Natural and antropogenic enrichments of trace metals in peat profiles

Abstract Samples of mosses, peats, lake sediments and clays were collected from 35 Canadian peatlands and analyzed for Cr, Cu, Fe, Mn, Ni, Pb, U, V and Zn. The average composition of the analyzed peats is significantly depleted in Fe and Mn, and enriched in Cu, U, Zn and Pb compared to typical crustal abundance. In contrast, Ni, V and Cr are neither significantly enriched nor depleted, relative to typical crustal abundance. The compositions of the peats vary widely depending on their botanical composition and degree of decomposition, the amount of mineral matter present and depth in the peatland. To summarize the voluminous trace metal chemistry data, a composite Sphagnum bog profile was constructed for each metal from the individual profiles using the peat stratigraphy typical of Sphagnum bogs in eastern Canada. To do this the trace metal concentrations of samples of the same botanical composition and similar degree of decomposition were averaged. After taking into account the differences in mineral matter contents of the sediments, enrichments and depletions through the composite bog profile have been calculated for each stratigraphic layer relative to the average composition of the underlying mineral sediments (clays). These calculations emphasize the dynamic behaviour of Cu, U, Zn and Pb and the conservative behaviour of Ni, V and Cr, through the composite peat profile: Cu, Zn and Pb are enriched in ombrotrophic surface peat layers because of significant anthropogenic atmospheric inputs; Cu and U are enriched in minerotrophic basal peat layers because of natural geochemical processes: Ni, V and Cr are neither significantly enriched nor depleted. We present a summary of the pore water chemistry (pH, SO42−, CH4) of a representative Sphagnum bog which shows that these sediments typically range from being acidic (pH approximately 4) and “oxidizing” at the surface (above the water table) to neutral (pH approximately 7) and “strongly reducing” in the subsurface layers. Predominance area diagrams (log PO2 − pH) based upon equilibrium chemical thermodynamics were constructed and are presented for Cr, Cu, Fe, Mn, Pb, U and Zn. Using the predominance area diagrams, the behaviour of the dynamic metals in peatland environments is explained in terms of the influence of pH and redox potential on the relative stabilities of solid and aqueous species.

[1]  R. Garrels,et al.  Solutions, Minerals and Equilibria , 1965 .

[2]  W. B. Coker,et al.  Initial geochemical results and exploration significance of two uraniferous peat bogs, Kasmere Lake, Manitoba , 1979 .

[3]  D. Read,et al.  The Speciation of Uranium and Thorium at the Broubster Natural Analogue Site, Caithness, Scotland , 1988 .

[4]  C. H. V. D. Weijden,et al.  The effect of the pH on the adsorption of uranyl onto peat , 1985 .

[5]  D. D. Runnells,et al.  Ground Water Redox Reactions: An Analysis of Equilibrium State Applied to Eh Measurements and Geochemical Modeling , 1984, Science.

[6]  P. Halbach,et al.  Binding and Oxidation State of Uranium in Recent Phytogenic Sediments, Peats, and Lignites of Selected Areas, Influenced by Physico-Chemical Parameters , 1982 .

[7]  D. C. Fraser.  A syngenetic copper deposit of Recent age , 1961 .

[8]  H. F. Bergman.  The Relation of Aeration to the Growth and Activity of Roots and its Influence on the Ecesis of Plants in Swamps1 , 1920 .

[9]  M. Szilágyi,et al.  The association of vanadium with humic acids , 1967 .

[10]  D. P. Brezinski.  Influence of colloidal charge on response of pH and reference electrodes: the suspension effect. , 1983, Talanta.

[11]  M. Walmsley.  4. Physical and Chemical Properties of Peat , 1977 .

[12]  D. C. Fraser.  Organic sequestration of copper , 1961 .

[13]  E. S. Moore.  The occurrence and origin of some bog iron deposits in the district of Thunder Bay, Ont , 1910 .

[14]  D. Postma.  The Occurrence and Chemical Composition of Recent Fe-Rich Mixed Carbonates in a River Bog , 1977 .

[15]  R. Lucas.  CHEMICAL AND PHYSICAL BEHAVIOR OF COPPER IN ORGANIC SOILS , 1948 .

[16]  N. Urban,et al.  Aluminum, Iron, Zinc, and Lead in Bog Waters of Northeastern North America , 1987 .

[17]  W. Shotyk.  Review of the inorganic geochemistry of peats and peatland waters , 1988 .

[18]  A. Ramsay.  On the Geology of the Gold-Bearing District of Merionethshire, North Wales , 1854, Quarterly Journal of the Geological Society of London.

[19]  P. Halbach,et al.  The uptake of uranium by organic substances in a peat bog environment on a granitic bedrock , 1980 .

[20]  J. Lee,et al.  Lead, Zinc and Copper Analyses of British Blanket Peats , 1979 .

[21]  J. D. Forrester.  A native copper deposit near Jefferson City, Montana , 1942 .

[22]  A. V. Kochenov,et al.  Some Features of the Accumulation of Uranium in Peat Bogs , 1965 .

[23]  S. Shvartsev.  Hydrochemical method of prospecting in northern swamp areas , 1966 .

[24]  A. Szalay.  Cation exchange properties of humic acids and their importance in the geochemical enrichment of UO2++ and other cations , 1964 .

