A Study Of Ecological Risk Assessment In Gannan Based On 3S Technology

Gannan located in the south part of Gansu province holds an area of 45000 square kilometer. Gannan pasture is a main pasture of gansu and ecotone of Tibetan Plateau and Loess Plateau. As the economy developed, a lot of ecological problems emerged in Gannan, such as water and soil erosion, rangeland desertification, natural hazards, biodiversity reduction, disease, insert damage, rat damage and unbalance of ecological system and so on, which restricts sustainable development of society and economy in Gannan.Regional ecological risk assessment, as a branch of ecological risk assessment, is the scientific fundament of environmental management and decision-making. In the large-scale, regional ecological risk assessment is defined to describe and evaluate the impact on ecosystem structure and functions by environmental pollution, human activities and assess possibility and level of hazard. Compared with single ecological risk assessment, regional ecological risk assessment emphasizes the uncertainty of risk source and spatial heterogeneity of risk source and receptor based on various risk sources and receptors to make the risk assessment more complicated and objective. The steps of regional ecological risk assessment are defining the study area, landscape type analysis, risk receptor analysis, risk source analysis, hazard analysis and risk synthetical evaluation.Considering the special natural environment, social economy and ecological situation of Gannan, the regional ecological risk is assessed based on the landscape structure. According to the ecological risk assessment theory and historical data, choose three risk sources-hailstone disasters, soil erosion disasters and over-grazing disasters, describe this tree sources, analyze metrically and spatially, determine risk probability and distribute division; In the exposure and risk analysis, based on 2000,2004 and 2008 land use images, synthetical ecological loss degree assessment model is built to calculate the risk respecter damage by the interference from the risk sources-the six landscape types. The results showed that:(1) the landscape is undergoing significant changes, which can be reflected by reduced area of cultivated land and increased area of grassland, the area reduction of water area, building area and unused land are more significant after disturbance, which is most significant for building area. These showed that disturbances of human activity have a more significant effect to cultivated land and grassland, and the loss of land will be transferred from cultivated land and grassland to building area. (2) The figures also showed that the overall ecological risks is low, which is concentrated at Amaniqin mountain of Maqu prefecture, Awancang township, northern part of Zhuoni prefecture, center part of Lingtan prefecture, western part of Diebu prefecture and some areas of Zhouqu prefecture; the distribution of ecological risks are closely related to the change of surface slope, such as Amaniqin mountain of Maqu prefecture and Die mountain at Diebu prefecture. the distribution of risks are also closely related to landuse/landcover, and the changes and shift of landscape pattern is a major reason for the change of risks, which is presented as the landscape change from cultivated land to grassland and woodland, and the corresponding risks are also transferred to the landscape pattern of grassland and forest.The results of this research can be used to make the ecological risk management decision, offer the suggestion for ecological construction and is the reference of regional ecological environment restoration and early warming.