Study On Ecological Model And Eutrophication Control In Dianshan Lake

Dianshan Lake is the biggest fresh water and the main source of water in shanghai.It is suffered from eutrophication problem and blue-green algal Bloom in recent years,and the source drinking water could be in danger.The eutrophication of lakes and ecological models were widely reviewed, especially the AQUATOX(USEPA)modeling system.Based on the experimental data, AQUATOX model was applied and developed to simulate the nutrition distribution and phytoplankton behavior in Dianshan Lake.Furthermore,the futher study was conducted,including Blue-green algal bloom and its impact factors,eutrophication controling scheme.Major aspects of the research are presented as follows:In-situ measurements of water quality are used for the model calibration and verification.The main parameters calibrated in the model are Extinct.Coeffwater,Max.Degrdn.Rate,Labile,Max.Degrdn.Rate,Refrac,Saturating ligh,P half-saturation,N half-saturation,Optimum Temperature,Max.photosynthetic Rate,Sedimentation Rate.The modeling result is in good coincide with the lab findings and the in-situ measurements,suggesting that the developed model represents the temporal distribution of nutrition and dynamic growth of algae reasonably well.The AQUATOX model doesn't simulate Chla directly,but convertes phytoplankton biomass estimates into approximate values for Chla,which lead to the simulantion error of Chla.The modeling study of temporal distribution of nutrition shows that Dianshan Lake is at the state of hyper-eutrophication.The modeling study of seasonal growth of algae shows that the structure of the community and dominant species of phytoplankton are green algae and blue-green algae,especially the blue-green algae bloom in summer.The modeling study on the eutrophication control scheme proves that good hydraulic condition is beneficial to the algae control.The loads of nutrients(nitrogen and phosphorus) in Dianshan Lake mainly come from upstream,and Blue-green is more sensitive on the Phosphorus than Nitrogen.The effective measures of eutrophication control are ecological restoration of aquatic plants and enhancement and releasing fish in Dianshan Lake.However,to control eutrophication in shallow lakes must take both external loading of nutrient and internal ecological restoration.Therefore,lake restoration must be conducted subsequent to control of nutrient loading.Thus,some advices are presented as below:eutrophication control is a long and complicated process;the major fators for early warning and forecasting the Blue-green algae bloom were pH,water temperature,wind and light.The overall eutrophication control schemes must be combined with the hydraulic condition improvement,source control and ecological restoration.