Study Of Spatial And Temporal Distribution Characteristics Of Metal Elements In Suspended Partical Matters In Middle And Lower Reaches Of Yangtze River

The concentration and chemical speciation of particulate metal elements were determined,which was collected from the middle and lower reaches of the Yangtze River Basin and major tributaries during the flood and dry season,Yangtze River Estuary during 2014-2015.Spatial and temporal variation of metal elements were investigated to reveal the adjustment of the seasonal pattern of the material source in the middle and lower reaches of the river with increasing anthropogenic activities in the basin.The major conclusions are as follows:The composition of particulate metal elements were different in the main stream and the tributaries.Concentrations of particulate Al,Fe,Cr,Ni,Cu,Zn,Pb,Cd and other elements in Qingjiang were 30%lower than that in the main stream,Mn was 7 times higher.Concentrations of particulate Al,Fe,Mn,Cr,Ni,Cu,Zn,Cd and Pb in Hanjiang were 50 percent lower than the main stream.Compared with Qingjiang and Hanjiang,Dongting Lake differs little to the main stream due to exceed 60%material in Dongting Lake was from the main stream.Al,Fe,Mn,Cr,Ni,Zn and other elements was 10%lower than the main stream,the difference of Cu,Cd,Pb were 20%.During the flood season,the concentration of metal elements were quite stable in the suspended particulate matter(SPM)although the concentration of SPM was decrease gradually along the river.The coefficient of variation(Cv)of Al,Fe,Mn,Cr,Ni,Zn,Cd,Pb are less than 10%.The average concentrations of above elements were 8.3%,5.2%,0.12%,108?g/g,56?g/g,191?g/g,1.06?g/g,79?g/g,these data were similar to estimates made thirty years ago.It indicated that the composition of SPM was still controlled by the chemical composition of rock/soil and weathering of the drainage basin.The contributions of riverbed erosion in the middle reach and discharge of tributaries were limited,and anthropogenic activities influenced less on the composition of SPM.During the dry season,the composition of elements varied considerably from Yichang to the estuary.The Cv of metal elements were over 20%,Cv of Mn,Cd,Pb were greater than 30%.It indicated that the source of material in middle and lower reaches was changed.The contributions of riverbed erosion in the middle reach and discharge of tributaries can't be ignored during dry season.The inflow of Hanjiang and riverbed erosion lead to the concentration of Cu,Zn,Cd,Pb in Huangshi station decreased 30%.The inflow of Poyang Lake caused the concentration of Cu,Zn,Cd,Pb in Pengze station reduced by 20%.The disturibution of REEs also reflect the difference of material source.The Cv was less than 10%during the flood season,the concentration of REE was stable along the main stream.The Cv was over 30%during the dry season.The difference was caused by the difference material source between the two seasons.The suspended partical matters in Changjiang was come from the nature weathering of upper crust.Standardized by chondrite and NASC,we found that the composition of REEs in the main stream was similar with the NASC.The concentrations of Zn,Pb and Cd in SPM were significantly higher during dry season than that during the flood season,when normalized by Al,the normalized concentrations in Honghu station and Huangshi station still higher than that during the flood season.The phenomenon,indicated that the concentration of Zn,Pb and Cd was influenced by anthropogenic activities.Sand mining in Poyang Lake caused the resuspension of old sediment with low concentration of metal element.The concentration of Zn,Pb,Cd was diluted by the old sediment,they were decreased in Pengze station.The variety were more significantly in extractable fractions,concentration of Cu,Zn,Cd,Pb extractable fractions were reduced by 15%,60%,68%,41%,respectively.The seasonal variations of concentration and chemical speciation of particulate metal elements at Xuliujing were similar to the basin.Most of the elements such as Cu,Zn,Cd,Pb had a higher concentration during the dry season than the flood season.Concentrations of Cr,Ni,Zn,Cd,Pb extractable fractions are higher during dry season,it indicated that the effect of anthropogenic activities during the dry season was more significant than the flood season.