Distribution,Speciation And Migration Of Heavy Metals In The Baihe River Basin In The Upstream Of Miyun Reservoir

Considering that Miyun reservoir is the primary drinking water source in Beijing,it is particularly critical to ensure its water quality.Although the relevant departments have strengthened the environmental management measures in recent years,and the industrial and mining enterprises producing sewage around the reservoir have been shut down successively,the residual tailings and slag contain a lot of heavy metals,which still pose a potential threat to drinking water.After the completion of the the Middle Line South-to-North Water Diversion Project,Miyun reservoir,as the final water storage area,has further improved the requirements for the surrounding environmental safety.In this context,this paper took the Baihe River Basin in the upper reaches of Miyun Reservoir as the research object,took tributaries,main rivers,estuaries and reservoirs as the spatial context,comprehensively used X-Ray absorption spectroscopy and other technologies,combined with chemical speciation and isotope technology,and studied the spatial distribution of heavy metals in this area by analyzing the distribution of heavy metals in different media,such as soil,water,suspended solids and sediments source,form,species and accumulation.From the perspective of mining area(source)-Baihe(transport channel)-reservoir(sink),this paper systematically evaluated the potential threat of heavy metals to the water quality safety of Miyun reservoir,and provided theoretical guidance for the prevention and control of heavy metal pollution in the upper reaches of Miyun reservoir.The main conclusions and findings are as follows:According to the research results of the source,transport channel and sink of heavy metals in the Baihe River Basin,the heavy metals in the source(soil in the mining area)were enriched seriously,but there was no obvious migration from the transport channel(Baihe River)to the sink(Miyun Reservoir).The concentration of heavy metals in soil or sediment was:Zn,Cu,V concentration:mine soil ≈Baihe River Basin Soil and sediment≈Miyun reservoir sediment,Cr,Ni concentration:mine soil>Baihe River Basin Soil and sediment≈Miyun reservoir sediment,Cd and Pb concentration:Mine soil>Baihe River bank soil and sediment>Miyun reservoir sediment.The concentration of heavy metals in the sediment profile of Baihe River was lower than that in the surface,and the heavy metals entering the river were mainly concentrated in the surface sediments.The heavy metals in the samples of mining area,river and reservoir are mainly in residual state,which was relatively stable.In all samples,heavy metals were mainly residual,accounting for more than 95%;the total of three extractable form concentrations indicated the potential migration ability of metals.The order of potential migration of metals in surface samples was Pb>Zn>Cr>Ni>Cu>Cd,and the order of potential migration of heavy metals in profile samples was Cd>Zn>Ni>Cr>Cu>Pb.The XANES spectra of synchrotron radiation showed that Pb in the samples with high enrichment mainly existed in the form of PbSO4,PbO and other minerals.B-08 was slightly different from other sampling points.Due to the double effects of agricultural activities and mining in the farmland near the gold mine,the point was enriched by Pb ultrasound,the proportion of its occurrence form PbSO4 increases,and the soil pH was acid.Considering the acid mine wastewater and other reasons,the proportion of lead sulfate in the Pb form of the sampling point increased.With the exception of Cd,most of the heavy metals did not migrate along the migration pathway(Baihe),and most of them were concentrated in the surface sediments near the mining area.The heavy metal concentration points of tributaries and main rivers were located near the mining area;most of the heavy metals in the mine were transported in the Baihe River through suspended solids,mainly deposited in the surface sediments,and existed in a relatively stable mineral form,while Cd from the mine had formed a certain concentration in the sediments of Miyun reservoir.Source analysis showed that Cu,Zn,Cd and Pb are mainly affected by human activities,while Sc,V,Ni and Cr are mainly affected by natural sources.The results of different risk assessment methods indicate that the high risk only stayed in the mining area and its surrounding areas,while the heavy metals in river channel,entrance and Miyun reservoir were mostly of low risk.According to the analysis of chemical forms,the metals except Cd mainly existed in the form of stable residue,which had little impact on water quality safety.The combined form of carbonate was relatively high in the chemical form of Cd,with strong potential migration capacity,which needed to be focused on its potential ecological risk.