The significance of the erosion-induced terrestrial carbonsink

Estimating carbon (C) balance in erosional and depositionallandscapes is complicated by the effects of soil redistribution on bothnet primary productivity (NPP) and decomposition. Recent studies arecontradictory as to whether soil erosion does or does not constitute a Csink. Here we clarify the conceptual basis for how erosion can constitutea C sink. Specifically, the criterion for an erosional C sink is thatdynamic replacement of eroded C, and reduced decomposition rates indepositional sites, must together more than compensate for erosionallosses. This criterion is in fact met in many erosional settings, andthus erosion and deposition can make a net positive contribution to Csequestration. We show that, in a cultivated Mississippi watershed and acoastal California watershed, the magnitude of the erosion-induced C sinkis likely to be on the order of 1 percent of NPP and 16 percent of erodedC. Although soil erosion has serious environmental impacts, the annualerosion-induced C sink offsets up to 10 percent of the global fossil fuelemissions of carbon dioxide for 2005