Pedogenic carbonate in Chernozemic soils and landscapes of southeastern Saskatchewan

The objective of this study was to characterize soil carbonates and estimat e their accumulation by using a method based on delta(13)C values of soil c arbonate in pedons and landscapes. Dark Brown Chernozem soils of the Amulet Association (with mixed C-3 and C-4 plants) and native Black Chernozem soi ls of the Oxbow Association (with a pure C-3 plants) were included. Six soi l samples representing the Cca and Ck horizons of the Oxbow and Amulet Asso ciations were chosen for detailed pedogenic carbonate studies, which includ e particle size fractionation, mineralogical identification, surface morpho logy examination, and stable carbon isotopic compositions analysis on the p article size fractions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses of the fractionated particle sizes indicated that dolomite dominates the carbo nate occurring in the Ck horizons, and is mainly in medium and coarse silt fractions. In the Cca horizons, carbonate in clay and fine silt fractions i s mostly calcite, whereas dolomite dominates the carbonates in medium and c oarse silt fractions. Calcitic coatings on the surfaces of both silt and sa nd particles were observed. Stable carbon isotope ratio (delta(13)C value) of carbonate was -8 parts per thousand in the clay fraction of Cca horizons in which carbonate is dominated by calcite. Carbonate in the fine particle size fractions of the Cca horizons is dominated by calcite and has the mos t depleted delta(13)C values, indicating that pedogenic carbonate occurs as calcite and mainly in the fine particle size fractions. In contrast, carbo nates from coarse silts of Ck horizons were composed solely of dolomite and had the most enriched delta(13)C values (-1.1 to -1.4 parts per thousand), a character of lithogenic carbonate. On a landscape basis, carbonate occur s mainly in the Cca horizons in mid- and upper slope soils as a result of m oisture movement and ground water fluxes. Soils in the depressions were mor e leached and contained small amounts of carbonate, mostly in the 60- to 90 -cm depth. Calculations from the delta(13)C values of soil carbonates indic ate that about 50-68% of the carbonate in the Cca horizons of middle slope soils is of pedogenic origin, which is equivalent to a CaCO3 storage of 136 -188 kg m(-2). In contrast, 5 to 39% (0-36 kg m(-2) CaCO3) of carbonate sto red in the lower slope soils is of pedogenic origin. Thirty-one to fifty pe rcent of the carbonate (equivalent to 100-134 kg m(-2) CaCO3) in upper slop e soils is of pedogenic origin.