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INVESTIGATING COMPLEXITY IN FOOD WEB BIOACCUMULATION MODELING USING THE BIOACCUMULATION AND AQUATIC SYSTEM SIMULATOR
Citation:
BARBER, M. C. AND J. M. JOHNSTON. INVESTIGATING COMPLEXITY IN FOOD WEB BIOACCUMULATION MODELING USING THE BIOACCUMULATION AND AQUATIC SYSTEM SIMULATOR. Presented at Eighth International Conference on Mercury as a Global Pollutant, Madison, WI, August 06 - 11, 2006.
Impact/Purpose:
The objective of this task is to develop, support and transfer a wide variety of tools and mathematical models that can be used to support watershed and water quality protection programs in support of OW, OSWER, and the Regions.
Description:
Bioaccumulation of methylmercury in exposed fish communities is primarily mediated via dietary uptake rather than direct gill uptake from the ambient water. Consequently, accurate predication of fish methylmercury concentrations demands reasonably realistic presentations of a community's food web and trophic dynamics. Although many fish bioaccumulation models have characterized fish diets as simple food chains or as static food webs whose dietary proportions are constant, real world food webs and trophic dynamics are much more complex. Fish, for example, often feed opportunistically or selectively on prey items based on their availability. Foraging patterns and strategies of fish also typically follow well-defined relationships with the fish?s age or body size (i.e., length or weight). The size of prey consumed by fish also strongly correlated to its own body size. Each of these relationships, and others, makes characterization of food webs for bioaccumulation modeling a nontrivial challenge. In the work presented here, we use the BASS Bioaccumulation and Aquatic System Simulator to investigate the effects of different dynamic food web structures on methylmercury bioaccumulation in three structurally and regionally different fish communities. Communities analyzed by this research include canal, alligator hole, and marsh fish communities in the Florida Everglades, riverine fish communities of the Shenandoah River Basin, VA, and reservoir fish communities of the Cheyenne River, SD. This research demonstrates that food web complexity does strongly influence simulated methylmercury bioaccumulation in fish. Simulated patterns that are compared to field observations are both species and community dependent. Key parameters influencing simulated bioaccumulation dynamics include elective versus fixed dietary percentages, predator-prey size relationships, and assumed prey switching behavior when nominal prey are unavailable. Other key parameters, that are mediated by the assumed predator-prey size relationships, are the growth rates and recruitments patterns of forage fish within the community of interest.