Abstract

 Bioaccumulation of hydrophobic organic chemicals (HOCs) in aquatic ecosystems is dependent on site-specific ecosystem structure and function. In most contemporary bioaccumulation models, food web structure and function are externally specified and do not explicitly represent site-specific ecosystems. The changes in the ecosystem dynamics caused by zebra mussel invasion have the potential to affect the bioaccumulation of HOCs. An integrated screening-level model of eutrophication, EPCB fate, transport, and bioaccumulation was developed to provide a quantitative tool to assess the ecosystem level impacts of zebra mussel in Saginaw Bay. The model computes phytoplankton biomass and distribution of functional groups, EPCB concentration in water, sediments, and biota (phytoplankton, zooplankton, and zebra mussels) as a function of nutrient and PCB loading and zebra mussel density. Results showed that the invasion of zebra mussels has transferred a portion of the contaminant inventory from the water column to the sediments. This was due to the increased flux of particles shunted to the sediments by zebra mussels. At steady state with respect to external PCB loading, the comparison of EPCB mass stored in surficial sediments and in zebra mussels showed a significantly higher mass in sediments. The model forecasts a shift in the pattern of bioaccumulation of PCBs in the pelagic lower food chain. 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. Results also demonstrated that the increase in external phosphorus loading, and the resulting increase in primary production, tends to mitigate PCB bioaccumulation in the pelagic food web.