ANALYSIS ON THE DISTRIBUTION CHANGE AND INFLUENCING FACTORS OF THE WETLANDS IN SONGNEN PLAIN

The ecologic environment in the Songnen Plain changed extremely in the last 20 years. One of the significant expressions is the intensive retrogression of wetland. Based on the remote sensing data of 1986 (TM) and 2001 (ETM), this research analyzes the present situation and changing trend of the wetlands in Songnen Plain with RS-GIS technology. The result shows that, during the 15 years, the area of wetland in Songnen Plain reduced 658 042 hm², by 38.81%. Among them, the surface water reduced 127 429 hm²; while the marsh, 530 612 hm². The reasons for the retrogression of wetland include the reduction of rainfall, increasing evaporation, excessive development of water resources, pasture and cultivation.