Soil Organic Carbon Loss through Water Erosion in Loess Hilly Region of Northwestern China

Soils are a major reservoir of global carbon. Loss of agricultural soil carbon through erosion, management, and decomposition adds to the atmospheric loading of CO₂. Soil erosion is a major driving force to help release the soil carbon to waterbodies and the atmosphere. The present study monitored transportation of SOC accompanying with soil erosion process at field runoff plots in the loess hilly region of Ansai, Shaanxi, China. The results show the SOC loss amount was mainly influenced by soil erosion intensity, linearly increasing with soil erosion intensity. Soil erosion occurred much intensively on the slopes of 20° and 30°. The organic carbon (OC) concentration in sediment decreased as a power function with increasing soil erosion intensity. Organic carbon enrichment ratio (ERoc) was negatively related to the increasing slope gradient, declining from 4.36 at the slope of 10° to 2.50 at the slope of 30°. According to the plot monitoring data, the annual SOC loss amount in this loess hilly region is estimated up to 71.8 tons.