Study On The Characteristics Of Slope Runoff And Sediment Yield Of Degraded Alpine Meadow In The Three-river Headwaters Region

The high elevation of the Qinghai-Tibet Plateau determines the particularity of its natural conditions and its sensitivity to climate change,since the 1990 s,90% of the alpine meadows in the region have been degraded to varying degrees due to climate change and human activities,and soil erosion is becoming more and more serious.Therefore,this study takes lightly,moderately and severely degraded alpine meadows in the Qinghai-Tibet Plateau as research objects.The changes of vegetation and soil characteristics of different degradation and the process of runoff and sediment production on slopes were explored through field investigate the combination of sample acquisition,artificial simulation rainfall.The objectives of the study were to determine soil erosion process of degraded alpine meadow on slope,and to reveal the soil erosion mechanism of degraded alpine meadows.The results may provide a basic for soil erosion regulation of degraded alpine meadows on the Qinghai-Tibet Plateau.The main results were as follows:(1)Vegetation degradation leads to a significant decrease in vegetation coverage and biomass of alpine meadows,aggravates soil erosion and soil nutrient loss,leads to soil degradation,and further affects the ecological function of meadow ecosystem.As the degradation of alpine meadows,the vegetation coverage,aboveground and belowground biomass,root-soil volume ratio decreased by 69.86%,50.00%,90.48%,85.25%,respectively.The species diversity index increased first and then decreased,and reached the maximum in the moderately degraded meadow.Soil water content decreased by 39.39%,soil bulk density increased by 23.06%,soil total porosity decreased by 12.00%,soil water holding capacity decreased.The content of soil carbon,nitrogen and phosphorus decreased by 78.09%,50.91%,20.53%,respectively.Soil shear strength decreased by 75.06%,the structural stability of soil water-stable aggregates decreased,the soil erosion resistance decreased sharply,and the surface soil erodibility increased significantly.(2)With the aggravation of alpine meadow degradation,the erosion and sediment carrying capacity of slope runoff to surface soil increased,which intensified slope soil erosion.When the rainfall intensity was 30 mm/h,compared to lightly degraded meadows,the runoff volume of moderately degraded meadow and severely degraded meadow decreased by 76.70%and 6.00% respectively,and the cumulative infiltration increased by 58.61% and 15.77%,respectively.The sediment yield of moderately degraded meadow and severely degraded meadow was 1.87 and 9.31 times that of lightly degraded meadow,respectively.When the rainfall intensity was 60 mm/h,compared to lightly degraded meadows,the runoff volume of moderately degraded meadow and severely degraded meadow decreased by 54.96% and 32.25%respectively,and the cumulative infiltration increased by 73.97% and 48.71%,respectively.The sediment yield of moderately degraded meadow and severely degraded meadow was 2.62 and 9.15 times that of lightly degraded meadow,respectively.When the rainfall intensity was90 mm/h,compared to lightly degraded meadows,the runoff volume of moderately degraded meadow and severely degraded meadow decreased by 39.84% and 4.21% respectively,and the cumulative infiltration increased by 67.23% and 19.34%,respectively.The sediment yield of moderately degraded meadow and severely degraded meadow was 5.13 and 12.38 times that of lightly degraded meadow,respectively.(3)The degree of meadow degradation and rainfall intensity and their interaction had a significant effect on slope runoff,sediment volume and sediment concentration.The soil physicochemical properties of alpine meadow are closely related to the slope runoff and sediment yield,which is significantly positively correlated with the fractal dimension of soil aggregates,and soil erodibility,and negatively correlated with soil organic matter and the geometric mean diameter of the aggregates.In the same rainfall intensity,the difference of slope hydraulic parameters of different degraded meadows is significant,and the hydraulic parameters such as average velocity of slope flow,resistance coefficient and manning coefficient have a power function relationship with the slope sediment yield of degraded meadows.Degraded alpine meadow changes the plant community composition,which deteriorates the soil structure and weakens the erosion resistance of the soil,thus affecting the process of runoff and sediment yield.Lightly degraded meadows are characterized by high runoff and low sediment yield,allowing them to maintain surface runoff while controlling erosion.Moderately degraded meadows have high soil infiltration rates and low sediment yield,while severely degraded meadows have high runoff and sediment yield.Therefore,it is of great importance to take appropriate measures to strengthen the ecological protection of alpine meadows,prevent their serious degradation and thus maintain the sustainability of meadow ecosystems to protect the ecological environment and regional soil and water conservation in the Three-River headwaters region.