Wetland, which is described as a "Gene Pool of Natural Wildlife", plays a key role in natural resource management. And it is a vital component in the natural ecosystems with the title of the "kidney of the Earth". Fresh water wetlands in flooding plain are of great significance in protecting biodiversity. But natural wetland faces the threat of decrease and degradation due to the global climatic change and human disturbances all over the world. The area of wetlands decreased significantly after 1970 because of the regionally extensive agriculture development in Sanjiang Plain, Northeast China. Wetland ecological health assessment, as a key issue of the wetland research, is an important tool for wetland management. The ecological Assessment of the wetland health deals with multiple subjects, various methods and the scale exchange. It also helps us a better understanding of the ecological system structure and functional status of wetland. Due to the disturbances from both global climate change and human activities, wetland ecological health condition gets worse continuously. Hence, the health condition of these remained natural wetlands needs to be assessed urgently with the support of the updated geoinformatic technology.
Due to the rapid decrease of the natural wetlands in Sanjiang Plain, authors selected the Honghe region in the northeast of Sanjiang Plain as the study area, which is the typical inland marsh and consists of the Honghe natural reserve, Honghe farm, Qianfeng farm and Yaluhe farm. A quantitative analysis method was proposed for assessment of the wetland ecological health in this paper based on integration of remote sensing images, digital elevation model, regional statistical data, meteorological monitoring data filed survey data and various indices of wetland ecological health condition. The Hierarchical indices consist of ten indicators mostly concerning three aspects of hydrogeomorphics, landscape characteristics and human disturbances. Hydrogeomorphic characteristic aspect includes the indicators of average annual rainfall, soil water content, spatial distance to a water body, geomorphological type;Landscape characteristic aspect includes four indicators of surrounding patch type, landscape type, marsh patch density, leaf area index; Human disturbance aspect includes two indicators of the distance to a road, distance to a farmland. The research area was divided into cell based assessing units according to the resolution of remote sensing images and GIS data. Based on which, wetland ecological health assessment was carried out using spatial overlaying methods. Analytic Hierarchy Process (AHP) method was used for getting the calculation weight of each indicator. Then a comprehensive and quantitative index was defined and calculated at spatial grid level. Finally, the authors analyzed the spatial variations in the research area. The research results show: (1) Hydrogeomorphic characteristic is the key element that affects wetland ecological health conditions. (2) The health condition in Honghe National Nature Reserve takes the best ecological status. It decreased sequentially from good to bad within Yaluhe farm, Qianfeng farm and Honghe farm.(3) For the functional zones in Honghe National Nature Reserve, the ecological health condition in core zone is the best while the experimental zone is the worst. That is coincided with the actual condition tested by our field work. The paper shows that integration of geographical information system (GIS), remote sensing (RS) and traditional ecology methods is valuable of assessing wetland ecological health condition efficiently.