Importance of temperature in modeling food web bioaccumulation in large aquatic systems

In present food web bioaccumulation model formulations, the exposure temperature of a food web is typically defined using a single spatial compartment. This essentially assumes that the predator and prey of a food web are exposed to the same environmental temperature. This study investigates the impact of this homogeneous approach of exposure temperature on the model outputs for a food web where the exposure temperature varies among species. Using a bioenergetics-based chemical bioaccumulation model as a case study, the temperature sensitivity of the model equation is first analyzed without consideration of the aggregated effect of food web interactions. The result shows that the model for highly hydrophobic chemicals is very sensitive to temperature. For less hydrophobic chemicals, the sensitivity is marginal. The model is then examined for its temperature sensitivity on a food web basis. The actual lake trout food web at Saugatuck, Michigan is selected for this examination, and the model responses to different exposure temperatures are compared. The result shows that the PCBs bioaccumulations in top predator (lake trout) obtained with the exposure temperatures for all species being represented by surface water temperature can be substantially higher than those obtained with the exposure temperatures being represented individually with species-specific values. A multi-compartment modeling approach is proposed that allows the exposure temperature of each species be defined independently.