Research On The Evolution And Regulation Of Urban Lake Water Environment

Urban lakes have received constant attention in recent years.Urban lake water bodies often face problems such as substandard water quality,imperfect water ecological functions,and frequent algal blooms.In order to restore the vitality of urban lakes,different control facilities are often used to restore and improve the water environment.It is of great significance to grasp the evolution law of urban lake water environment and quantitatively study the effects of physical regulation,biological ecological regulation and physical-biological ecological joint regulation on the evolution of water environment.In this thesis,taking Lianshi Lake in Yongding River as an example,based on the analysis of the evolution law of the water environment of Lianshi Lake,the coupling model of hydrodynamics,water quality and water ecology was established by using EFDC,and the Ecopath model was used to analyze the nutritional structure and the ecological system of Lianshi Lake ecosystem.The energy flow was analyzed,and the effect of different regulation measures on the improvement of the water ecological function of Lianshi Lake was discussed.The research draws the optimal regulation scheme of water environment.The main conclusions of this article are:(1)Judging from the overall water environment monitoring of Lianshi Lake in different months,after the implementation of the Lianshi Lake"Underwater Forest"demonstration project in May 2020,the concentrations of TN and TP showed a downward trend,and the concentration of Chl-a was much lower than that in 2018.year and 2019.There is a risk of eutrophication in Lianshi Lake,and the release of nutrients from the decay of submerged plants plays a certain role in the increase of nutrient concentration in the study area.The study shows that nitrogen-containing nutrients and aerobic organic matter play a major role in the water pollution of Lianshi Lake.(2)Under the current flow rate Q=0.36 m~3/s,the water flow in the study area is extremely slow,and the average flow velocity in different areas is 0 m/s～0.003 m/s.The distribution of the flow field in the lake area is significantly affected by the underwater topography,and the circulation pattern is relatively In July and September,the Chl-a concentration in the whole lake gradually increased,and the maximum value appeared around 90μg/L.With the increase of make-up water flow,the improvement of hydrodynamic characteristics is obvious,and the average velocity of different zones is significantly improved,and when Q=20 m~3/s in May,July and September,the circulation structure in the study area is the least,and the circulation structure in the study area is the least.The improvement effect ofρ(Chl-a)in area 7 is the most significant,and the corresponding critical flow velocity is 0.02 m/s-0.03 m/s.It can be seen that it is feasible to control planktonic algae growth and water eutrophication by changing hydrodynamic conditions.(3)In May,July and September,the distribution of flow fields in different subregions was less affected by the planting area of different submerged plants.In May,under plan 3(Planting area 3.6ha),the overallρ(Chl-a)in the study area decreased.In July and September,compared with the no-planting scheme,scheme 3 had the best improvement effect onρ(Chl-a)in area 4(respectively decreased from 54.208μg/L to27.028μg/L,and from 70.296μg/L to 27.028μg/L,respectively.39.474μg/L).In July,theρ(Chl-a)for region 7 decreased most significantly(from 66.961 ug/L to 33.697 ug/L)in plan 3 compared with plan 1(Planting area 0.9ha).Therefore,within the range suitable for submerged plant growth,increasing the planting area can improveρ(Chl-a)to a certain extent.(4)According to the analysis of the nutritional structure and energy flow of Lianshi Lake and the research on the typical biological chain of algae control (phytoplankton-zooplankton-shrimp and crab-carnivorous fish)with zooplankton and shrimp and crab as the key species,Increasing the biomass of zooplankton and shrimp and crab to 3 times(respectively from 7.85 t/km~2-23.55 t/km~2,1.58 t/km~2-4.74 t/km~2)can significantly improve the problem of planktonic algae biomass,and can improve the Ecosystem maturity.