Origin and rate of pedogenic carbonate accumulation in Saskatchewan soils, Canada

Limited information is available about inorganic carbon stocks in the boreal regions. The objective of this study was to determine the amount and accumulation rate of pedogenic carbonate (PC) in soils of the boreal grassland and forest regions of Saskatchewan, Canada. The storage of pedogenic carbonate increases from 134 kg m−2 in semiarid grassland (Brown soils) in the southwest to 165 kg m−2 in the northeast, under forest (Gray soils), within the time decreasing from 17,000 years in the southwest to 11,500 years in the northeast. The rate of pedogenic carbonate accumulation likewise increases from 8.3 to 14.3 g m−2 year−1 in the same direction. The results show that the soils of the prairies and forests have sequestered 1.4 times more C in the form of pedogenic carbonates than as organic matter. Stable carbon isotope values of pedogenic carbonate decreases from southwest to northeast. This is consistent with decreasing representation of C4 plants in the vegetation in the same direction. The rate of pedogenic carbonate accumulation increases with increasing annual precipitation. This suggests that the rate-limiting factor to precipitate with CO2 is Ca in the boreal region of Canada. Silicate weathering is more significant in Luvisols (Alfisols), suggesting that they may be most effective in truly sequestering additional amount of C in the soil.