH,CDIP30itHk<CDU)CDH,HSHCD 1ft90mineral solid phase. However, the weatherable primarymineral content is usually low in podzols, especially in theeluvial horizon and the rate of cation release fromweathering is lower than the rate of base leaching at thePodzol stage of soil development. Therefore, leaching of Alis inevitable. Since the storage of exchangeable Al is toosmall to be considered as a capacity factor controllingacidity transfer from soils to surface waters, we have tochoose other parameters, such as Al0, to indicate the soiPscapacity (in the longer term) to supply Al which may betransferred to surface waters.2. Justification of Al0 as a capacity factorThe following text will explain the rationale ofselecting Al0 as a capacity factor through statistical andexperimental approaches.As shown in Table 3-8, both Al0 and Ainta correlatewell with ANC (r=0.92** and Q73**, respectively) . Thissuggests the importance of organic-bound Al and amorphous Al(organic + inorganic) as acid buffering constituents. Thepossible mechanisms may be explained by the reactions ofinorganic Al monomerization (Eq. [4-10]) and organic-Alcomplex dissociation (Eq. [4-11]) at low pH conditions (e.g.pH 3.5):Al (OH)3° + H Al (OH)14 + H20 [4-10]The logK values for Eq. [4-10] can be derived from reactions91No. 2, 6, and 7 in Table 1-1 and are 4.99, 5.14, and -0.47for X=l, 2, and 3, respectively.Al-Org + H AlHOrg [4-111(Org naturally occurring organic anion)The LogK value of Eq. [4-11] can be calculated from reactionsNo. 18-19 in Table 1-1 and is 4.70. Since Al0 is supposed toinclude both organic-bound Al and inorganic amorphous Al,Al0 is responsible for both Eq. [4-101 and Eq. [4-11] . Thus,Al0 may be used as a capacity factor from the above-mentioned statistical evidence.Results of two experiments will be used to demonstratethe suitability of Al0 as a capacity factor. The firstexperiment was done with little acidic input. 0.01 M CaC12solution, which is often used to approximate ionic strengthof soil solution, is assumed to simulate this condition.This solution may also include the role of CO2. Alconcentration or activity in CaCl2 extract represent the Alsubjected to transfer to surface water under conditions oflow acid inputs from acidic deposition and organic acids. Inthe second experiment, a pre-set amount of organic acids andmineral acids (HNO3+H2S04) is added to a soil column, Alconcentration in the leachate are used to represent theamount of Al that may be transferred under the conditions ofhaving acidic inputs from both natural and anthropogenicsources.In the first experiment, Al concentration in the CaC12J0U)PiC)H-QCDf-CUCDI1HiCUI-01\)C)CD0C)k<•CU>CDCUQCrH-I-i—’ftH-ftHCr1C)F-’ftSNU)U)Q.H-hI)JCUI—aH-H-CDCDH--CUQCDU)<0H5CUftWUU)CDCU><U)hjF-’‘dU)CDftH-><C/)CD3H-C)IICDCrhCrCrH-HCU3CDftH-H-ftt-Q0ftH-H-F’-CDCDU)CD5çtCD-II1CD00HCDCDC)1IIU)H-QCDCU>ftHIQ--C)HCDC)CrI-I—’U)‘‘•,0H-U)U)CDcSH-CDft‘oU)ftHCl)_HH-0H-CDU)+IIft0C)ZU)‘<0w00HiHHH-IQ—JpD3H-H-P1CDHi5CUftH-CUCUI+DC)ftbflftF-’CU0CDHCDU)ftI-F.jQI-LOU)U)SHCUhftftC)Z3CD0Q)--H---0U)F’-CD0HU)-hrI-F-’H-U)H-<CU30CUCUCD0SCDLiiagH-HIHOftF’-SZHH-U)CU3HIHHCl)rt0QH-CDCDCUQft-hU)1<Clftk<Cl)CDCDCD0bH-CDCl‘.DIi)U)hCDwi-piCDF-’H-U)<HCDHCUCD0U)CUiU)3IHU)‘ftO00-.ftftCUQC)p•+0.ftH-0•H--CDClU)CDCDftH-CrU)0CDH-ftSI-CUCD—‘U)ft0‘-<CD(QCDftftOCUftU)H--bCU0F’CU-CUU)HCU+HCUU)H-0bCU-—SCDU)CDCDft—U)ftH-HU)HiHftCDft‘ti1ftCUInICUft-I—L.DCDH-0ftF’-CDC)C)H-CU0lH‘d000-’Hi5.—ftCUHU)ftaH-U)HHCrCDCD‘tiH-ft.DU)H-—CDH-0CD‘OU)CDH-0)00-U)ftHH-P-.+0)5U)F-’H-H-CUUiHH-hC+UiI00H-oHft‘d1YC)CDHiU)HC)-H-<ftC)H-ftftCUwH--CUU)ftCUCUH-CUH-i-CDHCDftU)C)CDH0CDHCU0U)H0U)F’CD-‘,HICD0.F’-CD><CD3CDCDU)‘dft0-.0CDCDHU)U)pi1_IU)U)CD‘<CDH->CDftIIF’-0C)SC)ftCD0H-CDC)HiCU0U)ctHH-CUC)HiCUftI-ftHftHHi1IIftH-‘<H-HCDCDI-H-CD0CDCDCDCDU)ftbCDC)i.QSCDCDft110F-’hU)ftH-CDftH-CUft0CL)C)HiCDU)CUU)ftCD0ftHH-ftCDftH-CUII,H-5ftftF-’U)CDDCU10U)oC)F-’-fthCDbF-’H-ftCD01)CUftHCDCUCD.CUCU‘ftCUo‘‘0-.HCD-bCD-Li]o-iU)0CDHk<CDHU)CDCDftU).DH-CDH-CUSU)C)5‘DftHiHH-CDH-HWCD0‘CD‘‘CUft--iCDHCUIQH-U)CDM5-ft-0-.CUb’-)L’J932A AA AAA03 3.2 3.4 3.6 3.8pH4 4.2Figure 4-2 pAl3 and pH Relationship in Soil Extract(Gibbsite Solubility