GEOGRAPHICAL RESEARCH ›› 2005, Vol. 24 ›› Issue (4): 501-512.

• Earth Surface Processes •

### Analysis on the shrinkage of wetlands in Nongjiang and Bielahong region in Sanjiang Plain and the causes

HOU Wei1,2, ZHANG Shu-wen2, ZHANG Yang-zhen2, LI Ying2, CHANG Li-ping2

1. 1. Department of Environment Science of Liaoning University, Shenyang 110036, China;
2. Northeast Institute of Geography and Agricultural Ecology, CAS, Changchun 130012, China
• Received:2004-07-12 Revised:2004-10-23 Online:2005-08-15 Published:2005-08-15

Abstract:

Since the 1950s large-scale reclamation of the wetlands has been carried out in Nongjiang and Bielahong River Region of the northern Sanjiang plain. Cultivated land instead of wetland has become the main landscape after large-scale reclamation since 1954. Great changes have taken place in ecological feature of wetlands in the study area. Nongjiang and Bielahong River Region is an important part of Sanjiang Plain. Wetland changes can seriously affect the sustainable development of this region. From 1954, the area of wetlands reduced greatly. At the same time, the area of cultivated land expanded substantially. Wetland environment was badly disturbed and destroyed. Using theory and methods of landscape ecology, land use and land cover change in 1954,1967,1976,1986 and 2000 are analyzed based on RS and GIS. The data sources mainly come from the Landsat TM digital images, topographic maps and statistical data. The processes of land reclamation and wetland shrinkage are also analyzed. Comparative studies of the landscapes between 1954 and 2000 and 1976 and 1986 are mainly conducted. The percentage of the area of wetlands is 64.83% of the total area in 1954, while that of the cultivated land, 0.68%. Wetland, grassland and forestland are the main landscape types in 1954. The percentage of cultivated land increased from 0.68% to 2.26% during the time from 1954 to 1967. The percentage of wetland was separately 50.30%, 19.96% and 16.22% in 1976, 1986 and 2000, and the cultivated land, 9.7%, 29.16% and 39.38% accordingly. The area of wetlands decreases rapidly while that of the cultivated land increases greatly. In 1954, wetland was the main landscape type and was evenly distributed. In 2000, cultivated land became the main landscape type, accounting for 39.38% of the whole area. And its distribution was even while the distribution of wetland was fragmentized. From the transformation of land use types, from 1954 to 2000, 41.79% of the wetlands was converted into cultivated land, indicating that 68.8% of the cultivated land came from wetland.Based on the analysis of the spatial and time variations of wetlands, the causes of wetland shrinkage are further analyzed. Wetlands are distributed in the region with favorable climate and the water-heat arrangement is favorable to the crops. So wetlands are most suitable to crops and easily to be reclaimed into cultivated land. In 1954, the population was only 4,300, but in 2000, the population in the study area increased to 230,700. The increasing population is the main driving force for land use and land cover change in the study area. The reclamation activity has been the main reason for wetland shrinkage since 1954 in this region.