LEGACY OF TOPOGRAPHY AND LAND USE ON EROSION AND SOIL ORGANIC CARBON BURIAL OVER DECADAL TIMESCALES

There is a growing body of evidence to suggest that soil erosion in agricultural landscapes can function as a net carbon (C) sink due to burial of carbon-rich topsoil at depositional sites. It has been argued, however, that soil organic carbon (SOC) degradation during erosion may represent an important source of C to the atmosphere and weaken the overall strength of the erosion-induced C sink. In this study we compare SOC in the top 1.5 m of soil in grassland and cropland landscapes and employ ¹³⁷Cs (from atmospheric testing of thermonuclear bombs) as a proxy for soil movement over the past half-century. Using soil depth and terrain attributes calculated from LiDAR-derived digital elevation models, we are able to account for 82 and 83% of the variability observed in SOC and ¹³⁷Cs content from grassland sites. For cropland sites, we are able to explain 78 and 50% of SOC and ¹³⁷Cs variability, respectively. For cropland sites, slope steepness and curvature play a stronger predictive role than in grassland sites. Comparing SOC and ¹³⁷Cs content between grassland and agricultural sites shows that there is not preferential SOC depletion in eroded soils. This suggests that over decadal timescales, for the soils studied here, erosion functions to redistribute SOC around the landscape but does not accelerate SOC decomposition beyond what can be replaced by primary productivity.