Soil loss and sedimentation rates in a subcatchment of the Yellow river Basin in China

Soil loss by water erosion is one of the main threats to soil health and food production in intensively used agricultural areas. To assess its significance to overall sediment production, we applied the Water and Tillage Erosion Model/Sediment Delivery model (WaTEM/SEDEM) to the Luoyugou catchment, a subcatchment of the Yellow River Basin within the Chinese Loess Plateau. WaTEM/SEDEM considers rill and interrill erosion and deposition rates to calculate the sediment yield rates leaving the catchment. Terraces were established in the 1990s to reduce soil loss in this area, but no soil erosion modeling has been published regarding the effect of this mitigation measure. Therefore, we applied 1000 Monte Carlo simulations of the WaTEM/SEDEM, and the modeled average soil loss by rill and interrill erosion for 2020 was 12.2 ± 0.5 t ha−1 yr−1, with a sediment yield at the outlet of 53,207.8 ± 11,244.1 t yr−1. The results indicated that the terracing reduced gross soil loss rates (from 51.8 t ha−1 yr−1 in 1986 to 12.2 ± 0.5 t ha−1 yr−1 in 2020), while land cover changes, mainly the conversion of forests and grassland, partly counteracted the mitigation (combined effect: 76% reduction). Modeled sediment loads by rill and interrill erosion accounted for 22.8% of the total long-term sediment production recorded by flow discharge measurements. Other processes not considered by the model, such as landslides, gully erosion, riverbank erosion, and sediment production by construction, seem to predominantly influence the overall sediment yield. Considering years with baseline sediment production only, the measured and modeled sediment yields compared favorably, indicating that the latter processes primarily contribute during extreme events.