A Continuous-Flow Model Ecosystem for Studying Effects of Herbicides on Aquatic Plants

A continuous-flow system was designed for the culture of aquatic weeds in the laboratory and used to examine the effects of low concentrations of terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] and diquat cation (6,7-dihydrodipyrido [1,2-:2′,1′-c] pyrazinediium ion) on algae (epiphyton) growing on surfaces of common elodea (Elodea canadensis L. C. Rich # ELDCA). Terbutryn did not affect the density of the epiphytic algal community, although development of the diatom component was favored at the highest concentration (50 μg/L). Diquat cation stimulated the growth of the epiphyton, particularly the diatoms, at concentrations as low as 5 μg/L. Possible reasons for this response included hormesis, differential tolerance to diquat, and facultative heterotrophy.