Study On Eutrophication Assessment And Numerical Simulation For Baiyandian Lake

The lakes are playing an important role in ecological environment, and the eutrophication is the lake's universal issue. The mathematic model is one of the important technologies for developing environmental synthetical study in the lakes. This paper summarized the methods of euthophication assessment and eco-hydrodynamic model. Based on it, the following researches were carried out in this paper:(1) This paper use the methods such as grading method, trophic state index, genetic algorithms, grey cluster set to assess eutrophication in Baiyangdian. The result showed that, trophic state index and genetic algorithms reflect the various sections of the eutrophication level, but grading method and gray cluster set can improve on level division and weight choosing.(2) Based on a comprehensive analysis of the hydrodynamic processes in the Baiyangdian water environment, 2D hydrodynamic model which included the effect of reed resistance on flow was developed in this paper. This paper adopted the ADI method to solve the control equations and simulated the flow of Baiyangdian Lake.(3) The effects of zooplankton on nutrition and dissolved oxygen were incorporated into the Water Quality Analysis Simulation Program Modeling System(WASP) lake eutrophication model formerly developed by USEPA, so as to describe the lake eutrophication processes more comprehensively. An ecological model was built, which involved 9 variables including phytoplankton, zooplankton, nitrogen, phosphorus, dissolved oxygen and so on, revealing the correlation of variables and the variation rule of lake eutrophication. The original and improved WASP model was comparatively used for the Baiyangdian lake locating at Hebei province of China, to describe the variation of total nitrogen, total phosphorus, dissolved oxygen and carbonaceous biochemical oxygen demand in 2004. The results indicated that the improved WASP model was more consistent with the observed data.(4) This research fully coupled the hydrodynamics governing equations, which included the effect of reed resistance on flow with WASP (Water Quality Analysis Simulation Program), a modeling system introduced by the US EPA an improved model which introduced the zooplankton kinetic equation. A eutrophication eco-dynamics model in Baiyangdian Lake was established. This model simulated nine water quality constituents associated with eutrophication in the lake and included phytoplankton, zooplankton, nitrogen, phosphorus, and dissolved oxygen. The calibrated model was applied to study eutrophication in this lake. The results showed that the field data including ammonia nitrogen, total nitrogen, total phosphorus and dissolved oxygen were consistent with the values obtained using the model. The simulation showed the changes in the processes related to nutrition and dissolved oxygen. In this study, the present model described the time variation in water quality in Baiyangdian Lake with reasonable accuracy.