Changes in Total Organic Carbon in Sediment Produced Via Interrill Erosion at Low and High Kinetic Energy.

Interrill erosion mobilizes fine particles at the land surface due to its selective nature and generally low transport capacity. Thus, this form of erosion is likely the only process that can systematically remove organic carbon (OC) in large quantities. The objective of this work was to analyze relationships among wetting rate (kinetic energy), particle movement, particle size distribution and the amount of OC released in sediment under low slope conditions. A field rainfall simulation experiment was performed on two soils differing in texture, both intensively tilled and no-tilled. Despite soil texture differences, soil loss depended largely on tillage and kinetic energy. Sediment particle size distribution was changed by treatments, even in those cases where soil loss was not influenced by treatments. The fraction of particles smaller than 0.053 mm was always high, independent of wetting rate (kinetic energy). An equation relating soil loss to soil carbon loss was derived for these data. The initial OC loss was related to texture, but not to total soil organic carbon (SOC), suggesting particle adsorption of OC during transport. No relationship was found between water stable aggregates (WSA) and SOC, or between WSA and OC loss, which suggests that OC found in sediment is a labile form of SOC. When the sediment to soil OC enrichment ratio (EROC) was plotted against rainfall duration (time), and then modeled with an exponential equation, the initial value of EROC found for the model was not related with any measured soil parameter. Thus, we assumed that OC enrichment of moving particles depended on overland flow during transport. The increase in EROC with time was related to SOC, but not to WSA, which suggests that with aggregate rupture only labile OC was responsible for increased EROC.