Soil organic carbon pools of the Torneträsk catchment area : The importance of soil depth and stone and boulder content for carbon inventories in formerly glaciated subarctic soils

High latitude soils are estimated to store a considerable part of the global pool of soil organic carbon (SOC). Studies of global and regional SOC pools have estimated total inventories in northern Sweden’s subarctic region to fall within 10-50 kg m-2. However, correction factors for stone and boulder content of soils are often overlooked in SOC-studies and soil profiles are commonly normalized to a depth of 1 m, which can result in substantial overestimates of the SOC pool if a large part of the soil volume is occupied by stones/boulders or if the soil depth is shallower than 1 m. This study was performed to quantify SOC in soils of the Torneträsk catchment area using detailed measures of soil depth and stone/boulder contents. Two non-destructive sampling methods, ground penetrating radar (GPR) and rod penetration, were used to measure soil depth and stone and boulder content in the catchment area. Results show that average soil depth (n = 52344) varied between 0.95 – 2.14 m depending on elevation and the average mire depth was 0.63 m. Stone and boulder content of the soil was estimated to 49 – 68 % depending on elevation. The results were added to existing carbon and soil density data from the Torneträsk catchment area and total SOC inventories were calculated to 6.8 – 13.1 kg m-2. The results of this study indicate that previous studies on regional and global scale may have overestimated the SOC pools in the subarctic regions of northern Sweden