ORIGINAL ABSTRACT

Glyphosate herbicide is ubiquitously used in agriculture and weed control. It has now been identified in aquatic ecosystems worldwide, where numerous studies have suggested that it may have both suppressive and stimulatory effects on diverse non-target organisms. We cultured natural biofilms from a hypereutrophic environment to test the effects on periphytic diatoms of exposure to a glyphosate-based herbicide formulation at concentrations from 0 to 10 mg L-1 of active ingredient. There were clear and significant differences between treatments in diatom community structure after the 15-day experiments. Diversity increased more in low glyphosate treatments relative to higher concentrations, and compositional analyses indicated statistically significant differences between glyphosate treatments. The magnitude of change observed was significantly correlated with glyphosate-based herbicide concentration. Our results show that glyphosate-based herbicides have species-selective effects on benthic diatoms that may significantly alter trajectories of community development and therefore may affect benthic habitats and whole ecosystem function.