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(101) Impact of Lambda-cyhalothrin on the zooplankton in two ditches that differ in trophic status. Roessink, Ivo1, van Wijngaarden, René1, Udoh, Christiana1, Maund, Stephen2, 1 2 ABSTRACT- Aquatic ecosystems in agricultural landscapes may be impacted by both eutrophication and pesticide stress. These two stress-factors, however, are rarely studied in concert. The aim of the study was to investigate the fate and ecological impact of lambda-cyhalothrin in a macrophyte-dominated mesotrophic ditch and a plankton-dominated eutrophic ditch. In each ditch 14 enclosures (diameter 1.05m, height 0.9m, water volume 0.43m3) were placed, of which 12 were used to study the impact on zooplankton while the others served to study fate. The insecticide was applied three times, with a 1 week interval, at nominal concentrations of 0, 10, 25, 50, 100, and 250 ng.l-1 (n=2). The DT50 values (for the highest doses, 250 ng.l-1) of the insecticide in water of the mesotrophic and the eutrophic ditch were 1.07 and 0.96 days, respectively. In both ditches and in decreasing order of sensitivity, direct toxic effects were observed on the phantom midge Chaoborus obscuripes, copepods and cladocerans. The decline of these taxa resulted in cascading effects. In both ditches increases of cladocerans were observed at intermediate treatment levels. In the plankton-dominated ditch, in particular, numbers of rotifers increased. It is concluded that, despite the large difference in ecosystem structure, the ecological response to insecticide application was similar in both ditches. This can be attributed to a comparable exposure regime between test systems. Key words: lambda-cyhalothrin, trophic state, zooplankton, enclosures |
