Hydraulic erosion response of pika mound slopes to vegetation restoration in the source region of the Yellow River

This study employed artificial simulated rainfall erosion experiments to investigate the response mechanisms of plateau pika mound patches to soil erosion and nutrient loss in the alpine meadow region of Henan County, Qinghai Province, China. The objectives were to elucidate the hydraulic erosion characteristics of pika mound patches, the patterns of soil nutrient loss during different vegetation recovery stages, and the influence of vegetation recovery on slope hydraulic erosion. The results showed that: (1) With increasing slope gradient, both the physical-mechanical properties and biological characteristics of soil in pika mound patches declined under the same recovery period. However, under identical slope gradients with varying recovery periods, soil loss volume initially increased and then decreased with rainfall duration, with the 15–20 min interval identified as the sensitive period for soil loss; soil sediment yield exhibited a sharp initial increase followed by a gradual decline, peaking between 20 and 25 min. (2) Nutrient loss rates followed the order: organic matter > available potassium > total potassium > alkali-hydrolyzable nitrogen > available phosphorus > total nitrogen > total phosphorus. Soil nutrient loss was most pronounced during the 2–3 year recovery period. Average flow velocity, Reynolds number, and Manning's roughness coefficient were identified as the primary controlling factors influencing soil nutrient loss. (3) Correlation analysis revealed a significant negative relationship (P < 0.05) between the biotic characteristics of rodent mound patches and soil loss rates. Runoff width, average flow velocity, Reynolds number, and Manning's roughness coefficient were all significant factors influencing soil nutrient loss (P < 0.05). (4) Structural equation modeling indicated that vegetation and soil properties significantly altered slope hydrodynamics, with vegetation characteristics in pika mound patches exerting indirect effects by influencing soil physical and mechanical properties. The study demonstrates that during vegetation recovery, pika mound patches in alpine regions enhance erosion suppression over time through improved soil and biological properties, thereby effectively reducing soil erosion risk.