Heavy Metal Distribution Characteristics Of Daxi Reservoir

As a non-degradable and cumulative pollutant,heavy metals are usually produced by natural and human activities.Heavy metals enter aquatic systems through surface runoff and other means,thus posing a threat to the aquatic environment,organisms and humans.Daxi Reservoir is an important water source in Liyang.The sources of pollution from agricultural surface sources,domestic point sources and mining in Daxi reservoir.Heavy metals enter water bodies through surface runoff and atmospheric deposition.In addition,the interaction between water bodies and sediments can cause heavy metals to accumulate in the sediments.In this study,the spatial and temporal distribution characteristics of 12 heavy metals（vanadium,chromium,cobalt,nickel,copper,zinc,arsenic,selenium,cadmium,lead,mercury,and manganese）in water bodies and sediments were investigated and analyzed.Analysis of the sources of heavy metals in the Daxi Reservoir basin using multivariate statistical methods and absolute principal component score-multiple linear regression（APCS-MLR）.The environmental,ecological and human health risk assessment of heavy metals in water bodies and sediments in the Daxi Reservoir basin has been carried out,which can provide stronger technical support for the protection of the aquatic environment in the Daxi Reservoir basin.The main findings are as follows:（1）Seasonally,the maximum annual average concentration of each heavy metal accumulated in the water bodies in the Daxi Reservoir basin in autumn.Meanwhile,the annual average concentration of zinc was the largest,and the annual average concentrations of 12heavy metals did not exceed the concentration limits of surface water environmental quality standards for Class III water,the concentration limits of supplementary and specific items.Seasonal variability in vanadium,chromium,copper,zinc,arsenic,selenium,cadmium,mercury,and manganese across the four seasons.Spatially,the cumulative annual average heavy metal concentration in the Zhucao River is higher than that in the reservoir bank zone.Spatial variability of chromium,nickel,copper,lead,cadmium,selenium,mercury,and manganese in the reservoir zone and the Zhucao River.（2）Seasonally,the highest annual average winter accumulation of each heavy metal in the sediments of the Daxi Reservoir basin.Meanwhile,the annual average content of manganese is the largest,and the annual average content of vanadium,cobalt,zinc,selenium,lead,mercury and manganese exceeds the soil background value in Jiangsu Province.Except for Mn,all the eleven heavy metals have seasonal differences.Spatially,the cumulative annual average heavy metal content of the Zhucao River is higher than that of the reservoir bank zone.Spatial variability of chromium and selenium in the reservoir bank zone and Zhucao River.（3）The correlation of heavy metals between water and sediment showed a significant positive linear relationship for vanadium,chromium,cobalt,arsenic,lead and mercury.Overall,water content,p H,Chla,LOI,and sediment of DOC were significantly and positively correlated with sediment heavy metals;a significant negative correlation between water temperature and sediment heavy metals.WT,Chla,COD_Mn and heavy metals in water were significantly and positively correlated;DO,ORP,sediment DOC and heavy metals in water bodies were significantly and negatively correlated.（4）In the water,cluster analysis showed that zinc and manganese were grouped in one category and the remaining 10 heavy metals were grouped in another category;the space is mainly divided into two categories:Zhucao River and reservoir bank zone.In the sediments,cluster analysis showed that Mn was classified in a single group,the other eleven heavy metals were classified in another group.Except for arsenic,selenium,mercury and manganese,The correlations of heavy metals in water bodies showed positive correlations among the other eight heavy metals.The correlation of sediment heavy metals showed that most of the heavy metals were positively correlated with each other,but mercury was basically negatively correlated with the other eleven heavy metals.Overall,sediment heavy metals are more strongly correlated than aqueous heavy metals.In water bodies,the principal component analysis was divided into four main sources:mixed sources of natural and agricultural activities,mixed sources of natural and industrial activities,mixed sources of atmospheric deposition and agriculture,and agricultural activities.The sources of vanadium,nickel,selenium and cadmium are agricultural and natural mainly.The sources of nickel,copper and zinc are agricultural activities mainly.In addition,there are also unknown sources.In the sediment,the principal component analysis was divided into three sources:mixed natural and agricultural sources,mixed agricultural and atmospheric deposition sources,and natural sources.The sources of vanadium,cobalt,nickel,copper,arsenic,lead and manganese are agricultural and natural mainly.The source of zinc,arsenic,cadmium and mercury are agricultural and atmospheric deposition mainly.The source of chromium,selenium,and mercury are natural mainly.（5）Based on heavy metals in water bodies,Nemero comprehensive pollution evaluation show that the overall environment of water bodies in the Daxi Reservoir basin is in the non-pollution to moderate pollution level.Heavy metals in water bodies have caused seasonal pollution in the Daxi Reservoir basin,but the overall pollution level is light and mainly belongs to the Zhucao River.The comprehensive potential ecological risk shows that the overall ecology of water bodies in the Daxi Reservoir basin is at a slight ecological risk,but the ecological risk level of mercury is high.Based on sediment heavy metals,the overall ground accumulation index indicates that the Daxi Reservoir basin is at an uncontaminated level.However,chromium,cobalt,nickel,selenium,lead,mercury and manganese are at some points in the uncontaminated to lightly contaminated level,with the most contaminated points of Hg.Sediment heavy metals also produce seasonal contamination of the environment in the Daxi Reservoir basin.Overall sediment heavy metals pose a slight ecological risk to watershed ecology,but the potential ecological risk of cadmium and mercury is high.（6）Overall human health risks to adults and children from heavy metals in water and sediment in the Daxi Reservoir basin are at acceptable levels.In water bodies,nickel,arsenic and chromium have carcinogenic risks above maximum acceptable levels for adults,and arsenic negatively affects non-carcinogenic risks for children.In sediment,heavy metals did not have significant negative effects on adults and children at both carcinogenic and non-carcinogenic levels.