Fates of eroded soil organic carbon: Mississippi Basin case study

We have developed a mass balance analysis of organic carbon (OC) across the five major river subsystems of the Mississippi (MS) Basin (an area of 3.2 × 10⁶ km²). This largely agricultural landscape undergoes a bulk soil erosion rate of ∼480 t·km⁻²·yr⁻¹ (∼1500 × 10⁶ t/yr, across the MS Basin), and a soil organic carbon (SOC) erosion rate of ∼7 t·km⁻²·yr⁻¹ (∼22 × 10⁶ t/yr). Erosion translocates upland SOC to alluvial deposits, water impoundments, and the ocean. Soil erosion is generally considered to be a net source of CO₂ release to the atmosphere in global budgets. However, our results indicate that SOC erosion and relocation of soil apparently can reduce the net SOC oxidation rate of the original upland SOC while promoting net replacement of eroded SOC in upland soils that were eroded. Soil erosion at the MS Basin scale is, therefore, a net CO₂ sink rather than a source.