Geochemistry And Heavy Metal Accumulation Of Soils On The Alluvial Islands In The Anhui Section Of Changjiang River

As an important natural record of watershed environment,alluvial islands formed from different causes and formation time can provide the basis for a comprehensive understanding of riverbank ecological environment.In this study,soil samples were collected from both the topsoils(0?20 cm)and subsoils(150?200 cm)from fifteen large alluvial islands in the Anhui section of Changjiang River,by analyzing environmental geochemical and accumulation characteristics of heavy metals,this article aimed to reveal the formation causes,and evaluate potential ecological risks.The main conclusions are:1.Compared with the initial period,alluvial islands experienced continuous dynamics process,some alluvial islands experienced big changes.The main reason of that the degree of chemical weathering of soil is not consistent with the initial formation time is the evolution of alluvial islands.As an indicator of soil development degree,Chemical Index of Alteration(CIA)can indicate the formation time of alluvial islands.In other words,the spatial distribution of CIA can indicate the evolution of alluvial islands to some extent.2.Compared with other alluvial islands in the Anhui section of Changjiang River,The particle size of Fenghuang Island is small and the leaching of Na is obvious.Affected by Qiupu River,the southern margin of Fenghuang Island is the strong belt of sedimentation,the provenance of Fenghuang Island may be affected.3.Most elements especially elements with weak activity and small disturbance in the supergene environment between the topsoils and subsoils had significant correlation,Cd,Hg,Pb,Cu and Zn,which are easily affected by human influence,are obviously enriched in the topsoils.4.The concentrations of Cu,Pb,Zn,As and Hg in the topsoils are within the limits of the Standard of Soil Environment Quality of China(Grade ?)(GB15618-1995),44%and 8%samples of Cd content exceeded the standard of Grade? and Grade ?,respectively.The inter-and intra-island disparities of these elements were mainly associated with the formative causes and evolution process of the islands.The concentrations of heavy metals in topsoils were normally high in newly formed parts of the islands.5.Preliminary analysis of pollutant sources shows that three major factors,including grain size effect,fixation by calcic minerals and atmospheric deposition from coal combusion,were responsible for the enrichment of heavy metals in the study area.The contributions of various sources of heavy metals were quantified with the method of Principal Component Scores&Multipal Linear Regressions(PCS--MLR)analysis.Grain size effect was the dominant factor controlling the heavy metals in study area,contributing more than 70%for Ni?Cu?Pb?Zn?As and Cd in topsoils.6.Taking the background values of the Changjiang River sediments as baseline levels,the geo-accumulation indexes of these heavy metals were found in the order of Cd>Hg>Cu>Zn>As>Pb.The results of potential ecological risk assessment showed that the order of the contribution of single heavy metal potential ecological risk factors was Cd>Hg>As>Cu>Ni>Pb>Cr>Zn.The comprehensive potential ecological risk index(RI)showed that most of the samples were strong ecological hazard,accounting for 53.14%,Secondly,the sample of moderate ecological risk,accounting for 29.95%.Sanhao Island and Fenghuang Island have the highest ecological risk of heavy metal pollution.other alluvial islands appeared varying degrees of pollution,and the sampling points containing two or more elements reached different levels of pollution,which shows the compound pollution.