Construction Of Multi-Function Ecological Network In The Three Gorges Reservoir Area

In order to solve to the complex environmental issues occurred in The three Gorges reservoir area, this paper chose Xiangxi watershed as a study area and through planning ecological network to meet the targets of soil and water loss control, water conservation capacity maintain and improvement, non-point source pollution mitigation, biodiversity conservation. Based on watershed segmentation, the paper identified the critical areas of soil and water loss and non-point source pollution and the ideal location for vegetation buffer placement, quantified the width of vegetation buffer as well. Based on runoff coefficient, drainage density and slope, the space level and the key distribution area of water conservation capacity were classified, and then the ecological network for biodiversity conservation was planned with using least-cost model. Through identifying the single target space ecological network and its priority, the multi-function ecological network was planned with the spatial overlay function in GIS. The results are as follows:(1) The critical areas were located in the central or south of Xiangxi watershed in The three Gorges reservoir area, the total area reached 581.44km2, accounted for 25.84% of the entire Xiangxi watershed area. When quantifying the width and area of vegetation buffer, the "source-sink" model theory was applied, the results suggested that the average optimum width of vegetation buffer in the critical areas was 194.4m, its total length and area was 288.02km and 47.26km2, accounted for 22.13% and 62.60% respectively of the total length and area of vegetation buffer of whole Xiangxi watershed, while the average optimum width of vegetation buffer outside the critical area was 25.9m and its total area and area was 1013.20km and 28.24km2, accounted for 77.87% and 37.40% respectively, for the whole Xiangxi watershed,81.7m wide vegetation buffer was proper and its total length and area was 1301.22km and 75.50km2.(2) These catchments with poor water conservation capacity were distributed in the central or south area of Xiangxi watershed, while other catchments had a strong water conservation capacity. The areas with strong water conservation capacity were relative concentrated in the south, north or southeast distribution of Xiangxi watershed.The total area with strong water conservation capacity was 140.50km2, accounted for 6.25% of the whole watershed, these areas with poor water conservation was 129.63km2, covered a total area of about 5.76% area, while the total area with general water conservation capacity accounted for 87.99%. Thus the water conservation situation was not serious for the whole Xiangxi watershed. Through analysis the relationship between water conservation capacity and vegetation, the results indicated that water conservation capacity and the vegetation proportion had a positive correlation (r=0.813, p<<0.001), but it was not suitable when these catchments with similar proportion of vegetation, so much more factors (such as Topography, rainfall, soil and human disturbance, etc.) should be considered in that situation.(3) When using vegetation coverage to assess the level of biodiversity, the result showed that these areas with high biodiversity were most distributed in high attitude of Xiangxi watershed, at the edge of the entire watershed, less occurred in the middle watershed. The total area and amount of the key sources for biodiversity conservation was 202.27km2 and 20 respectively, its average area was 10.11km2, "source 17" had the largest area, reached 42.04km2, accounted for 20.78% of the total key source areas, "source 10、 6、16、14、 3、8" had smaller area. As far as the whole Xiangxi watershed, the habitat fragmentation was serious and these remaining habitat patches were small, thus the biodiversity conservation issue was serious.20 key animal movement paths was identified with using least cost path model, the total length was 132.83km, average length was 6.64km, These critical corridors based on key animal movement paths were mainly appeared in the edge of Xiangxi watershed and rarely distributed in the south central, for those key animal movement corridors with longer length and more unit resistance were mainly occurred in the middle of Xiangxi watershed of low altitude.(4) The ecological network for soil and water loss control and non-point source pollution mitigation was mainly distributed in the middle or south of Xiangxi watershed where with intensive human activity, the ecological network for biodiversity conservation was mostly appeared at the edge of Xiangxi watershed, while the patches for water conservation capacity maintain was mainly distributed in upstream region of Xiangxi watershed. Through using the spatial overlay function of GIS, the solution for a single target in spatial was overlaid in spatial, the multi-function ecological network was planned. After optimization, the y and a index of the multi-function ecological network were 0.39 and 0.07 respectively, the connectivity and ring degree were increased as a whole, the large ring network in the ecological network was reduced, the small ring network was increased, and the stability was enhanced. After optimization, the total area of the multi-function ecological network and its key zone for application was 387.28km2 and 204.41km2 respectively, the proportion of vegetation in it was 91.85%, both total area of it and urban and farmland in it were decreased compared with non-optimization.