| Environmental pollution is the primary issue that needs to be resolved in the current development of the basin.Jurong catchment belongs to the Qinhuai basin,a tributary of the Yangtze River.It is located in the Yangtze River Delta region with rapid economic growth.The basin has been threatened by the pollution of organic matter,persistent organic pollutants and heavy metals brought about by industrial development in recent decades.Pollutants can migrate through various media in the basin such as water,soil,gas and so on,resulting in a serious threat to environmental safety and human life.Therefore,from the perspective of ecological security and basin development,the study of pollutants distribution characteristics,sources identification and influencing factors were of importance.And the assessment of ecological risk is required for the environmental pollution control and basin management.In this study,Jurong catchment was taken as the research target area.From the perspective of ecological environment,the spatial distribution characteristics of nutrients and the contents of various elements in the water environment of the small catchment were analyzed.The particle size distribution and structure changes of the sediments in different sampling sites were compared.The characteristics of polycyclic aromatic hydrocarbons(PAHs)and heavy metals contents in different depths of the sediments were studied.The effects of land use types changes and organic matter contents on pollutants distribution were discussed.Combined with multivariate statistical methods,molecular ratio method and PMF model,the sources of pollutants were identified and ecological risk assessment was carried out.The main conclusions obtained are as follows:(1)The water quality in the study area is at a moderate pollution level.However,high TN concentrations were found here and there in the small catchment.The concentration of TN in Jurong catchment is between 0.94?2.14 mg/L,with a mean value of 1.55±0.29 mg/L,which belongs to the national surface water class IV water standard.The TN concentration in the water body of Jurong catchment is lower than that of the downstream.The nitrogen in the small catchment comes mainly from the catchment itself and is enriched along the river in the downstream.The TP concentration in the small catchment ranges from 0.02 to 0.23 mg/L,and the average value is 0.09±0.07 mg/L,which is equivalent to the national surface water class ?standard and is relatively clean.The TP concentration in the downstream is slightly higher than that in the small catchment.The contents of some elements in water bodies is below the national standard limit,indicating no pollution.The water in the small catchment can be used for agricultural irrigation and fish farming.The results of the water quality index and the Nemero pollution index show that the water quality is at a moderate level of pollution.The result of principal component analysis indicates that the main factors affecting the water quality include the losses of chemical fertilizer,discharge of domestic and aquaculture wastewater and the temperature.(2)The sedimentary environment is stable with a rich content of the organic matter.The results of particle size analysis show that the content of silt(fine silt+coarse silt)in the sediments of Jurong catchment is high(93.05%),and the difference among the particle size is not obvious,indicating that the hydrodynamics in the catchment is weak and the sedimentary environment is stable.Scanning electron microscopy analysis shows that the sediments in the small catchment are rich in organic matter.The concentration of TN in the sediment profile ranges from 192.74 to 4764.46?g/g.The TN concentration first increases then decreases with the deposition time.The mean TN concentration is higher than the US EPA standard of 2000 ?g/g.(3)The pollution levels of heavy metals in the sediments of the small catchment are quite different,and the pollution of Cd,As and Ni is serious.The main source of heavy metals in the catchment is pesticide application.The contents of Cr,Mn,Co,Ni,Cu,Zn,As,Cd and Pb in the sediments of the small catchment are quite different.The result of principal component analysis shows that the use of pesticides contributed to the highest proportion,33.40%.The landfill of metal waste contributes 27.41%,and the metal smelting accounts for 16.15%.The sources of Cd-As,Co-Mn,and Cu-As may be the same.The results of heavy metal enrichment index and geoaccumulation index show that the order of heavy metal pollution is as follows:Cd>As>Ni>Pb>Cu>Cr>Zn>Co>Mn.Cd has the highest pollution degree.Cd,As and Ni are highly enriched and the evaluation of the accumulation index reaches high.Cu and Pb are moderately enriched and lightly polluted.No pollution of Cr,Mn,Co and Zn were found.(4)The concentration of PAHs in the small catchment is at a high pollution level.The PAHs are derived mainly from tail gas emissions and coal combustion.The source of PAHs in the catchment was analyzed by molecular ratio method,principal component analysis and PMF model.The result of the molecular ratio method shows that the PAHs in the catchment are mainly from fossil fuel combustion.Principal component analysis shows that the most important input source of PAHs in Jurong catchment is tail gas emission,followed by coal combustion,coke oven combustion and biomass combustion.The result of the PMF model shows that tail gas source(diesel and gasoline combustion)(28.31%),followed by coal combustion source(25.02%),followed by mixed sources(14.83%)are dominant.Coke combustion source(14.60%),petroleum combustion source(12.07%)and biomass combustion source(5.17%)are also the contributors for the sedimentary PAHs.The results of principal component analysis and PMF model analysis are consistent with the molecular ratio method,indicating that the PAHs in the catchment are mainly derived from high-temperature combustion of fossil fuels.The first input source is the exhaust gas emission,and the second input source is the coal combustion.(5)The ecological risks of pollutants in Jurong catchment exist.Eco-risk interval(ERL/ERM)and toxic equivalent factor(TEF)methods were used to evaluate the ecological risk of the PAHs in the catchment.The result of ERL/ERM shows that the average concentration of three PAHs of Ace,Ant and Flua exceeded the low value of ecological effect interval by 4.76,5.06 and 8.37 times.In addition,the mean values of BaP and IcdP are higher,and there is an ecological risk.The result of TEF shows that the toxic equivalent concentration of ?PAHs in the catchment ranges from 3.29 to 757.77 ng/g,and the overall pollution level is higher.The toxic equivalent concentration of BaP and IcdP exceeds 100 ng/g,which is the main toxic equivalent of Jurong small catchment. |
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