Research On Ecological Security Assessment Of Land Use In Taihu Lake Basin

Located in the midst of Yangtze River delta, Taihu Lake Basin is blessed with a superior geographic position, a pleasant climate and abundant nature resources. Compared with other cities in China, Taihu Lake Basin is more densely inhabited and has a much intense urbanization level. Due to the increasingly influence of human behavior, Taihu Lake Basin has been suffering from a series of eco-environmental problems including water pollution, ecosystem degradation and other polluting issues, leaving the ecological security vulnerable to threats and damages. The regional land use change is directly affected by economic activities and the change of environment condition, so is the condition of regional ecological security. Under this case, researches on spatial pattern evolution of land use and ecological security assessment have significant theoretical and realistic influences on improving sustainable utilization of land resource and coordinated development of ecology and society. This paper adopted relating methods of ecological security assessment and analyzed the current status and the spatial pattern evolution of land use in Taihu Lake Basin with the support of GIS technology. Ecological-security-assessment indicators system on different scales was established and the ecological security condition and its aggregation features were evaluated. Main conclusions are as follows:(1) Arable land is the main land type, covering 35.38%of the territory of Taihu Lake Basin. Construction land accounts for 23.55% of the acreage. Unused land (mostly wasteland and bare land) accounts only for 1.8%. More arable land is distributed in the east than the west. Forest land is mostly located in the western-south area, including Huzhou, Hangzhou and Wuxi. Water resources are comparably rich in Taihu Lake area, and gradually decrease from eastern-north to western-south. Construction land is mostly distributed in the east and intertwined with arable land, indicating the spatial pattern and intensity of human activities. Grass land and unused land is scattered and only adds up to 4.42% of the whole study area.(2)By calculating landscape indices of each type of land, the results showed that arable land in the western-south and east is more fragment with shapes more irregular, while arable land in the east-north and western-south is less fragment. Forest land in western-south is more fragment with shapes more irregular, compared with the land in the east. Water area in the western-north and construction land in the north of Taihu Lake Basin is more fragmented with shapes more irregular. Grass land and unused land is unevenly distributed in study area, areas where these lands are densely distributed are more fragment with shapes more irregular.(3)By calculating Shannon’s diversity index, Shannon’s evenness index, interspersion juxtaposition index and contagion index, the results indicate that Taihu Lake Basin is abundant and diversified in spatial pattern. Each type of landscape is evenly distributed in the western-north of Taihu Lake Basin and other areas. The landscape types at the edge of the study area like Lin’an County of Hangzhou, the eastern-south area of Shanghai and the lake region of Taihu is on a simplified trend. The fragmentation degree of a few dominant landscape is low. Different types of landscape patches are barery adjacent to each other.(4)Based on statistics of land use, landscape pattern and relating data, ecological security evaluation system on County scale and grid scale are established and adopted to calculate the ecological security index and level. The results indicate that, on county scale, the ecological security condition in Taihu Lake Basin are mainly secure and relatively secure, while few areas are "semi-secure" and "relatively insecure". The ecological security condition in Huzhou is "secure", with an index of 0.7299. The ecological security indexes in Hangzhou and Zhenjiang are 0.6483 and 0.6157, which suggests a security condition of "relatively secure". The ecological security condition in Shanghai, Jiaxing and Nanjing are "relatively insecure", with security index below 0.45. Overall, the ecological security index decreases from the western-south to the east.On the scale of 5×5km, the ecological security index ranges from 0.2807 to 0.7111. Results shows that the data followed normal distribution. The security condition is mainly "relatively secure". Areas with better condition are clustered in the north of Taihu Lake Basin and basically borders to each other. The water region of Taihu Lake is in "relatively insecure" condition. The distribution of high-score-area and low-score-area is similar to that of county scale. The spatial pattern of the ecological security index presented a intensively trend of agglomeration.