Research On Runoff Formation And Sediment Yield In The Natural Conservation Area Of Tianchi Lake In Xinjiang

The middle mountains with the elevation of 1500²000 meters are areas where there is abundant precipitation and the best vegetation cover in Tianshan Mountains.On the basis of observed records and monitoring experiment on runoff plots located in the Natural Conservation Area of Tianchi Lake in Xinjiang with the elevation of 2000 meters,to provide scientific evidence and reference for protecting eco-environment and for preventing the soil and water loss and for researching the soil erosion prediction model,by the investigation of the process and mechanism of runoff formation and sediment yield in the Natural Conservation Area of Tianchi Lake in Xinjiang at different substrate,it is significant to research temporal and spatial distribution laws of soil and water loss and the variation of stream flow in arid inland river basins.The main results were as follows:(1)the formation of snowmelt runoff.During the experiment from Februrary to April in 2008,snowmelt runoff depth of P.schrenkiana and Poplor coverage is 0(mm) and 3.2(mm),and runoff formation ratio of them is 0 and 8.5% respectively.Due to much more interception of snowfall under P.schrenkiana canopy,there is no snowmelt runoff in P.schrenkiana forest.Snowmelt runoff depth in grassland and bare surface are 0.6(mm) and 5.9(mm),and runoff formation ratio of them is 1.6 and 15.6% respectively because grassland play an important role in the resident and storage of snowmelt water.The soil erosion modulus in bare land in a year is 0.444 g/m².(2)the redistribution of rainfall in P.schrenkiana forest.During the observation from April to August in 2008, the gross precipitation was 390.0mm, and throughfall, stemflow and interception were 232.5mm,1.9mm and 155.6mm respectively which accounts for 59.5%,0.5% and 40% of gross precipitation respectively.The most rainfall interception of grass layer in P.schrenkiana forest was 0.2mm,and most rainfall interception of humus layer(the upper layer) was 3.7mm.The relationship among throughfall, stemflow, interception, interception ratio and the gross precipitation in P.schrenkiana forest could be expressed as y=-2.5236+0.3329 x+0.0064x², y=-0.0038-0.0004x+0.0001x², y=3.7744x^1.0976 and y=106.910-10.044x function respectively.(3) The soil erosion in the Natural Conservation Area of Tianchi Lake in Xinjiang was concentrated in June,July and August.Total runoff depths and erosion in three months amount to 95% of the total runoff depth and 89% of the total erosion in a year.The impact of rainfall on runoff depth and erosion yields depended greatly on rainfall intensity,and their relationship were expressed y=285.02x²-686.44x+794.67 and y=2.22x²-7.516x+5.535 function.(4)The impact of vegetation on sediment yields was more than that on runoff,and the relationship among total runoff depth,total sediment yields and vegetation coverage were both expressed as y=37.19e^-0.2482x and y=158.05×e^-0.7485x function respectively. To keep the soil erosion modulus within permissible scope in the Natural Conservation Area of Tianchi Lake in Xinjiang,the vegetation coverage should be more than 65%.(5) The relationship among the sediment yield and runoff coefficient and runoff depth and antecedent rainfall amount and soil bulk density and rainfall eroding force in grassland could be expressed as the function of y=0.335x₁ +3.064x₂ -0.156x₃ -0.064x₄ +12.719x₅ +0.162x₆-10.457 in the Natural Conservation Area of Tianchi Lake in Xinjiang(6)On the basis of factor analysis and stepwise regression analysis of SAS for the relationship between sediment yields and its influential factors which included the surface erosion index(runoff depth,runoff coefficient) and soil characteristic index(total hole,density) and the vegetation index(vegetation cover) and topographic characteristic index (slope) ,the relationship among them was expressed as the function of s=5.277F₄-1.148F₃-0.828F₆+2.542.(7)The soil erosion type in grassland was mainly rainfall erosion in the Natural Conservation Area of Tianchi Lake in Xinjiang.The soil erosion modulus in a year was 131.33 (g/m²) in 2007 and 61.20(g/m²) in 2008 when vegetation cover is poor. The soil erosion modulus in a year was 74.00 (g/m²) in 2007 and 7.84(g/m²) in 2008 when vegetation cover is good,and there is no soil erosion in P.schrenkiana forest.Therefore,vegetation cover has great influence on runoff formation and sediment yield.It is obvious that soil erosion modulus in a year is within permissible scope in the Natural Conservation Area of Tianchi Lake in Xinjiang.