[25]  V. Auer.  Peat bogs in southeastern Canada , 1930 .

[26]  K. Bunzl,et al.  KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER. IV. ADSORPTION AND DESORPTION OF Pb2+, Cu2+, Cd2+, Zn2+ AND Ca2+ BY PEAT , 1976 .

[27]  I. Kaplan,et al.  Interaction between organic matter and trace metals in a uranium rich bog, Kern County, California, U.S.A. , 1986 .

[28]  C. Williams,et al.  Uranium content of peaty soils rich in molybdenum and selenium from Co. Limerick, Eire , 1971 .

[29]  G. Pruden,et al.  The behaviour of Cr(VI) in soil under aerobic and anaerobic conditions , 1980 .

[30]  Werner Lutze,et al.  Scientific basis for nuclear waste management , 1979 .

[31]  N. T. Coleman,et al.  Formation Constants for Cu(II)-Peat Complexes. , 1956, Science.

[32]  S. Chapman.  Chemistry of Peat Profiles and the Development of Bog Systems , 1964 .

[33]  R. J. Myers.  The new low value for the second dissociation constant for H2S: Its history, its best value, and its impact on the teaching of sulfide equilibria , 1986 .

[34]  C. O. Rost.  OCCURRENCE OF SULFIDES IN MINNESOTA PEAT SOILS , 1922 .

[35]  A. Szalay.  The Rôle of humus in the geochemical enrichment of u in coal and other bioliths , 1957 .

[36]  W. Goodfellow,et al.  Metal accumulation by bryophytes in some zinc-rich blanket bogs, Selwyn Mountains, Yukon Territory , 1984 .

[37]  H. Nesbitt,et al.  The behaviour of major and trace elements in complete vertical peat profiles from three Sphagnum bogs , 1990 .

[38]  V. E. Swanson,et al.  Adsorption of copper by peat, lignite, and bituminous coal , 1966 .

[39]  Konrad B. Krauskopf,et al.  Introduction to geochemistry , 1967 .

[40]  A. P. Dachnowski-Stokes.  Peat deposits of Ohio: their origin, formation and uses , 2008 .

[41]  R. Fuge,et al.  Cupriferous bogs of the Coed y Brenin area, north Wales and their significance in mineral exploration , 1986 .

[42]  M. M. Schnepfe,et al.  Sulfur Diagenesis in Everglades Peat and Origin of Pyrite in Coal , 1983, Science.

[43]  K. Walton-Day,et al.  Mechanisms controlling Cu, Fe, Mn, and Co profiles in peat of the Filson Creek Fen, northeastern Minnesota , 1990 .

[44]  A. W. Damman.  Distribution and movement of elements in ombrotrophic peat , 1978 .

[45]  J. Murray,et al.  The determination of chromium species in natural waters , 1978 .

[46]  R. Boyle.  Cupriferous bogs in the Sackville area, New Brunswick, Canada , 1977 .

[47]  A. Szalay.  The significance of humus in the geochemical enrichment of uranium , 1958 .

[48]  Garrison Sposito,et al.  The thermodynamics of soil solutions , 1981 .

[49]  E. Gorham,et al.  The mineral content of Sphagnum fuscum as affected by human settlement , 1978 .

[50]  J. M. Jones.  Chemical fractionation of copper, lead and zinc in ombrotrophic peat. , 1987, Environmental pollution.

[51]  J. M. Bemmelen,et al.  Über das Vorkommen, die Zusammensetzung und die Bildung von Eisenanhäufungen in und unter Mooren , 1899 .

[52]  W. K. Fletcher,et al.  Syngenetic sulphide minerals in a copper-rich bog , 1980 .

[53]  C. Jeandel,et al.  Isotope dilution measurement of inorganic chromium(III) and total chromium in seawater , 1984 .

[54]  A. Szalay.  THE ENRICHMENT OF URANIUM IN SOME BROWN COALS IN HUNGARY , 1954 .

[55]  C. T. Pierson,et al.  The geochemistry of water near a surficial organic-rich uranium deposit, Northeastern Washington state, U.S.A. , 1987 .

[56]  G. Moore.  Extraction of uranium from aqueous solution by coal and some other materials , 1954 .

[57]  J. Otton,et al.  Geology of the Holocene surficial uranium deposit of the north fork of Flodelle Creek, northeastern Washington , 1987 .

[58]  D. Jeffries,et al.  Atmospheric deposition of heavy metals in central Ontario , 1981 .

[59]  Jerome O. Nriagu,et al.  Global Metal Pollution: Poisoning the Biosphere? , 1990 .

[60]  V. Puustjarvi.  Peat and its Use in Horticulture. , 1977 .

[61]  W. Stumm,et al.  Redox Equilibria and Measurements of Potentials in the Aquatic Environment , 1967 .

[62]  D. Postma.  Formation of siderite and vivianite and the pore-water composition of a Recent bog sediment in Denmark , 1980 .

[63]  R. Berner.  A New Geochemical Classification of Sedimentary Environments , 1981 .

[64]  R. J. Bartlett,et al.  Behavior of chromium in soils. III. Oxidation , 1979 .

[65]  H. Lees.  A note on the copper-retaining power of a humic acid from peat soil. , 1950, The Biochemical journal.