Spatio-temporal Change Of Sediment By Soil Erosion And Nutrient Loss In Xiangjiang River Basin

The hilly red soil region of southern China is the key area of soil and water loss control.Due to nature and human activities,it has become an area with a wide range and high degree of soil erosion in my country.In order to understand the Spatio-temporal change of sediment by soil erosion and nutrient loss in the hilly red soil region of southern China,the research takes the Xiangjiang River Basin as the research object.The research collected the daily rainfall,temperature,and humidity data of 20meteorological stations around the Xiangjiang River Basin from 1961 to 2020,three phases of land use data in 2000,2010,and 2020,30m DEM data,1:50,000 soil map data,observation data of Xiangtan meteorological station from 1998 to 2017,etc.and analyzed the Spatio-temporal change of sediment by soil erosion and nutrient loss,and effects of land use change and climate change on sediment by soil erosion and their contribution rates in the Xiangjiang River Basin,by using mathematical statistics,spatial analysis,SWAT model simulation,scenario simulation and other methods.The results showed that:During the simulation of SWAT runoff and sediment volume in the Xiangjiang River Basin,the R~2 and NSE for the runoff calibration period were 0.93 and 0.91,respectively,and R~2 and NSE were 0.94 and 0.93 for the validation period.The R~2 and NSE for the sediment calibration period were 0.85 and 0.81,respectively,and R~2 and NSE were 0.81 and 0.68 for the validation period.It shows that the SWAT model has good applicability in the simulation of runoff and sediment production in the Xiangjiang River Basin,and the simulated value of the model can represent the actual situation of runoff and sediment production to a certain extent.Through the comparative analysis of the land use status of three different periods in 2000,2010 and 2020,it is found that cultivated land and woodland are the main land use types in the Xiangjiang River,both accounting for more than 80%of the total basin,but the total amount has a decreasing trend.Since 2010,the area of cultivated land in the basin has been greatly reduced,the area of grassland has doubled,and the area of construction land has increased dramatically.The total area of the sub-basins with average sediment yield less than 500t/km~2accounts for more than 80%of the whole basin.The sub-basins with higher average annual sediment yield mainly appear in the northeast,northwest and southwest of the basin.In 2000,2010 and 2020,the soil erosion and sediment yield in the Xiangjiang River Basin were respectively 226.60t/(km~2·a),252.63t/(km~2·a),286.47t/(km~2·a),sediment yield has increased.Based on scenario simulation analysis of sediment yield in the Xiangjiang River Basin,it is found that the impact of climate change on sediment yield is much greater than that of land use change.From 2000 to 2010,the contribution rate of climate change to erosion and sediment yield was 94.05%,and the contribution rate of land use change was 52.11%.From 2000 to 2020,the contribution rate of climate change to erosion and sediment yield was 91.18%,and the contribution rate of land use change was 15.72%.The overall amount of soil erosion in the Xiangjiang River Basin is significantly greater than the amount of sand production,and nutrient loss is mainly affected by the intensity of soil erosion.The spatial distribution is consistent with the distribution of soil erosion intensity,both showing high in the south and low in the north.The distribution is high in the South and low in the north.The losses of organic matter,total nitrogen,total phosphorus and available potassium in Xiangjiang River Basin in 2000were1.64×10~6t、8.62×10~4t、6.76×10~4t and 9.02×10~3t.In 2010,the loss of nutrition was in the order of 1.84×10~6t、9.75×10~4t、7.74×10~4t、1.03×10~4t.In 2020,the loss of nutrition was in the order of 1.62×10~6t、8.3×10~4t、6.47×10~4t and 9.82×10~3t.In2000,the total amount of organic matter,total nitrogen,total phosphorus and available potassium entering into the river with erosion sediment yield were 8.86×10~5t、4.96×10~4t、4.08×10~4t、4.56×10~3t,in 2020,the losses of nutrition were in the order of 1.41×10~6t、7.82×10~4t、6.49×10~4t、7.38×10~3t,in 2010,the losses of nutrition were in the order of 1.12×10~6t、6.22×10~4t、5.09×10~4t、5.92×10~3t.From the time scale,both the nutrient loss caused by soil erosion and the nutrient content entering the river channel with the erosion and sediment yield first increased and then decreased,which was consistent with the soil erosion trend.