The combined influence of two agricultural contaminants on natural communities of phytoplankton and zooplankton.
Concentrations of glyphosate observed in the environment are generally lower than those found to exert toxicity on aquatic organisms in the laboratory. Toxicity is often tested in the absence of other expected co-occurring contaminants. By examining changes in the phytoplankton and zooplankton communities of shallow, partitioned wetlands over a 5 month period, we assessed the potential for direct and indirect effects of the glyphosate-based herbicide, Roundup WeatherMax(©) applied at the maximum label rate, both in isolation and in a mixture with nutrients (from fertilizers). The co-application of herbicide and nutrients resulted in an immediate but transient decline in dietary quality of phytoplankton (8.3 % decline in edible carbon content/L) and zooplankton community similarity (27 % decline in similarity and loss of three taxa), whereas these effects were not evident in wetlands treated only with the herbicide. Thus, even at a worst-case exposure, this herbicide in isolation, did not produce the acutely toxic effects on plankton communities suggested by laboratory or mesocosm studies. Indirect effects of the herbicide-nutrient mixture were evident in mid-summer, when glyphosate residues were no longer detectable in surface water. Zooplankton abundance tripled, and zooplankton taxa richness increased by an average of four taxa in the herbicide and nutrient treated wetlands. The lack of significant toxicity of Roundup WeatherMax alone, as well as the observation of delayed interactive or indirect effects of the mixture of herbicide and nutrients attest to the value of manipulative field experiments as part of a comprehensive, tiered approach to risk assessments in ecotoxicology.
Biology Department and Canadian Rivers Institute, University of New Brunswick Saint John, 100 Tucker Park Rd, Saint John, NB, E2L 4L5, Canada. bakerleannef@gmail.com.
Leanne F
LF
Baker
Biology Department and Canadian Rivers Institute, University of New Brunswick Saint John, 100 Tucker Park Rd, Saint John, NB, E2L 4L5, Canada.
Joseph F
JF
Mudge
Canadian Forest Service, Natural Resources Canada, 1219 Queen St. E, Sault Ste. Marie, ON, P6A 2E5, Canada.
Dean G
DG
Thompson
Biology Department and Canadian Rivers Institute, University of New Brunswick Saint John, 100 Tucker Park Rd, Saint John, NB, E2L 4L5, Canada.
Jeff E
JE
Houlahan
Biology Department and Canadian Rivers Institute, University of New Brunswick Saint John, 100 Tucker Park Rd, Saint John, NB, E2L 4L5, Canada.
Karen A
KA
Kidd
D000383:Agriculture; D000818:Animals; D017753:Ecosystem; D004784:Environmental Monitoring; D005998:Glycine / Q000031:analogs & derivatives* / Q000633:toxicity; D006540:Herbicides / Q000633:toxicity*; D009584:Nitrogen / Q000633:toxicity; D010758:Phosphorus / Q000633:toxicity; D010839:Phytoplankton / Q000187:drug effects* / Q000502:physiology; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D053833:Wetlands; D015048:Zooplankton / Q000187:drug effects* / Q000502:physiology; D000097797:Glyphosate
D005998:Glycine; D006540:Herbicides; D009584:Nitrogen; D010758:Phosphorus; D014874:Water Pollutants, Chemical; D000097797:Glyphosate
Fertilizers; Glyphosate; Indirect effects; Mixture effects; Phytoplankton; Zooplankton