Consistent effects of pesticides on community structure and ecosystem function in freshwater systems

Predicting ecological effects of contaminants is challenging given the large number of chemicals and unclear roles of contaminants in biodiversity–ecosystem function relationships. Using 72 experimental pond mesocosms exposed to standardized concentrations of 12 pesticides (nested within four classes and two types), the study demonstrates consistent effects of herbicides and insecticides on ecosystem function and somewhat less consistent effects on community composition. Effects on ecosystem function were mediated by alterations in the abundance and composition of functional groups. Herbicides reduced respiration and primary productivity via bottom-up reductions of phytoplankton. Insecticides altered zooplankton composition and abundance (but not richness), producing top-down increases in phytoplankton primary production and respiration. By linking pesticide-induced changes in functional groups to ecosystem functions, results suggest ecological risk assessment could be simplified to chemical classes or types and organismal functional groups with similar roles and toxicities.