Comprehensive Water Requirement Analysis And Ecosystem Health Assessment Of Urban Lakes

As the significant city water and wealth resources,the main functions of urban lakes include tour,entertainment,flood regulation,climate regulation and eco-environment improvement.The overdevelopment and unreasonable utilization to lake resources result in shortage of water resources,deterioration of water environment and degeneration of ecosystem.Studies on water quantity,water quality and water ecology of urban lake ecosystems can provide foundations for their sustainable management and utilization.This paper presents a case study in Dongchang Lake.The results from this study can be summarized as follows:(1) Based on the analysis of the history of Dongchang Lake,its ecosystem service function evolution process is summarized.The influencing factors to its ecosystem service functions are respectively analyzed.The relative importance of every function and every influencing factor is studied for a lake to determine resonably its leading function and to array legitimately primary and secondary protective sequence of influencing factors to its ecosystem service functions and to realize the sustainable utilization of lake resources and the sustainable development of Lake District economy.(2) Calculation model for optimal water volume transferred to Dongchang Lake are established after considering demands to water volume and water quality for primary functions,such as sight tour,eco-environment and industry water supply.Water volume of Yellow River transferred via Tanzhuang Reservior corresponding to each month of different representative years is analyzed and calculated.The results can be used as warranties for transferring water of Yellow River scientifically under the precondition of favorable ecosystem cycle of Dongchang Lake and assuring water supply.(3) Spatial and temporal properties considered,the caculation method of eco-environmental water requirement of urban lake combining with water quantity-water quality coupling study and threshold study is discussed.The calculation of eco-environmental water requirement of Dongchang Lake is given as an example.It is divided into four parts.Then the multiannual mean optimal,moderate and minimal value are calculated.Eco-environment improvement water requirement and basic water requirement for water body occupate most of the whole water requirement.The calculation results can provide theoretical foundations for protecting eco-environment and promoting sustainable development of Dongchang Lake.(4) Considering that comprehensive evaluation of water quality and eutrophication evaluation involve many indexes,many classifications and interval values,variable fuzzy sets theory is applied.Based on the premise that the same mathematics model is used,index weights are determined by means of entropy value method,equal weight method and pute threshold value method.The application of this model in Dongchang Lake is given as an example.The stability of features of classification corresponding to each method is analyzed and grade of each sample is determined.The results all chime basically with reality.(5) Combining with the properties of ecosystem of an urban lake,the index system for its health assessment is built with the PSR(Pressure-State-Response) conceptual model.The index weights are determined with information entropy theory.The comprehensive health index method is used to assess ecosystem health of an urban lake.The application of this method in Dongchang Lake is given as an example.The states of its ecosystem health in 2002 to 2006 are assessed.The results conform basically to reality.Finally the suggestions are proposed for its management,protection and ecological restoration.