| Dongting Lake, the second largest freshwater lake in China, is an importantstorage lake in the middle reaches of the Yangtze River, as well as a world-famousscenic spot. The lake area is abundant in aquatic product and natural resources. Thefertile soil and convenient steamer service prepared the ground for the development oflake area. As the first lake connected to the Yangtze River in lower reaches of theThree Gorges, it is closely related to the function of flood control, regional ecologicalenvironment and economic development. Industry and agriculture developmentaround the lake brought about a series of problems: water quality deterioration,aggravated eutrophication, increasing shortage of water resources, ecological waterbeing occupied. Lake surface area shrinking and riverbed elevation resulted fromsediment accumulation and enclosing lakes for cultivation are also worthwhile toreceive attention. Therefore, it is necessary to carry out water quality assessment andto calculate the ecological water level of Dongting Lake, which could provide basisfor water environment management.Firstly, the complicated river-lake relationship in Dongting Lake area wasdescribed and its important role in flood-water control, environmental protection andeconomic promotion were illustrated. Simultaneously, a brief introduction for waterquality and quantity of Dongting Lake has been made. Then, allowing for theuncertainties in water environment, an integrated fuzzy-Bayesian water qualityassessment model based on triangular fuzzy numbers was developed by introducingBayesian Theory and Fuzzy Set Theory. The new model could express uncertaintiesfrom model structure and parameter uncertainty. Analysis of pollution sources ofDongting Lake was followed. The lake water is not only fishery water, but drinkingwater for nearby residents as well. To directly reflect the influence of lake water ondrinking people, health risk analysis was performed on East Dongting Lake, whichwas regarded as a supplement to the integrated fuzzy-Bayesian water qualityassessment. The results showed that the water quality of Xiaohe Zui, Hengling Lake,Muping Lake and the outlet of Dongting Lake attained water quality standards GradeII, and that of Nan Zui and Yueyang Tower reached water quality standards Grade III. The water quality of East Dongting Lake and Bianshan were between Grade II andGrade III with the grade value of0.4983III0.5017IIand0.7962III0.2038II,respectively. Compared with the current water quality standard, Nan Zui was failed toreach the corresponding water quality standard. The water quality assessment modeldeveloped in this paper is more comprehensive and reasonable in comparison withtraditional models. It made progress in the uncertain problems. The risk analysisresults indicated that carcinogenic risk of As excessed the standard, while otherhazards were controllable. For drinking water safety, special attentions should be paidto As. Agricultural pollution, industrial pollution and domestic pollution wereidentified as the main pollution sources of Dongting Lake. Agricultural pollutionmainly included chemical fertilizer, pesticides and livestock manure. Industrialpollution was serious, especially organic pollution and heavy metal pollution.Domestic pollution was mainly manifested in nitrogen and phosphorus pollution.Secondly, a hydrological index based method for determining EAWLR(ecologically acceptable water-level range) was illustrated by a case-study ofDongting Lake. Abundant species with different environmental tolerances in lakewould promote species coexistence and enhance the resistant and resilient abilities ofcommunities to disturbances. The ecosystems have adapted to water level fluctuationto some extent. It is therefore that the ecologically acceptable water level is not adefinite value, but an uncertain range. In this study, the RFD（Ratio flow deviation）was incorporated to analyse hydrological alterations resulted by anthropogenicactivities and climate changes. It was during this process that AAPFD (AmendedAnnual Proportional Flow Deviation) was regarded as indicator of ecosystem healthto determine the EAWLR. The final results indicated that EAWLRs of Beijinggang,Nanzui and Chenglingji during flood season were27.78~38.26m,25.19~38.45m and24.48~30.96m, respectively, while those during non-flood season were18.33~27.79m,17.68~29.19m and15.59~22.07m, respectively. The upper limit of the EAWLRduring flood season provide basis for the largest water storage capacity of DongtingLake, and the lower limit of the EAWLR during non-flood season spared as muchwater as possible to meet other water uses under the circumstances of maintainingbiodiversity and integrity. The method was feasible for hydraulic department toallocate water resources. Finally, the main problems in Dongting Lake area and the treatment measureshaving been adopted were summarized. Combined the discussions on water resourcesof Dongting Lake in this study and the Dongting Lake Ecological Economic ZonePlan, some targeted suggestions have been made for pollution abatement and watermanagement. The plan made the upgradation of Dongting Lake region a nationaldevelopment strategy, which is of great importance and will lead to exploration ofnew paths for economic and social development of great lake basins guided byecological civilization construction. It is an urgent and long-period task to improvethe conditions of Dongting Lake. |
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