Réponses écophysiologiques à une pollution d’origine anthropique chez un organisme sentinelle et conséquences sur le fonctionnement des bassins d’infiltration

Abstract : Human populations are exposed to numerous pollutants. It is now necessary to evaluate the toxicity of urban contaminants in receptor ecosystems. In anthropized areas, many pollutants (mainly hydrocarbons and heavy metals) accumulate on the impervious surfaces (roads, parks, buildings, rooftops…). During a rainfall event, these compounds are re-suspended and drained up to stormwater infiltration basins. These structures were built to detoxify and to infiltrate runoff water to underlying groundwater. Toxic compounds are captured and accumulated in the fine sediment layer of the infiltration basins, where their concentrations may achieve important concentrations. Despite this harsh constraint, a few invertebrates inhabit stormwater basin sediments and have developed specific metabolic, physiological and/or behavioural adaptations. One of the most spread is the oligochaeta Limnodrilus hoffmeisteri. This tubificid worm burrows galleries (bioturbation activity) in sediments where it enhances the organic matter mineralization and the nutrients recycling. This species has an essential role in the infiltration basin functioning and on groundwater quality. L. hoffmeisteri is considered both as a sentinel species of ecosystem health and an engineer species. The first aim of this work was to highlight the ecophysiological responses that allow L. hoffmeisteri to survive in these harsh conditions. We exposed this organism during 1, 3 or 6 months to polluted sediments (from 3 infiltration basins), under laboratory conditions. Then, we measured the survival, the oxygen consumption, the energy body stores, the oxidative stress induced by urban pollutants (through the lipid peroxidation level), and the antioxidant defence mechanisms (the activity of the antioxidant enzymes) in L. hoffmeisteri. The same analyses were realized on worms incubated 1 to 6 months in a sediment from a non-urbanized environment (considered as a low-polluted/control sediment). The second objective of the present work was to determine the impact of urban pollutants on aerobic and anaerobic metabolisms in L. hoffmeisteri. We measured several mitochondrial parameters (the mitochondrial respiratory chain activity and the ATP production rate) and anaerobic end product concentrations in worms exposed to the 4 same sediments (polluted or not). This study demonstrated that urban pollutants induced a shift from aerobic to the anaerobic metabolism, linked to a mitochondrial dysfunctioning. Moreover, this study also showed that two anaerobic end products (succinate and propionate) constitute relevant biomarkers of urban pollution. Lastly, the third goal of this thesis was to evaluate the impact of an anthropic pollution on the engineering activity of L. hoffmeisteri (i.e. its role in the infiltration basin functioning). To this end, we measured during 1 month the burrowing activity of this tubificid worm using X-ray tomography, in microcosms containing slightly or highly polluted sediments. We measured nutrients fluxes, dissolved oxygen, CO2 and CH4 concentrations during the experiment to determine the influence of the pollution rate on nutrients recycling. These measurements were also realized in microcosms with or without worms, to quantify the functional role of engineer organisms
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Mathilde Pigneret. Réponses écophysiologiques à une pollution d’origine anthropique chez un organisme sentinelle et conséquences sur le fonctionnement des bassins d’infiltration. Ecologie, Environnement. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSE1031⟩. ⟨tel-02157473⟩

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