Land Degradation Assessment And Sediment Yield In The Huangfuchuan Basin

The Hekou-Longmen section in the middle reaches of the Yellow River has long been suffered from severe soil erosion,and is the main source of the coarse sediment of the Yellow River.The Huangfuchuan Basin is located in the upper part of the Hekou-Longmen section.The basin faces a variety of ecological and environmental problems such as soil erosion,desertification,vegetation degradation and soil quality degradation.Therefore,it is necessary to investigate the changes in erosion and sediment yield and the problem of land degradation in the Huangfuchuan watershed.Comprehensive land evaluation can provide a basis for future water and soil conservation and ecological restoration in the basin.Four typical dam-controlled small watersheds were selected in the Huangfuchuan watershed to analyze the siltation characteristics of the dams.The sediment yields in the small watersheds were inferred by using the siltation and sedimentation.The land use/cover changes of the Huangfuchuan watershed in different periods were analyzed.The Revised Universal Soil Loss Equation was used to investigate the impact of land use/cover changes on soil erosion.A number of indicators were selected to assess the spatial pattern and temporal variation of land degradation.The indicators were consisted of select soil erosion modulus,vegetation coverage,slope,dryness,soil organic and the bareness of sandy land as land degradation for the current soil erosion,desertification,vegetation degradation,soil infertility and drought and water shortage.The evaluation index uses the fuzzy logic comprehensive evaluation method to obtain the land degradation index,and analyzes the temporal and spatial distribution characteristics of the land degradation degree.The main conclusions are as follows:(1)The sediment particles of the typical check dam in the Huangfuchuan Basin are mainly composed of sand and silt.The average annual sediment yield of a typical dam-controlled small watershed is between 11471 t/km~2/a and 101948 t/km~2/a.The different surface coverings in the basin affect the composition of sediment particles and the intensity of sediment erosion in the basin.The surface materials are mainly the basins of bare feldspathic sandstone,the sediment particles in the dam are coarse and the sediment yield are high.The surface material is mainly the watershed of loess,the sediment particles in the dam are relatively thin and the sediment yield are relatively small.(2)The main land use type in the Huangfuchuan Basin is grassland,accounting for 77.83%of the basin area(2006).The most important land use change in the basin from 1978 to 1990 was the conversion of grassland to cultivated land.Grassland reclamation and farmland expansion were the main land use changes in the Huangfuchuan Basin during this period.The main land use change in the basin between1990 and 2006 was the conversion of cultivated land,sandy land and unused land to grassland.Grassland vegetation restoration was the main way of land use change in the basin during this period.(3)The vegetation coverage of the Huangfuchuan Basin in 2006 was 30.56%,significantly higher than that in 1990(25.80%)and 2000(16.87%),and the vegetation coverage in the basin gradually improved.The evaluation of soil erosion intensity by RUSLE model shows that the soil erosion modulus of the basin is gradually decreasing with time,but the erosion phenomenon was still severe.(4)The distribution of land degradation index of Huangfuchuan Basin was obtained by fuzzy logic comprehensive evaluation method.The land degradation index of the basin is consistent with the trend of vegetation coverage.The land degradation index of the basin in 2006 is 0.69,lower than that of 1990(0.75)and 2000(0.80).The land degradation status of the basin is getting better and the watershed management effect is obvious.However,the management of feldspathic sandstone and sandy land is still the key to prevention and control of land degradation in the basin.