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(370) Modelling the toxic effects of nonylphenol on a lotic ecosystem. Hulot, Florence1, Magaud, Hélène2, Bonzom, Jean-Marc2, 1 2 ABSTRACT- An 18 month experiment is being run in lotic mesocosms in France to study the effect of nonylphenol on a freshwater ecosystem. These mesocosms (20 meters long, 1 meter wide and 30 and 70 cm deep) contain sediments, rocks, aquatic plants, primary producers (phytoplankton, periphyton), primary consumers (freshwater and sediment invertebrates), secondary consumers (fish) and detritivores. Two replicates of four nominal concentrations of nonylphenol (0, 0.33, 3.3, and 33 mg/l) were randomly assigned to separate channels. The mesocosms are continuously treated. The effect of nonylphenol on different levels of organisation (individuals, populations and communities) of the ecosystem are being measured. The aim of this work is to analyse the effect of nonylphenol on the functioning of the ecosystem, by analysing both direct and indirect effects of nonylphenol on the web of interactions. A conceptual model of our ecosystem, made up of functional groups defined according to major interactions between species (predation, competition), is built. The direct and indirect interactions between these functional groups are qualitatively analysed by loop analysis. With this method we can qualitatively predict the effects of a perturbation by taking into account the direct effects of the disturbance and their propagation within the interaction web. A comparison of the experimental results and the predictions allows us to disentangle direct and indirect effects of nonylphenol upon ecosystem functioning. It is thus possible to take into account both functional diversity and indirect interactions in the response of the ecosystem to a perturbation such as the exposure to a toxic substance. Key words: mesocosm, modelling, nonylphenol, ecosystem functionning |
