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Communication at the NABS Annual meeting, Keystone, 2000
(433) EFFECTS OF INORGANIC NUTRIENT AND INSECTICIDE ADDITIONS ON ALGAL COMMUNITIES IN A PRAIRIE LAKESHORE MARSH.
A.D. Kiers-North and L.G. Goldsborough. Department of Botany, University of Manitoba, Winnipeg, MB, Canada R3T 2N2
We added inorganic nitrogen and phosphorus and the arthropod-specific insecticide Lorsban 4E (chlorpyrifos) to 5 x 5 m mesocosms in Delta Marsh, Canada. Three treatments (procedural control, nutrient addition, and combined nutrient and insecticide addition) were applied to four replicate enclosures. Nutrients were added three times weekly over a two-month period for a total load of 23.9 g/m2 N and 3.1 g/m2 P. Insecticide was added mid-way through the experiment at a nominal concentration of 10 µg/L. Planktonic algal biomass (measured as chlorophyll content) increased in the nutrient treatment, and to a lesser degree in the combined treatment, during the first month of the experiment. This contradicted our prediction that the reduction in grazing pressure by insecticide treatment, combined with stimulatory nutrient input, would increase algal biomass more than the addition of nutrients alone. Periphyton biomass on artificial substrata increased in both treatments after phytoplankton blooms declined, possibly due to reduced competition for light and nutrients. The release of top-down control by zooplankton appears to have had a negligible effect on phytoplankton biomass in Delta Marsh, and it is likely that algal biomass is regulated primarily by bottom-up controls.
Presented at 1:00 PM on Wednesday, May 31, 2000 in Wetlands
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