John Wiley & Sons, Ltd.

A Comparative Study Of The Modeled Effects Of Atrazine On Aquatic Plant Communities In Midwestern Streams

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Potential effects of atrazine on the non-target aquatic plants characteristic of lower-order Midwestern streams were previously assessed using the Comprehensive Aquatic System Model (CASMATZ). Another similar bioenergetics-based, mechanistic model, AQUATOX, was examined in this study with the objectives of (a) developing an AQUATOX model simulation that was similar to the CASMATZ model reference simulation in describing temporal patterns of biomass production by modeled plant populations, (b) examining the implications of different approaches used by the models in deriving plant community-based levels of concern (LOCs) for atrazine, and (c) determining the feasibility of implementing alternative ecological models to assess ecological impacts of atrazine on lower-order Midwestern streams. The results of this comparative modeling study demonstrated that a similar reference simulation to that from the CASMATZ model could be developed using the AQUATOX model. It was also determined that development of LOCs and identification of streams with exposures in excess of the LOCs were feasible with the AQUATOX model. However, compared to the CASMATZ model results, the AQUATOX model consistently produced higher estimates of LOCs and generated non-monotonic variations of atrazine effects with increasing exposures. The results of this study suggest an opportunity for harmonization in the treatments of toxicity and toxicity parameter estimation in the CASMATZ and the AQUATOX models. Both models appear useful in characterizing the potential impacts of atrazine on non-target aquatic plant populations in lower-order Midwestern streams. This model comparison also suggests that with appropriate parameterization, these process-based models can be used to assess the potential effects of other xenobiotics on stream ecosystems.

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