| Hulun Lake, the country’s5th largest fresh water lake, with an international watershed crosing China, Mongolia and Russia, plays a critical role in the regional environmental protection and economic development due to its particular geographical location. In the context of regional climate change with a warmer and dryer trend, rapid economic development in the basin, and increased water pollution, the Hulun Lake wetland ecosystem is suffering serious disturbance and damage, giving rise to a series of environmental issues, such as wetland area decreased, ecological functions damaged, system health deteriorated and rehiblitation ability degrated. In this paper, evolution of the Lake wetland ecosystem in past36years as well as its driving forces has been analyzed, its health status has evaluated, the main stability thresholds were calculated, and suggestions for future protection of the wetland ecosystem were also porposed. The main results of this study are describled as follows:(1) Based on multi-sources and multi-phases remote sensing data of Landsat MSS/TM/ETM+and HJ-1A of the period from1975to2011, the dynamic variations of the wetland area were monitored, and the driving forces were analyzed from two aspects, i.e. nature and socio-economy, using the normal differential water index (NDWI) model and supervised classification method with man-machine interactive interpretation. Results show that the wetland area has presented a trend of shrinking and degradation in the past36years. Water body area of the Hulun Lake decreased by22.7%in2011compared with that in1975, and this figure of the non-water body wetland area declined by25.9%in2011compared with that of1975. It is believed that natural factors, such as temperature increase, precipitation decrease and evaporation increase, are the main causes that led to the reduction of the wetland area. Besides, socio-economic factors, such as population growth, long-term overgrazing, also accelerate the wetland degradation to some extent.(2) The health condition of the wetland ecosystem was evaluated using the Analytic Hierarchy Process(AHP). First,15indexes were selected to establish an indicator system for ecosystem health evaluation of the wetland, based on the consideration of the lake ecological environment, the overall function and the exterior social and economic environment. The indicator system includes a target layer(O), a guidelines layer(S) and an index layer(C). The weight factor of each index was asigned by experts and a judgment matrix was constructed. Then each index is divided into four grades according to the corresponding standard of quantitative, semi-quantitative and qualitative, qualitative description, which are good health, healthy, sub-healthy and illness. A rating scale vector was constructed to determine the grade of each index. The finally calculated the Hulun Lake wetland ecosystem health is0.536, which shows that the Hulun Lake wetland ecosystem is in sub-healthy grade.(3) A good correlation was detected among the Lake’s water level, area, water quantity and salinity from a long sequences of observed data series(1961to2011), thus the lake area which is more readily available was selected to inverse the lake salinity. Environmental water consumption of the wetland ecosystem was then calculated by curve correlation method. Results show that the minimum ecological water requirement of the wetland ecosystem is102.01×108m3, which corresponds to a mimimum safe ecological lake area of2137.87km2. For a healthy Hulun Lake wetland ecosystems in the future, a number of seggestions were given, including returning farmland to grassland and pasture, implement exterior water diversion and ecological resettlement project, keep moderate development of animal husbandry, strengthen the publicity of the protected wetlands, and pay equal attention to utilization and protection, etc. |
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