Line is Shown)76543AAA&AAA A AA A A AA194respect to Al (OH)3 is readily obtained from bothconditions of undersaturation and oversaturation within 0.3hours, and the Al3 in soil solution may be regulated byhydroxy-Al interlayer of expansible 2:1 layer silicatesinstead of gibbsite which is seldom found in Podzols (Ross,1980) . Other studies suggest that these waters may actuallybe in equilibrium with a solid phase humic adsorbent (Cronanet al., 1986; Mulder et al., 1989) and contribute theundersaturation cases to the complexation of Al with organicmatter (Bloom, et al, 1979; Prosser et al.,1993) . It isclear that the justification has not been fully demonstratedfor applying the geochemical model (which relies onsolubility alone) to soils in which both mineral and organiccomponents may exert influences on Al behaviour. Therefore,a general model for predicting aqueous aluminum chemistrymust incorporate organic solid phase reaction to account forthe undersaturation cases (Cronan et al., 1986)b. Relationship among A13, pH and Al0The correlation between pAl3 and other soil propertieswas shown in Table 4-3. The property best correlated withpAl3 is pH, followed by DOC, total carbon, and Al0, whereasclay content has no significant relationship with Al3activity. This implies crystalline minerals have littleeffect on actual Al3. Since both pH and organic mattercontent correlate significantly with Al3 activity, theyshould be taken into account in a model predicting AlTable 4-3. Correlation between pAl3 and other PropertiesPHextract DOC Total C Al0 ClaypAl3 0.83 -0.74 -0.60 0.52 -0.04for p=O.Ol and ra(2)40=±O.304 for p=O.O5Sample size n=39 for DOC9596activity. This applies to soil solution and surface waterbecause both of them dynamically exchange with soil orsediments.a. An exchange nodelCronan et al. (1986) use the modified mass actionexpression derived by Langmuir (1981) to describe Al3activity in natural waters. Given the exchange reaction,3H + A1X ‘ HX + Al3 [4-13]the empirical exchange function would be:Kex [(Al3)/(H)] [H3X/AlX] [4-14]where the parentheses denote activities of the ions, and AlXand H3X are their mole fractions on organic sorbent X.[H3X/A1X] can be estimated from organic-bound Al/titratableacidity (Cronan et al., 1986). Kex and n depend on thenature of sorbent X, they should be constants for a specificsoil. However, the values of Kex and n vary from soil tosoil. Thus, direct application of Eq. [4-14] to predict Al3activity is inconvenient, because five items in the model,i.e. Kexi (H), H3, A1X, and n, have to be determined. Takingnegative logarithms, Eq. [4-14] becomes (Mulder et al.,1989)pAl3-3pH= PKex -nLog[A1X/H3X] = PKapp [4-15]The calculated values of PKapp (pAl3-3pH) varies from -5.63to -7.44 for the soils studied. Plots of this PI<app withorganic-bound Al (Alnta) show a good correlation between them(r=_O.61**, n=42, Figure 4-3) . The significances of this978-i a a aaaaaaa aa a aa aa6 a5 I I I I0 5 10 15 20 25 30 35Ainta (cmol/Kg)Figure 4-3 Empirical Relationship between (PKap)and Alnta (Gibbsite Solubility line is Shown98correlation are double. Firstly, PKapp is not a constant, itvaries with Alnta• This is different from the geochemicalmodel in which pK is taken as a constant. Hence, theexchange model can not be used universally with a fixedparameter. Instead, the parameter, PKappi should bedetermined for different regions or soils. Secondly, PKappmay be calculated from the empirical relationship (Fig. 4-3)for soils with similar nature of the sorbent X. Once PKappcalculated, pAl3 can be predicted from pH. Since the Al inthe extract represents the transferrabie Al in situationswithout significant acidic input, and it is correlated wellwith Al0 (Table 4-3), the rationale for selecting Al0 as acapacity factor is shown for these situations.d. acidic input and transferrable AlIn the second experiment (Chap.2), the soil columnswere leached by solutions containing both organic acids(oxalic acid, citric acid, salicylic acid, and malic acid)and mineral acids (nitric acid and sulphuric acid). Thesimilar trend of Al in leachates and Al0, as shown in