The effects of a number of herbicides upon photosynthesis and heterotrophy of naturally occurring algal and bacterial communities in Delta Marsh, Manitoba

Abstract

The short term effects of a number of herbicides upon the photosynthetic rate of two algal communities, phytoplankton and periphyton, and heterotrophic assimilation of phyto- and bacterioplankton populations in the light and the dark were determined. All experimental work was conducted on samples of naturally occurring algal and bacterial communities in Delta Marsh, Manitoba and all such samples were treated in the laboratory under strictly controlled environmental conditions. Fourteen commercial grade herbicides from eight herbicidal groups: Phenoxyacetic Acids (2,4-D and MCPA), Benzoic Acids ("Amiben"), Aliphatic Acids (TCA and "Dalapon"), "N" Heterocyclics ("Simazine", "Atrazine" and "Amitrole"), Substituted Ureas ("Linuron"), Carbamates ("Barban", EPTC and "Triallate"), Bipyridyls ("Paraquat") and Inorganic (copper sulphate) were employed in this study. Only three herbicides, "Linuron", "Simazine" and "Atrazine" were capable of totally inhibiting phytoplankton photosynthesis as opposed to seven for periphyton photosynthesis, "Linuron", "Simazine", "Atrazine", "Barban", "Paraquat", copper sulphate and "Dalapon". Excluding 2,4-D, MCPA and "Amiben", 50% reductions of algal photosynthesis occurred with all other herbicides investigated in the experimental program. The herbicides most toxic to planktonic heterotrophs were copper sulphate, "Paraquat", "Barban", "Triallate", EPTC and "Linuron"; the only herbicides capable of reducing heterotrophic assimilation of 14C-glucose by photo- and bacterioplankton populations by 50%. 2,4-D and MCPA produced moderate inhibitions of planktonic heterotrophy whereas the six remaining herbicides exhibited slight or no inhibition. With the exception of "Barban", there appeared to be no apparent difference between illuminated and darkened samples of heterotrophs.