Evolution and spatial patterns of tidal wetland in North Jiangsu Province in the past 30 Years

Coastal wetlands and tidal land in North Jiangsu Province are the most typical mudflat in China,which lies between the estuaries of the Yangtze River and the former Yellow River channel. This article examines the evolution and spatial distribution of wetlands and tidal land in North Jiangsu Province between 1980 and2008 through image analysis of Landsat TM images from 1980 and 1992 and ALOS images from 2008. The results indicate that:(a) The study region had experienced enormous changes in this time period. The total area of coastal wetlands decreased by 1273.11 km2, that is, at an annual rate of 45.47 km2; the erosion-sedimentation area was 965.14 km2 and the erosion area was about 307.97 km2.(b)This region can be divide into six geographic units from the north to the south, and three zones from the east to the west(overlay unit, changed unit, and mudflat unit);(c) In these natural units, the proportion of transformed wetlands was 38.39%, while the proportion of lost wetlands was 14.97%. Natural wetlands decreased by 354.1 km2, constructed wetlands increased by 1061.45km2, and non- wetland area increased by 253.09 km2. Changed units were about 20.51% of the total area, in which most wetlands are in natural successions.(d) The study area also had distinct regional succession characteristics and distribution patterns of vegetation communities. Natural wetlands succession occurred mainly in the changed units with a total area of 554.52 km2, which is in agreement with the erosion/sedimentation situations of corresponding section.