Figure4-4, provides support for selecting Al0 as a capacity factorin situations where soils receive both natural andanthropogenic acidic inputs.The fact that samples V-4-AB. C-4-AB, and C-7-Bfl haveFed higher than or approximately equal to Aid (Table 3-3)but have more Al than Fe in the leachate (Table 3-4) meritsattention. In southwestern British Columbia logging and99surface 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 thisrelationship in British Columbia, studies in other regions(Likens et al., 1970) suggest the relationship exists. Theelevated Al concentration in surface waters is oftenascribed to acid precipitation. This may be anoversimplified explanation, since the pH values of theprecipitation in British Columbia are much higher than thatin eastern United States and some European countries(Science Council of Canada 1988). The main components ofacid precipitation, i.e. sulphate and nitrate, have littleability to complex Al (reaction no. 14-17, Table 1-1)Therefore, the amount of dissolved Al in weakly acid wateris quite small if no organic ligands exist in the solution.Table 4-4 shows the differences of Al concentrations in0.01 M CaC12 (no acidic input) and in simulated leachingsolutions (natural+anthropogenic acidic inputs) . Alconcentrations in leachates are much higher than those inCaCl2 extracts (3-23 times), especially in the Bf horizon.(Considering the solution/soil ratio in the leachingexperiment (6.0) is larger than that in the CaCl2 extractingexperiment (2.0), this Al ratio will be greater than that inTable 4-4). This ratio means, once acidic input to soil isincreased, Al in soil leachate will increase as well. If thesoil leachate moves out of the solum, the amount of Al100Table 4-4 Al Concentrations in Soil Extracts and LeachatesSample# Al in 0.O1M CaC12(A) Al in leachate(B) Ratio ofmM mM B/AV4AB 0.43 1.28 3.0C4AB 0.40 1.45 3.6C7Bf1 0.08 1.89 23.0Figure 4-4 Comparison of Al0in Soil Leachatesand Al Concentrations101:7-Bf 10a,‘Ia,.a,-IE21.751.51.251--0 10 20 30 40Alo (cmol/Kg)oJC)0)‘dFtCl)tO5Cl)(ClFt55Ft‘rjH-FtFtC))C)C))0CDH-QtI-Hi000F-1CDC)00H-31I-CdH-‘dH-I-CtQQFtC))HiI-’<.CDbH-I-C)H-HC))C))C))H1H-I-CNCC)CDH-FtCD<1w0Q,(Dft-3C)H-C)0C))030)C)NC))CDtQC))(I)FtI))(1)H-FtH-C)QFtF-1FtHiFt00FtI.Q-CDI0)HiHiFt‘-<Ft00H-H-H-CD02CDCDFtH-C))F-1-CDCD‘-<H-CN0h(1)FtPCDC)C)‘-C(1]1‘1Ft0)FtHi3C))00FtCl)F-1C))CDCD5-H-I-CHihjHiH-Ft-0HiI-(1)0FtCDi—a><(UC))(120CDC))C))C))5FtHiH-HihHiF-1WC))(UH-F-1F-1HiC)iC)SI-C0(1)U)0HiI-CC))0)HFtI-CFt02FtC))CDCD03H-0C))FtC)I-CC)FtCDFtoHi0I-C025HH-<Lii0tQCD(1)0)0H1H10‘-CCDI-CH--C))H-C)I—aCl)I-CCDC))0FtC))C))-l-N(1(1)0)CDHiH-C)I-CFtHiH-5tFt(I)CDP-0I-C))Ft0)CDH-H-H-C))FtCDC)HiH-H-C))Ft0CDH-0C)NCHQ0HI-’FtH5I-CFt(12HFt01Ci0)CD(I)I-CHi0()H-H1CDFtZ5I-CC))C))0)0FtFtI-CC))5—00FtC))0)H-5C))C)0F-10H-0)C))0CDC)Ft30I-CCI-C0FtH-FtI-CH-H1H-Ft02CDH-(PF-1H-0C))H-0HNH-0(12CD°F-1C))‘F-10CD0)HCD(I)H10H-<FtHi(ClFtCDQIHFtI--CD—Ft°(UHCDJI-CH-SCD0FtC))H-QIFt02CDHiF-Ft0-bI-CH-C))CDH1‘xJC)C)F-’-CDoFtC))C))03H-CDC)CDI-CI-CFtC))FtH-FtC)I-(1)C))C))(1)QC))H1(P0)ooCDIiCl)CD0)(U-C)0)I-’-FtC))5FtCDH-FtI-C0)3C))3I-CI-CFtCDC))CDFtC))0)I-CCDC))CDHI-CQIF-’I-C(QHiCDH-Ft0HH1C))I-CC))HiI—’00)Hi-C))CD0H-C))(I)I-CH0)FtC))(I)‘-<QIC))C)H-(PHC))0HiH-H-C))CDC)NI-C)SCDU)0)CDC))5FtI-CH-CDtYA0HiCDC))C))-CD(1)HiH-C)H-‘<H-(12[OHC))<C))I-C0I-CH-H-CDFtSCD(I)C)<1(1)00)CiC)FtC))HiC))C))CiC))QC)CDC))C))QICDCDI-FtC)I-CFtC))Ci‘-<FtFt5CDFtF-’(I)C)(PH-I-CCDH-C))H-C)FtCDCD-H-CD0)0)FtCiC)C))CDC))HCDC)-IFt0FtHiI-C3-FtC))1-C0H-C))CiC))0)0)I-0(1)‘dFtCDCD-C)LJ(P(1)C)H13CD02CDCiQI-C))0)FtCiFt0)CiC))CiH-(I)CDFtI-C°5F-’-I-CI-C0CD---Hi00CDCiCD(I)H-CiC)Ft0C))Ft-F-0d(QHiC)H-H•HiFtFtI-C(I)Ci‘-CCD0CDNH-I-CdC))I-CCiCDFtQICiI-C(12°FtCD0C)I-IH1H-F-’-H-CDCDH-(I)C))FtCDFtC)FtC))H-C)02CDCDC))C)C))C)(I)CDC))CiC))H-CDHiCiH QIH-CD02Ci0F-’CDCiC)JC)FtFtH-FtCiCiftC)QIC))H1Hi0QIFtCiCD05CDCDFtH-H-CiI-C)0(1)H-C))C))QII-CSCiFtF-’-CiICDC))FtFtIFtC))CD‘-C(QF-1H1CDCD0Z3F-1QCDFtH-CD(I)(I)C))C))3FtCD0)HFtCD00CDCDQI103further at other sites. The rationale can be shown fromstatistical correlation with ANC and from the relationshipsbetween Al0 and pAl3 in soil extracts and Al concentrationin soil leachates. Al3 activities in 0.01 