Study On The Variation In Hydrological Characteristics Of Alpine Meadow Soil In Biandukou Area In The Middle Reaches Of Hei River Basin

Because of the comprehensive effects of global climate change and human activities,the alpine meadow in the Hei River basin deteriorates severely in recent years:the rodent pest,the decline of grazing capacity and water conservation capacity,the reduction of basin area,soil erosion,the deteriorating ecological environment and growth ability of grassland.Dramatic changes in physical and chemical properties and hydrological characteristics of soil can lead to the degradation of alpine meadow.As one of the largest inland river basin in Northwest of China,Hei River basin has a significantly influence on the development level of region economy,the national stability and unity,as well as the living standard oflocal residents.Based on the hydrological characteristics of soil with different degradation degree of alpine meadow and shrub meadowin different soil depthin Hei River basin,the moisture retention capacity,soil chemical properties saturated hydraulic conductivity and soil fractal dimensionwere analyzedin this paper,in order to reveal the impact of alpine meadow degradation on the hydrological characteristics of soil in the Hei River basin.The conclusions are as follows:(1)Vegetation degradation causes dramatic effects on the soil environment of alpine meadow in the Hei River basin,and physicochemical properties of soil have a certain degree of degradation.Soil particle size analysis shows that surface soil with the depth of 0-20 cm has a lot ofcoarse sand and a little of gravel along with increasing of soil bulk density and saturated hydraulic conductivity,but decreasing of soil porosity.The chemical compositions of soil including soil organic matter,available nitrogen,available phosphorus,available potassium and pH,vary differently.The loss rate of the organic matter content of the surface soil with the depth of 0-15 cm is about 30.1%.The loss rate of available nitrogen,available potassium and available phosphorus content are 26.2%,56.3%and 58.5%respectively.Obviously,the degree of vegetation degradationis closely related to the variation in soil physical property.III(2)The characteristic curve of soil moisture can be fitted well to the power function equation8=aS-b which is developed by Gardnerand Van Genuehten,and the correlation coefficientis above 94%.The critical value of the soil water characteristic curve is 0.1 MPa.With the degradation of vegetation,both the moisture retention capacity of alpinemeadow soil,described as "a" value in the equation,and the water supply capacity of alpinemeadow soil,described as theproduct of"a" valueand "b" value in the equation,significantly decrease.(3)The soil fractal dimension calculated by particle-size grading shows that the soil fractal dimension of non-degraded soil is greater thanthe moderately degradedone,and the moderately degraded one is greater than the completely degraded one.Moreover,the soil fractal dimension ofalpine steppe meadow is slightly less than that of alpine shrub meadow.The soil type dinensioncalculated by the soil hydrological characteristic curve model is about 2.8,and the difference between the fractal dimensions of alpine meadowsoiland shrub meadowsoilin different deptharenot significant.The soil type dimension calculated byrelative size classification is over large on the whole.