Soil erosion and nitrogen loss characteristics of gravel-containing sloping farmland in the three gorges reservoir area

Study region: Three Gorges Reservoir (TGR) area, China. Study focus: Soil erosion and associated nitrogen loss from sloping farmland present a critical global environmental challenge. However, research on how hydrodynamic characteristics influence soil erosion and nitrogen loss in gravel-containing sloping farmland remains limited. To address this knowledge gap, we conducted simulated rainfall experiments on gravel-containing sloping farmlands to further clarify the regulatory roles and impact pathways of hydrodynamic parameters in processes. New hydrological insights: Gravel content significantly reduced infiltration rate and increased runoff rate. Sediment yield peaked at 20 % gravel content. Nitrate nitrogen (NO3-) loss in runoff consistently exceeded ammonium nitrogen (NH4+) loss. Gravel notably increased Stream power (ω), and the enhanced runoff further intensified the disparity between NO3- and NH4+ loss in runoff. Model fitting showed that gravel amplified the effects of rainfall intensity and slope gradient on soil erosion and nitrogen loss. Partial Least Squares Structural Equation Model (PLS-SEM) revealed that experimental variables influenced nitrogen loss both directly through hydrodynamic parameters (path coefficient = 0.346) and indirectly via erosion characteristics mediated by hydrodynamics (path coefficient = 0.389). These insights underscore that managing the hydrodynamic processes, for instance by increasing Darcy-Weisbach friction factor (f), is key to controlling soil erosion and nitrogen loss in gravel-containing sloping farmland.