Dynamic Change of Wetland and Driving Force Analysis of Sanjiang Plain

Using the 1993 and 2003 TM and ETM images as the basic source of information,based on the on-the-spot investigation and material analysis,the data of the Sanjiang Plain wetlands were extracted by Erdas software.The results showed that:(1) from the land change structure point of view,compared with 1993,the wetland,woodland and grassland in Sanjiang Plain tended to decrease in 2003,which wetlands decreased the most,up to 75.05%;cultivated land,water,residential area increased,of which the largest increase was cultivated land area,up to 23.32%.(2)Through the spatial variation of the Sanjiang Plain wetlands analysis,farmland increased 924 513.3 hm2,wetlands turned to arable land was 414 125.3 hm2,accounting for 70.46% of reducing wetlands area,wetlands turned into arable land contribution rate of 44.79%;but the farmland converted to other land use types was very little.The reasons that affected the change of wetland in the Sanjiang Plain were:increasing temperature and decreasing rainfall reduced the wetland area;Human population growth accelerated the pace of reclamation of wetlands;Spatial location factor had great impact on the reduction of wetlands.For these reasons,some protection policies of reasonable using the Sanjiang Plain wetlands were proposed.