M CaC12 extractsare much lower than the predicted values from gibbsitesolubility. The exchange model may be used to predict Al3activity if the parameter (PK9pp) in the model can bedetermined. The empirical relationship between PKapp and Alntaprovides a potential solution to calculate P1app for soilshaving a similar sorbent as the soils studied.III. Phosphorus in Relation to Soil AcidificationIn addition to the changes of pH values and Alsolubility, other changes in soils that may occur duringsoil acidification include loss of nutrients due toleaching, and loss or reduction in the availability ofcertain plant nutrients (such as phosphorus and molybdenum,which are more strongly retained in acid soils) . Thissection will discuss the phosphorus issue in podzols (Yuanand Lavkulich, 1994).Phosphorus is an important plant nutrient and ofconcern from the environmental point of view. The reactionsof phosphate with soil components have been extensivelystudied from the point of view of soil fertility, soil104chemistry, and environmental concerns (Sanyal and De Datta,1991; Parfitt, 1978) . In many acid soils, the oxides,hydroxides and oxyhydroxides of iron and aluminum are thecomponents that predominantly influence phosphate sorption(Parfitt, 1989; Borggaard, 1990; van der Zee and vanRiemsdijk, 1986) . For soils from various parts of the world,sorption of phosphate has been variously related todifferent forms of Fe and Al and other soil properties (Penaand Torrent, 1990; Wada and Gunjigake, 1979; Loganatham etal., 1987). Singh and Gilkes (1991) reported phosphorussorption capacity in Australian soils was predictable bymeasurements of citrate-bicarbonate-dithionite (CBD)extractable Fe and Al, oxalate extractable Al, and claycontent. Borggaard et al. (1990) found that the P sorptionmaximum was significantly correlated with poorly crystallineFe and Al oxides and well-crystallized Fe oxides. Therelationship 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 Feand Al ( Fe0÷Al), in non-calcareous soils, that initiallycontain little phosphorus. A coefficient could bedefined to express the relationship between P sorptioncapacity measured and the content of Fe0+A1. Freese et al.(1992) further demonstrated that oxalate extractable (p0)1which represents the phosphate originally sorbed byamorphous Fe and Al (hydr)oxides in acid soils, should be105taken into account in P sorption models. The idea ofincluding originally sorbed P in P sorption models can betraced to Mead (1981) and Holford et al. (1974)These kinds of models are very useful in monitoringsoil and environmental quality for sustainable development,but the applicability of these models outside the modelorigin regions is still to be verified. This part of thestudy investigated the effects of different forms of Fe andAl oxides on P sorption capacity of Podzols. Theapplicability of two European derived models was alsoassessed.1. Natively sorbed P (P0) versus P sorption maximum (Xm)Oxalate extractable (p0)1 which represents the Poriginally sorbed by amorphous Fe and Al (hydr)oxides inacid soils (Freese et al., 1992), has the lowest values inAe horizons and the highest in Ef horizons (Table 3-10).This is not difficult to understand if the sorptioncompetition 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 (Fox andComerford, 1992), its continuous addition to soils fromlitter and decaying wood will increase P in solution byreplacing P sorbed at metal-hydroxide surfaces throughligand-exchange reactions, by dissolving metal-oxidessurfaces that sorb P or by complexing metals in solution andthus preventing precipitation of metal phosphates (Fox