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(44-07) Seasonal variation in plankton community-level responses of mesocosms dosed with pentachlorophenol. Willis, Kate*,1, Van den Brink, Paul2, Green, John1, 1 Biological Sciences, Hamilton, New Zealand2 Alterra Green World Research, Wageningen, The Netherlands ABSTRACT- Seasonal variations in plankton community response to pentachlorophenol (PCP) were studied in four mesocosm experiments using enclosures in a small New Zealand lake. For each experiment, the mesocosms (860 L) were dosed with single applications (0, 4, 10, 24, 36, 54, 81 and 121 ppb) of technical grade PCP dissolved in ethanol. Multivariate analyses revealed sampling date, treatment and season were important factors explaining differences in species composition between samples. The plankton communities were very different between seasons and the winter community was very stable in time. The autumn and winter plankton communities were more sensitive to PCP (NOECcommunity 24 ppb) than the spring and summer communities (NOECcommunity 36 and 54 ppb respectively). However, the plankton communities were similar with respect to the species displaying a response to PCP. Calanoid copepods were the most sensitive zooplankton species in all seasons. Of the phytoplankton species, Cryptomonas spp. abundance increased in the two highest treatments in autumn and winter, and the highest treatment in spring. The data from all four mesocosm experiments was combined to determine the overall community NOEC. The NOECcommunity was 36 ppb PCP on days 4 to 16, and 24 ppb on day 20. Key words: mesocosm, plankton, pentachlorophenol, seasonal sensitivity |
