Research On Ecological Water Level Of Fuxian Lake Based On Habitat Simulation Metho

With the fast expansion of the 21st-century social economy,the influence of human production and lifestyle on the natural environment is expanding.Nowadays,the rate of growth and exploitation of water resources is continually growing,resulting in conflicts between humanity’s expanding social requirements and the carrying capacity of the water environment.Because certain river and lake ecosystems have been harmed,maintaining river and lake ecosystems and strengthening water bodies’ self-regulation abilities have been the focus of social concern.By literature study,this paper examines and summarizes the development process of ecological environmental water demand,lake ecological water level,and habitat modeling methods at home and abroad.A comprehensive analysis of the water level variation characteristics and influencing factors of Fuxian Lake was conducted using long-series hydrological data,and a three-dimensional hydrodynamic water quality model of Fuxian Lake with satisfactory accuracy was constructed.Choose the target species for Fuxian Lake and compute the habitat-weighted available area using the standard habitat simulation approach(WUA).According to the characteristics of deep water lakes,the concept of vertical weighted available area(V-WUA)is proposed to calculate the appropriate ecological water level corresponding to the maximum value of V-WUA,providing a scientific reference basis for the ecological water level regulation of Fuxian Lake.The primary conclusions of this study are as follows:(1)From 1953 to 2020,the interannual variation of the water level in Fuxian Lake is characterized by an upward downward downward downward trend,and the seasonal variation is characterized by a high water level in autumn and a low water level in spring.According to the water balance analysis,runoff into Fuxian Lake has decreased significantly in recent years,which could be one of the main reasons for the lake’s water level decline.Using the cumulative slope change rate method to quantify the impact of climate change and human activities on runoff change in the Fuxian Lake basin at various stages from 1962 to1974,it was discovered that human activities played a leading role,but the contribution rate has decreased in recent years.The relative contribution rates of climate change and human activities were 10.0% and 90.0%,respectively,from 1975 to 2008;from 2009 to 2020,the relative contribution rates of climate change and human activities were 18.1% and 81.9%,respectively.Human activities’ contribution rate to runoff has decreased as a result of factors such as the implementation of watershed water intake permit management,the relocation of industrial parks,and the operation of water diversion projects.(2)A three-dimensional hydrodynamic water quality model of Fuxian Lake was created based on EFDC.The results show that the model accurately reproduces the process of water level change with an average error of-0.004 m,a relative error of 0.001%,an average absolute error of 0.014 m,a root mean square error of 0.02 m,a correlation coefficient of0.995,and a Nash coefficient of 0.995.The average error of surface water temperature simulation is 0.184 ℃,the relative error is 1.049%,the average absolute error is 0.612 ℃,the root mean square error is 0.536 ℃,the correlation coefficient is 0.931,and the Nash coefficient is 0.836;The verification result of vertical water temperature calibration is consistent with the measured result.The relative error of vertical water temperature at all monitoring points is within 10%,and the correlation coefficient is greater than 0.85,accurately reproducing the water temperature change process.At the same time,a water quality model is further constructed based on the hydrodynamic model of Fuxian Lake.The simulated water quality indicators include dissolved oxygen,total phosphorus,total nitrogen,ammonia nitrogen,chemical oxygen demand,and chlorophyll a.The simulation results better reflect the trend and range of changes of the six indicators,and the error statistics are within a reasonable range.(3)The ecological water level of Fuxian Lake was calculated using the habitat simulation method.Select the anti-wave white fish as the target species,select water temperature,flow rate,and dissolved oxygen as key habitat factors,and draw the suitability curve of each habitat factor.Under the sustained action of southwest wind with an average wind speed of 4m/s for many years,different water level gradient scenarios are designed for hydrodynamic water quality model simulation.The WUA values obtained from the fitness index of three factors in each layer within the range of 0～20m underwater were calculated,and the vertical weighted utilization area(V-WUA)was accumulated.Establish a relationship curve between water level and V-WUA,and determine the suitable ecological water level of Fuxian Lake as 1722.63 m based on the maximum value of V-WUA.The rationality of the suitable ecological water level is demonstrated by comparing it with the statutory minimum ecological water level and the target water level for the operation and management of Fuxian Lake.