etH-CDH-II1X1H,Q0CD3‘-iJc-’))JU)>40H->40H-H-itH,0CDHCD•U)0Hct•çthC)HitHH,itH-0<itU)I-‘I-H0HCDCDU)CDtJCDPiCJSCU0CDHC)Q0CDU)itU)C)itC-o0CDitU)U)itI-HCDC)oU)H-(I)H0itCD—‘CtitC-QCDCUCD0H-C)050H-LOI-CUCDCDP-CDb0CUIIIICDCD-CUHHWHctH-0U)hooitHtU)b‘dCDC-o0HC)H-0CDrritC)CDH-CDH--Hk<Jk<CUQCUH-HI-’-CU0U)U)CDU)H(QCDitHCU003C)H0I—S°-H-CDH-HitH,uJ°HHI-C-fl•CU‘U)H,CD‘dH-C)HSU)H,itH°CUHCUH-hQdH0CUU)HI-itU)-CDHitC)0itC)CliH-PJitCUClUI‘i31jU)‘-<çtCD0nC)H00QCDCUUiCDC)0HitCDU)3itit•‘10CDtCDCDdU)H0U)HQp0LDCDI-H-H,rrC-tCDSC)CUitCUCDCDH,CDH-+U)H-FHU)QQIQ0U)‘-IIHU)H-110‘-dCUC):iH,itCDitI-CUCU--CCDciCUH-0H,itH-00CDCDitCDH-‘-xJ0itH-CDI-’SU)U)-Hitit-‘-‘iH-0Cl30H-HH-CD1QIQ0CUCUCDCDH-‘d0itClit-H,itHi-CDCDQCUitU)iiCDH05CDU)U)H-U)CDHU)CDICUSU)U)CD0H-CDH,I-’U)it‘-<HCDCDHH-0H-H-it0)°‘SCUU)H-CDU)hCrCUCDnCDHit0I-’U)HCDCDHSitCD‘-itoCl-CDH-H-H-HU)CUHH-CUCDtHH-ituitCDH-$iCD00•U)00H-CrU)HCU,<H-U)d-CDCl0H0C)ititU)H-ii5itU)CDitCD0H-H,5t-HitU)JCDWU)it‘-00CDH-‘dCD0U)CD,CldCDCU,0k<p0CUCU•CD0I-C)HH,H‘CDI-hH-itCDH-CDitU)U)-•U)CUCl‘iCDSI-dH:iQH-ciH0CDU)(I)H-0CUCDCDIjCU0C)ci0,CUHoH-H,itC)CDitH0it-itCDH,0itCDCUdCDCD0—HH-LCUC)QCDClCitCDiti0itCDH,U)HC)0•Cl-CDCDCD0ci-CU0i-H-itCDU)H-Ii•°H-Z0--20t—HC)CDH,-itU)CD0>4CDHU)CUCUHCl-‘-xiCDmititCDI--CU0‘--aCDH-CD‘-<ciClCDit5ClCDHClCDCD0()HCDClI•aN(1)0Ha)a)-cci0j1LALALAH0000—1N‘O.DoHCi)U000m0+1II1NHa)cHODU)O00a)4)a)cHiimH0000II-Ha)LA(NCOo0H0Cl)i-Da)000a)a)0omCO(Y)a)a)CO0cCD•••+0000HOcNHU)NCOOH000a)4-1-HC)LA-H0cCOomm4-Ia)•••0a)000oUU)HHCO-Ho0H0-HUH000H(Iia)HHmNO‘D‘D4Jo••.U000C)LA-H-HEa)tT)H+-HE00())-I-108humus complexes are very reactive toward phosphate(Gunjigake and Wada, 1981; Parf±tt, 1989). The significantrelationship between Alnta and P sorption parameters may beimportant from the point of view of soil management. Haynesand Swift (1989) showed that Al-organic matter associationshad a significant phosphate sorption capacity; similarly,Gerke and Hermann (1992) reported that the molar ratio ofP(sorbed) :Fe was nearly 1 for Fe freshly complexed to humicsubstances, whereas the ratio for amorphous Fe-oxides wastenfold lower. For soils in this study, organicallycomplexed Al (Alnta)i not Fenta, correlates well with Psorption parameters and the mean value of the molar ratio of(Po+Xm) :Alnta is 0.80. Since organically complexed Al (Alnta)accounts for a significant portion of Al0 (Alnta/Alo = 0.15-0.64), any change in organic matter dynamics resulting fromeither environmental factors or managementpractices (acid-rain, slashburning, liming, fertilization)will affect Alnta and consequently the P sorption capacity,as long as the relationships between Alnta and P sorptionparameters remain.3. The applicability of two European modelsBoth van der Zee et al. (1988) and Borggaard (1990)proposed models relating P sorption capacity to oxides of Feand Al. These kinds of models are useful since they allowprediction of P sorption capacity from routine analysis data(Freese et al., 1992). Whether these European-derived modelsC) 0 S H CD 0 CD it CD CD S CD CD CD C) H C) H it CD + 0‘xjU<CDCl)C)HiC)QPiC)H-it><CDCl)UCDUititCD00H-000H-hDi-CD0+CDiCl.CDC)SC)PiCDC)C)JCDhCDCDitCuCD0CDCDCD-CDH-I-H-<0H-+0‘-‘1CDitHH-çt0CDitC)Q.CDit1tiQ--JLI.-CDH0tQNH-CuitCuLIuHCDH-C)(QCD5ftH--ft—itPCDCD--C)pi)<CuCDCDCuCDH-<1H-MCDH-CDCD‘iCDCu-<CD0CDH0ft0H-I-0QIICDH-ctH‘DH-CDH-HJoPCuHiNH-CuHCDCD-5itCuHCu-H-Cl.CDoCD><0H-HHitCDS—CDC)CD<CDCDitCDClQC)k<‘--itH-05+CDA0CDCuCD+CDCDCDCl-CD0HHU’I-Cl)CD00oCuH-wCl0CuCDSftH-CDClHiCliiSHCDH-HiitftZCDHCD0H-H-CD1<HHCDCDCD-itC)Hik<3H-CDCD0itC)CDHiCD-.ft5itIIHi0-HC)+H-.-SpiCD>j0CuH-CD0CD0CDCDIH-itCDwCDCu‘1‘d3HaiClCDhCDHCD,,CD(CMCDCD0I—’CDCuI-ijCuCDH-HH-‘xJH--Hil-I--Cu0itCDCDCDHCuk<0CuCDCD0H-itIICDJo0.CDi-toL-0itHH-C)+HCD0CD+CDCDCuCDClH-o<ititCDH-0CD+3.QCDCD0LOCDH-H-HCDCDHCDH0CD00CDH-itHiHi0pJ0CuClQ--‘-<3H-CDZCui-CDCDHACDCDH-it000H-Mit<1HCD(QititI-itCDCuCu><CDCDCD‘•d0i‘1CuCDCDititH-CDH-CDCuL’JHH-0DCD—CDClCDI-0--çuHbCuo‘xJ0-CDCDCDH-PClCDCDI-CDtJCuCu5CDCDi-i-i-i°_HHCuCD<—CD0piJC)WCuHClIINpjitCDH-CD+piitI<CDCDU’itH—CD°°Cu‘dCDCDSH-CDCDpiCDH-CuCuwCuH-A5C)it00CDCu00H-Hi-HiClHHi—,itUiCuClHi0i4CuitHH0)I-H-I13CuH<0HiCuH-3HHHiH-CuHit0CDClI-QUi0CD.