Landscape structure around the reservoir based on Landsat-TM data - a case study of the Longyangxia Reservoir

The Longyangxia Reservoir lies in Qinghai-Tibet Platean, upstream of Yellow River. Some ecological problems, such as drought, water shortage; soil erosion and meadow degeneration are major factors to threaten the safety of water resources. The reservoir usually contained great area and its effects are complex and uncertain. Some effects can be shown after a few years. Thus, it is very hard to assess the eco-environmental impacts of large reservoir. Fortunately, there are few human activities in this area except for reservoir building. The changes of ecosystem are mainly caused by the water resources development. By analyzing these changes, the eco-environmental impacts of the reservoir can be assessed clearly. In this study, the measures of landscape ecology and remoting sense are used to analyze the structural changes of local ecosystem and some factors, which impact the stability of ecosystem, are discussed. Based on the interpretation of the Landsat-TM data around the Longyangxia Reservoir, which includes two digital images taken in 1986 and 2001, the landscape structure was studied by analyzing landscape pattern indices and transfer matrix of landscape. The results showed that grassland and unused lands were the main landscape types around the Longyangxia Reservoir, and the proportion of rivers, ponds and lakes, farmland and building zone had increased as the construction of the Longyangxia Reservoir and other artificial disturbance from 1986 to 2001. The landscape pattern had a trend of heterogeneity and had not a trend of fragmentation. From 1986 to 2001, parts of woodland had changed to grassland and parts of grassland and farmland had changed to unused lands, which indicate there is a trend of desertification. In this way, the environmental impacts of Longyangxia reservoir are assessed. Finally, the possibility of this method to use in eco-environmental impact assessment of reservoir is also discussed in this paper