Metals in sediment of the lower Great Lakes and region-wide discoveries

Abstract

Thirteen elements were measured in 76 surface grab sediment samples and 90 segments of four cores from Lakes Erie and Ontario. By combining the data obtained previously from Lakes Superior, Michigan, and Huron, the spatial distribution, temporal trends, major influencing factors, anthropogenic enrichments, categorization, and ecological risks of target metals in sediment were evaluated for the Great Lakes region. Regionwide, Lake Ontario had the highest median concentrations for Ag, As, Cd, Zn, and Pb, while the highest Cr concentration was found in the Western Basin of Lake Erie. Within Lake Ontario, Ag concentration tended to be higher towards the east. Temporal trends of the net fluxes were described by pseudo first order kinetics for selected metals in Lake Ontario. It may take more than a hundred years for the surface fluxes to decrease to the background level. The highest enrichment factor was found in Lake Ontario for Ag; while for Pb, Lake Michigan was more enriched than the other lakes. Pearson correlation, principal component, and hierarchical clustering analyses were applied to the concentration data, and, for the first time, to the estimated enrichment factor to gain insight to the human impact. Results of risk quotient analysis showed high environmental risks in most cases. Overall, the highest risk was found for Lake Ontario, followed by Lakes Erie, Superior, Huron, and Michigan. The risk quotient was strongly correlated with the enrichment factor, implying that human activities could have unfavorably affected benthic biota in the sediment of the Great Lakes.