Accumulation and recycling of PCBs and PAHs in artificially eutrophied Lake 227

Abstract

The influence of lake trophic status on the cycling and burial of polychlorinated biphenyls (PCB's) and polycyclic aromatic hydrocarbons (PAH's) was examined in Lake 227 (L227), an artificially eutrophied lake in the Experimental Lakes Area, northwestern Ontario, Canada. Sedimentary accumulation of PCB's, PAH's, and organic carbon (OC) was determined pre- and post-eutrophication in L227 and compared with accumulation in other regional lakes. Mass and OC accumulation increased an average of 1.4 and 2.0 times, respectively, since nutrient addition began in June 1969. ΣPCB and ΣPAH sediment accumulation rates and profiles in L227 were similar to those in Lake Superior and other proximate and midlatitude lakes unimpacted by point sources. Eutrophication did not increase contaminant accumulation. In general, individual PAH accumulation rates declined following eutrophication, which coincided with similar signals elsewhere. Perylene declined markedly (4 times) since eutrophication as a result of decreased in situ formation. An increase in OC accumulation did not enhance contaminant accumulation in L227 because phytoplankton community structure shifted to species characterized by lower bioaccumulation factors, and water column recycling rates were high. Accumulation rates of mass, OC, PCB's, and PAH's, when compared with ice-free settling fluxes in 1993 and 1994, exhibited similar recycling ratios in eutrophic L227 and oligotrophic L110 due to the efficient preservation of organic matter in sediments.