Research On The Water Quality Reaching Standard Of Section Based On The Analysis Of Pollution Sources

Wuzhong District is located in the geographic center of Suzhou City,bordered by Taihu Lake to the west and across the lake from Wuxi City and Huzhou City.The water area of Taihu Lake under its jurisdiction accounts for about three-fifths of the total area of Taihu Lake,and it is crucial to do a good job of water environmental protection in Wuzhong District to ensure the ecological safety of Taihu Lake and the sustainable development of Suzhou City.This paper selects surface water in Wuzhong District,Suzhou as the research object,and analyzes the interannual dynamic trends of water quality in different types of surface water bodies and the structure of pollution sources from 2015 to 2020based on the water quality monitoring data of each section.The spatial and temporal distribution characteristics of six water quality indicators in Wuzhong District,such as ammonia nitrogen（NH₃-N）,total phosphorus（TP）,permanganate index(COD_Mn),dissolved oxygen（DO）,five-day biochemical oxygen demand（BOD₅）and chemical oxygen demand（COD）,were selected as the mainline,and 16 municipal control sections were selected,and the improved Numero index method was used to make a comprehensive evaluation of water quality in Wuzhong District,and the multivariate based on zoning,the pollution source analysis of each monitoring section was carried out to analyze the sources of pollution in the water bodies of Wuzhong District from the source,and to get the contribution rate of the corresponding pollution sources,and to propose corresponding pollutant reduction measures,to provide a reference basis for the prevention and protection of water pollution in Wuzhong District in the future.The main research results are as follows.（1）Wuzhong District water environment quality is generally good,but some sections have exceeded the standard,the exceedance factor is mainly ammonia nitrogen and permanganate index.2015-2020 ferry bridge,Chefang Bridge,Hushan Bridge,goose real pond,anti-cultivation bridge,Dalongjiang Bridge,north gate mouth bridge,north port bridge gate,White Tower Bay and navigation control station and other 10 sections are to meet the water environment functional area water quality requirements,while in several other sections,Huanghua Jing section exceeded the standard for ammonia nitrogen in 2016;Guajingkou North and Yinshan Bridge sections exceeded the standard for ammonia nitrogen in 2015 and 2016;West Cross Pond Bridge section exceeded the standard for ammonia nitrogen in 2015 and 2018;Yuexi Bridge and Shanren Bridge sections exceeded the standard for permanganate index in 2015 and 2016.（2）After summarizing the emissions of various pollutants（COD,NH₃-N,TN,TP）in the Wuzhong District,it can be seen that urban domestic sources account for the highest proportion of total wastewater emissions,81%;industrial sources and aquaculture account for the highest proportion of COD emissions,47%and 13%,respectively;urban domestic sources account for the highest proportion of ammonia nitrogen emissions,76%;industrial sources account for the highest proportion of total nitrogen emissions,75%;and total phosphorus emissions,75%.The highest proportion of industrial sources and aquaculture in total nitrogen emissions is 75percent;the highest proportion of industrial sources and aquaculture in total phosphorus emissions is 44 percent and 26 percent,respectively.（3）Based on clustering partition,the pollution sources were identified and the contribution rates of each water quality index in different spatial groupings were obtained through principal component multiple linear regression.Among them,69.523%of pollution in group A（Guajingkou North,Yinshan Bridge,Huanghuajing）comes from domestic sources and industrial sources;73.281%of pollution in group B（Chefang Bridge,West Crossing Pond Bridge,Anti-Xiu Bridge,Shanren Bridge,North Zhakou Bridge,Baitawan,Yuexi Bridge,Dalongjiang Bridge）comes from agricultural sources and domestic sources;63.088%of pollution in group C（Hushan Bridge,Beigang Bridge Gate,Pendulum Bridge,Goshen Pond,Navigation Control Station）Pollution from agricultural sources,life sources.And combined with the results of water quality evaluation,Huanghuajing,Guajingkou North,Yinshan Bridge sections a key concerns,West Crossing Pond Bridge,Yuexi Bridge,Shanren Bridge sections a secondary key concerns.（4）Through on-site investigation of the six exceeded cross-sections and their surroundings,and combined with satellite maps,the main causes of exceedance of each cross-section were determined,and then specific management suggestions were made to achieve the standards to meet the requirements of the Class III water assessment target.For the Huanghuajing,Guajingkou North and Yinshan Bridge sections in the Beijing-Hangzhou Canal,it is necessary to strengthen the management of ships,crews and docks,improve the sewage collection device for ships,increase the publicity and education for the crew on centralized sewage and garbage discharge,and do a good job in the transformation of the docked barge to avoid sand and gravel into the river.For the West Cross Pond Bridge,Yuexi Bridge cross-section exists in the sewage treatment plant overload operation,the effluent concentration exceeds the standard problem,need to actively carry out the expansion of sewage treatment plant,complete the upgrading of sewage treatment facilities,to ensure that the tailwater stable discharge up to standard.Urban domestic sewage takeover rate of 100%,rural domestic sewage network coverage of decentralized treatment rate of 100%,strictly prohibit the direct discharge of domestic sewage into the river.For the phenomenon of agricultural surface source pollution at the Shanren Bridge section,it is forbidden to encroach on the ecological buffer zone of the river to reclaim private farmland and build nitrogen and phosphorus interception buffer ditches.