The relative importance of species invasions and sediment disturbance in regulating chemical dynamics in western Lake Erie

Abstract

PCB congener concentrations were measured in aquatic biota and sediment from the western basin of Lake Erie during 1993–1994 and 1996–1997. Between these time periods the round goby ( Neogobius melanostomus) invaded and proliferated in the basin and mean annual particulate organic carbon (POC), dissolved organic carbon (DOC) and PCB congener concentrations in sediment changed. The objectives of this study were to use a food web bioaccumulation model and field data to quantify the relative importance of the round goby, POC, DOC and chemical concentration in sediment, to PCB congener levels in aquatic biota prior to (1993–1994) and since (1996–1997) the invasion of the basin by round gobies. The predicted effects of round gobies on PCB congener transfer, mediated through alterations in food web structure, were small increases (range 2–6%) in PCB burdens of pelagic fish species such as alewife and walleye. Larger increases (range 8–19%) in PCB burdens were predicted for benthic feeding sport fish species such as yellow perch and largemouth bass. Small decreases (range 1–5%) in PCB congener concentrations in fish were predicted to result from decreases in bioavailable concentrations of PCBs in water. Bioavailable concentrations of PCBs in water were predicted to decrease as a result of observed changes in POC and DOC concentrations. However, in all cases predicted changes in PCB concentrations in fish, resulting from changes in food web structure and POC and DOC, were smaller than those predicted from measured increases in PCB congener concentrations in sediment between 1993 and 1994 and 1996–1997. Increased concentrations of PCBs in sediment were attributed to exposure of older and more heavily contaminanted sediments from turbulence caused by higher wind speeds in 1996–1997 compared to 1993–1994.