Water Environment Security Assessment For The Pearl River Estuary And River Network

The Pearl River Estuary and River Network are core areas in the Guangdong-Hong Kong-Marco Greater Bay Area,which is densely populated and economically developed.So its water environment security is of great significanc.There are dense river networks formed by three main streams（the East River,the West River and the North River）,which flow into the South China Sea through Eight Major Outlet,making the area complex.The water quality control section and sudden change section of the three main streams and the key outlets（Modaomen and Humen）were selected to set up sampling sites to collect the water samples and analyze them separately,which were divided into low and abundant water periods,and each sampling period was divided into high tide and low tide.Firstly,the spatial and temporal distribution of heavy metals and nitrogen and phosphorus nutrients was studied,and then the health risk assessment of heavy metals was carried out.Secondly,the eutrophication assessment of water was carried out based on the entropy weight set pair analysis method,and the threshold of nitrogen and phosphorus for eutrophication was studied.Finally,based on the fuzzy comprehensive evaluation method,each evaluation index and its weight were determined to establish the water environment security assessment system of the Pearl River estuary and river network and evaluate it.The main results of this paper are as follows:（1）Based on the single factor and Nemero comprehensive pollution index method,the results show that the comprehensive pollution index values（P_N）of Lingdingyang 3,Lingdingyang4,Lingdingyang 5,Makou,Sanshui,and Modaomemen sections were 4.08,4.36,4.36,4.68,7.40,4.30 and 4.67,whicn belong to serious pollution level.The P_N values of Lingdingyang 1 and Lingdingyang 2 are 2.5 and 2.35 for medium pollution level,while the P_N values of Humen,North Shilong and South Shilong are 1.51,1.82 and 1.25,at mild pollution level.（2）The results of deterministic health risk assessment for heavy metals show that the order of health risk in each region was tidal priority estuary=the West River>river priority estuary>the East River>the North River.The results of uncertain health risk assessment show that tidal priority estuary>the East River>river priority estuary>the North River>the West River.Children’s health risk is higher than that of adults in both models,both of which are grade IV or V level risks.（3）Based on the entropy weight set pair analysis model,the eutrophication assessment of the study area shows that the East River is in a light eutrophication state,while the trophic levels of tidal priority estuary,river priority estuary,the North River and the West River are in a medium eutrophication state.According to set pair situation,the order of eutrophication degree in five areas is:the North River<tidal priority estuary<the West River<river priority estuary<the East River.The threshold of total nitrogen and total phosphorus for eutrophication is 2.11mg·L^-1 and 0.16 mg·L^-1 respectively.（4）The water environment security assessment system of the Pearl River estuary and river network is established by using the method of fuzzy comprehensive evaluation.The evaluation index is determined and its comprehensive weight is obtained by analytic hierarchy process（AHP）and entropy weight method,so as to carry out the fuzzy comprehensive evaluation According to the principle of maximum membership degree,the water environment security risk levels of tidal priority estuary,river priority estuary,the North River,the West River and the East River are level II low risk,level II low risk,level I non-risk,level II low risk and level II low risk respectively.The Pearl River estuary and river network as a whole is level II low risk.In conclusion,the heavy metal content was relatively high in the West River,the North River and their estuaries of the Pearl River estuary and river network,which represented security risk.The concentration of nitrogen and phosphorus was relatively high in the East River,which may lead to eutrophication.Except for the North River,the other areas are all level II low risk,and the Pearl River estuary and river network as a whole is level II low risk.