Seasonal variation in soil erosion resistance of gullies covered by different plant communities on the Loess Plateau of China

Abstract

Vegetation growth can effectively alter near soil surface characteristics of plant communities, which is likely to impact the seasonal variation in soil erosion resistance of gullies, particularly in semi-arid and arid regions. However, few studies have been focused on quantifying the temporal variations in soil erosion resistance of gullies restored with different vegetation communities at the seasonal scale. This study investigated the seasonal variation in soil erosion resistance of gullies covered by five different plant communities on the Loess Plateau. The experiment was conducted 7 times from 15 May to October 4, 2023 at an approximately 3-week interval. For each time, 90 natural undisturbed topsoil samples were carefully collected from the bottom, left, and right banks of each gully. The collected samples were subjected to scouring under different hydraulic conditions to measure soil detachment capacity and then to determine soil erosion resistance, reflected by rill erodibility (K_r) and soil critical shear stress (τ_c). Near soil surface characteristics of plant community were also measured at the same sites with an identical frequency. The results showed that soil erosion resistance differed significantly for gullies covered by different plant communities. The mean K_r of grass communities was 0.17 m s⁻¹, which was 47.8 % and 30.6 % to that of shrub and forest communities, respectively. The mean τ_c of grass communities was 1.45 and 1.26 times that of shrub and forest communities. During the vegetation growth season, soil erosion resistance of gullies covered by different plant communities increased gradually. The seasonal variations in soil erosion resistance were dominantly influenced by the temporal changes of soil cohesion (Coh), soil penetration resistance (PR), water stable aggregate (WSA), and root mass density (RMD). K_r decreased exponentially with Coh and WSA, and logarithmically with PR and RMD, while τ_c increased linearly with these four factors. Rill erodibility could be well estimated by Coh, PR, WSA, and RMD (R² = 0.91, NSE = 0.91). The results are conducive to insight into the seasonal variation in erosion of relatively stable gullies covered by vegetation in semi-arid regions.