Towards the Development of a Site-Specific Water Quality Objective for Atrazine in the Yamaska River, Quebec, for the Protection of Aquatic Life

Abstract

Abstract The biological effects of xenobiotics in aquatic environments are often a function of the water quality of these systems. The aquatic green alga Selenastrum capricomutum was exposed to 11 concentrations of the herbicide atrazine in the range of 0.8 to 882 μg/L. The incubation media consisted of water collected from the Yamaska River Lac Brome (control) site in the spring and fall. Algae incubated in fall water displayed a significant increase in the intensity of fluorescence as compared to those incubated in spring water. This effect (Kautsky effect) was observed for six intermediate atrazine concentrations which are representative of those found in the field. In situ investigations were also performed on the water quality of four Yamaska River sites to measure both biotic and abiotic (physicochemical) parameters. Of the 35 water quality parameters analyzed, 32 differed significantly spatio-temporally. Of these, only atrazine levels (max. 40 μg/L) exceeded national water quality guidelines for the protection of aquatic life (2 μg/L). Two Yamaska tributaries experienced a reduction in populations of chlorophytic algae immediately following the atrazine application period in early June. These investigations show that herbicide spring “pulse” in river systems may alter the normal succession of phytoplankton communities. Local environmental biotic and abiotic variables likely affect the toxicity of atrazine in the Yamaska River. These results provide the initial basis towards the establishment of a site-specific objective for atrazine in this river basin.