| Poyang Lake is a large-scale shallow lake.In recent years,the water quality of Poyang Lake has decreased significantly due to the continuous increase of pollution load in the basin,etc.The simulation of hydrodynamic and water quality model can effectively research the changes of hydrodynamics and water quality in the lake.Firstly,based on the hydrological and water quality data of Poyang Lake,the paper analyzed the temporal and spatial variation of water level,lake runoff and water quality indicators.Then,based on MIKE21 software,the hydrological data of five lakes were used as the boundary condition to construct hydrodynamic model.On this basis,CODMn,NH3-N and TP water were selected as water quality indicators to build a coupled model of hydrodynamics and water quality.Then the disturbance method was used to analyze the sensitivity of the water quality model parameters,then the water quality parameters were adjusted to calibrate the model.Finally,changing the runoff or pollution load and setting up three different scenario simulation schemes:10% increase in runoff into the lake,10% reduction in runoff into the lake and 5% increase in pollution load,obtaining the water environment changes of Poyang Lake under different conditions,which provides a theoretical basis for improving the water quality of Poyang Lake in the future.The main conclusions of the paper were as follows:(1)From 1953 to 2016,the annual average water level of Xingzi,Duchang,Tangyin,Kangshan and Hukou was Kangshan>Tangyin>Duchang>Xingzi>Hukou,showing the trend of decreasing from south to north in Poyang Lake.During the year,the trend of daily average water level of four points was basically the same,with a single peak.The annual average runoff of five rivers in Poyang Lake varied greatly,computing the ratio of the maximum and minimum annual runoff of five rivers,Fuhe gained 6.87,it was the biggest.During the year,the trend of average daily water level of five rivers was basically the same,with seasonal characteristics.(2)The CODMn of fiver rivers and four points reached the Class II standard in 2016-2018.Except for Xiushui and Raohe,the NH3-N reached the Class II standard.TP of Each point was the Class IV or Class V standard.During the year,CODMn fluctuated more than NH3-N and TP,and the water quality indexes of each point in the lake fluctuated more than the the entrance of fiver rivers.(3)As for parameters of water quality model,the diffusion coefficient can be regarded as insensitive parameter,and the sensitivity of the degradation coefficient is high.Calibrating the parameters according to hydrodynamic and water quality model,then calculating deterministic coefficient,Nash coefficient and average relative error of four points,and the simulation effect of the hydrodynamic model was great.In the water quality model,the simulation effect of CODMn was consistent with the actual situation,which was better than NH3-N and TP.Among the four points,the simulation effect of the water quality indicators at Xingzi was best.(4)Under the three simulation scenarios,the water level changes were as follows: the change rate of runoff was 10%,which made the water level change rate from 0 to 2% at each point,and only a few rivers exceeded 2%.The water level changes of Poyang Lake during dry season were bigger than that of wet season.The water quality changes were as follows: the CODMn,NH3-N and TP concentration values were ranked,Scheme 2> Scheme 3> Benchmark> Scheme 1.During the year,the change ratio of NH3-N fluctuated greatly.In terms of space,the impact of the change of the runoff on the three water quality indicators was CODMn>TP>NH3-N,and the change rate of the water quality indicators in the mainstream and western lake was higher than that of the eastern lake.The rate of change was basically less than the rate of change of runoff.The change of pollution load into the lake had the same impact on the three water quality indicators,and the points in the whole lake were consistent,which was equal to the change rate of pollution load. |
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