The Effect of Four Terrestrial Herbicides on the Productivity of Artificial Stream Algal Communities

Abstract

Abstract Artificial streams containing algal communities derived from a spring and an agriculturally impacted stream were used to assess the effect of 0.1, 1, and 10 mg kg −1 atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐ s ‐triazine], trifluralin ( α,α,α ‐trifluoro‐2,6‐dinitro‐ N,N ‐dipropyl‐ p ‐toluidine), MSMA (monosodium methanearsonate), and paraquat (1,1′‐dimethyl‐4,4′‐bipyridylium cation) on the productivity (photosynthesis and respiration) of stream algae. The importance of induced resistance to the herbicides was evaluated by comparing the responses of the spring and stream algae and by determining if allowing the streams to be colonized for 3 weeks in the presence of 0.01 mg kg −1 of the herbicide under test would modify response by selecting for a more resistant flora. Productivity was measured by open‐water oxygen methods for 3 weeks before and 3 weeks after herbicide injection. The communities derived from both the spring and the stream were dominated by diatoms, and responded similarly to trifluralin, atrazine, and MSMA, but had divergent responses to paraquat. Trifluralin had no effect on productivity. Photosynthesis was significantly depressed by 1 and 10 mg kg −1 atrazine and by 10 mg kg −1 MSMA, and there were indications of a slight inhibition by 0.01 mg kg −1 atrazine. Paraquat at 10 mg kg −1 had little effect on the spring‐derived communities but caused severe inhibition of the stream‐derived algae. There was little evidence that exposure to 0.01 mg kg −1 herbicide during colonization modified the response of the algae to any of the herbicides.