Landscape Ecological Risk Assessment Of Yanhe Watershed Based On Land Use Change

Yanhe watershed is located in the middle of northern Shaanxi Loess Plateau, belongs to the typical Loess Hilly-gully Region, and its ecological environment is fragile. Affected by both natural factors and human activities, the ecological environment and ecological system of Yanhe watershed have faced enormous pressure. In order to promote coordinated development of social economy and ecological environment, we urgently need to make ecological risk assessment and environmental management research, it has important practical significance for strengthening the comprehensive management of watershed ecosystem, recovery of ecological environment management and maintenance of watershed ecological security. This article constructed an ecological risk evaluation model of the human activities as the risk source, on the basis of a comprehensive analysis of land use and landscape pattern change for Yanhe watershed, analyzed the spatial and temporal variation characteristics of ecological risk in the Yanhe watershed, and proposed the corresponding risk management countermeasures and suggestions. The main research conclusions are as follows:(1) From 2000 to 2010, grassland, dry land and shrub forest had always been the dominant land cover types in the Yanhe watershed. Grassland, shrub forest, building and industrial land, and forestland showed continued growth state, while the dryland were opposite. Dry land, grassland, shrub forest and water area of the bidirectional conversion was more frequent, while performance of other land use types was not obvious. The building and industrial land was always in a one-way into a state of steady growth. The Pt values of building and industrial land, grassland, forestland, and shrub forest were close to 1, showed an extreme nonequilibrium steady increase trend. Whereas the Pt values of dry land and bare land were between (-1,0), in a state of "potential". The comprehensive land use dynamic degree was 1.98%, and the Pt value was 0.99.(2)At landscape level, the number of patches increased year by year, and he degree of fragmentation has strengthened. The LSI and LPI from 181.247,27.870% in 2000, fell to 161.987,37.148% respectively in 2010. The SHDI showed a declining trend, while CONTAG had continued to increase. At type level, dry land, bare land and water area were strangely influenced landscapes by human activities, the degree of fragmentation and discretization reduced. The building and industrial land, grass land, forest land and shrub forest were less affected by the human being, which patches area increased and the connectivity between various patches had enhanced. Overall, influenced by ecological protection and regional development planning policies, landscape pattern of Yanhe watershed was in an orderly adjustment period, and in a stable development trend.(3) The medium risk and high risk area occupied the main position in Yanhe watershed from 2000 to 2010. The medium risk area showed a trend of increasing, and the total increase was 65406.64ha. While the high risk area showed a first increased and then decreased trend. Overall, ecological risk threat in Yanhe watershed had been appeared a trend of decline and ease. However, ecological risk threats of Yanhe watershed was still higher, the ecological environment pressure was still large. The medium risk area and the above risk grade accounted for a larger area ratio in all landscapes in watershed. The regions which ecological risk level was relatively high, were mainly distributed in the dry land, building and industrial land, and bare land, etc.While the regions which ecological risk level was relatively low, were mainly distributed in grassland landscape.(4) Based on spatial distribution characteristics of ecologic risk in Yanhe watershed and the relationship between the landscape types, etc. In different risk level areas, we should implement targeted ecological risk management measures. By a series of measures, such as reasonable adjustment of land use structure, returning farmland to forest and grass, forbid to steep slope cultivation and carry out the small watershed comprehensive control project, to improve natural restoration ability and ecological carrying capacity of ecosystem, enhance the ability to resist human activity disturbance, reduce the ecological risk.