Study On Ecological Simulation And Ecological Water Demand Based On PCLake In Baiyangdian Lake

Baiyangdian Lake,the largest freshwater lake in the North China Plain,is the most important component of the blue-green space in Xiong’an New Area.Its water ecology is directly related to the process and quality of ecological city construction in Xiong’an New Area,which is“blue-green interweaving,fresh and bright water quality,and water-city integration”.In recent years,the scarcity in water quantity and deterioration in water quality in Baiyangdian Lake has been effectively alleviated through ecological water replenishment and external pollution control,however,its impact on the lake ecosystem and its stabilization mechanism are still unclear.The shallow lakes may show the clear state dominated by macro submerged vegetation or the turbid state dominated by phytoplankton.The mutual shift process between the two states is called regime shift.To some extent,regime shift can reflect the response law and change trend of lake ecosystem with the change of external conditions.In this study,a simulation model of Baiyangdian ecosystem was constructed based on the PCLake model.On the basis of parameter calibration and model verification,the response laws of Chl-a concentration under different P loadings are simulated,and the results fit well with the measured values.This research finds that the catastrophe threshold and the recovery threshold of Baiyangdian Lake are 1.57 mg/m~2/d and 0.835 mg/m~2/d,and the main influencing factors can be divided into internal factors(sediment type,water surface area and lake depth,etc.)and external factors(nitrogen-phosphorus ratio in nutrient loading,climate change,and fishery rate,etc.).The suitable water depth of Baiyangdian for promoting the shift from the turbid state to clear or maintaining the clear state is about 2.0～3.1 m,and the optimum water depth is about 2.2～2.9 m.The monthly average appropriate depths has been obtained,which are 2.2～2.9 m in January,February,November and December,2.2～3 m in March,April and October,2.3～3.1 m in May and September,2.6～3.3 m in June and July,and 2.5～3.3 m in August.The appropriate ecological water replenishment of Baiyangdian is 400 million m~3.And the optimal ecological water replenishment schemes is 90 days from December in winter,60 days from April in spring,and 90 days from August in summer.Replenish water in advance from July if it happens serious water shortage.This study explaines the clear-turbid regime shift law of Baiyangdian ecosystem,obtains the thresholds,analyzes the main influencing factors and puts forward the suitable water depth and ecological water replenishment scheme in line with the ecological water demand of Baiyangdian Lake with the goal of the clear state,which can provide a scientific basis for the ecological restoration,the formulation of long-term environmental management measures and the implementation of ecological water replenishment project.