Abstract: The alpine grassland in the source of the Changjiang River has degraded to different degrees, resulting in an increasing trend of local soil erosion. To study the effect of alpine grassland degradation on soil detachment rate, we conducted runoff scour experiments on slopes with different vegetation degradation degrees. Results show that the average detachment rate of alpine meadow soil on fully degraded slopes is 0.54 g/(cm²·min), significantly higher than those on severely (0.34 g/(cm²·min)) and moderately degraded slopes (0.12 g/(cm²·min)), and much more higher than that on lightly degraded slopes (0.03 g/(cm²·min)). The average detachment rate of lightly frigid calcic soils on fully degraded slopes is 4.29 g/(cm²·min), 3.25, 7.27 and 7.94 times that of frigid calcic soil, meadow swamp soil and alpine meadow soil, respectively. Soil detachment rates on slopes of different degradation degrees have a good linear or power function relationship with the increase of shear force of water flow, runoff power and unit energy of water cross section, but have the best fitting effect with water flow power. Under the same flow power condition, soil detachment rate in the source region of the Changjiang River is higher than those in the southwest and the loess plateau. The findings can provide reference for studying soil erosion mechanism and optimal allocation of soil and water conservation measures in the source region of the Changjiang River.

Key words: headwaters of the Changjiang River, alpine grassland, soil erosion, vegetation degradation, soil detachment rate