2,4-D and Glyphosate affect aquatic biofilm accrual, gross primary production, and community respiration

Abstract

2,4-Dichlorophenoxyacetic acid (2,4-D) and glyphosate are widely used agricultural herbicides commonly found in surface waters near cultivated land. Field experiments were conducted to determine the effects of 2,4-D and glyphosate on biofilms in a pond next to agricultural land in Athabasca, Alberta. Diffusing substrates consisted of specimen jars filled with agar that contained low levels of nitrogen and phosphorus, and different concentrations (15, 9.0, 1.5 mM) of either 2,4-D or glyphosate. A circular hole in the lid of the jar was covered with either a GF/C glass fiber or a cellulose filter paper which functioned as the biofilm substrate. Nutrients and herbicide diffused freely through the agar to the substrate surface. Arrays of diffusing substrates were suspended 15 cm below the water surface for 22 days, after which O2 production and consumption were measured to give the rates of primary production and respiration. Biomass was measured as Chl-a. 2,4-D and glyphosate caused significant decreases in rates of biomass accrual, primary production, and respiration. For both compounds, dose responses were highest at the highest concentrations.