Risk Assessment Of Heavy Metals In Sediments From The Input River (Yang River) Of Guanting Reservoir

As a spare water source in Beijing,the water quality of Guanting Reservoir is highly concerned,and the improvement of water quality of Guanting Reservoir is largely determined by the water quality of the most important input rivers of Guanting Reservoir-Yang River,and the Beijing-Zhangjiakou Olympic Winter Games put forward higher requirements of water environment and water resources of Yang River Basin.However,there are distributions of iron and steel,thermoelectric,chemical and other industrial enterprises in Hebei Zhangjiakou section of Yanghe River Basin,the riverway accept a large number of industrial wastewater and domestic sewage.Clarifying the pollution characteristics and potential risks of heavy metals in Yanghe River by researching into the total content and chemical speciation and potential ecological risk of six kinds of heavy metals（Cd,Cr,Cu,Ni,Pb and Zn）of surface sediments ang sedimentary column from Yang River System.Research indicates that:1.The average concentrations of Cd,Cr,Cu,Ni,Pb,and Zn were 0.34,59.91,30.64,30.85,39.51 and 129.27 mg·kg-1,respectively.The source identification indicated that Cd,Pb,and Zn were mainly originated from the anthropogenic activities,while Cr,Cu and Ni were originated from the natural processes.The single-element potential ecological risk of heavy metals in Yang River System followed the order of:Cd>Pb>Cu>Ni>Cr>Zn.Among the studied metals,the potential ecological risk of Cd belonged to strong environmental risk,especially in Qingshui River,which is the tributary of Yang River,the ecological risk was extremely high,while Pb,Cu,Ni,Cr,and Zn posed slight ecological risk at catchment scale.The results of the integrated potential ecological risk index revealed that heavy metals in the surface sediments of Yang River had slight ecological risk with the average index of 143.70.The heavy metals in surface sediment from Yang River System had no or lower rate of bio-toxicity occurrence,while in Qingshui River and middle reaches of Yang River,the occurrence rate of bio-toxicity was relatively high.2.All the six heavy metals in the study area were dominated by residual state.In the secondary phase,Cd,Cu,Ni,Pb and Zn were dominated by B2 state and Cr was dominated by B3 state.However,Cd in the middle reach of the mainstream and in Qingshui River segment are distributed mainly in B2 state,Zn in the middle reach mainly distributed in B2 and B1 state,while in Qingshui River segment,Zn was mainly distributed in B2 state.A significant positive correlation（p≤0.01）was found between organic matter and B3 state Cr,Cu and Zn.The RSP showed that Cd and Zn were lightly polluted,Cr,Ni,Cu and Pb were pollution-free.Ecological risk assessment showed that Cd and Zn posed a medium risk to the environment,Ni and Cu posed low risk to the environment,while Cr and Pb posed no risk.3.The vertical distribution of heavy metals showed that the concentrations of Zn and Cr were higher,the concentrations of Cd and Pb were lower,but the multiple that the average concentrations of Cd and Zn exceed background value was highest.Cd,Pb and Zn were highest in the middle stream of Yang River,and the other heavy metals were highest in the upstream of Yang River.The single-element potential ecological risk of heavy metals in Yang River showed that Cd in the middle section（S7）and Qingshui River section（S14）,which is the tributary of Yang river,reached strong risk level,and Cd in the source section（S1）,the upstream section（S4）and the downstream section（S11）reached moderate risk level,and other heavy metals posed slight ecological risk.The integrated potential ecological risk index（RI）revealed that the heavy metals in the sedimentary columns of the Yang River had slight ecological risk.The Q_m-PEC indicated that the incidence of biological toxicity in the sedimentary column of Yang River is relatively low,but the incidence of biological toxicity in the middle stream was relatively higher that of the other sections.Zn in sedimentary columns S7 had the highest contribution to Q_m-PEC,and Ni and Cr in other sedimentary columns had the highest contribution to Q_m-PEC.