Characteristics of sediment sorting and sediment bound organic carbon loss during soil erosion under different soil organic carbon levels.

introductionSoil erosion-induced soil organic carbon (SOC) loss is a key driver of land degradation. SOC acts as both the target of loss and a key property influencing erosion processes. However, the mechanisms through which SOC content influences SOC loss during erosion, particularly its linkage to sediment sorting, remain unclear.

objectivesThis study aimed to investigate the effects of SOC content on sediment yield, sediment sorting characteristics, and sediment-bound organic carbon (SBOC) loss, and explore their interrelationships.

methodsSix soil with varying SOC contents were tested under simulated rainfall with varying rainfall intensities and slopes. Runoff samples were collected to analyze sediment yield, sediment effective particle size distribution, and SBOC loss.

resultsSOC reduced sediment yield by enhancing aggregate stability. Andstream power was the optimal predictor of sediment yield. The enrichment ratios (ER) of < 0.002 mm, 0.002-0.02 mm, and 0.02-0.05 mm particles in sediment decreased as a power function with increasing SOC content, whereas the ER of > 0.05 mm particles increased. Sediment sorting weakened with increasing SOC content, as evidenced by ER values approaching 1 across all particle sizes in soils with higher SOC. In addition, SOC exhibited dual effects on SBOC loss, namely increasing carbon sources to promote SBOC loss while simultaneously stabilizing soil structure to reduce SBOC loss. However, the carbon source effect was dominant in this study, leading to a logarithmic increase in SBOC loss rate with increasing SOC content. Further analyses revealed that SBOC concentration was mainly dominated by sediment sorting and soil properties, whereas SBOC loss rate was mainly driven by the coupling of flow hydraulics and sediment yield.

conclusionThese findings clarifies the mechanisms linking SOC content to SBOC loss and sediment sorting, providing a theoretical foundation for improving carbon-loss modeling and erosion control strategies.