PCBs and PAHs as Tracers of Particulate Dynamics in Large Lakes

Abstract

Internal cycling of particles within the water columns of the Great Lakes results in spatial and temporal variability in concentrations of hydrophobic organic contaminants. Concentrations of organic carbon, fourteen polycyclic aromatic hydrocarbons (PAHs), and thirty-five polychlorobiphenyl (PCBs) congeners were measured in particles collected in detailed vertical profiles of the atmosphere, water column, and sediments of Lake Superior to assess the dynamics of organic matter and particle transport in large lakes. A benthic nepheloid layer (BNL), a particle-rich zone extending up from the lake floor, was observed from a manned submersible during a NOAA National Undersea Research Program cruise on Lake Superior in 1986. This region contains large numbers of both living organisms and detritus, indicating that the BNL is supplied with significant quantities of reduced carbon from above. Patterns of organic contaminants associated with particles were examined by principal components analysis to determine the sources of particles to the BNL. Settling of surface water particles is the dominant source of solids containing PAHs and PCBs to the BNL during stratification, while resuspension of surf icial sediments also contributes to BNL formation. Large vertical fluxes of organic-rich particles serve to rapidly transport hydrophobic organic contaminants to the benthic region. Once in the BNL, however, particulate organic matter is rapidly degraded and is largely not incorporated into underlying sediments. Rates of particulate organic matter utilization in the BNL are estimated to be orders of magnitude faster than corresponding rates in Lake Superior surf icial sediments. Internal cycling of particles and organic matter significantly impacts the behavior and residence times of nutrients and contaminants in the water column of large lakes.