Changes of Hongze Lake Wetlands in the past Three Decades

The main purpose of this paper was to assess the change of wetlands in Hongze Lake over the past three decades. The raw data comprised two digital images acquired in 1979 and 2006 respectively. The task proceeded in three parts. First, following preprocessing and registration of 2006 imagery to the topography at the scale of 1:50,000, the TM image of 2006 was segmented and classified by using object-oriented classification technique. A thematic feature space image of near-infrared versus red was created based on the 2006 classification results and the location of each class and its relations with other classes in scatter plot and in geographical space were analyzed. Second, the 1979 Landsat MSS imagery was registered to 2006 georeferenced TM. The geometrically corrected MSS image was segmented and classified under the aid of the feature and geographical space analysis. Third, according to field investigation, specific change detection scheme was mad and the main change types of wetlands in Hongze Lake were extracted for further analysis. The results showed that a great loss of wetland has occurred in the study area in the past nearly 30 years. 58.31% of natural wetlands have been reclaimed for aquaculture, mainly fish ponds and fishing network waters. 32.14% of submerged aquatic vegetation has been replaced by open due to the change of water environment.