was slightly lower than in the three-application (0.116 µg/L) and single-application (0.126 µg/L) treatments. The application of chlorpyrifos resulted in decreased abundances in the arthropod community, with the largest adverse effects reported for the mayfly Cloeon dipterum and cladocerans Daphnia gr. longispina and Alona sp., while smaller effects were observed for other insects, copepods, and amphipods. At the population level, however, the mayfly C. dipterum only responded to the single-application treatment, which could be explained by the toxicokinetics of chlorpyrifos in this species. At the end of the experimental period the invertebrate community showed approximately the same effect magnitude for all treatment regimes. These results suggest that for this combination of concentrations and duration of the TWA, the TWA concentration is more important for most species than the peak concentration for the assessment of long-term risks of chlorpyrifos.