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

Effects of the herbicide metazachlor on macrophytes and ecosystem function in freshwater pond and stream mesocosms
Publication Type
Journal Article
Year of Publication

Mohr S, Berghahn R, Feibicke M, Meinecke S, Ottenstroer T, Schmiedling I, Schmiediche R, Schmidt R

Aquatic Toxicology
ISBN Number

Metazachlor, Herbicides, Pond and stream, mesocosm, Ecosystem effects, Macrophytes, Germany, 15 m3


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

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