Spatial and Temporal Changes in Coastal Wetlands in Guangxi Beibu Gulf in Recent 20 Years

The 1990, 2000 and 2010 Landsat TM images of coastal wetlands in Beibu Gulf were used for an analysis of spatial distribution and its changes based on object-oriented data-mining. The coastal wetlands were classified into 6 types, including tidal flat, mangrove, water, paddy field, reservoir pond and aquatic farm. The distribution and the spatial changes of the coastal wetlands were analyzed and compared using GIS spatial analysis function. The results showed that:The precision of classification for the three periods in the area were 91.02%、89.06% and 89.84 % respectively based on object-oriented method,and all kappa indices reached 0.80 and above. The natural wetland accounted for an absolute majority for all the 3 periods. The area of natural wetlands during the 3 periods were 66.96%,65.65% and 64.90% respectively of the total area of all types of wetlands. The total area of coastal wetlands had increased stably from 1990 to 2010, with the area increased from 3138.08 km2 to 3165.77 km2. Among the wetland types, the increase of aquatic farm was most evident, from 3.19 % in 1990 to 6.15% in 2010. During the period of 1990 to 2010, evident changes were found in the coastal wetlands. There were frequent transitions among wetlands and between wetland and non-wetland types,and human disturbance was evident.