Effects of the herbicide metazachlor on macrophytes and ecosystem function in freshwater pond and stream mesocosms

The chloroacetamide metazachlor is a commonly used pre-emergent herbicide to inhibit growth of plants especially in rape culture. It occurs in surface and ground water due to spray-drift or run-off in concentrations up to 100 _x0002_gL−1. Direct and indirect effects of metazachlor on aquatic macrophytes were investigated at oligo- to mesotrophic nutrient levels employing eight stream and eight pond indoor mesocosms. Five systems of each type were dosed once with 5, 20, 80, 200 and 500 _x0002_gL−1 metazachlor and three ponds and three streams served as controls. Pronounced direct negative effects on macrophyte biomass of Potamogeton natans, Myriophyllum verticillatum and filamentous green algae as well’as associated changes in water chemistry were detected in the course of the summer 2003 in both pond and stream mesocosms. Filamentous green algae dominated by Cladophora glomerata were the most sensitive organisms in both pond and stream systems with EC50 ranging from 3 (streams) to 9 (ponds) _x0002_gL−1 metazachlor. In the contaminated pond mesocosms with high toxicant concentrations (200 and 500 _x0002_gL−1), a species shift from filamentous green algae to the yellow-green alga Vaucheria spec. was detected. The herbicide effects for the différent macrophyte species were partly masked by interspecific competition. No recovery of macrophytes was observed at the highest metazachlor concentrations in both pond and stream mesocosms until the end of the study after 140 and 170 days. Based on the lowest EC50 value of 4_x0002_gL−1 for total macrophyte biomass, it is argued that single exposure of aquatic macrophytes to metazachlor to nominal concentrations >5 _x0002_gL−1 is likely to have pronounced long-term effects on aquatic biota and ecosystem function.

  • Genre de document : Revue
  • Type de document : À préciser

  • Auteurs principaux : Mohr S., Berghahn R., Feibicke M.
  • Date de publication : 1 janvier 2007