| This research was conducted in Lake Taihu,which was suffered from fluctuant decline of water quality and large amounts of pollutants flow into it because of heavy rainfall,using the method of numerical modelling.We established the relationship between rainfall and inflows and used a three-dimensional hydrodynamic-water quality model ELCOM-CAEDYM,based on measured hydrological and water quality data,to analysis temporal and spatial distributions and variations of water quality in spring(May),summer(August),autumn(November)and winter(February)in 2016.We simulated the water quality by setting different rainfall scenarios in order to understand the change of water quality under continuous heavy rainfall and provide theoretical support for comprehensive management of water environment.The results of calibration and validation of coupled model showed that the values of water temperature and dissolved oxygen were in good agreement with the measured values,but the values of total nitrogen and total phosphorus had some deviation from the measured values.The simulation results and the measured values were consistent in the trend of change.The study found that the water temperature in Lake Taihu showed obvious seasonal variation characteristics,the summer temperature was high,the winter temperature was low,and the spring and autumn were the transitional season.In the spring and summer,the water temperature in the western coastal lake area was slightly higher than that in the eastern lake area;in the autumn and winter,the temperature in the southwest lake was lower than that in the northwest lake.The variation of dissolved oxygen was high in winter and small in summer.In the spatial change,the dissolved oxygen concentration in the northwest lake area was lower than that in other areas.The TN simulations showed that the nitrogen concentration in winter and spring were higher than that in summer and autumn.For phosphorus,the concentration of total phosphorus in summer was the highest,the concentration of total phosphorus in autumn was the lowest,and the concentration of total phosphorus in Lake Taihu fluctuated in the whole year,which showed the trend of increasing first and then decreasing.In spatial variation,the northwest lake area appeared the total nitrogen and total phosphorus concentration peak because of mainly affected by the external input.The relationship between rainfall and inflow of Tiaoxi,Tao River and South River water system were significant,and R2 values were 0.79,0.7,and 0.61.The forecast values of the three different water systems were within the scope of the permissible error.The precision level of the Tiaoxi water system and the Tao River system could reach Grade C,which can be used for reference forecast.The accuracy level of the South River water system was below Grade C and can only be used for reference Estimated.In this paper,the design of two different levels of rainfall program,sustained heavy rainfall would increase the concentration of nitrogen into the lake,but the phosphorus concentration didn't significantly increase.In addition,the increase of rainfall in the basin had a certain degree of dilution effects on the nitrogen and phosphorus concentrations.From the response of nitrogen and phosphorus nutrients to different levels of rainfall,it is recommended to control the input of exogenous nitrogen,so as to ensure the long-term development of Lake Taihu. |
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