Landscape stability and its pattern transition of typical wetlands in three river sources, southwestern China.

Based on the 1977 MSS images, 1990, 1997 and 2007 Landsat TM images, landscape stability of typical wetlands in three river sources and its process of landscape conversion were analyzed in this paper. Considering the spatial resolution, the study area was divided into 6 types, such as river, lake, marsh, river beach, bare rock, etc. After the geometrical correction by using topographic maps, tasseled cap transformation, normalized difference water index (NDWI) and shape index were chosen to enhance the wetland spectral information. Expert classification system based on the multilayer information extraction was adopted to extract the main wetland types in the study area. The results indicated that the area and number of river land got the highest stability condition in 1977-2007, the stability index was especially close to 1 in 1977-1990, while the structural stability of river was at low level. The stability of lake wetland had been stably strengthened and it was the most stable type. The stability of marsh wetland trended to be decreasing, and was at the lowest level in 2007, so it was the most unstable. The stability of flood bed was at the low level during 1977-2007 and changed irregularly. The process of landscape conversion among different periods showed that the transformation between wetland and nonwetland was the most in 1977-1990, and it was gentle during 1990-1997 and 1997-2007. Wetland was mainly transferred to grassland, the conversion between river land and flood bed was frequent, lake wetland was converted to more than one type, while marsh land was transferred to almost the grassland，and few area was changed to other types.