Enrichment of organic carbon in sediment under field simulated rainfall experiments

A better understanding of the transport processes of soil organic carbon (SOC) during soil erosion is critical for evaluating the carbon fate and subsequent dynamics. This study was designed to reveal the effects of rainfall intensity and rainfall duration on enrichment ratio of organic carbon (ERoc) in sediment and conduct a preliminary explore on the enrichment mechanisms. Field rainfall simulation experiments at 2 m (width) × 5 m (length) plots were conducted to assess the selective transportation of SOC. The ERoc in sediment as well as the sediment particle size distribution was monitored during the erosion processes. The relationships between ERoc and ERclay were also studied. The results showed that the ERoc ranged from 0.61 to 2.13 and was inversely related to rainfall intensity and rainfall duration. Three trends (exponential decline, Gaussian distribution and disorder variation) were observed in ERoc when varied with rainfall time. Whereas the ERoc values decreased with rainfall intensity, and negative correlations were found between ERoc and the sediment yield or runoff volume. These results indicate that the SOC migration is a selective process, which is based on erosion process. In addition, the transportation of clay takes precedence over sand and presents highly selective migration capacity. Significant correlations between ERclay and ERoc were found in some but not all rainfall events. This suggests that the selective transportation of clay or finer particles is one of the many reasons for the enrichment of OC in sediment, but the specific enrich mechanisms should be studied in the future.