Ecological Impact Assessment Of Soil And Water Erosion On Dianchi Lake Basin Based On The Fractal Theroy

In this paper, natural condition and socioeconomic status of Dianchi lake basin were investigated and analysed, then some maps were drawed, such as geographic location of Dianchi lake basin. Current situation, characteristic, causes, damage and variation tendency of soil and water erosion were comprehensively and systematically analysed in Dianchi lake basin. The work contains three parts about soil and water erosion ecological impact assessment based on the fractal theory in Dianchi lake basin.(1) Based on fractal method and GIS technology, the naturalness index of land utilizationcan be classified into 5 types:cropland, woodland, grassland, water land, industrial and residential areas, and analysis on fractal dimension of Dianchi lake basin in Yunnan province. The algorithm is a fractal dimension expression about area and perimeter. The results indicate that land use type can be described with fractal structure. Fractal dimension (D) values vary from 1.09 to 1.35 in the case application of Dianchi lake basin. The D of land use types reflects the degree of complexity, stability and developing trend. When the value of fractal dimension (D) is 1.15, namely D is critical value; the change mode of land use types means Brownian motion. The value of D is closer to the critical value, the stability of land use type is worse, and the complexity of land use type is higher. Without considering the impact of water land, the stability indexes of 80.18 percent of study areas are between 0.2 and 0.5, which means the total stability is in a good condition. Due to ecosystem sensitivity evaluation is very important to the stability analysis of regional ecological system, then the fractal theory combined with ecological sensitivity evaluation were used together for the ecological sensitivearea divisions in Dianchi lake basin. Finally, the study area was divided into five different ecological sensitivearea, and brief measures would be put forward to them.(2) Based on GIS technology, two factors of impacting soil erison which are the water system and terrain would be made the fractal value calculation. The results show that the value of stream fractal dimension (Db) is 1.07and terrain fractal dimension (Db) is 0.93. Then, the other two factors of impacting soil erison which are the mid-value of slope and the mid-value of elevation combined with the value of stream fractal dimension and the value of terrain fractal dimension were applied to the improved fuzzy comprehensive assessment model based on information diffusion principle. The result shows that the level of soil and water erosion is 2 and comprehensive evaluation index is 2.26 in Dianchi lake basin.(3) The system of eco-environmental appraisal index was established by using the Analytical Hierarchy Process (AHP) model in Dianchi lake basin. Using the related data, the ecological index (EI) of this basin in 2005 was assessed. The results show that grading value of eco-environmental status is 0.31 which is compared with the related value of the "water pollution prevention in Dianchi lake basin "five-year" plan". Then, the relevant improved suggestion was put forward according to the result. Finally, map of soil and water erosion treatment plan and map of soil and water erosion control measures were drawed according to the actual circumstances of Dianchi lake basin.To sum up, through the application of fractal theory that is a methodology, and through the use of Arc GIS that is a strong space data management and treatment tool, ecological impact assessment were systematically taken for the soil and water erosion of Dianchi lake basin, which has expanded and enriched the ecological impact assessment methodology system, which has injected new blood to ecological impact assessment, and has provided a new thinking for ecological security in Dianchi lake basin and the other lakes.