Ecological environment effect analysis of Wetland change in Beijing region using GIS and RS

摘要

By utilizing TM/ETM+ remote sensing images from 1984 to 2004 as the major data sources, combining with the field survey to get the rule of dynamic process of Beijing wetland ecosystem, this paper systematic analyzed the hydrology, soil, plant condition of the typical wetland area- Widgeon Lake Wetland Natural Reserve in Beijing. And the results are as follows: In recent years, wetland areas were sharply reduced by half. The negative ecological effects around wetland areas have a close relationship with the deterioration of wetland resources. Salinized area had increased every year and reached to a head in 2004, which accounted for about 21.79 square kilometers. The serious and medium level salinity areas were in the majority in region. Due to the soil salinization, the marsh vegetation species changed to the mesophytic, xeromorphic and salt tolerable ones. Along with the continuously shrinking of water area, wetland dominated the low coverage. The area of medium to high and high coverage in 2004 reduced 71.09 percent and 99.26 percent respectively compared with those in 1998. The regional vegetation cover had shown the degradation trend. Accordingly the soil conservation function of vegetation weakened and soil fertility declined. The cold-humid effect of wetland had been impaired for the breakage of wetland environment in recent years, which led to the drying and warming tendency of regional microclimate. The phenomenon of the decrease amount of regional daily evapotranspiration proved that the climate was drying and warming. The serious disequilibrium between source and sink landscape in every sub-watershed of wetland was an important factor to cause non-point source pollution. The nonpoint source pollution in upper reaches of wetland had caused the high eutrophic water in recent years. From the field water quality monitor we could find the main contaminations were total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD) and fluorid (F). Water qual-ity has reduced up to IV or V grade. The wetland landscape shape fragmentation indexes were all over 0.99 from 1998 to 2002, which showed the impacts of human disturbance on landscape was intensive, the wetland landscape had suffered a serious destruction and the ecology was instability. Based on the above analysis, the regional ecological negative effects were closely connected with the decrease of wetland resources. We should bring forward corresponding effective protection and utilization measures and give the scientific basis for the restoration of wetland resources.