Simulation of Phosphorus Inflow and Outflow Fluxes and Water Quality Prediction in Dongting Lake Area of the Yangtze River Basin:A Coupled Approach of Machine Learning and Traditional Hydrological Modeling
Fluctuations in phosphorus fluxes to and from the lake have a direct impact on the stability of river ecosystems.In the Dongting Lake area,where water quality fluctuates,the SWAT model was used to simulate the phosphorus inflow and outflow fluxes and to analyze the retention rate in each area.A coupled model was constructed based on hydrophysical processes,being trained by the results of the SWAT model and using the model to make scenario predictions of recent water quality in the lake area.The results showed that the inflow and outflow phosphorus fluxes in Dongting Lake showed obvious seasonal variations,with inorganic phosphorus being the main phosphorus format.From 2012 to 2021,the average TP inflow flux in Dongting Lake was 2.94× 104 t/a,the average TP outflow flux was 3.34×104 t/a,and the average TP outflow concentration was 0.13 mg/L.Among the sub-basins,the Sankou area as the area with the largest contribution of phosphorus flux into the lake and the highest TP output concentration,should be emphasized to manage the phosphorus pollution in this area.The low TP retention rate in the Dongting Lake area may turn it into an important source of TP in the lower reaches of the Yangtze River.Coupled modeling is relatively precise for simulating the output process of river phosphorus fluxes,with all NSE values>0.8,and all RMSE values are low at the RPE value at 10%level,which realizes the simulation modeling of the LSTM network instead of the large-scale distributed physical model.Based on the above model,the recent TP output concentration of Dongting Lake area was predicted according to the"Dongting Lake Water Environment Comprehensive Management Plan",and the scenario of controlling the TP concentration inflow into the lake in each area at 0.1 mg/L can realize the water environment planning objectives of the lake area.
phosphorus inflow and ouflow fluxescoupled modelmachine learningphosphorus retentionwater quality predictionDongting Lake areahydrogeologyenvironmental geology