Soil erosion, soil and water conservation and water environment coupling in the Luofu River watershed, Dongjiang River Basin

Soil erosion and its coupled interaction with water environment have become critical threats to drinking water security in the hilly red soil regions of southern China. This study targeted the Luofu River Watershed, a typical agricultural headwater catchment in the upper reaches of Dongjiang River Basin. We integrated the Revised Universal Soil Loss Equation (RUSLE), field monitoring, geospatial analysis, and principal component analysis (PCA), coupling coordination degree model and Pearson correlation analysis to systematically quantify the spatiotemporal patterns, driving mechanisms of soil erosion, its coupling relationship with water environment, and the comprehensive efficiency of soil and water conservation (SWC) measures. The results revealed that hydraulic erosion is the dominant erosion type across the watershed. The average soil erosion modulus was 892 t·km⁻²·a⁻¹, which falls into the mild erosion grade at the watershed scale, while local high-intensity erosion hotspots were widely distributed. Moderate and intense erosion areas only accounted for 8.38% of the total watershed area, and these regions were mainly concentrated in densely populated agricultural villages. Sloping farmland acted as the primary sediment source, contributing 67.2% of the total soil loss. Significant positive coupling relationships were detected between soil erosion and water quality degradation: the erosion modulus showed extremely significant positive correlations with sediment concentration and total phosphorus (TP) concentration, with correlation coefficients of 0.96 and 0.93 respectively ( P < 0.001). TP derived from soil erosion contributed 78.5% to the total agricultural non-point source TP loading, which pushed the water environment carrying capacity (WECC) close to the early warning threshold. Natural factors explained 58.2% of the total variability in soil erosion, among which topographic (LS) factor and rainfall erosivity (R) were the dominant natural controls. Anthropogenic activities accounted for 41.8% of erosion variation and served as key amplifiers for local high-intensity erosion. The combined application of engineering, ecological and agronomic SWC measures reduced total soil loss by 60.1% and TP loading by 45.8%. The zoned classified management framework proposed in this study can provide scientific support for soil erosion control and drinking‑water‑source protection within the Luofu River watershed in the upper Dongjiang River Basin, and may serve as a potential practical reference for comparable small agricultural headwater catchments in southern China’s red‑soil hilly regions. Further local calibration would be required before direct application to other watersheds.