—.0Cl‘—z55QCDH-CuCDHCDHCDCDHit0it-, 20MEASURED (cmollkg)Figure 4-5 Comparison of Measured P Sorption Capacitywith Calculated Values from van der Zee’sModel (A) and Borggaard’s Model (+), 1:1Line is Shown110254-1--1-10 -A-k +++AA A4++00 5 10 15 20 25111shows good agreement Cr2 >0.85, Fig.4-5) . This implies bothmodels are applicable to the soils in this study. They mayalso be applicable to soils in other regions. When using vander Zee’s model, the coefficient, o, should be determinedempirically if the P sorption capacity of concern differsfrom that in the model, since P sorption capacity isdependent on experimental conditions. In Borggaard’s model,inclusion of Fed-FeO is unnecessary for the soils in thisstudy, since it has no significant correlation with Psorption parameters (Table 4-5) . In fact, Borggaard’s modelpredicts P sorption capacity better if Fed-FeO is omitted(data not shown in Fig.4-4). The contribution to Po+Xm fromFed-FeO is much smaller than that from Al0 and Fe0 (0.04<<0.120 or 0.223) . However, in the general case Fed-FeO may bekept in the model.In conclusion, P0 should be included in sorptioncapacity in assessment of P sorption models. Fe0 and Al0correlate better with Po+Xm than with X. For the soilsstudied in this thesis, the most important P sorbents areamorphous Fe and Al, especially Al. Although total C contentwas found not to have a significant effect on P sorptioncapacity, the fraction of Al that complexed with organicmatter has a close relationship with P sorption parameters.This fact may be important for environmental and forestmanagement since organically complexed Al may be relativelyeasily changed by management practices. P sorption capacityJPiH0-U)dU.I-iH-U)I-CDFtCDS CDH-FtC)oFtFt Pi‘tI0tToHiF- CDNFto I-CDk<U)C)FtH-0 CD0HiFtHiSH-0CDC) H-CD‘dCDI—’piiU)oFtH-HiH-CDH-0CL)FtHz0oCD‘d CDFtSP0 Q-H-CDCDU)I—’FtU)LiH-FlU)0FlCDCD-H-FlFtCD H- HiH H M113Chapter 5 CONCLUSIONSChemical criteria of Podzolic B (Spodic) horizons areassociated with a generally accepted assumption that Fe andAl behave in a similar way in podzolization. This studyshowed that Al and Fe behave differently, at least inquantity, based on extraction data and column leachingexperiments. During podzolization, more Al is leached fromthe top mineral horizon and deposited in the underlying Bfhorizon than is Fe. This may be explained by the combinationof the solubility products of Al- and Fe-bearing mineralsand the stability constants of Fe and Al with organic acids.Mechanical and faunal perturbations, which bring Bf horizonmaterial to the land surface, can lower the apparent upperboundary of the Bf horizon. Since illuviation of Al in theBf horizon produces no visually observable morphologicalfeatures required for Podzolic B horizons, the disagreementof morphological criteria with chemical criteria may bringdifficulties in the identification of some Podzols in thefield, when Al accounts for a great portion of theilluviated Fe and Al.The widespread occurrence of imogolite in Podzolic B(Spodic) horizons has prompted the recognition of protoimogolite’s role in podzolization. Extraction of soils witha cation-exchange resin shows that 16-84% of amorphous Al114constituents are composed of positive-charged Al. Aluminumcontent in proto-imogolite, calculated by resin extractableSi, is negligible in Ae or AB horizons but significant insome Bf horizons. The competition among Al-O-Si, A1-O-C, andAl-O-H bonds, which determines the proportion of inorganicand organic processes, is related to annual precipitationand pH, but not significantly influenced by dissolvedorganic carbon or total carbon content. Intensive leaching,a result of higher precipitation, hampered the formation ofAl-O-Si by lowering Si concentration, while higher pHfavoured Al-O-Si by increasing hydroxy—Al content. Thedisagreement between this study and some frequently citedpapers on the effects of organic matter on noncrystalline Alconstituents may be explained by the different pHenvironments.Two global environmental awakenings are now occurring:the greenhouse effect on global warming and theacidification of ecosystems. While the former remainslargely hypothetical, the latter is a reality in manyregions. There has been much discussion concerning theability of soil to transfer acidity to surface waters. Boththe intensive factor (pH) and the capacity factor (ANC) havetheir limitations in characterizing acidity transfer. A newcapacity factor (Al0) was proposed. Its rationale can beexplained by the statistical correlation with ANC and the bythe relationships with Al activity in soil extract and Al115concentration in soil leachate. Al activity (orconcentration) in 0.01 