The Study On The Distribution Characteristics And Controlling Factors Of Particulate Metal Elements In The Changjiang Estuary

For the study on estuarine geochemical behavior of particulate metal elements in Changjiang estuary in different flow regime conditions,investigations were carried in two seasons in July 2013,January 2014 in Changjiang estuary.34 surface water samples were gathered,16 samples for flood season,while 18 samples for dry seasons.Contents of Al、Fe、Mn、Cr、Co、Ni、Cu、Pb、Zn、Cd、rare earth elements and their chemical speciations were determined.The distribution characteristics of particulate heavy metals and their non-residues in Changjiang estuary in both flood and dry seasons were analyzed.Combined with the salinity、SPM and other parameters in the Changjiang estuary,the variation characteristics of particulate metal elements in the Changjiang estuary and its adjacent waters and the influences that different controlling factors in different regions were discussed.The main results are as follows:Both in the dry and flood season,the distribution characteristics of particulate metals in Changjiang estuary and its adjacent waters are showing zonal distributionwhich is decreasing downwards from river to sea.Among these particulate metals,the zonal distribution characteristics of Cu、Pb、Zn、Cd is relatively significant.The zonal distribution characteristics of particulate metals are also presented in adjacent waters.Most metal has higher concentration in the southern zone than the northern zone.There is significant difference in speciation of particulate heavy metals in suspended matters in Changjiang estuary.Cr,Co and Ni are mainly in residue,the percentage of non-residue of Cr、Ni are less than 20%.Cu and Zn are also mainly in residue,but their percentage of non-residue are 30-40%.Pb and Cd are mainly in non-residue,the percentage of non-residue of Pb and Cd are 55-65%.Overall,Cu、Pb、Zn and Cd are relative typical pollute elements in Changjiang estuary.The distribution of particulate metals in the Changjiang Estuary shows some regional differences by the different parameters.The content of particulate metals is affected by SPM concentration in low salinity area.The concentration of SPM in flood season is larger than that in dry season,and the dilution effect is relatively strong.The contents of Cu,Pb,Zn and Cd are higher in dry season than in flood season,while the proportion of non-residual fractions is also higher in dry season.Among them,the proportion of non-residue Pb was 51.3%in the flood season and 66.5%in the dry season,respectively,the proportion of non-residual Cd was 77.2%in the flood season and 84.9%in the dry season,respectively.It can be seen that there are obvious differences in human activity metal pollution input between the flood and dry seasons in the Yangtze River Estuary.Under the background of low water and sediment discharge in dry season,the input of metal pollution from human activities is relatively enhanced.In high turbidity area,the difference of the total amount of Cu、Pb、Zn、Cd、and their forms in the flood and dry season is small.Most of the metal concentration are lower than that of low salinity area because of the concentration of SPM in the high turbidity area increased by 5-10 times than that in the low salinity area.The content of Cu decreased by 13%in the flood season and 27%in the dry season,the content of Pb decreased by 16%in the flood season and 21%in the dry season,the content of Cd decreased by 57%in the flood season and 73%in the dry season.Under the influence of the dilution effect of large amount of suspended sediments in the estuary,the difference of the total amount of metal and its form in the flood and dry season decreases when and after passes through the estuarine turbidity maximum zone.It can be seen that the estuarine turbidity maximum zone has a certain modulation effect on the matter into the sea.In high salinity area.with the decrease of runoff,the particles gradually settle down,most of the heavy metals in content are decreased compared to the high turbidity area,such as Cu、Zn、Cd.The distribution of particulate metal content is mainly affected by particle size,especially the fine particles.While the contents of particulate metals and non-residual fractions in the southern region are significantly higher than those in the high turbidity area.According to the metal distribution of sediments in the Changjiang estuary,the contents of Cu,Pb,Zn,Cd in the sediments of the southern Changjiang estuary were significantly higher than that in other areas,coupled with the erosion of the Yangtze River delta.Under the influence of sediment resuspension,the particulate metal content increases.It can be seen that the addition of suspended sediment may be an important factor in the secondary pollution.Compared to the zonal distribution characteristics of Cu、Pb、Zn、Cd and other metal content in the Changjiang estuary,there is no difference in different forms and their proportion of Cr,Co and Ni,which are dominated by the residual fraction,in different regions of the Changjiang Estuary.The average concentration of REEs in suspended sediments is 168.32μg/g in flood season,175.18μg/g in dry season.The content level of particulate REEs in the Changjiang estuary is close to that of the sediments in the lower reaches of the Yellow River and estuary,and the post Archean Australian shale and the world rivers.By theNorth American shale standardization,the normalized values of the distribution curve from La to Lu were close to 1.It shows that the composition of REEs in suspended matter in the Changjiang estuary is similar to that of North America,with moderate Ce loss and moderate Eu enrichment.In the study of the speciation of REEs,MREEs enrichment can be found in the extracted fractions.The content of the extracted fractions accounts for the total content of 19-48%。The extractable content of REEs in suspended matter was significantly higher than that in sediments,it is more likely to be related to the difference of the samples.