The Records Of Modern Human Activity In CHX Sedimentary Column Lake Chaohu

A sediment core(CHX hereafter)was collected at the center of the West Chaohu Lake,Anhui Province,East China.The core was then sectioned at the intervals of 1cm.Based on analyses of sediment grain size,magnetic susceptibility,loss on ignition(LOI),major and trace elements,as well as 210Pb-based chronology,the present study analyzed the impacts of human activities on the environmental evolution during approximately the last two hundred years,and also investigated both productivity and heavy metal pollution records.Based on dating results of 210 Pb test from the core CHX,the averaged sedimentation rate is around 0.13cm/yr.Sediments from the core CHX consist of silt,clay and sand.From XRD analysis,it is found that main clay minerals in the bulk sediments are chlorite,illite and kaolinite,and the main clastic material contain quartz,plagioclase and carbonates.Magnetic susceptibility of sediments in the surface layer of the sediment core increased sharply,which reflects possible human activities.Meanwhile,the study of the primary productivity shows that the productivity levels in the surface are significantly elevated,also implying gradual eutrophication of the lake in recent times.Rear earth element(REE)contents and ΣLREE/ΣHREE values in the sediments above 30 cm depth are significantly higher than those below.210 Pb ages indicate that sediments above 30 cm are accumulated within approximately the last 200 years.Our study suggests that the level of REE is not restricted by clay concentration.This may reflect the increasing impact of modern human activities on recent sediments of the lake.Furthermore,a total of 24 major and trace elements in the sediment core CHX were analyzed in the present study.Down-core distributions of all these elements show significant fluctuations.Both principal component analysis(PCA)and cluster analysis(CA)show that those elements can be divided into several groups.The enrichment factors(EFs)of such human-related elements indicate that the concentrations of Pb,Zn,As,P and Hg have been significantly impacted by anthropogenic emissions.Our study suggests that both primary productivity and heavy metal records in the past 200 years show evident anthropogenic impacts on the sediment environment of the Chaohu Lake.