The use of outdoor freshwater pond microcosms. III. Responses of phytoplankton and periphyton to pyridaben

An outdoor freshwater microcosm study was conducted in which pyridaben, an insecticide-miticide, was directly applied to water to determine its biolog ical effects on phytoplankton and periphyton. Twenty-four microcosms (24 m( 3) each) were monitored for 11 months, then four treatments of pyridaben we re applied two times at three concentrations (0.34, 3.4, 34.0 mug/L), inclu ding an untreated control. The succession of algal groups observed and the major genera found in microcosms during the baseline phase of the study wer e typical of oligo-mesotrophic systems in Florida. Following application of pyridaben, the most remarkable effect was a positive correlation of phytop lankton abundance with pyridaben concentrations in water; indicating increa sed abundance as a result of exposure. Both Chlorophyta and Pyrrophyta exhi bited a significant increase (p=0.05) in population abundance at 3.4 and 34 .0 mug/L pyridaben. Chrysophyta also elicited a trend of increased abundanc e at 34.0 mug/L, although the effect was not significant. The effects on ph ytoplankton populations were associated with the decline of zooplankton pop ulations as a result of a direct effect of pyridaben exposure. There were n o effects of pyridaben on periphyton communities or on functional endpoints . (C) 2001 by John Wiley & Sons, Inc.