Land Use Change And Soil Erosion In The Danjiangkou Reservoir Area

With the increasing confliction between population increase, limited resources and the environment, land use has been deeply changed by human activities. Human-induced land use change will disturb matter cycling and energy flow in ecosystems, causing natural erosion change, exacerbating soil erosion, result in a series of environmental issues.Soil erosion in the Danjiangkou reservoir area has a crucial effect on water quality, which is related to the long-term success of the South-to-North Water Diversion Project (Middle Route). Increasing anthropogenic pressure, especially human-induced land use change, will undoubtedly change soil erosion dynamics in the Danjiangkou reservoir area. Therefore, the research on the relationship between land use change and soil erosion is of great significance for ecological environment protection of the Danjiangkou reservoir area, and water quality assurance in the South-to-North Water Diversion Project.Using land use types interpreted by Landsat remote sensing images, we analyzed the land use changes in the Danjiangkou reservoir area between 2002 and 2013. Additionally, using the revised universal soil loss equation (RUSLE), we simulated soil erosion between 2002 and 2013. Furthermore, we explored the response of soil erosion to land use change in the aspect of land use types shifting and landscape patterns change, respectively. The main results are as follows:1. Between the year 2002 and 2013, policy implementation of grain-for-green, closing hillsides to facilitate afforestation, and urbanization contributed to land use change in the Danjiangkou reservoir area. The main land use changes are conversions among forest, farmland and shrub-grass land, as well as expansion of construction area. Specifically, forest area increased significantly, expanded 13.72%(475.44 km2); the area of farmland only increased 5.76%(58.81 km2); shrub-grass land area has greatly decreased 37.61%(895.85 km2); the expansion rate of construction area was rapid, increasing twice times (265.70 km2) in the Danjiangkou reservoir area in 2002-2013.2. In 2002,2008 and 2013, slight soil erosion dominated the most areas in the Danjiangkou reservoir area. In spite of the increased soil erosion intensity in construction area, the overall soil erosion intensity was reduced. The soil erosion in reservoir area shifted from a higher intensity situation to a milder intensity situation in 2002-2013. Shifting from longitudinal, medium, strong, extremely strong and violent soil erosion area, slight soil erosion area total increased 936.52 km2. However, the longitudinal, medium, strong soil erosion area gradually decreased. The extremely strong and violent soil erosion area decreased at first and then increased in 2008.3. The changes in soil erosion intensity are associated with the transition of the land use types, mainly depending on the vegetation coverage and slope. The transition among land use types with similar vegetation coverage in the gentle slope did not result in significant changes in soil erosion. The soil erosion intensity decreased mainly due to shrub-grass land conversion to forest and farmland, and the grade of reduction was depend on the vegetation coverage. The transition from forest, farmland to shrub-grass land in the large wavy terrain as well as the transition from the high vegetation cover types to construction area were leading to the increase of the soil erosion intensity.4. The changes in number of patches, shape index, average patch size and largest patch index for both landscape and class level were closely related to the changes in soil erosion. As the number of patches and shape index increase, the watershed has a greater variation in its soil erosion. In addition, the increase of the average patch size and the largest patch index of shrub-grass land exacerbated the soil erosion intensity in the watershed, the largest patch index of construction area as well. Conversely, the increase of the largest patch area of farmland had weaken the soil erosion intensity.5. Land use change is the main factor that cause soil erosion change in the Danjiangkou reservoir area. In order to ensure the water quality in the Danjiangkou reservoir, the land use types should be reasonably arranged and the land use pattern should be optimized. Appropriate measures should be taken into consideration to reduce the soil erosion associated with urbanization.