| The Xinshui River Basin is one of the most serious soil erosion areas in the Loess Plateau,and it is also a typical experimental area for watershed management.Exploring the spatial and temporal variation characteristics of sediment connectivity in Xinshui River Basin is of great significance to the control of erosion and sediment production in the basin.Taking Xinshui River Basin in the Loess Plateau as the research object,this paper analyzes the characteristics and driving factors of temporal and spatial changes of land use types in different stages of the study area(1986,1995,2005 and 2015).On this basis,the relationship between the modified connectivity index(IC)and the topographic hydrological response unit index(Slope-HRU)and the sediment transport in the study area is analyzed to reflect the ability of different indexes to characterize the characteristics of erosion and sediment production in the study area.Based on the two indexes,the temporal and spatial changes of sediment connectivity in the study area are analyzed,and the factors affecting the potential control process of sediment connectivity and its contribution rate are analyzed.The role of the two indexes in revealing the erosion and sediment production in the Xinshui River Basin is compared and analyzed.The main conclusions are as follows:(1)From 1986 to 2015,the area of grassland and cultivated land in Xinshui River Basin continued to decrease,while the area of forest land continued to increase.Compared with 1986,the forest land increased by 174.71%,the cultivated land and grassland decreased by 68.02%and 65.90%,and the construction land and water increased by 53.95%and 23.62%.In the past 30 years,the dominant land use type of Xinshui River Basin has gradually changed from grassland to woodland,and the main source of woodland is the conversion of grassland and cultivated land.The main influencing factors of land use change in Xinshui River Basin are returning farmland to forest and grassland,three North Shelterbelt Project,and the secondary influencing factors are the rapid development of local economy.(2)The R value of Slope-HRU index was significantly correlated with sediment yield(R2=0.75).This index can effectively characterize the characteristics of erosion and sediment yield in Xinshui River Basin,and the fitting model can be used to predict the erosion and sediment yield in the non observed area of the study area.On the scale of sub watershed,the R value of Slope-HRU index shows obvious regional differentiation,showing an increasing trend from north to South and from west to East.The first controlling factor of R value is land use type,the second is soil erodibility,and the third is terrain slope.(3)There was a positive correlation between the annual average value of IC and the annual sediment discharge(R2=0.86).This index can effectively characterize the characteristics of erosion and sediment yield in Xinshui River Basin.In the four years of 2005,2010,2015 and 2020,the index of Xinshui River Basin is small in the East and south,and large in the north,West and central.The variation range of IC average value is-5.66—-5.14,showing a slow decreasing trend over time.Compared with 2005,the average value of sediment connectivity index in 2010,2015 and 2020 decreased by 0.25,0.32 and 0.48 respectively,with the decreasing rates of 4.42%,5.65%and 8.48%respectively.The IC value of sediment connectivity index is higher in the early and late growth stages,and lower in the middle growth stage,which means that the sediment resistance increases and the soil erosion decreases in the middle growth stage.(4)The modified IC index and Slope-HRU index can effectively characterize the characteristics of erosion and sediment yield in Xinshui River Basin,and the fitting effect of IC index is slightly better than that of Slope-HRU index and annual sediment discharge.The construction of IC index has strong mechanism,and it has good characterization effect on erosion and sediment yield in small scale.Slope-HRU index takes soil factors into account,and it has good characterization effect on sub watershed scale,which is more suitable for simple evaluation of erosion and sediment yield characteristics in practical application,However,the construction of Slope-HRU index is lack of depth mechanism research,and further study on the influence mechanism of influencing factors on soil erosion is needed. |
