Research On Preventing And Controlling Countermeasures Of Lake Eutrophication Based On Delft-3D-AQUATOX Coupling Model

Qinglong Lake is located in the National Bird National Nature Reserve of Xinxiang,Henan,and is an important transfer station for migratory birds in my country.Man-made disturbances such as the influx of pollutants and the interception of sluices and dams have affected the quality of the lake water environment and aggravated the eutrophication trend.In order to improve the water environment quality of Qinglong Lake,based on field investigations,this study obtained the lake’s hydrology,water quality,phytoplankton data,and analyzed the lake’s physical and chemical properties and phytoplankton community characteristics;based on Delft-3D and AQUATOX models,An integrated model of hydrodynamics,water quality,and water ecology of Qinglong Lake was constructed.After checking,the water quantity,water quality and phytoplankton community of Qinglong Lake were simulated;based on the simulation data,the trophic level index at different periods was calculated;the phytoplankton was simulated and analyzed.Through correlation analysis and algae restriction factor analysis,the influence of environmental factors on the phytoplankton community was analyzed;combined with the trophic level index in different seasons,through simulation analysis,the response relationship between the water quanitity and the trophic level index in different periods was discussed,and the water supplement threshold was clarified.The main conclusions were as follows:(1)The water volume fluctuates slightly,and the p H value remains basically stable;the total nitrogen content in Qinglong Lake fluctuated betweenⅣ～Ⅴ;the total phosphorus content varies betweenⅢ～Ⅳ;the ammonia nitrogen fluctuates betweenⅡ～Ⅲ;the dissolved oxygen met theⅠstandard.The seasonal variation range of chlorophyll a was 0.87～94.12μg/L,and the average mass concentration was 27.93μg/L;The seasonal variation range of the trophic level index was between 48.1 and 67.1,with an annual average of 57.8.In spring,Qinglong Lake was mildly eutrophic state;in summer and autumn,the lake was moderately eutrophic;in winter,it was in a moderately eutrophic state.(2)The dominant phytoplankton communities in Qinglong Lake were mainly green algae,diatoms and cyanobacteria.Diatoms dominate at low temperatures,green algae and cyanobacteria were dominant species at high temperatures;the seasonal variation trend of total algae biomass was summer>autumn>spring>winter;the dominant community presents a seasonal succession of silicon-green-blue;related The analysis shows that environmental factors such as nitrogen,phosphorus,dissolved oxygen,water volume,water temperature,and p H have a greater impact on algae biomass.(3)The trophic level index of Qinglong Lake decreases with the increase of water volume.When the average annual water volume of the lake was between 30.82×10~4～47.37×10~4 m~3,the trophic level index was 53.2～57.3,and Qinglong Lake was in a mildly eutrophic state.When the average annual water volume of the lake was between 47.37×10~4～56.04×10~4 m~3,the trophic level index was between 49.1～53.2,and Qinglong Lake was in the middle-mild eutrophication state.When the average annual water volume was greater than 56.04×10~4 m~3,the trophic level index was less than 49.1,and Qinglong Lake was in a mesotrophic state.(4)When the water supplement reaches about 0.04 m~3/s,the nutritional status of Qinglong Lake can be improved to a certain extent.In addition to the medium nutrition in winter,the three seasons of spring,summer and autumn are all mildly eutrophic;the water supplement was0.05～0.06 m~3/s,Qinglong Lake was in a mesotrophic state in different seasons.