Study On Wudalianchi Hydrodynamic Water Quality Simulation And Eutrophication Evaluation

With the rapid development of China's industry and agriculture,the pollution of lake water is serious,and the problem of eutrophication of lakes,reservoirs and other bodies of water is a major concern in today's society.The lake is ornamental and independent and is an indispensable part of the terrestrial water ecosystem.Most lakes are polluted by the over-breeding of algae and other plankton,and the self-purification capacity of water bodies is destroyed,resulting in the eutrophication of water bodies,reducing the transparency of water quality and the biodiversity in water,and destroying the water ecological balance.The study of lake water environment has two parts: field observation experiment and numerical model simulation.A large number of scholars at home and abroad have conducted theoretical research in the field of numerical simulation.Based on the existing models,the boundary conditions have been continuously improved.The modules have been input,and the new theories and methods have been added to optimize hydrodynamic water quality models.Combining the evaluation system can provide an effective and convenient scientific basis for managing and safeguarding the ecological health of lakes and other bodies of water.Wudalianchi Lake is located in the west of Wudalianchi City,Heilongjiang Province and is a national nature reserve.Wudalianchi City fully promotes green development.The city adhere to the development concept of “Lucid waters and lush mountains are invaluable assets” and strictly implement the environmental protection system.In order to maintain the ecological safety of rivers and lakes,perfect the water quality at mountain pass,lake outlet and estuary,the automatic monitoring system and the pipe network project of living area sewage have been developed,and lake ecological environmental protection projects and water pollution prevention and control projects in the Nagar River Basin and so on have been well-established.Focusing on the construction of key national ecological function areas,the city carries out special treatment of water pollution.In recent years,the rapid development of urban economy around Wudalianchi and the agricultural pollution caused by long-term farmland cultivation have increased the lake pollutants in Wudalianchi,and the water quality of lakes has deteriorated significantly,resulting in a moderately eutrophic state.In order to prevent the deepening of eutrophication in Wudalianchi,effectively protect and purify lake water quality,protect the safety of drinking water in downstream towns,and effectively manage and monitor lakes,comprehensively understand the temporal and spatial relationships of lake water quality,the study chose the urban landscape lakes-Heilongjiang Province Wudalianchi Lake was as a research object.The EFDC model was used to establish a model,and the water quality of Wudalianchi was evaluated by using the AHP method and a variety of lake eutrophication assessment methods,and the eutrophication degree of Wudalianchi was graded.The main research results of this paper are as follows:1.Based on the ?-coordinate system,the three-dimensional hydrodynamic and water quality model of Wudalianchi was established using the EFDC model.The parameters of the model were calibrated and verified according to the hydrological and water quality monitoring data collected in each month of 2015-2016 to reveal the change characteristics of water quality of Wudalianchi with time and space.2.The water temperature,dissolved oxygen,total nitrogen,total phosphorus,chlorophyll a,and ammonia nitrogen simulated by the constructed EFDC model conformed to its actual annual variation in the temporal and spatial relationship.The total error between the simulated value and the detected value did not exceed 30%,which proved that EFDC model has feasibility and effectiveness in Wudalianchi water quality hydrodynamic simulation.The characteristics of water quality changes in Wudalian Lake were analyzed,and the correlation between water quality changes and geological structure,hydrological characteristics and nutrient input was obtained.3.From the concentration of pollutants entering the lake,three kinds of extreme load scenarios were set up,and the EFDC model was used to simulate the eutrophication status under the three different load conditions.The study found that: Compared with the normal situation,the control effect of algae outbreaks was most significant when the pollution concentration of the control pollution source was reduced by 20%,and the peak value of chlorophyll a was reduced by 33%;and when 50% of the pollutants flowed in unexpected rainstorm during farming period,the case of algal blooms significantly,the peak value of chlorophyll a increased by 94.4%.Therefore,controlling the influent concentration of pollution sources is the main measure to suppress algal blooms and reduce the degree of eutrophication.4.The water environment indicators of seven sampling sites were evaluated,and the evaluation results of total nitrogen,total phosphorus,and permanganate exceeded the standards of environmental water quality indicators.Five associating pools took eutrophication of water to varying degrees,and the third pool had the highest risk of bryophyte with the highest eutrophication score.The research results provide an effective basis for decision-making for Wudalianchi pollution emergencies and water quality assessment.