Study On Dynamic Numerical Simulation Of Water Quality For Wuliangsuhai Lake In Inner Mongolia

As one of the main global water environmental problems, Lake Eutrophication has been caused serious negative effects for biodiversity, wetland utilization, and human activities. Lake water environment is a well known complex system which is varied with so many related factors with complicated biological and chemical reaction mechanisms that usually deed to be getting better understanding through numerical modeling. There would hardly be able to obtain analytical solutions for the numerical models due to uncertainty parameters and nonlinear differential expressions. However, the latest development of IT technology could help to get numerical solutions for the water environment related models.Grey-Stochastic risk method was employed for environment risk analysis in Lake Wulangsuhai, which is located in a cold-dry region in Inner Mongolia. The lake has an average depth of about 1.5m with wide range species of aquatic plants and algae. It also acts as the receiver of agricultural drainage and sewage water collected from all over Hetao Irrigation District. Coupled Environmental Fluid Dynamics Code (EFDC) and CE-QUAL-ICM model were applied to analyze the concentration distribution and degradation processes of eutrophic contaminants, during which Geology statistics and ArcGIS were used to analyze the temporal and spatial distribution characteristics and variations of the parameters. The results could be concluded as:(1) Grey-Stochastic risk method could be used to get more accurate explanations on environment risk analysis for Lake Wulangsuhai as the lake water environment is influenced by both random and gray variables. The results shown that the area dear to the inlet is the heaviest polluted area in terms of both eutrophication and organic pollution. This method can better simulate the variation processes of eutrophication and sensitivity of the parameters under different concentrations of contaminants.(2) In order to get better understanding on the characteristics of parameters'temporal and spatial distribution and variation, geology statistics and ArcGIS were used to interpolate data based on the observed data. The results suggested that the parameters shown different variation characteristics within different growing periods of aquatic plants especially when the water body was covered by ice. (3) Water flow field and transport processes were simulated by using coupled EFDC and CE-QUAL-ICM. The use of CE-QUAL-ICM could involve the effects of phytoplankton such as its growing dynamics, metabolism, preyed, and receipted processes. It could also consider the effects of circulation and conversation processes between the species of nutrient salts.(4) Hydrodynamic eutrophication model was built and the errors were less than 30% between the modeled and observed data. It should be mentioned that the model involved the effects of as many as affected factors like meteorological factors (wind speed, evaporation, radiation) and aquatic plants factors (spatial distribution, density, height, diameter).(5) The major factors of eutrophication were modeled by means of only varying the inlet concentrations of eutrophic elements. The results shown that the water quality within the lake varied significantly with the change of the inlet concentrations of eutrophic elements. It implies that the degradation capability of the lake is far from the input load of eutrophic contaminants.