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Invasive Species

EPA Contract
No. GL985600-01

Table of Contents

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Photo of several zebra mussels clumped togetherThe Effect of Zebra Mussels on Cycling and Potential Bioavailability of PCBs: Case Study of Saginaw Bay


6.1 CONCLUSIONS and Recommendations   

6.1.1   Conclusions

A screening-level multi-stressor aquatic ecosystem modeling framework was developed, incorporating numerous processes, interactions, and feedbacks present in the Saginaw Bay ecosystem. The model included hydrology, hydraulic transport, nutrient dynamics, multi-class phytoplankton growth and succession, zebra mussel growth and dynamics, particulate matter processing and cycling by mussels, PCB loading, fate and transport of PCBs, and bioaccumulation of PCBs in the lower food chain. The model simulation evaluates the PCB concentration in water column, sediments, and in participating organisms such as phytoplankton, zooplankton, and zebra mussels in Saginaw Bay. The results were field tested with the published data on PCB concentration both in zebra mussels and water column. The match of the predictions with the available data showed that the model demonstrated a reasonably accurate representation of physical reality. Although necessary data for model calibration was lacking, the exercise was tremendously useful in identifying data deficiencies and theoretical gaps. Also, this dynamic modeling approach highlights the important feedback interactions and major impacts on PCB cycling and bioaccumulation arising from the zebra mussel invasion.

It is envisaged that the integrated screening-level model comprising of europhication and fate and transport of PCBs is a preliminary tool to assess the ecosystem level impacts of zebra mussel stressor in Saginaw Bay. Better understanding of the cycling processes and the factors governing the accumulation and distribution of contaminants within zebra mussels are critical to analyzing the mussel-mediated trophic transfer. The inclusion of effects of zebra mussel stressor in cycling and bioaccumulation of contaminants is important for research and management of Great Lakes water resources.

The following conclusions can be drawn based on the model results:

6.1.2   Recommendations 

6.1.3 Model Limitations 

A number of limitations in present model formulation that may impact the PCB dynamics in the system are the following:  


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