M CaC12 extracts of soils indicatesthe amount of transferable acidity in situations with littleacid input to soils. This activity can be described by anexchange model : pAl3 -3pH= PKappi but the parameter (PKapp)may vary from soil to soil. An empirical relationshipbetween the parameter and Alnta has been established. It maybe applicable to soils with a similar sorbent as the soilsstudied.When a soil column was leached by organic and mineralacids, Al concentration in the soil leachate indicated theamount of transferable Al in situations where soils receiveacidic inputs from natural and anthropogenic sources. ThisAl concentration is much higher than Al activity in CaC12extracts and is related to amorphous Al (Al0) contents insoils. Compared with other parameters characterizing soil’sability to transfer acidity, such as acid neutralizingcapacity, Al0 is more distinct in concept and easier inmeasurement.Numerous studies on the relationship between P sorptioncharacteristics and other soil properties have been done,however, most of these studies do not include originallysorbed P (P0) . Since P0 accounts for 17-66 percent of thetotal sorption capacity (Po+Xm) in the soils studied, itshould not be ignored in P sorption models. The goodcorrelations between oxalate extractable iron and aluminum116(Fe0-i-A1) and P sorption parameters (P0, Xm or Po+Xm) indicateamorphous Fe and Al oxides are the major P sorbents. Psorption capacity is predictable from Al0 and Fe0 by twoexisting models. The relationship between organicallycomplexed Al and P sorption parameters may be important inforest and soil management, since the organically complexedfraction is relatively easily altered if environmentalfactors or management practices change.117BIBLIOGRAPHYAgriculture Canada Expert Committee on Soil Survey. 1987.The Canadian system of soil classification. 2nd ed.Agric. Can. Publ. 1646. 164pp.Anderson, H.A., M.L. Berrow, V.C. Farmer, A. Hepburn, J.D.Russel, and A.D. Walker. 1982. A reassessment of Podzolformation processes. J. Soil Sci. 33:125-136.Aveston, J. 1965. 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J. 58:343-346.132Appendix 1 Soil DescriptionPedon: Vancouver 1, dominated by Western hemlock with someDouglas fir, having decaying woodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH+Decaying 20-0 Slightly, medium to wellwood decomposed needle litter overreddish brown decaying wood (2.5YR4/4) ; plentiful fine roots; pH3 . 52.Ae 0-2 Light brownish gray (1OYR 6/2);sandy loam; structureless; loose;few fine roots; pH 3.87.Bf 1 2-10 Strong brown (7.5YR 5/6); sandyloam; weak fine subangular blocky;friable; few fine roots; pH 5.34.Bf2 10-30 Strong brown (7.5YR 5/6); sandyloam; weak medium subangularblocky; friable; few medium roots;pH 5.83.Bm 30-60 Strong brown (7.5YR 5/6); sandyloam; weak medium subangularblocky; friable; few medium roots;pH 5.57.BC 60-73 Light yellowish brown (1OYR 6/4);loam; weak medium subangularblocky; 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; noroot.Pedon: Vancouver 2, dominated by Western hemlock with someDouglas fir, having no decaying woodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH 5-0 Needle litter with various degreeof decomposition; plentiful mediumroots; pH 3.84.Bf 1 0-10 Strong brown (7.5YR 5/6); sandyloam; weak fine subangular blocky;friable; plentiful fine roots; pH4.51.Bf 2 10-30 Strong brown (7.5YR 5/6); sandyloam; weak medium subangularblocky; friable; few medium roots;pH 4.75.Bf3 30-60 Reddish yellow (7.5YR 6/8); sandyloam; weak to medium coarsesubangular blocky; friable; few133fine roots; pH 5.39Pedon: Vancouver 3, dominated by Douglas fir with someWestern hemlock, having decaying woodClassification: Orthic Humo-Ferric PodzolHorizon Deth(cm) DescriptionLFH 24-15Decaying 15-0Ae 0-2Bhf 2-10Bfl 10-30Bf2 30-60Needle litter with various degreeof decomposition; few fine roots;pH 3.70.few fine roots; pH 3.72.Yellowish brown (1OYR 5/4); loamysandy; weak very fine subangularblocky; very friable; few fineroots; pH 3.95.Strong brown (7.5YR 5/6); sandyloam; weak to moderate finesubangular blocky; friable;plentiful medium