Ecosystem Health Evaluation And Total Pollution Load Control Of Hongze Lake

Hongze Lake is the fourth largest freshwater lake in our country and an important storage lake for the South-to-North Water Diversion Project.In recent years,purse seine farming,industrial and agricultural pollution load input,and high-intensity development and utilization of the shoreline have seriously affected the water environment quality of Hongze Lake and threatened the health of the water ecosystem in the lake area,and has a huge impact on the sustainable development of the society and economy in the Hongze Lake area.Therefore,to accurately and objectively evaluate the health of the Hongze Lake ecosystem,and to guide the improvement of Hongze Lake’s water quality and water ecological restoration,is of great significance for improving the ecological environment of Hongze Lake.Based on historical data analysis and supplementary monitoring and investigation,this paper comprehensively analyzes the current status and evolution of the water quality and ecology of Hongze Lake,diagnoses the key issues of water quality and water ecology,and provides a scientific basis for the construction of the Hongze Lake ecosystem health evaluation system;Through preliminary screening of evaluation indicators,optimization of independence and rationality,and integration of water quality,aquatic organisms,hydrology and morphology,and social service function elements,a comprehensive evaluation index system for the health of the Hongze Lake ecosystem has been constructed.Through the evaluation system,a comprehensive assessment of the health of the Hongze Lake ecosystem has been carried out,and the main water quality,aquatic biological and Lake morphology indicators that affect the ecological health of the Hongze Lake have been identified.Focusing on the water quality improvement and water ecology improvement goals of Hongze Lake,the nitrogen and phosphorus pollution load and water environment capacity of Hongze Lake into the lake were calculated,and a regional pollution load reduction space distribution system serving the improvement of water quality in key lake areas was constructed.And the spatial distribution of pollution load reduction in Hongze Lake was optimized,and total pollution load control measures aimed at improving water quality and water ecological restoration measures aimed at improving water ecological health were proposed.The main research conclusions are as follows:(1)The key water quality control indicators of the Hongze Lake area are total nitrogen(TN)and total phosphorus(TP),and the key water quality control indicators of the rivers entering the lake are TN and ammonia nitrogen(NH3-N).The water body is slightly eutrophication and heavy metal Hg pollution is serious;The phytoplankton diversity index of Hongze Lake in July was 2.76,and the phytoplankton diversity index was 2.05 in October.The dominant species changed from a single cyanobacteria to a variety of algae;The benthic diversity index in July was 1.05,and the benthic diversity index in October was 1.5.The status of benthic diversity is poor.(2)According to the results of the water ecological analysis of the Hongze Lake water quality,the integrated water quality,aquatic organisms,hydrology and morphology,and social service function indicators have constructed a comprehensive evaluation index system for the water ecological health of the Hongze Lake.The overall ecosystem health evaluation level is "medium".Compared with the local standards for evaluating the status of ecological rivers and lakes in Jiangsu Province,the constructed evaluation system highlights the shoreline morphology and hydrological indicators of Hongze Lake,removes the cyanobacteria density index,and can more accurately reflect the health of the Hongze Lake ecosystem.(3)According to the results of the Hongze Lake ecosystem health assessment,the total amount of TN and TP loads that affect the water ecological health of Hongze Lake is controlled.Taking the III water standard as the target,the load reduction of TN and TP into the lake should reach 57973.19 t/a and 2955.19 t/a,respectively.A multi-layer distribution system for regional pollution load reduction including fairness and considering the differences in the water quality status of different lake areas and the differences in water quality goals is to optimize the spatial distribution of the reduction of pollution load in Hongze Lake.The TN reduction of Huaihe input load is 33941.97 t/a,and the corresponding reduction of TP is 853.5 t/a;The TN reductions in Sihong County,Siyang County,Sucheng District,Xuyi County,Huaiyin District,and Hongze District along the lake are 5,422.33 t/a,2499.79 t/a,1976.29 t/a,5404.92 t/a,3132.82 t /a、2359.72t/a,and the corresponding reduction of TP is 556.77 t/a,268.66 t/a,103.18 t/a,606.5 t/a,186.07 t/a,and 380.51 t/a.Based on the distribution results of Hongze Lake pollution reduction and the health assessment results of Hongze Lake,measures to control the pollution load of Hongze Lake are proposed.(4)According to the key factors affecting the health of the Hongze Lake ecosystem,based on the idea of "point(biology)→ line(lake shore zone)→ surface(lake surface)",biological control measures for the restoration of biodiversity in Hongze Lake are proposed;A three-level ecological restoration system for the coastal zone around the lake,which aims at the restoration of vegetation in the lakeshore zone,combines the near lake area,the first-level buffer zone and the second-level buffer zone;And a measure to retreat to the lake for the restoration of the free surface of Hongze Lake are proposed.