Canadian Forest Service Publications
The direct and indirect effects of a glyphosate-based herbicide and nutrients on chironomidae (Diptera) emerging from small wetlands.2014. Baker, L.F.; Mudge, J.F.; Houlahan, J.E.; Thompson, D.G.; Kidd, K.A. Environmental Toxicology and Chemistry 33: 2076-2085.
Issued by: Great Lakes Forestry Centre
Catalog ID: 36548
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Laboratory and mesocosm experiments have demonstrated that some glyphosate-based herbicides can have negative effects on benthic invertebrate species. Although these herbicides are among the most widely used in agriculture, there have been few multiple-stressor, natural system–based investigations of the impacts of glyphosate-based herbicides in combination with fertilizers on the emergence patterns of chironomids from wetlands. Using a replicated, split-wetland experiment, the authors examined the effects of 2 nominal concentrations (2.88 mg acid equivalents/L and 0.21 mg acid equivalents/L) of the glyphosate herbicide Roundup WeatherMax, alone or in combination with nutrient additions, on the emergence of _Chironomidae _(Diptera) before and after herbicide-induced damage to macrophytes. There were no direct effects of treatment on the structure of the Chironomidae community or on the overall emergence rates. However, after macrophyte cover declined as a result of herbicide application, there were statistically significant increases in emergence in all but the highest herbicide treatment, which had also received no nutrients. There was a negative relationship between chironomid abundance and macrophyte cover on the treated sides of wetlands. Fertilizer application did not appear to compound the effects of the herbicide treatments. Although direct toxicity of Roundup WeatherMax was not apparent, the authors observed longer-term impacts, suggesting that the indirect effects of this herbicide deserve more consideration when assessing the ecological risk of using herbicides in proximity to wetlands.
Plain Language Summary
We conducted a field-based study to assess the impact of the glyphosate-based herbicide Roundup WeatherMax ® in small, shallow wetlands. We tested worst case and more environmentally realistic exposure scenarios, both with and without nutrient addition to simulate fertilizer inputs. We examined the abundance and composition of Chironomidae (midges), insects that are a large component of wetlands and an important food source for terrestrial birds. We found no direct effects from the herbicide alone or in combination with the fertilizer application. Three months after treatment, when wetland vegetation had been reduced by the herbicide and glyphosate could no longer be detected, there was an increase in the total abundance of emerging chironomids. While the herbicide treatment had no direct effects on total abundance or species present in the midge community in the short term, longer term effects could occur if the herbicide were to impact wetland plants.