Research On Evolution Of Water Quality And Water Environmental Regulation In An Artificial Lake

In recent years,the development of urban artificial lake is becoming a hot topic.Landscape function and self-purification capacity are often affected by environmental issues relating to water quality and water renewal capacity.Water exchange is an important physical process that determines the ultimate destination of pollutants.Through physical processes such as the advection and diffusion mechanisms,water mass is exchanged and transported out of a domain of interest,benefiting reducing pollutant concentration and thus improving water quality.In order to improve lake water environment,a series of methods relevant to water environmental regulations are commonly used to transfer freshwater into a lake by flushing the original water mass out of the study area.Therefore,it is meaningful and vital to grasp the evolution of water quality and conduct quantitative researches on water renewal capacity and the transport and diffusion process for a lake ecosystem system.In the study,an urban artificial lake was used as an example to conduct researches on the evolution of water quality,the water renewal capacity,the water renewal timescales,and the material transport process on a basis of a numerical model.(1)Details of the Environmental Fluid Dynamics Code(EFDC)were given.The numerical lake models of hydrodynamics and water quality were set up.The lake model was calibrated and verified using measured data and simulated values.The main parameters of the model were confirmed.The results show that the numerical model can effectively simulate hydrodynamic features of the lake with high accuracy.(2)The lake model was used to study the evolution of water quality under conditions of multi-year average wind and typical wind,thus summing up the rules of water quality variations in urban artificial lakes after a long term of rest.(3)Based on previous researches that mainly focused on flow field or concentration variations of water quality components,this paper used exchange rate and water renewal pathway as another two more indicators to study the influences of water environmental regulations upon water renewal capacity.The results illustrate that exchange rates become higher and tend to be stable gradually with increasing freshwater discharges and operation time.However,the increasing trend of exchange rates will not be significant any more once freshwater discharges are beyond the half of the biggest design value.Regulative measures are proved to be efficient in improving water renewal capacity among the whole lake.(4)On the basis of previous studies about water transport timescales applied in coastal waters,this paper broadened its application scopes to artificial lakes.Renewal time,water age and residence time were studied under water environmental regulations.The results demonstrate high renewal time in dead water bodies,spatial and temporal variability of water age distribution,and effectiveness of regulative measures on reducing residence times.(5)The calculation method of connectivity was improved and proposed to be exclusively applicable to artificial lakes for researches on material transport process.Understandings of transport and diffusion processes of pollutants and spatiotemporal variations within artificial lakes were deepened.It would help administrative authorities to determine the influence range of pollution issues and provide data support for water quality management.