| Ecological water demand for wetland is a newly integrated concept, which include maintaining ecosystem structure and function, protecting biodiversity, sustaining human life and activities, and improving environment quality. In this paper,the concept of ecological water demand and calculating methods were discussed systemically.The characteristics of Wuliangsuhai Lake ecosystem were studied at first, and different calculating methods were deduced under different protected targets such as water amount keeping, water quality maintenance and its improvement,meet the function demand. Based on the hydrological and water cycling features, ecological water demand of Wuliangsuhai Lake were calculated under different targets by selecting suitable methods. The results of this study consisted of four aspects. Firstly, when drainage amount from adjacent farmland to the lake reach 5.48×10~8m~3 /a, the water balance of Wuliangsuhai Lake in amount could be kept. Secondly, the total Nitrogen concentration in Huanghe River, which is the source of ecological water, is higher than that in Wuliangshuhai Lake. Under this condition, from the viewpoint of water quality maintenance, it is impossible for the lake to meet the relative national standard. But if only the salts and total Phosphorus be considered, under the present drainage amount from farmland of 5.48×10~8m~3/a, the ecological water demand amount to maintain the salts and P concentration should be 3.2×10~8m~3/a and 26.5×10~8m~3/a respectively.Thirdly, from the point of view of water quality improvement, the ecological water demand amount that can improve the salts and P to meet the national standard in one year should be 6.42×10~8m~3/a and 15.2×10~8m~3/a respectively, and in ten years, it should be 4.16×10~8 m~3/a and 13.8×10~8m~3/a respectively. Finally, to meet the function demand, the ecological water demand amount should be 12.45×10~8m~3/a. In the end of the paper, measures were proposed to achieve the continuable utilizing of the water.
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