Speciation and vertical distribution of heavy metals in sediments of Baiyangdian Lake

In order to find out the heavy metal concentrations and their potential ecological risks on sediments in Baiyangdian Lake,0-14 cm surface sediments had been collected by the no-disturbance-gravity sampler at seven representative sampling points of Baiyangdian Lake.Optimized BCR sequential extraction procedure was used to carry out the analysis of heavy metal forms in the surface sediments.The heavy metal contents of different forms and in different depths were determined.The relationship between different forms of heavy metal and total organic carbon(TOC) in the sediments was analyzed.The geo-accumulation index(Igeo) was employed to evaluate the extent of heavy metal contamination.The results demonstrated that Co,Fe,Mn,Pb,Zn were mainly in residual form,acid soluble form,Fe-Mn oxide and organic matter bound forms respectively.The tendency of organic bound form of heavy metals and TOC of sediments was greater than the others.The concentration of Co,Pb,Zn decreased with the increase of sediment depth,with the maximal concentration was between 0-2 cm,while the concentration of Mn was the minimal between 6-8 cm and the maximal was at 14 cm.Baiyangdian sediments were not contaminated as a whole by Co,Mn,apart from medium pollution in the entrance of the Fuhe River.The other regions were lightly polluted by Zn and Pb.