Study on the dynamic monitoring and succession analysis of wetland types in Dongting Lake area

In this paper, three period times (1987, 1996, 2004) of Landsat TM remote sensing images data are chosen to monitor the main wetland types changes in Dongting Lake area. According to the main wetland types distributed in the Dongting Lake area, a classification system of wetland types is built first. Then the software of Erdas Images and Fragstats are used to process remote sensing images and statistical analysis. After comparison of land use types, landscape pattern indices and transfer matrixes among three period times, the result is that the area of the wetland types decreased heavily, especially mudflat and paddy field from 1987 to 1996 because of the history of ldquoreclaiming the land from the lakerdquo, but some wetland types change and trend presented a turning point around 1996, which effected by the national policy of ldquoreturning farmland to lakerdquo launched in 1998. From 1987 to 1996, the main succession of wetland in Dongting Lake was lake water rarr mudflat rarr sedge land rarr reed flat rarr forest. However, from 1996 to 2004, the natural wetland types presented the change in jumps from other various wetland types directly to forest land. The major factors influencing the wetland changes in Dongting Lake are human activities, sediment accumulation and local policies etc. Among them, the implementation of ldquoreturning land to the lakerdquo has relieved the shrinking of the lake and promotes the renewal of natural wetland to a certain extent.