roots; pH 4.79.Reddish brown (7.5YR 6/8); sandyloam; weak to moderate mediumsubangular blocky; friable;plentiful medium roots; pH 4.87.Light brown (7.5YR 6/4); sandyloam; weak to moderate mediumsubangular blocky; friable; fewcoarse roots; pH 5.06.Pedon: Vancouver 4, dominated by Douglas fir with someWestern hemlock, having no decaying woodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH 6-0 Needle litter with variousdegree of decomposition; pH 4.41.AB 0-10 Yellowish brownish (1OYR 5/4);sandy loam; weak fine subangularblocky; very friable; few mediumroots; pH 4.23.Bf 1 10-30 Strong brown (7.5YR 5/6); sandyloam; weak to moderate mediumsubangular blocky; friable; fewmedium roots; pH 5.18.Bf2 30-60 Reddish brown (7.5YR 6/8); sandyloam; weak to moderate mediumsubangular blocky; friable; fewmedium roots; pH 5.50.BC 60-75 Very pale brown (1OYR 7/4) withlight brown (7.5YR 6/4) mottles;sandy loam; moderate mediumsubangular blocky; firm; fewfine roots; pH 4.84.IIC 75+134Pedon: Cowichan 1, dominated by Douglas fir, having decayingwoodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH 25-15 Variously decomposed needle litterDecaying wood 15-0Bfl 0-10 Yellowish brown (1OYR 5/4); loam;field descriptions of structure,consistence, root distributionhereon were not made due to timelimitation. pH 4.08.Bf2 10-35 Brown (7.5YR 5/4) with darkreddish brown (5YR 3/2) coating;loam; pH 4.37.Bm 35-55 Light yellowish brown (1OYR 6/4)with yellowish red (5YR 5/6)coating; loam; pH 4.68.pedon: Cowichan 2, dominated by Douglas fir, having nodecaying woodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH 5-0Bfl 0-20 Yellowish red (5YR 5/6) ; loam;pH 4.66.Bf2 20-40 Yellowish red (5YR 5/6) ; loam;pH 5.06.Bm 40-70 Strong brown (7.5YR 5/6); loam;pH 5.06.BC 70-80 Pale brown (1OYR 6/3) ; loam;pH 4.97.Pedon: Cowichan 3, dominated by Western hemlock with decayingwoodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH+Decaying 20-0 Slightly, medium to wellwood decomposed needle litterBfl 0-15 Reddish yellow (7.5YR 6/6); loam;pH 4.80.Bf2 15-35 Reddish yellow (7.5YR 6/6); loam;pH 5.10.BC 35-65 Very pale brown (1OYR 7/3); sandyloam; pH 5.15.pedon: Cowichan 4, dominated by Western hemlock withoutdecaying woodClassification: Orthic Humo-Ferric PodzolHorizon Depth(cm) DescriptionLFH 20-0AB 0-2 Light gray (1OYR 6/1); silty loam;pH 4.28.Brown (7.5YR 5/4); loam; pH 4.89.Bf 1 2-15flOH“JOHCDOHCD‘iOF—CDI-JQtnWH-UWWW+H-D0WWWIiH-O)0W+H-W0WWH,H,H,’JNU)‘H,H,H,NWC)H,H,WiNWH,H,WNWflH,WMHQH-WMHCDOH---MHOH-MHCDOH-M_QH,H,QH,H-1UH-flH-flJH-EQ0CD“<000OCDOk<000H-PJOJOH-J0rtQH-rtPJH-rtPHH-’<.IQH-0H--<0QH-0OH-0OH-0piIti--(Q’Id..iId”-QIti--lCDlCDlCDlCDUiro0UitJQM0iQ-1CX)Ui)oWrJQoPoplrJQUiWHooiiIctO00iolrrF--0UiU,IIIrt0-0UiI0Icth-U,U,IMoIrrOIIMI1Jrt+IIM0lct0IIHIctII—JUi0-]ool—Q0)U,U,—3PC1—)U,Ol—ZQWoC)10H-U,010H-00U,10H-00010H-0U,U,150.IS05IS05IS05H-H-[—HI—,zii;-5Cl-5Cl-Srl0r-0CD0CD0CDII1W<HiHF<PF<IIPdCiW0CDCDOCDJ4E1CDOCDhJCD0CDOCD0CDfrrJ0H-0CDrtPJF—PPCDPP)P0CDJP)F-P)F--CDbPJ1QOP)l—’CDb5PU,P5hU,15pl-k<5U,5Hl--<U,OhH---H-iI‘<--H--0-0-.c-t---.QCl)H-MCflCl)H-‘CIU)H-tiPH-dOQ0Hd—0CDHJddH-’dH-0O1dtTO—JtH-000-rcn.—JU)OF-U)Wh-—]U)-1J-JbddbtY•ddrl-PJCD‘-<dd0ddQ-U,U,(DOU,U,(DOCD$U,(U,CDOHU,U,(DOPOUi•ty•0U)1-0•0Cl)-.b-H-.i-upi•i-<-tYCnPMCDPON0iONOH0CD0)CDONCClMONU)j001Mj0-JOOWOi1HQI-SO-.J---.WQO••H-P•U,H-H••H-HH,.—JU,.H-PH,—.U,CDi—.-H••—.H-—)—.U,U,Cl-U,UiMçtU,U,Cl-IIU,ft-I-<I-<H-,-I<I-<H-H----U,i-<I-<H-I-<——H--H0-000)HI-<0-..H00-000ZI0JZJI-<U,U,“U,U,H‘T•i-<i4U,p.)OCl)-<H—.—.—.—.0O——.<—.P)U,0ii—.O’O’H-i1H-—.PJU,-—5H-—)O—-Q,U,—.—...—.—.ft—..-.—-k<-..(-_-—.w--—‘HCl)PCJ)’d—Cl)U)U)H—0H-.0H-tt-.Cl)PiH-0PJ0-.CDPPJHPiHCDp.)PPi00U)5Cl-SCl-F0Cl-15Cl)PiH---<-.1<.(UQk<.H-h<5.0)IQ.WIQU,*1)C)flC)(:2()(_)C)IIIIII(71WHWMH]CDCDI-joIIH-ErIN<H00WL’JHWJH1’JH1’JHMHJHMH1’JHWbJH.JHHL’JH0•CD çt CDHC-I•IICDJZHCDHZZ’ZZZ’ZZZ’ZZ’ZOQQHHOHHOcDocooooQHCD C) 0 CD (-Io)C)HO•rtC)‘ç)H(QH CD HH wBiographical Information1963 Born, P. R. China1984 B.Sc. Nanjing Agricultural University, China1984 M.Sc. Chinese Academy of Sciences1991- Ph.D. candidate, Department of Soil Science,1994 University of British Columbia

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