Distribution Characteristics And Ecological Risk Assessment Of Heavy Metals In Sediments Of The Upper Reaches Of Zhanghe River

The development of industry and agriculture is accompanied by soil erosion,which carries heavy metals into rivers.After the occurrence of resuspended heavy metals changes,they may be released twice,potentially affecting the environment.The pollution analysis and ecological risk assessment of heavy metals in the sediments of the upper reaches of Zhanghe River can provide scientific basis for the formulation of water ecological security strategies in the Haihe basin and the Beijing-Tianjin-Hebei region.In this study,the sediment in the upper reaches of Zhanghe River is used as the medium,this study systematically explored the concentrations,forms,and sources of Cr,As,Cd,and Pb.Through soil erosion models,heavy metal fluxes into the river caused by soil erosion were calculated,and the geochemical baseline values of heavy metals were obtained using the normalization method.The ecological risks of the upper reaches of Zhanghe River were evaluated using different methods and standards,The main conclusions are as follows:(1)The sediments in the upper reaches of Zhanghe River are mainly composed of silt and sand.The inflow of sediment from the tributaries thickens the particle size of the sediments from the source to the main stream.The average concentrations of Cr,As,Cd,and Pb in the sediments are 91.51,18.30,9.81,and 0.12 mg/kg,respectively.The average concentrations of Cr,As,and Pb are higher than the background value,with the highest exceeding rate of Cr and the lowest average concentration of Cd.The sequence of heavy metal concentrations in each tributary is Zhuozhang River>Qingzhang River>main stream of Zhanghe River.Correlation analysis and principal component analysis show that As and Cd mainly come from fertilizers and pesticides in agricultural activities,while Cr and Pb mainly come from mineral mining activities and road dust.(2)The soil erosion in the upper reaches of Zhanghe River has shown a zigzag downward trend in the past 20 years,with an average soil modulus of 1090.13 t/(km~2·a)for many years,presenting a medium risk level.Soil erosion and heavy metal release patterns are similar,mainly distributed in the main rivers of Qingzhang River and Zhuozhang River.The weights of Cr,As,Cd,and Pb input into the upper reaches of Zhanghe River through soil erosion are 604.03 t/a,64.52 t/a,0.80 t/a,and 124.70 t/a,respectively.(3)The sediment Cr,As,and Pb in the upper reaches of Zhanghe River are mainly in the residual state,while Cd is mainly in the exchangeable state.The proportion of Cd forms varies,resulting in a high risk of secondary release.Cr has a residue state of 96.32%,with the highest stability.The secondary phases of As and Pb are significantly higher than Cr,and the biochemical activity increases.The secondary phases of Cd and Pb are mainly distributed in the main stream of Qingzhang River and the sources of Zhuozhang River,while the secondary phases of Cr and As are rare,and the spatial distribution characteristics are not obvious.RDA analysis showed that the speciation of heavy metals was mainly influenced by Mn and TS.(4)The geochemical baseline values of Cr and Pb are larger than the background values,resulting in a low human contribution rate.The geochemical baseline values of As and Cd are smaller than the background values,resulting in a high human contribution rate.The ecological risk assessment based on the total amount is generally the same.The study area is moderately enriched in heavy metals,with moderate or above pollution,low potential ecological risk,and point source risk.The ecological risk assessment based on morphology shows that Cr,As,and Pb have no risk or may cause slight risk,while Cd reaches extremely high risk,which is extremely high.