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PW12 Pesticide II
(PW198) Zooplankton community responses to a toxic perturbation in a mature lentic mesocosm.
Blake, N1, Arnold, D1, Kane, D2, 1 Cambridge Environmental Assessments, Cambridge, UK2 Landis Kane Consulting, Fullinsdorf, Switzerland
ABSTRACT- Experimental mesocosms allow the fate and effects of chemicals in semi-natural systems to be determined. A static outdoor mesocosm study was carried out to determine the effects of a synthetic insecticide on a natural community of freshwater organisms. The mesocosm communities at Cambridge Environmental Assessments had been allowed to establish undisturbed for three years prior to the introduction of the experimental enclosures. Treatment concentrations were selected to represent a wide range of exposure conditions including predicted environmental concentrations associated with diverse agricultural uses. The responses of benthic populations and communities of zooplankton, emergent insects, benthic and sediment fauna were analysed. We present the responses of zooplankton populations and communities sampled during the study using a depth integrated water sampler here. Prior to treatment the zooplankton community was dominated by Copepoda and Rotifera. The zooplankton data were analysed using Analysis of Variance (ANOVA), Principal Response Curves (PRC) and Redundancy Analysis (RDA) in order to determine NOEC and NOECcommunity. The fate of the insecticide in water and sediment samples was also analysed. The insecticide dissipated rapidly, with the lowest concentration below the limit of detection on the day of application. Concentrations in all enclosures were below the limit of detection by Day 14. Clear dose-response effects were evident from Day 0 (ca. three hours post application), with Copepoda nauplii, Calanoida, Daphniidae adults and Rotifera all contributing to the NOECcommunity. Copepoda nauplii, Calanoida and Daphniidae adults all decreased in abundance in treated enclosures relative to the control enclosures, whereas Rotifera increased in abundance. The rapid degradation of the insecticide in the water phase allowed taxa with short lifecycles (i.e. Copepoda) to recover quickly with no significant effects observed after Day 14. The response of all measured biological compartments were considered in the recommendation of an Ecologically Acceptable Concentration (EAC).
Key words: mesocosm, higher-tier, PRC, risk assessment
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