| Taihu lake is the third largest freshwater lake in China with an area of 2338 km2, which is 74% of the total area of all lakes in Taihu basin. Its aquatic system provides lots of ecosystem services such as flood controlling, water supplying, fishery, shipping, touring and culture, and affords a undisplaced natural supporting system for the sustainable social and economic development of Taihu basin. In the recent 40 years, Taihu lake sustained more and more stress from fisheries and pollution. The water quality reduced one class every 10 years and the water body sustained serious eutrophication. The biodiversity declined remarkably and the composition of fishery products was composed of small species with lower value. In 2000, Taihu lake was listed in "water pollution prevention and control on the three rivers and three lakes" by the state environmental protection administration of China. The government planed to solve its eutrophication problem with a investment of 20.43 billion yuan RMB in 1997-2010. And 4.1-9.24 million fry was put into Taihu lake every year to maintain the fishery resources. But the efforts of pollution controlling and fishery management have not been integrated in the "frame of ecosystem". As the pollution sources were controlled, the rebuild of the aquatic ecosystem was not processed on schedule. The composition of catches was not reasonable and the fishing intensity was not controlled effectively yet. The excessive fishery and aquaculture kept on destroying the structure of Taihu lake ecosystem.For revealing the facts affects the health of Taihu ecosystem and figuring out the problems of environmental pollution and fishery degradation, some academic groups have carried out several large-scale investigations and long-term monitoring on the environment, ecology, fishery and biological resources of Taihu lake. Lots of the researches have studied the relationship between pollution, fishery and ecology, andprovided comprehensive and systematic information about Taihu ecosystem. But the former studies just focused on one or several environmental and biological facts of the system. Most of the basal data was not utilized and integrated in them. The study based on food-web models, which was constructed in the "frame of ecosystem", was still few in the study of lake ecosystem in China. The paper constructed static and dynamic models using Ecopath with Ecosim, which was a ecosystem modeling software based on food-web. The structures, functions and services value of Taihu lake ecosystem in different decades were studied by 3 static mass-balanced models as viewed form maturity and ecosystem development. The developments of the ecosystem in the stress of fishery and pollution were simulated by several dynamic food-web models. The mechanisms of eutrophication and fishery degradation were revealed, and the effects of future alternative management strategies on ecosystem and fishery profits were evaluated. The results and conclusions are described in detail as follows. 1. The modeling analysis of the structure of Taihu lake ecosystemUsing the basic and network analysis function of Ecopath, a mass-balanced model with 22 groups was constructed to proceed a quantitative and synthetic analysis for the structure of Taihu lake ecosystem. The Taihu lake ecosystem was composed of 4 aggregated trophic levels. Because of the eutrophication, the throughput of trophic level I was as high as 9956.11t/km2/y. But the ecotrophic efficiency (EE) of phytoplankton and detritus were only 0.413 and 0.362. It meaned that the utilizing efficiency of trophic level I was very low. Small pelagic species such as tapertail anchovy (TapA), silver fish (SilF), macrocrustacean (MacC) and other pelagic fishes (OthF) dominate the ecosystem. The prey overlap index of TapA, OthF, SilF and MarC were higher than 0.8, which meant that there was intensive food competition between the small pelagic species. The negative mixed thophic effects (MTE) of large culters (LarC) on most of its preys were much lower than the trawl fishery. On the oth...
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