FIELD-EVALUATION OF THE LITTORAL ECOSYSTEM RISK ASSESSMENT MODELS PREDICTIONS OF THE EFFECTS OF CHLORPYRIFOS

1. The Littoral Ecosystem Risk Assessment Model (LERAM) is described and evaluated using field data from a littoral enclosure study of the effects of the insecticide chlorpyrifos. LERAM is a bioenergetic ecosystem effects model that links single species toxicity data to a bioenergetic model of the trophic structure of an ecosystem in order to simulate community and ecosystem level effects of chemical stressors. It uses Monte Carlo iterations of these simulations in order to calculate probabilistic ecological risk assessments of chemical stressors. 2. The means and standard deviations of the model parameters were calibrated using data from the control enclosures in the field. LERAM produced reasonable representations of the ecosystems in the littoral enclosures. 3 The data from enclosures treated at 0.5, 6.3, and 32.0 mug l-1 chlorpyrifos (average peak concentration) were then used to evaluate LERAM predictions of the effect of chlorpyrifos on a littoral ecosystem. The LERAM deterministic, time-series predictions were usually within a factor of two for all populations on all field sampling dates. The divergence on a few days, however, was more, with the worst case being a factor Of Six for a population with very high variability in the field. The LERAM probabilistic predictions of the relative effect on total production, which is the quantity LERAM uses for ecological risk assessment, were not significantly different from the relative effects measured in the field. 4. Recommendations for further evaluation of LERAM and for further research on its components are summarized.