Carbon Distribution in a Hummocky Landscape from Saskatchewan, Canada

Abstract

Changes in the topography influence organic and inorganic C contents and δ13C values of soil C across a landscape. The objectives of this research were to: (i) study the effect of landscape on the formation and distribution of pedogenic carbonate and organic matter distribution in a hummocky landscape, and (ii) estimate the amount of organic C and pedogenic carbonate accumulation in local scale in comparison with regional scale using the stable isotope geochemistry techniques and standard characterization analyses. A hummocky landscape, typical of 38% of Saskatchewan's land, with glacial till parent material under virgin grassland, was studied. Organic C content of A horizons range between 20 to 98 g kg−1 Both extremes occurred in level positions of the south‐facing and north‐facing slopes. The lowest δ13C value of organic C (−29.6‰) was measured in a depression and the highest (more positive) was obtained on a shoulder (−21.7‰). The δ13C values of carbonate ranged from −0.9‰ (carbonated parent material) at the 114‐cm depth in level complex to −7.9‰ at depth of 100 cm in footslope complex and depression. The amount and percentage of pedogenic carbonate was higher in north‐facing slopes than in southward slopes. The highest proportion and amount of pedogenic carbonate up to 1‐m depth was found in Calcicryolls in footslope complex position in the north‐facing slope, and likely represents a gain in carbonate through lateral flows. The lowest proportion and amount (34.4% and 33.9 kg m−2) was found in the shoulder complex segment of west‐facing slope and in footslope complex position in east‐west direction. On average, the rate of accumulation is about 1.25 g C m−2 yr−1 of inorganic C (pedogenic carbonate) and 1.25 g C m−2 yr−1 as organic C. These are close to the calculated rate of 1.4 g C m−2 yr−1 for Dark Brown, and 1.3 g C m−2 yr−1 for Black soils (Mollisols) in Saskatchewan.