Response Of Soil Erosion And Water And Sediment To Land Use Change In The Hantaichuan Basin

The Ten Big Kongdui is one of the ten first-order tributaries with seasonal high sediment floods on the right bank of the Inner Mongolia reach of the Yellow River.It is an important ecologically fragile area in the Yellow River Basin and one of the important energy bases in China.The study area is located in the wind-water composite erosion area.It has long been a key area for national soil and water loss control,and plays an important role in ecological protection and sediment control in the Yellow River Basin.Since the 1980 s,Hantaichuan Basin has successively implemented a series of soil and water conservation ecological construction projects,such as comprehensive management of small watersheds,returning farmland to forest and grass,sand prevention and control,planting trees and grass,closing hillsides to facilitate afforestation and grass cultivation,global grazing prohibition,gully dam reservoir control project,and ecological sediment reduction of Pisha sandstone and seabuckthorn.After years of comprehensive management,the land use in Hantaichuan Basin has undergone tremendous changes,the vegetation coverage of forest and grass has been greatly improved,the soil erosion has been improved,the runoff and sediment transport have changed significantly,and the overall ecological environment has improved.In this paper,the Hantaichuan Basin,a typical tributary of The Ten Big Kongdui,is taken as the research area.The characteristics of water and sediment changes and the spatial and temporal differentiation characteristics of soil erosion in the Hantaichuan Basin are analyzed in order to provide scientific and technological support for the comprehensive management of soil and water loss in the Kongdui Basin in the future and alleviate the siltation of the Yellow River in Inner Mongolia.In this study,the characteristics of land use/cover change in the Hantaichuan Basin in1990,2000,2010 and 2020 were analyzed.The RUSLE model was used to analyze and evaluate the erosion characteristics of different land use changes in the basin.The characteristics of water and sediment changes in the basin were discussed,and the effects of climate change and human activities on water and sediment changes were quantified.The conclusions of the paper are as follows:(1)From 1990 to 2020,the annual average NDVI and growing season NDVI in the Hantaichuan Basin showed a fluctuating increase trend,and the growth rates were 0.0052/a and 0.0049/a,respectively.In the basin,the area with an average annual NDVI upward trend accounted for 94.89%,and the area with a downward trend accounted for 5.11%.The areas with significant vegetation improvement are mostly concentrated in the central and northern regions of the basin,and the areas with poor vegetation are mostly concentrated in the northwest and southeast corners of the basin.The land use types in Hantaichuan Basin are mainly grassland,forest land,cultivated land,water area,construction land and unused land.In the past 30 years,grassland,forest land and construction land have shown an increasing trend as a whole,of which construction land has increased the most,reaching 54.65 km~2.Cultivated land,water area and unused land have shown a decreasing trend as a whole,and the area of unused land has decreased the most,reaching 57.22 km~2.(2)From 1990 to 2020,the intensity of soil erosion and the area of water and soil loss in the Hantaichuan Basin showed a decreasing trend.The annual average soil erosion intensity in 1990,2000,2010 and 2020 were 5706.85 t/km~2/a(intense erosion),5464.14t/km~2/a(intense erosion),4980.52 t/km~2/a(moderate erosion),3038.28 t/km~2/a(moderate erosion).The area of slight erosion and slight erosion shows an increasing trend,while the area of moderate erosion,strong erosion,extremely strong erosion and severe erosion shows a decreasing trend.(3)In recent 39 years,precipitation in Hantaichuan watershed has not shown a significant upward trend,while runoff and sediment discharge have shown a significant downward trend as a whole.The Pettitt mutation test showed that 1998 was the mutation point of runoff and sediment transport in the Hantaichuan Basin.The annual average runoff and sediment transport in the basin from 1980 to 1997 before the mutation were 12.301million m~3 and 2.7807 million t,respectively.The average runoff and sediment transport from 1998 to 2018 after the mutation were 7.5515 million m~3 and 539,100 t,respectively.The average annual runoff and sediment transport reduction rates were 38.61%and 80.61%,respectively.(4)Human activities such as returning farmland to forest and grassland and siltation dam project are the main influencing factors of runoff and sediment reduction in Hantaichuan Basin.The contribution rates of runoff and sediment are 60.38%and 59.73%,respectively,while the contribution rates of precipitation changes are 39.62%and 40.27%.