Development of a coupled plankton - zebra mussel - PCB aquatic ecosystem model: Application to Saginaw Bay (Michigan)

With the introduction of zebra mussels (Dreissena polymorpha ), the Great Lakes have experienced many ecological changes. The objectives of this dissertation were to understand and quantify the effects of zebra mussels on cycling and bioaccumulation of polychlorinated biphenyls (PCBs). To accomplish this goal, a screening level multi-stressor aquatic ecosystem model was developed by integrating various processes involving nutrient-plankton-zebra mussels-PCB dynamics. The model was configured to the Saginaw Bay system. The bay has extensive areas of hard bottom, along with temperature and food regimes suitable for zebra mussel colonization.; The integrated modeling framework has demonstrated how the invasion of mussels has led to a re-direction of energy and nutrients from the pelagic to the benthic food chain through enhanced removal of particles from the water column to the surface sediments. This additional particle flux is leading also to an increased flux of total PCBs (ΣPCBs) to the sediments. Assuming a constant (ΣPCBs) load to the system, ΣPCB concentration in the sediments was higher than it was before zebra mussels arrived. This suggests that the introduction of mussels has also transferred a portion of the contaminant inventory to the sediments.; The influence of mussels' filtering activities on ΣPCB concentration in the lower pelagic food web was examined using a bioaccumulation model. The model explicitly represents the food web structure and function for the site-specific ecosystem. It forecasts a shift in the pattern of bioaccumulation. The exact shift depends on the dominance of various ecosystem interactions and feedbacks in the system, especially the impacts of whether or not zebra mussels filter herbivorous zooplankton and blue-green algae.; The presence of mussels has impacted not only particle dynamics, but also nutrient cycling in the system. The model was applied to investigate the effect of trophic status of the system. Enhanced production of algae with higher nutrient load not only decreased the bioaccumulation of (ΣPCBs) in the base of the food chain, but also increased ΣPCB concentration in the sediments that may serve as a potential source of increased bioaccumulation in the benthic food chain. A sensitivity analysis indicated that ΣPCB concentration in Dreissena is sensitive to hydrophobicity of PCBs and lipid content of mussels.