Lake Eco-system Variation And Health Evaluation During The Construction Period

The middle and lower reaches of the Yangtze River have been affected by frequent human activities in the past few decades.The area of lakes has been decreasing and the eutrophication level has also increased significantly.The operation of the upstream Three Gorge Project change the hydrological rhythm of the Yangtze River,aggravated the low water situation of the lakes along the river,changed the structure and function of the wetland ecosystem,and led to the degradation of fish and migratory bird habitats.Therefore,the monitoring of the water environment and water ecology of lake in the middle reaches of the Yangtze River will be carry out,the water environment management and water ecology restoration of damaged lakes will be carried out,the ecological evaluation health system will be built to evaluate the ecological health of the lakes,and the comprehensive management of the lake ecology will be based on the evaluation results The restoration and management of lakes in the middle reaches of the Yangtze River under dry conditions are of great significance.However,most of the existing evaluation method are based on single physical and chemical index of water quality,which is difficult to meet the need of lake ecological management.This thesis combines the"Research and Demonstration of Ecological Restoration Technologies for Typical River-Tong Lake Lake Wetland Ecological Restoration Technology"of the Chinese Academy of Sciences Class A Strategic Leading Science and Technology Special Project,and focuses on Poyang Lake,and is selected Fanglan Lake as the research object,which is a typical lake on the shore of Poyang Lake,and on-site monitoring and investigation of the water environment and water ecology of the Fanglan Lake area have been carried out,and the background of the water environment indicators and water ecological indicators of the Fanglan Lake area has been mastered And evaluate the quality of the water environment;calculate the background value of pollution source in the Fanglan Lake area,identify the main water ecology and water environment problems faced by the Fanglan Lake area;carry out the ecological restoration of the Fanglan Lake Long-term water quality and water ecology monitoring,analysis of the temporal and spatial characteristics of the water ecological environment and the current status of water ecology in the Fanglan Lake area.On this basis,the biological integrity index applicable to the lakes in the region was determined,the comprehensive evaluation index of lake ecological health was constructed,and the ecological health of Fanglan Lake was evaluated.The main findings are as follows:（1）I had evaluated the environmental quality of the background water using the single factor index method with Class III water as the standard in the Fanglan Lake area.The result showed that the incoming water of Fanglan Lake was under Class V water and the inner lake was in Class V water.Among them,the maximum over-standard multiple of TN at the lake entrance is 3.43 times,which is inferior to Grade V water.The maximum excess of TP is 1.96 times,which is inferior to Class V water.Ammonia nitrogen and COD_Mnbelong to Type II and III water respectively.DO belongs to II water standard.In Inner lake,the maximum excess multiple of TN is 2.60 times,which is inferior to Category V water;the maximum TP excess multiple is 3.98 times,which is on the edge of Category V water;ammonia nitrogen and COD_Mn belong to Category II and III water respectively.DO is in the category I-II water.（2）A total of 181 species of aquatic algae were collected from the investigation of Fanglan Lake’s aquatic ecological background,of which Chlorophyta was the dominant species,with a total of 89 species,accounting for 49.17%.（2）There has 32 species of zooplankton,of which rotifers are the dominant species.There are 21 species in total,accounting for 65.63%.（3）There has 27 species of benthic animals,and arthropods are the dominant species,totaling 19 species,accounting for 70.4%.（4）There has 16kinds of aquatic plants,.（3）The pollution source accounting and problem diagnosis results of Fanglan Lake show that the water quality in the Fanglan Lake area is poor at this stage,which is basically Category V,mainly because TN and TP exceed the standard.The Fanglan Lake area has environmental problems such as serious rainwater non-point source pollution in the early stage,serious agricultural non-point source pollution,most of the domestic sewage directly into the river,and the small amount of upstream water leading to the weakening of the dilution and self-purification capacity of the water body and the deterioration of water quality.（4）During the restoration period of Fanglan Lake,the annual average concentration of TN and TP indicators at each entrance of the lake exceeded the surface water level V standard.The annual average ammonia nitrogen at the entrance of the lake reached the level III water standard,and the annual average ammonia nitrogen at the spring ridge The value belongs to Grade V water,and other points belong to Grade IV water;the average concentration of DO at all entrances to the lake has reached the standard of Grade II water;the annual average concentration of COD_Mnat the mouth of the lake is in Grade IV water;Chl-a at the entrance of the lake The overall annual average concentration is low.The main over-standard indicators of Fanglan Lake’s inner lake are TN and TP,the ratio of the two is 10.76,and the average content of Chl-a exceeds 10ug/L,indicating that the Fanglan lake has the conditions suitable for algae growth.The average concentrations of ammonia nitrogen,COD_Mnand DO belong to the water standards of Type II,II and I respectively.The average concentration of TN,TP,ammonia nitrogen and COD_Mn at the mouth of the Fanglan Lake changes over time,showing the time change characteristics of autumn high and spring low.The average DO concentration changes over time showing the time change characteristics of winter high and summer low.Chl-a average The content changes over time showing a time trend of high in spring and low in winter.（5）The water ecology monitoring results of Fanglan Lake during the ecological restoration period are:（1）Fanlan Lake has 105 species of phytoplankton,of which Chlorophyta is the dominant species,a total of 49 species,accounting for 47%（2）Fanlan Lake has 36 species of zooplankton,and rotifers as the dominant species.20kinds,accounting for 55.6%.（3）Fanlan Lake has 30 species of benthic organisms,mollusks are the dominant species,a total of 24 species,accounting for 80%.（4）Fanlan Lake has 19 kinds of aquatic plants,8 kinds of emergent plants,5 kinds of submerged plants,4 kinds of floating plants,and 2 kinds of wet plants.（6）Based on the constructed lake water ecological health evaluation system,the water ecological health before and during the restoration of Fanglan Lake were evaluated respectively.The evaluation results show that the current restoration project of Fanglan Lake has been effective,and the ecological health status has changed from that before restoration.The"poor"level was upgraded to the current"medium"level.At the water environment system level,the evaluation level of Fanglan Lake under restoration was"good",which is a good improvement compared to before the restoration.At the level of aquatic ecosystems,the evaluation grade of Fanglan Lake under restoration is"medium",which has not changed from that before restoration,but the evaluation score is slightly lower.At the social service system level,the evaluation level of the Fanglan Lake social service system under restoration has been upgraded from“bad”to“medium”before restoration,indicating that although the restoration project has improved the water environment and surrounding environment of Fanglan Lake well,it has won the public Recognition.It also proposed the establishment of a comprehensive management agency for Fanglan Lake,speeding up the formulation of relevant laws,regulations and standards,perfecting the existing Fanglan Lake monitoring system,realizing the transformation of the lake from water quality management to water ecosystem management,and increasing public participation.Several future Fanglan Lake ecological health maintenance and management strategies.