Abstract: A vertical-averagee 2-D ecosystem hydrodynamic model was established based on the principles of hydrodynamics and in light of the status quo of eutrophication of Lake Dianchi,the program for reconstruction Lake Dianchi eco-environment,research works done in the past,and changes in vegetation,sediment and water of the wetland,to simulate and study flow fields and concentration fields of the existing waterbody,expanded waterbody by removing the breakwater and the whole waterbody after construcition of wetland and concentration field of the water in inflowing rivers that have met the criteria of discharege.The effects of wetland plants and expansion of the waters on flow field of the lake and effects of expansion of the waters,wetland plants and up-to-standard discharge of inflowing rivers on water quality of the lake have been analysed.Results show that the effect on flow field of expansion of the waters was only to a part of the lake,while the effect of wetland plants was limited to the wetland area.Expansion of the waters may have some effect on water quality,lowering the mean concentrations of TN&TP from 2.08 and 0.19 mg·L^-1 to 1.69 amd 0.16 mg·L^-1 ,separately,but construction of wetlands may have greater effect on TN&TP,lowering their mean concentrations down to 0.76 and 0.05 mg·L^-1 ,which basically meet with Grade Ⅲ Criteria of Water Quality Standard.Once construction of artifical wetlands is accomplished and the water of inflowing rivers made up to the standard for discharge,the mean concentration of TN&TP may be lowered to 0.17 and 0.01 mg·L^-1 ,respectively,thus significantly improving the water quality of the lake.Therefore,the combination of the last two measures may play a critical role in improving the ecological environment of Lake Dianchi.

Key words: Lake Dianchi, ecological wetland, ecosystem hydrodynamic model, water quality