Response of soil aggregate stability and splash erosion to different breakdown mechanisms along natural vegetation restoration

Vegetation restoration may effectively improve aggregate stability and reduce soil erosion by increasing soil organic matter (SOM). Soil internal and raindrop impact forces are the main breakdown mechanisms of soil aggregates, and the main erosive factors that generate splash erosion. However, it remains unclear about how these forces affect the aggregate stability and the splash erosion during natural vegetation restoration. In this study, four soils at different succession stages (farmland, grassland, shrub, and forest) were selected. Deionized water and ethanol were employed to evaluate the effect of soil internal and raindrop impact forces on aggregate stability and splash erosion during vegetation restoration, by performing fast-wetting test and simulated rainfall experiment. Deionized water was used to simulate the combined effects of soil internal and raindrop impact forces, whereas ethanol was used to simulate the sole effect of raindrop impact force. The results indicated that soil organic matter (SOM) content, cation exchange capacity (CEC), specific surface area (SSA), and soil aggregate stability for the four soils increased with revegetation. The soil aggregate stability in deionized water test (MWDW) was lower than these in ethanol test (MWDE), and the relative difference of the MWD (R-MWD) decreased with revegetation. Besides, the splash erosion rate in deionized water test (S-W) was much higher than those in ethanol test (S-E). S-W and S-E decreased with the order of grassland < shrub < forest. With the increasing rainfall kinetic energy, splash erosion rates increased in both deionized water and ethanol tests; but the contribution rates of soil internal forces to rainfall splash erosion decreased. The overall results suggested that the process of vegetation restoration altered soil particle surface properties mainly due to the increase SOM, and decreased the net repulsive internal forces, which thereby improved aggregate stability and erosion resistance with revegetation.