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2I - High-tiered Studies (MO7/9) Some ecological implications of pesticide perturbations to zooplankton communities in pond enclosures. Kreutzweiser, David1, Sutton, Trent2, 3, Back, Richard3, Pangle, Kevin2, 3, Thompson, Dean1, 1 Canadian Forest Service, Sault Ste. Marie, Ontario, Canada2 Purdue University, West Lafayette, Indiana, U.S.A.3 Lake Superior State University, Sault Ste. Marie, Michigan, U.S.A. ABSTRACT- A neem-based insecticide, Neemix® 4.5, was applied to forest pond enclosures at concentrations of 10, 17, and 28 Key words: impact, pesticide, zooplankton, ecosystem |
g/L azadirachtin (the active ingredient). At these test concentrations, significant, concentration-dependent reductions in adults copepods were observed. However, juvenile copepod and cladoceran populations were unaffected. There was no evidence of recovery of adult copepods within the sampling season (May to October). The ecological significance of this disturbance to the zooplankton community was examined by determining biomass as a measure of food availability for higher predators, plankton community respiration, dissolved oxygen concentrations, and conductivity as functional indicators of ecosystem stress, and zooplankton food web stability as a measure of effects on trophic structure. The selective removal or reduction of adult copepods was sufficient to measurably reduce total zooplankton biomass for several weeks mid season. During the period of maximal impact (about 4 to 9 weeks after the applications), total plankton community respiration was significantly reduced, and this was reflected by concentration-dependent increases in dissolved oxygen and decreases in conductivity among treated enclosures. The reduction in adult copepods resulted in negative effects on zooplankton food web stability through eliminations of a trophic link and reduced interactions and connectance. Results were compared to a previous enclosure study in which the pesticide being tested was selectively toxic to cladocerans, and in which there were little or no negative effects on food web stability. The study illustrates that differential sensitivities among taxa will have some bearing on the ecological significance of pesticide-induced disturbances to zooplankton communities.