GEOCHEMICAL COMPOSITION OF THE NEPHELOID LAYER IN LAKE-ONTARIO

The origin, characteristics, and geochemical composition of suspended matter in the nepheloid layer was investigated in the western, central, and eastern basins of Lake Ontario to evaluate the role of the nepheloid layer in transport of contaminants across the lake. Suspended matter was collected from the nepheloid layer by means of continuous flow centrifuges at eleven stations in the lake in August 1987, 1988, and 1989. The nepheloid layer formation in Lake Ontario commenced in July and its thickness increased gradually up to about 40 m in September. Silica, calcite, and organic matter were the major components of the suspended matter in the nepheloid layer, particularly in the central and eastern basins. The concentrations of Pb, Zn, and Cu in the suspended matter in the nepheloid (up to 683, 1,180, and 396-mu-g/g, respectively) were greater than those in the bottom sediments (up to 203, 665, and 298, respectively). The concentrations of As, Co, Ni, Cr, V, and Hg were similar or lower than those in the sediments. The concentrations of PCBs in the suspended matter in the nepheloid layer ranged from 151 to 728 ng/g, and were greater than those in most of the sediments. Further, the suspended matter in the nepheloid layer contained more lower chlorinated biphenyls, particularly tetra- and pentachlorobiphenyls, than the sediments. The results of the study indicated that the suspended matter in the nepheloid layer is an important medium in accumulation, recycling, and transport of contaminants in Lake Ontario.