Wetlands dynamic in west Songnen plain, China since 1950s

摘要

In the past several decades, land cover in the region underwent dramatic changes and the progressive loss and conversion of wetlands has become a key conservation issue. Based on the theory and methods of landscape and GIS, topographic map in 1954, Landsat MSS in 1976, Landsat TM/ETM imagery in 2000 were used to detect the wetland pattern and its change in middle and lower Wuyu'er River, west Songnen Plain since the mid 1950s. The results showed that area of marsh decreased from 56.04 ×10~4 ha to 32.04×10~4 ha, while the area of cropland increase 24.94×10~4 ha during 1954-2000. Calculated from change dynamic model, the annual loss rate of marsh was -1.48% (from 1954 to 1976) and -0.76% (from 1976 to 2000) respectively. Due to shortage of water supply, marsh land were turned into dry grassland and degraded to saline-alkaline land. The number and size of marsh patch decreased significantly which indicated that the wetland landscape became more fragmental. The grassland decreased by 40.26×10~4 ha dramatically due to having been opened up to cropland and degraded into hardly-used land. The study indicates that the loss and degradation of wetlands was closely related to warmer and drier regional climate during the past 50 years. Intensive human activities including irrational reclamation, overgrazing, and ditches drainage and road construction accelerated the process.