Carbon distribution in a hummocky landscape from Saskatchewan, Canada

Changes in the topography influence organic and inorganic C contents and delta13C 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 delta13C value of organic C (-29.6 ppt) was measured in a depression and the highest (more positive) was obtained on a shoulder (-21.7 ppt). The delta13C values of carbonate ranged from -0.9 ppt (carbonated parent material) at the 114-cm depth in level complex to -7.9 ppt 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 -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.