Analysis on the Dynamic Change and Degradation Factors of Wetland in Bay-Type City

With the aid of remote sensing and GIS techniques,this paper quantitatively studied the spatial distribution and dynamic changes of wetlands in Xiamen city over the last 18 year,based on interpreted data from TM image and(in 1986 and 1997) and SPOT5 image(in 2004).Meanwhile the reasons for the degeneration of wetland are analyzed.The results show that the main wetland types are dominated by shallow sea(40.84%),silt beach(22.56%) and breed(25.77%) at present, there is plenty of reserve land resources of wetland in Xiang'an district.The area of natural wetland including silt beach,river,pond and mangrove decreased,while the area of breed increased,the changes of mangrove and breed were most obvious,and the most types of wetland changed dramatically in the first period,from 1986～1997.The total area of wetland decreased,it was reduced to 3 632 hm2 during the past 18 years,and the natural wetlands were severely fragmented and shrank,meanwhile the breed extended and dispersed rapidly along the coastline from the distribution maps of wetland.Coastal wetland is one of characteristics Xiamen's scenery,however,the ecological environment quality of wetland was suffered from serious degradation in the past 18 years.As far as the reasons for wetland degradation are concerned,there are wetland reclamation,coastal engineering,pollution,disaster climate and so on.Among them,wetland reclamation and pollution are the most important environmental pressure factors.Degradation of wetland leads to the habitat worsening and biodiversity decreasing.