Impacts of nutrients and insecticide on algal production in a prairie wetland

Abstract

I added nutrients (inorganic nitrogen and phosphorus) and the arthropod-specific insecticide chlorpyrifos to large (20,000L) experimental enclosures in the Blind Channel of Delta Marsh, Manitoba. I hypothesized that nutrient addition would lead to an increase in algal production (approximated by chlorophyll 'a' concentration), that the application of insecticide would indirectly result in increased algal production (through the elimination of herbivorous zooplankton), and that the combination of both nutrients and insecticide would elicit greater algal production than either factor alone. I conducted two ancillary experiments to assess the limiting nutrient at the study site. I conclude that Delta Marsh, Manitoba is susceptible to nutrient inputs from the surrounding agricultural land, especially in areas where nitrogen-based fertilizers are used. Although it is widely believed that wetlands are inexhaustible filters for pollutants, I predict that continual nutrient enrichment of this wetland will evoke irreparable changes to the base of the food web. A shift away from macrophytes and epiphyton to phytoplankton dominance will negatively impact the ability of Delta Marsh to sustain its upper trophic levels (fish and waterfowl). (Abstract shortened by UMI.)