Vegetation restoration restrains rill erosion on slag heaps in high-altitude goldfields

Soil erosion leads to soil degradation and depletion of land resources, posing a significant threat to industrial production and ecological sustainability. In high-altitude regions, rill erosion is the main form of soil erosion in mining areas, however, our understanding of morphology and developmental characteristics of rills and the mechanisms influencing them remains limited. In this study, data were collected from 96 rill plots across two gold mines in the eastern Tibetan Plateau according to vegetation restoration modes (natural restoration (CK) and planted with Elymus dahuricus (ED), Medicago sativa (MS), and multi-plant mixed (Avena fatua L. + Elymus dahuricus + Medicago sativa + Oxytropis coerulea, MM)) and restoration periods (1 year, 3 years, 4 years, and 6 years). We investigated the variations of 7 indicators that can reveal rill morphological and developmental characteristics across different restoration modes and restoration periods, and utilized a partial least squares structural equation model (PLS-SEM) to analyze the effects of 15 indicators from topography, soil, and vegetation on rill erosion modulus (REM). The results indicated that artificial vegetation restoration effectively restrained rill development, notably by decreasing the frequency of wider (>15 cm) and deeper (>10 cm) rills when compared to CK plots. Planting MM and ED exhibited greater efficacy in controlling rill erosion than planting MS. However, the effectiveness of planting ED in controlling rill erosion gradually weakened with time, while MM consistently maintained a strong inhibitory effect. Topographic features, soil texture, and vegetation significantly influenced the REM through direct or indirect effects. Plant root functional traits were the main driving factors in reducing REM, affecting not only REM directly but also influencing vegetation-induced soil properties to indirectly effect REM.