Forms and Fluxes of Soil Organic Carbon Transport via Overland Flow, Interflow, and Soil Erosion

Core Ideas Interflow is another crucial route of soil organic carbon lateral transport. Overland flow, interflow, and sediment contributed 5, 24, and 71%, respectively, of annual loss loads of soil organic carbon lateral transport. Dissolved organic carbon is another important component for SOC lateral transport. The contributions of hydrological pathways (including overland flow, interflow, and soil erosion) to lateral soil organic carbon (SOC) transport have remained unclear until now. Hillslopes were monitored using free‐draining lysimeters (8 m by 4 m) to quantify dissolved organic carbon (DOC) losses due to overland flow and interflow and the total organic carbon (TOC), water extractable organic carbon (WEOC), particulate organic carbon (POC), and mineral‐associated organic carbon (MOC) fractions in sediments from sloping croplands containing Regosols in Southwest China. The average annual DOC losses due to overland flow and interflow were 158.8 ± 33.0 and 750.4 ± 79.3 mg C m–2, respectively, and the TOC lost with sediment was 2201.0 ± 429.2 mg C m‒2. Overland flow, interflow, and sediment accounted for 5, 24, and 71%, respectively, of the annual SOC losses. The average annual DOC, POC, and MOC loss fluxes were 918.6 ± 115.3, 375.2 ± 94.4, and 1816.4 ± 331.8 mg C m–2, respectively. The MOC contents in the sediments were positively correlated with rainfall, and the DOC concentrations in the interflow water were negatively correlated with rainfall. In conclusion, soil erosion is the dominant hydrological route for lateral SOC transport, and interflow is another crucial route that is usually underestimated. Soil organic C is mainly lost in the forms of MOC and DOC, which is an important component of water ecosystems. Therefore, the mitigation of SOC losses would be more effective if soil erosion and interflow conservation practices were adopted together, particularly for Regosols on hillslopes.