Effects of microtopography on sediments eroded from bare slopes of zokor mounds in the Yellow River source area, Western China

The mound-making behavior of plateau zokors is one of the most important factors in remodeling meadow microtopography and causing soil erosion in the Yellow River source area of western China, but little is known about the effects of microtopography on particle size characteristics (PSC) of eroded sediments from the bare slopes of zokor mounds during different rainfall events. In this study, we analyzed the relationship of microtopographic features derived from laser point cloud data and PSC of eroded sediments at six simulated rainfall intensities (all lasting 60 min). The effects of microtopography on PSC of eroded sediments were studied via partial least squares regression (PLSR) and structural equation modeling (SEM). The results showed that: (1) 15-20 minutes from the beginning of rainfall was the sensitive period of soil loss from the slopes, and the function relationship between the rate of sediment and runoff and rainfall intensity can better predict the development trend of soil erosion; (2) Intense erosion occurred mainly in the upper half of the zokor mound, while deposition was mainly limited to its lower half. It is suggested that diminished plateau zokor activity intensity can effectively prevent and control soil erosion; (3) The PSC of eroded sediment is dominated by silt, followed by sand, with clay being the least abundant, and the eroded sediments with a particle size of 10-20 μm were sensitive and highly susceptible to rainfall erosion. This finding facilitates the understanding of the formation process of surface geomorphology and the mechanism of soil erosion; (4) The PLSR model indicates that microtopography has an extensive influence on eroded sediments during hydraulic erosion, and the SEM analysis results further confirm that the fractal dimension was the best parameter to represent the PSC of eroded sediments, whereas surface cutting degree was the dominant factor controlling the PSC of eroded sediments. These findings are crucial for predicting soil erosion in the Yellow River source area and provide a new perspective for understanding soil erosion mechanisms in alpine meadow ecosystems.