Herbicide indirectly reduces physiological condition of a benthic grazer

Freshwater ecosystems are polluted with various environmental chemicals. For example, pesticides enter the aquatic environment via spray drift or surface runoff from catchment areas used for industrialised agriculture. In the present study, we investigated the response of the grazeraufwuchs interaction when exposed to the herbicide terbutryn in a microcosm experiment. Terbutryn induced a trophic cascade with negative effects on grazers by inhibiting growth of pri- mary producers. We determined a no-observed-effect concentration (measured as particulate organic carbon, NOECPOC) of 0.21 µg l �1 for aufwuchs biomass and a lowest-observed-effect con- centration (LOECPOC) of 2.01 µg l �1 . Furthermore, a shift in the aufwuchs community was detected in all terbutryn treatments nearly 4 wk after exposure, and this shift persisted until the end of the experiment in the treatment with the highest terbutryn concentration. In addition, reduced energy stores (triglycerides, TG) of the grazer Rhithrogena semicolorata (Heptageniidae: Ephemeroptera) were found (NOECTG = 0.03 µg l �1 , LOECTG = 0.21 µg l �1 ), which was interpreted as an indication of moderate starvation during the experiment. While starvation did not result in reduced larval growth as might have been expected, the ob served reduction of TG content in larvae (24%) is consistent with results from a separate experiment in which starvation alone induced a 15% reduction of TG content as well as reduced emergence, reduced size at emergence, and reduced egg production.