Analysis Of Ecological Water Requirement And Ecosystem Health Assessment For Lake Wuliangsuhai

Lakes are one of the important water bodies that is closly linked to the regional economic and social development. However, some of them are exercising the problems of environmental degradation and deterioration due to the impacts of global climate change, and human activities etc. As a result of this, the lakes have been gradually loosing their functions. Lake Wuliangsuhai is located in an arid and semi arid area. It has been contaminated by the discharge of irrigation water, domestic and industry waste waters with relatively high concentrations of TP and TN. This paper analyzed its environmental quality, amount of water lost through evaporation and transpiration, ecological water requirement, replenishment program, eco-service functions, and ecosystem health conditions.The variable fuzzy set theory was applied to comprehensively evaluate the water environment quality of Lake Wuliangsuhai in which both mathematical models and biological indicators were evaluated. The results indicated that the lake had been seriously contaminated by means of eutrophication and heavy metals. As a result of this, it could not meet the requirements of some environmental functions as before.As water losses through evaporation and transpiration is one of the key water balance terms, a set of field tests were carried out to determine the losses. During the growing season, the losses were higher in reed area than that in the open water area with an average Kp of 1.43. While the losses in swamp area were lower than that in the open water area with an average Kp of 0.89. The total annual losses within Lake Wuliangsuhai were estimated as 589 million m3. According to the estimation of the losses, the ecological water requirement of Lake Wuliangsuhai was analyzed for 3 different planning cases. The estimated ecological water requirement were 3782.31m3/a in the case of maintaining the current inlet water amount,15019 million m3/a and 162877 million m3/a in the case of maintaining the current concentration of salts and total phosphorus respectively,57100 million m3 and 186930 million m3 in the case of reducing the salts and total phosphorus concentrations to Class IV of the national standard in one yea respectively (48550 million m3 and 155900 million m3 in ten years respectively). Based on the estimations, the optimal replenishment model at present,2015. and 2020 were proposed for Lake Wuliangsuhai to meet the requirements of ecological service functions, which were adjusting functions of inflow and outflow. water supply function, supporting function, and landscape function.Overall, Impact-State-Response model was used to set up the ecosystem health assessment index system for Lake Wuliangsuhai. The index weights were determined with entropy method. The comprehensive health index method was used to access its ecosystem health. The results show that Lake Wuliangsuhai was in the middle level health level.