Effects of hillslope aspect on erosion rate of alpine meadows in the Three-River Headwater Region, China

• Published in: Catena (Giessen) 2024-04, Vol.239, p.107971, Article 107971
• Main Authors: Li, Li, Liu, Jing, Liu, Honghu, Sun, Baoyang, Zhang, Zhihua, Shi, Zhe, Ren, Feipeng, Li, Jianming
• Format: Article
• Language: English
• Subjects: 137Cs; Hillslope aspect; Soil erosion; Soil water content; Three-River Headwater Region
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/j.catena.2024.107971

•Soil erosion rate was 3 times greater on the south-facing hillslope as compared to the north-facing hillslope.•Soil water content was the dominant factor causing the difference in erosion rates under a water-limited condition.•Greater soil erosion rates resulted in elevational distributions of soil physicochemical properties on the south-facing hillslope. Soil erosion causes serious grassland degradation in the Three-River Headwater Region (TRHR) of the Qinghai-Tibet Plateau. Identifying source areas of erosion is important, including understanding the influences of hillslope aspect on soil erosion. However, the effect of hillslope aspect on soil erosion is a much-debated process, wherein contrasting results were previously reported. We hypothesized that aspect-induced differences in environmental variables will be related to differences in erosion magnitude and spatial pattern, and that these differences will impact soil physiochemical characteristics as well. To test this hypothesis, soil samples were collected at conjoined south- and north-facing hillslopes along elevational profiles in a small watershed in Yushu County, with measurements of soil water content (SWC), soil organic carbon (SOC), soil organic matter (SOM), soil particle size distribution, soil total nitrogen (STN) and phosphorus (STP). Soil erosion rate was estimated using 137Cs technology. The results showed that soil erosion rates of the two hillslopes ranged from 0.073 to 10.83 t ha-1 yr-1, and were 3 times greater on the south-facing hillslope. Soil water content ranged from 7.6% to 76.8% on the two hillslopes with lower values on the south-facing hillslope due to the greater solar radiation. By Spearman correlation analysis and path analysis, we concluded that lower soil water content on the south-facing hillslope restricts vegetation growth, and hence resulting in greater soil erosion under the case where vegetation growth is dominantly controlled by water availability. Greater soil erosion on the south-facing hillslope caused greater surficial accumulation of coarser materials and greater loss of soil nutrients, which are expected to complicate the hydrological erosion process. Moreover, the downslope increased soil erosion rate should be fully considered in conservation practices. These results will improve our understanding of the interaction and feedback mechanisms between soil characteristics, vegetation function, and soil erosion in the TRHR.