Seasonal variation and distribution characteristics of heavy metals in phytoplankton of different parts of Lake Taihu

Abstract

In recent years,the content of heavy metals in waste water which is discharged into Lake Taihu has been increasing continuously. In order to study the contamination status of heavy metals in phytoplankton of Lake Taihu,investigations were carried out in different parts of the lake in spring( April),summer( July) and winter( December),2009. During the research,hierarchical cluster analysis( HCA) and Pearson correlation analysis were used to discuss the seasonal variation of heavy metals in phytoplankton in different parts of the lake. Canonical correspondence analysis( CCA) with dominant algae was applied to make a preliminary study of the relationship between heavy metals in phytoplankton and each alga. The results indicated that the sequence of heavy metals content in phytoplankton was Zn Mn Pb Cu Ni Cr As Cd Hg. Besides,the seasonal variation of Zn,Cu,Mn,Pb and Ni was obvious and there's strong dependency between Cu,Pb,Ni,Cr and Zn,which reveals their homology dramatically.By comparing different parts of Lake Taihu,the content of heavy metals in phytoplankton was discovered the highest in the North Bay and the content in east and center of the lake was lower than that in lakeshore district. Based on the CCA results,generally there's a positive correlation between heavy metals and dominant algae in spring,while a negative correlation in summer and winter on the contrary. What's more,it shows that heavy metals have the highest correlation with Cyanophyta and Chlorophyta and the lowest correlation with Cryptophyta. Among Cyanophyta,heavy metals have a higher correlation with Microcystis aeruginosa than those with Microcystis flos-aquae.