Projected changes to the trophodynamics of PCBs in the western Lake Erie ecosystem attributed to the presence of zebra mussels (Dreissena polymorpha)

A food web bioaccumulation model was used to hindcast PCB congener concentr ations in aquatic biota from western Lake Erie in the years prior to the ze bra musset invasion, and these results were compared to post-mussel predict ed concentrations that had been verified previously against measured data t o estimate the effects of mussels on the trophodynamics of PCB congeners in western Lake Erie. Two hindcasting scenarios were compared to a third, pre viously verified, scenario to determine the changes in PCB congener concent rations in biota in response to (i) modifications to food web structure, be fore and after the introduction of mussels, and (ii) modifications to food web structure combined with a decline in particulate organic carbon (POC) c oncentrations resulting from removal of seston from the water column by mus sel filtering activities. The reduction in the concentration of POC, attrib uted to the prodigious filter;feeding of large zebra mussel populations, wa s predicted to have caused increases in the freely dissolved concentrations of PCB congeners ranging from 2.9% to 9.3%. These increases in dissolved c hemical were predicted by the model to cause small increases (range 0-7.3%) in the PCB congener burdens of many biota including zooplankton, prey fish species, and walleye. Other organisms, such as Gammarus, small white sucke rs, and freshwater drum, were predicted to have larger increases in their P CB body burdens (9.1-22.2%) as a result of the increase in freely dissolved chemical and a shift in diet. For crayfish, yellow perch, black crappie, w hite perch, large white suckers, gizzard shad, and largemouth bass, the inc reased exposure to chemical via water was offset by decreased chemical expo sure via the diet, which resulted from shifts in diet toward less contamina ted items brought about by the presense of zebra mussels. The results of th is study are relevant to Lake Erie resource managers that are concerned abo ut the potential of zebra mussels to alter PCB congener dynamics in the wes tern basin.