An approximate semi‐analytical model of sediment and nutrient transport on slopes under rainfall conditions

Under natural rainfall, the surface runoff erosion of sloping farmland tends to remove large quantities of soil particles and constitutes nonpoint source pollution. The existing sediment and nutrient loss models focus on estimating the total amount of pollutants in the long term. The Existing mathematical models that describe the nutrient loss process on slopes have some shortcomings, which have not accounted for the effect of infiltration on nutrient concentrations in the exchange layer before runoff starts. Here, an approximate semianalytical model of sediment yield and nutrient loss was based on surface runoff processes. Simulated rainfall experiments were performed to calibrate the model's parameters and verify its reliability. The established model incorporated raindrop splashing, diffusion, and water infiltration effects on nutrient transfer in the exchange layer. Raindrop splashing played a leading role in nutrient translocation from the exchange layer to runoff. The simulated runoff, sediment, and nutrient matched their measured values reasonably well (R2 > 0.8; Nash–Sutcliffe efficiency > 0.347). The model's sediment yield items were more sensitive to runoff erosion than splash erosion. The raindrop‐induced water transfer rate in the nutrient loss simulation dramatically affected the peak nutrient loss rates, whereas the depth of the exchange layer clearly affected the overall range of change in nutrient loss rate and boosted the total nutrient loss. Therefore, measures such as vegetation coverage or deep fertilization should be adopted to weaken raindrops’ kinetic energy and reduce nutrient concentrations in the exchange layer to prevent agricultural nonpoint source pollution in the Loess Plateau.