Effects of Hydraulic Erosion on the Spatial Redistribution Characteristics of Soil Aggregates and SOC on Pisha Sandstone Slope

Under the long-term effects of hydraulic erosion, soil particles and nutrients are continuously lost and enriched in the process of runoff and sediment movement, leading to a change in soil organic carbon (SOC) in different spatial positions on the slope, which is closely related to the carbon balance of the ecosystem. Therefore, the changes in slope erosion intensity and the spatial redistribution characteristics of soil aggregates and SOC under water erosion conditions were quantitatively analyzed by combining field runoff plots with three-dimensional (3D) laser scanning technology. The results showed that: (1) After rainfall, the slope erosion intensity successively declined from the upper to the lower parts of the slope, and the content of soil aggregates in each soil layer changed obviously. The loss of 1–2 mm soil aggregates was the largest in the sedimentary area of the 2–4 cm soil layer, at 0.38 g/kg. The concentration of 0.5–1 mm soil aggregates was the largest in the micro-erosion area of the 2–4 cm soil layer, at 0.36 g/kg. (2) After rainfall, the overall SOC on the slope showed a loss state in the 0–2 cm soil layer and an enrichment state in the 2–4 cm soil layer. Among them, the loss of SOC in the medium erosion area of the 0–1 cm soil layer was the largest, and its content decreased by 57.58%. The enrichment in the 2–4 cm soil layer was the maximum in the micro-eroded area, with a content increase of 79.23%. (3) Before and after rainfall, the SOC of each soil layer was positively correlated with small aggregates, and the correlation gradually tended to be negative with the increase in the particle size of soil aggregates, and the SOC showed a negative correlation with large aggregates (>2 mm).