Modeling the effects of thiamethoxam on Midwestern farm ponds and emergent wetlands

Potential toxic effects of thiamethoxam (TMX) on non-target organisms and community structure of a generic Midwestern farm pond and emergent wetland were assessed using two versions of the Comprehensive Aquatic System Model, the CASMGFP – a generic farm pond model, and the CASMGWL – a generic wetland model. The CASMGFP and CASMGWL are integrated bioenergetics-based and habitat quality models that describe the daily biomass values of selected producer and consumer populations representative of generalized Midwestern farm ponds and emergent wetlands. The CASMGFP demonstrated the ability to reproduce values of population biomass reported for Midwestern (and other) pond ecosystems; the CASMGWL provided a similar modeling capability for Midwestern emergent wetlands. Lethal and sublethal effects of TMX were modeled as extrapolations of laboratory toxicity assays using the CASMGFP the CASMGWL. Time series of daily environmental concentrations of TMX constructed for six regional pesticide applications across the United States failed to produce any calculated impacts on modeled population biomass or changes in community structure of modeled trophic guilds in the CASMGFP or the CASMGWL. However, evaluation of systematically increased daily concentrations demonstrated the ability of both models to simulate direct and indirect toxic effects of this pesticide. This model study suggests that process-based food web/ecosystem models can be used to characterize the potential ecological effects of TMX on generalized farm pond and emergent wetland ecosystems. This article is protected by copyright. All rights reserved