Lawrence Berkeley National Laboratory

Estimating carbon (C) balance in erosional and depositional landscapes is complicated by the effects of soil redistribution on both net primary productivity (NPP) and decomposition. Recent studies are contradictory as to whether soil erosion does or does not constitute a C sink. Here we clarify the conceptual basis for how erosion can constitute a C sink. Specifically, the criterion for an erosional C sink is that dynamic replacement of eroded C, and reduced decomposition rates in depositional sites, must together more than compensate for erosional losses. This criterion is in fact met in many erosional settings, and thus erosion and deposition can make a net positive contribution to C sequestration. We show that, in a cultivated Mississippi watershed and a coastal California watershed, the magnitude of the erosion-induced C sink is likely to be on the order of 1 percent of NPP and 16 percent of eroded C. Although soil erosion has serious environmental impacts, the annual erosion-induced C sink offsets up to 10 percent of the global fossil fuel emissions of carbon dioxide for 2005.