Effects of rock fragment coverage on soil erosion: Differ among rock fragment sizes?

Abstract

The presence of rock fragments can change land cover and thus profoundly perturb soil erosion process. This study aimed to identify the effects of rock coverage on soil erosion, and how such effects were influenced by rock fragment sizes. A series of simulated rainfall experiments were applied to erosion plots with two initial soil moisture contents (dry run and wet run), under rock fragment coverage (15%, 30%, 45%, 60%) composed of eight different fragment sizes (0.7, 1.1, 3.0, 5.5, 12.0, 18.8, 26.4, 36.0 cm) from May to September in 2021. The results show that total runoff and sediment concentration increased with rock fragment size. When rock fragments with the sizes were less than 12.0 cm, the total runoff and sediment concentration were respectively 0.81–16.02% and 16.45–50.88% lower than the bare soil. Consequently, the soil loss decreased exponentially with rock fragment coverage. When rock fragment with the sizes were large than 12.0 cm, they decreased sediment concentration by 7.91–33.32% in the dry run, but increased the total runoff by 0.26–10.28% and sediment concentration by 9.33–82.91% in the wet run. As a result, the soil loss ratio firstly enhanced as rock fragment coverage up to 45% and then declined at the rock fragment coverage of 60%. Our findings demonstrate that the effects of rock fragment coverage on soil erosion are rock fragment size dependent. This can help to better parameterize the effects of rock fragment coverage in current soil erosion models, in turn providing guiding information for soil erosion control in stony regions.