Accelerated soil erosion shifts the location and fate of terrestrial carbon by moving particulate organic carbon (POC) and dissolved organic carbon (DOC) from upland soils into rivers, floodplains, reservoirs, and coastal zones. Rattan Lal Ohio State University has long emphasized that erosion redistributes soil organic carbon and can both deplete source soils and bury carbon elsewhere. David R. Montgomery University of Washington documents how human land use intensifies sediment and carbon fluxes and alters where carbon is stored or released.
Mechanisms of mobilization and transformation
Erosion detaches carbon-rich soil particles and mobilizes dissolved compounds. During transport, physical abrasion and changing oxygen exposure increase the fraction of carbon that becomes available for microbial decomposition, raising the chance of mineralization to CO2. At the same time, some mobilized POC is rapidly buried in floodplain or reservoir sediments under anoxic conditions, where it is less likely to be respired and may be preserved for decades to centuries. The balance between these pathways depends on transport distance, hydrology, and sediment deposition patterns.
Downstream fates and climatic implications
Downstream consequences are mixed. Sediment burial in depositional environments can act as a carbon sink, sequestering material removed from eroding landscapes. Conversely, increased DOC export fuels aquatic respiration and may enhance CO2 and methane emissions along river networks and from reservoirs. In coastal systems, buried sediment carbon can contribute to long-term sequestration, but nutrient co-transport with sediments also promotes eutrophication and hypoxia, altering greenhouse gas fluxes and ecosystem services. Human activities such as intensive agriculture, deforestation, and dam construction influence these outcomes by changing erosion rates, sediment connectivity, and residence times.
Context matters: in steep, highly erodible landscapes most mobilized carbon reaches rivers quickly and has greater opportunity for mineralization, while in flat or vegetated corridors more material is likely to be trapped and buried. Policy-relevant implications include the promotion of soil conservation to reduce net carbon loss and careful management of reservoirs and floodplains to reduce greenhouse gas emissions. Accurately assessing whether accelerated erosion is a net source or sink of atmospheric carbon requires integrated monitoring across hillslope, river, and coastal systems and collaboration between soil scientists, hydrologists, and resource managers.