| Sediment is a major concentration of heavy metals in aquatic ecosytems,and heavy metals in nature are classified as heavy pollutants,different forms of heavy metals can cause different environment effects.Therefore,analyzed and polluted evaluation the heavy metals in water sediments,the ecological risk assessment of water environment has a certain theoretical and practical significance.In this study,the Nanchang section of Ganjiang River was selected as the research object,and the sediment samples of 9 sections were selected for the four seasons(2016.9-2017.6).The total amount and morpHology of heavy metals(Cr,Cu,Zn,As,Cd,Pb)were analyzed,and determination of microbial communities to analyze the correlation between microbial communities and heavy metals.Based on correlation analysis,cluster analysis and principal component analysis,the source of different heavy metals was traced back,and the influence of heavy metals on the water environment was studied by Nemeru comprehensive index method,accumulation index method and potential ecological risk index method.Comprehensive evaluation,with a view to the water environment protection and decision-making to provide basic data.The main findings are as follows:(1)The total amount of heavy metals showed that the content of heavy metals in the two quarters of 2016 showed Zn > Cr > Pb > Cu > As > Cd,and the total amount of heavy metals in the two quarters of 2017 was Zn > Pb > Cr > Cu > As > Cd;From the morpHological analysis,Pb and Cd are the main ones,and the proportion of acid-soluble Cd is the largest,as the content of oxidized Pb decreases,the content of reduced state increases,indicating that the forms of Cd and Pb elements in coastal surface sediments are most sensitive to environmental changes.Cu and Zn are equivalent to the residual state,with the change of time,the Cu content in the oxidized state is decreased,in the acid soluble state is increased,and the amount of available Zn can be increased,which indicates that the Cu and Zn contents in the water may be disturbed by the change of the external environment.Cr,As in four quarters are mainly in the residual state,less prone to secondary pollution.(2)Different chemical forms of heavy metals in surface sediments of Nanchang section of Ganjiang River have a big difference between the effects on microbial community structure,there was a significant positive correlation between oxidizable state Cr,acid-soluble Cu and reducible As in Gramsus,Gram-negative bacteria,Gram-negative bacteria,is showed that the content of oxidized Cr,acid soluble Cu and reducible As could be determined according to the number of gram positive bacteria and gram negative bacteria.The reducible Pb and oxidized Pb were significantly positively correlated with fungi in March 2017,and negatively correlated with fungi in June 2017,indicating that in June 2017 by the rainy season and human disturbance,the increase of available Pb content inhibited the cell metabolism and activity of fungi.However,there was a significant positive correlation between the chemical forms of different heavy metals and the microbial communities in the surface sediments of the Nanchang section of the Ganjiang River,indicating that the microbial biomass in the surface sediments was not inhibited by heavy metals.(3)The correlation coefficient of heavy metal total shows that Cd,Pb,Zn and Cu have similar migration and transport behaviors in water environment,Cr and As are more likely to come from the same source of pollution.In June 2017,Cu-Zn?Cu-Pb and As-Cd was significantly related,indicating that more than one source of heavy metals might be available.From the point of view of cluster analysis,from September 2016 to June 2017,each quarter classification is As/Cd,Pb/Cr/Cu,Zn,Cr,As/Cd,Cu,Zn,Pb,Cr/As/Pb/Cd,Cu,Zn,Cr/Pb/Cu,Zn/As/Cd.From the clustering analysis between sampling points,it is found that the high value is divided into one class and the low value is divided into one class.From the principal component analysis is divided into two main components,the accumulation of the first principal components including Cu,Zn,As,Cd,Pb,mainly by the shore of the river sand mining activities,agricultural non-point source pollution composite effect,the second principal components of Cr have a higher load,small range the content in the section between the sampling,may be by natural geological control,no disturbance.(4)The coastal surface sediments in the study area were evaluated by Nemeru comprehensive index method,cumulative index method and potential ecological risk assessment method,The result shows: Three evaluation methods showed that the Gan River in Nanchang has slight ecological risk,while the north and south branches downstream in the potential ecological risk is relatively light,and there was no interference except for the human activities,three evaluation methods are basically consistent results.The cumulative index method and the Nemero composite index method show that Zn and Cd have some ecological risks in different sections,especially in the middle reaches of the south.The potential ecological risk assessment also indicated that the 6 species of heavy metals Cd had the greatest potential ecological risk coefficient,followed by As.(5)Based on the analysis of the total amount of heavy metals,morp Hology and microbial community,the risk of heavy metals in surface sediments was evaluated by Nemeru comprehensive index method,land accumulation index method and potential ecological risk index method.Combining with cluster analysis,Analysis of heavy metal sources for analysis.In general,the high value area of heavy metal content in the surface sediments of Nanchang section of Ganjiang River is mainly concentrated in the middle reaches of the south branch of Jiangxiang and Chucuo section,and it is mainly caused by agricultural surface source,sand mining vessel and domestic sewage discharge.The middle and lower reaches of the North Branch show great differences in the four seasons due to different regions,and the Changyi section is the least affected by human interference.The Ganjiang Nanchang section is subject to different levels of human disturbance,in the future environmental monitoring should be strengthened on the sand industry and agriculture pollution monitoring,especially Jiangxiang,Chucuo rolling section,to minimize the impact of human disturbance on the water quality caused by the city of Nanchang to provide a good ecological environment. |
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