Evolution Characteristics Of Sediment By Soil Erosion In Zhengshui River Basin And Its Response To Land Use Change

In the red soil hilly region of southern China,the complex topography of interlaced mountains and hills,heavy and concentrated rainfall,and artificial destruction of natural vegetation on the surface have comprehensively formed the characteristics of water and soil loss.Land use is the main human-controlled factor leading to the change of sediment yield by soil erosion in the short term.Therefore,correctly understand the impact of regional land use changes on sediment by soil erosion,it has practical reference significance for formulating regional soil and water conservation programs and optimizing land use structure.In this paper,the change trend of precipitation and sediment transport over time and the change of land use types in the typical red soil hilly area of southern China,Zhengshui River Basin.Using the SWAT to simulate the runoff and sediment transport in Zhengshui River Basin as a monthly step,and using SWAT-CUP to analyze the parameter sensitivity of the model.The model was calibrated with measured runoff and sediment data from 1998-2002,the measured data for 2003-2007were used as validation.Using SWAT models to simulate nine different land-use and meteorological scenarios in Zhengshui River Basin,and to analyze the influence of land use and meteorological change on sediment by soil erosion in Zhengshui River Basin.The main conclusions are as following:(1)The change of precipitation in the Zhengshui River Basin was fluctuated from 1961 to 2020,and the change trend of annual precipitation is not obvious,with no mutation point.The sediment transport in 1961-2017 showed a fluctuating and decreasing trend,and the downtrend was obvious.The year of sediment transport mutation occurred in 1999,with a significant decrease in 2004.(2)The rate of reduction of cultivated land in 2000-2010 is greater than the rate of increase in 2010-2020,and the total area of cultivated land is reduced.The rate of reduction of forestland and grassland from 2010 to 2020 is greater than the rate of increase from 2000 to 2010,its area is also decreasing in general.The rate of increase of water and construction land from 2010 to 2020 is much higher than that from 2000to 2010.Its area increased more,especially construction land.In 2020,there was an increase of 153.21 percent over 2010.(3)SWAT model’s simulation results are consistent with the trend of measured data.In the calibration period and validation period,the R~2 and NSE coefficients of runoff were 0.79,0.76 and 0.83,0.76,respectively;the R~2 and NSE coefficients of sediment were 0.56,0.54 and 0.61,0.53,respectively.The result can meet the accuracy requirements of the model,and the model has good applicability in Zhengshui River Basin.Monthly runoff and sediment occur simultaneously with precipitation,and runoff and sediment are closely related to precipitation.(4)The contribution rates of single meteorological change and single land-use change to sand transport modulus moduli in 2000-2010,2010-2020 and 2000-2020were 123.34%,102.73%,88.45%and 6.39%,-4.22%,-1.35%,respectively.The influence of meteorological change on sediment by soil erosion is greater than land use.