Impact of the fungicide carbendazim in freshwater microcosms. II. Zooplankton, primary producers and final conclusions

Effects of chronic application of the fungicide Derosal(R) (active ingredie nt carbendazim) were studied in indoor macrophyte-dominated freshwater micr ocosms. The concentrations (0, 3.3, 33, 100, 330 and 1000 mu g/l) were kept at a constant level for 4 weeks. This paper is the second of a series of t wo; it describes the effects on zooplankton and primary producers and prese nts an overall discussion. The zooplankton community was negatively affecte d by the three highest treatment levels (NOECcommunity = 33 mu g/l). At hig her treatment levels Cladocera taxa were completely eliminated, while Copep od numbers were reduced. Rotatoria taxa decreased (Keratella quadrata and L ecane sp.) or increased in abundance (Testudinella parva) at the highest tr eatment level only. Due to the reduced grazing pressure, the abundance of s ome phytoplankton taxa and the chlorophyll-a content of the phytoplankton i ncreased at the three highest treatment levels (NOECcommunity = 33 mu g/l). This effect was not observed for the periphyton, most probably because the reduced grazing pressure was compensated by the increased abundance of som e snail species such as Lymnaea stagnalis and Physella acuta. At the end of the experimental period the biomass of the macrophyte Elodea nuttallii was significantly elevated at the two highest treatment levels. It is hypothes ised that carbendazim might have caused, directly or indirectly, the remova l of pathogene organisms from the macrophyte. (C) 2000 Elsevier Science B.V . All rights reserved.