| To maintain a healthy life for the Dongting Lake and to realize the harmony between humans and waters is the concept regarding China's treatment of the Lake in this new era. It has become a hotspot in lakes' researches both at home and abroad that how to construct a reasonable evaluation index system or standard and to explore the health status and those affecting factors on the basis of the actual conditions of our lakes.Dongting Lake, the second-largest fresh lake in China, is not only a natural storage place for flood of the Yangtze River, but also a chief treasure-house of keeping the biological diversity of the Yangtze River, and the most important is an prominent foundation for the development of the people living around the lake district. Nevertheless, its present environment has been greatly influenced, for those projects in Dongting Lake of blocking branches, converting lakes to farmland, building flood embankment, engineering the lake treatment constructions lasting for two phases and operating the impoundment of The-Three-Gorges project. This passage will quest into the concept and connotation of the lake's health from the system combined with nature, society and economy, to diagnose the spatial-temporal dynamics changes in the health status of the lakes in typical years from the three aspects of structural characteristics, eco-system and service functions. In this way, those affecting factors can be found out so that the targeted treating work will be carried out on a scientific basis.Water environment and hydro-biological resources remain important indicators of lake health. At first, this passage explores the spatial-temporal variation on water quality of the Dongting Lake with the assistance of BP Neural Network, Nemerow Index and comprehensive pollution index. Second, the level of Dongting lake eutrophication is analyzed with the method of Comprehensive Trophic State Index.Results show that from the point of water quality, west Dongting Lake is the best, next is south Dongting Lake and east Dongting Lake, and in common water period water quality is the best, next is wet season and drought period; There is an upward trend in Dongting Lake nutrition level, especially in East Dongting Lake, there have been mild eutrophication in recent years, while south Dongting Lake and west Dongting Lake have reached the medium pollution level. And finally, the distribution of aquatic life in the Lake is revealed.The dominant species of phytoplankton in eastern and southern waters of Dongting Lake are diatoms and cryptophyta,while in western waters are diatoms, cryptophyta and green algae, the fluctuation in whose quantity, species, variety is on the rise; Software classes,aquatic insects and oligochaeta are dominant species of population structure of zoobenthos in east,south and west Dongting lake; The fluctuation in population density and diversity of species, is a downward trend, especially in East Dongting Lake waters.Morphology is the material base of formation and development of the Lake's eco-system. Based on the catastrophe progression model, issues on morphological system health of Dongting Lake are explored. Results have shown us that:considering the interannual variability of the health status of the Eas,South and West Dongting Lake,2004is a turning point. In1986and1991, the conditions of the three lakes are all critical. And in1998, Dongting Lake's health deteriorated significantly. But in2004significant improvements arouse in health on the whole, moreover in2006and2010East Dongting Lake still maintains a healthy state, while the healthy conditions of West,South Dongting Lake decline to a critical state.Eco-systems are important indicators reflecting health situation of Lakes. And in this passage, ecosystem health of Dongting Lake is evaluated based on the projection pursuit model of accelerating genetic algorithm. From1986to2010, Dongting Lake's eco-system health sees a changeable decrease, reflecting its trend of worsening on the whole; The highest level of ecosystem health has achieved in South Dongting Lake, followed by the West Dongting Lake and the East Dongting Lake in a row. Depending on the component size by optimal projection vector, we can conclude that hydrodynamic conditions, ecological flow requirements, the area size of oncomelania hupensis and the diversity of hydrobios are all essential to the ecosystem health of the Dongting LakeEcological service function is the symbol of Lakes' health and vitality. This passage goes on with the research on the health of Dongting Lake through estimation of ecological services value. We then come into the conclusion:from1986to2010, Dongting Lake's health is improving; East Dongting Lake's health is the best, followed by the South Dongting Lake and the West Dongting Lake.Overall health of Dongting Lake is on the basis of the lake's morphology,eco-systems and service functions. In view of this, this passage constructs a comprehensive evaluation system of Dongting Lake health based on the "PSR" model and selects the ways of principal component analysis and fuzzy evaluation method to evaluate health status in the Dongting Lake. In general, the better is the South Dongting Lake, followed by the East Dongting Lake and the West Dongting Lake;In typical years, the year of critical health accounts for a large proportion-about66.67%, the unhealthy years for33.33%, without absolutely healthy years; The limiting factors affecting the overall health of Dongting Lake is mainly industrial and agricultural output load in each unit volume of the lake, ecological flow requirement and landscape fragmentation, as well as indicators such as the area size of oncomelania hupensis.Through this study, the impoundment of The-Three-Gorges project operation on health states of Dongting Lake has more positive affect than negative, indicating that the project is conducive to raising the level of overall health of Dongting Lake.To sum up, this passage provides new ideas and new perspectives for study of lake-related problems, a scientific basis for the safety of flood control, water safety and ecological security of Dongting Lake, a possibility for sustainable economic and social development of the Lake District.
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