Effects of herbicide mixture on microbial communities in prairie wetland ecosystems: A whole wetland approach

Wetlands in the prairie pothole region of Saskatchewan and Manitoba serve an important role in providing wildlife habitat, water storage and water filtration. These wetlands are regularly interspersed among agricultural operations where multiple pesticides are commonly used. Although mixtures of pesticides are often detected in these important aquatic ecosystems, very little information is known, regarding their effects. In this study, a curtained wetland approach was used to investigate the effects of a herbicide mixture (2,4-D, MCPA, clopyralid, dicamba, dichlorprop, mecoprop, bromoxynil, and glyphosate) on the structure and function of microbial communities in an ephemeral wetland and a semi-permanent wetland. In the two studied wetlands, located in Manitoba Zero Till Research Association Farm, Brandon, Manitoba, Canada, herbicide treatment based on maximum-exposure scenarios had a significant effect on pelagic and biofilm phytoplankton productivity over relatively short time periods. The stimulation of phytoplankton productivity in the ephemeral wetland appeared to be the result of a hormonal effect of the auxin-type herbicides present in the mixture, similar to naturally occurring auxins. Herbicidal effects of auxin-type herbicides were also noticed in the semi-permanent wetland where phytoplankton productivity was suppressed during the first week as a result of the concentration addition effect of the auxin-type herbicides present in the mixture. BIOLOG and pigment profiles of the biofilm community suggested a change in the community structure in both wetlands.

► Effects of herbicide mixture on microbial communities using curtained wetlands.
► Evidence of effects of herbicide mixture on pelagic and biofilm communities.
► Herbicides at low concentrations appear to be exerting effects as a result of concentration addition.
► Herbicides suppressed primary production, bacterial production and chlorophyll a.