Decoupling analysis of soil properties and slope-position interactions affecting erosion rates on long gentle slopes

Abstract

Soil erosion exhibits significant spatial heterogeneity and scale dependence. The relative uniformity of external conditions along the slope magnifies existing differences in soil properties, thereby reinforcing a dynamic feedback loop. Consequently, this study aimed to elucidate the mechanistic role of internal soil factors, with a particular focus on the hierarchical coupling between slope-scale response parameters and localized regulatory factors. A field investigation was conducted on a rolling hillslope in Northeast China. Cesium-137 (¹³⁷Cs) radionuclide tracing was employed to quantify soil redistribution patterns, and soil parameters (aggregate stability, chemistry, fractal structure, and physical texture) were measured to explain spatial variations in erosion. The results showed that the synergistic effect of soil organic carbon (SOC) and pH played a key parameter influencing erosion processes, explaining up to 60 % of the variation in erosion rates. Soil moisture content served as an intrinsic regulatory factor, and at a moderate level (13.97 %), SOC exhibited a stable and significant resistance to erosion within a pH range of 5.23–6.32. The upper slope was primarily influenced by the coupled process of clay particles swelling and dispersion (contributing 62.3 %); the middle slope experienced cumulative effects of internal soil structure and runoff disturbance, leading to magnified erosion rates (21.3 % and 30.5 %, respectively); the lower slope was highly sensitive to the combined effects of raindrop impact and runoff disturbance, contributing 47.6 %. An increased proportion of the 0.2–0.1 mm aggregate fraction significantly intensified erosion, while the 0.5–0.2 mm fraction acted as an effective indicator of particle sorting and spatial redistribution. These findings provide a scientific basis for developing precision soil management strategies in agricultural landscapes.