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Impacts biosédimentaires des expérimentations de clapages en baie de Seine sur la communauté des sables moyens propres à Nephtys cirrosa

Abstract : Two experiments consisting in a series of sediment deposits from maintenance dredging for the access channel to Rouen Harbour on two adjacent sites were conducted in 2012-2013. The aim is to monitor the biosedimentary impacts and to test several deposit procedures (i.e. different amounts of sediment, deposit time…). Based on a Before-After-Control-Impact (BACI) approach, spatio-temporal changes on various parameters (sedimentary, physicochemical and biological) were analyzed to assess the short term consequences of deposits on benthic habitats during 12 surveys from April 2010 to March 2013. The results showed that the impact of the 2 experiments remain very local and limited to the stations directly affected by the deposits. The effects were rapid on deposits stations: disappearance of the macrofauna just after the deposit, but rapid colonisation of organisms occurring during a favourable spring-summer period. Abundance peaks are observed on some stations caused by the presence of pioneer species exhibiting variations in very high densities resulting high capacity of dispersal and colonization. Such species sustain high amounts of fine particles until 50% in impacted stations ~ against about 1% in the reference stations. This adaptability is favored by strong hydrodynamic conditions in the eastern bay of Seine that allows the development of resilient species able to tolerate significant variations of the environment. An adaptative management of dredged material disposal has then been proposed by the implementation of protocol management of dredged sediments suitable for future deposits and a benthic monitoring to minimise impacts on environment.
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Stella Marmin. Impacts biosédimentaires des expérimentations de clapages en baie de Seine sur la communauté des sables moyens propres à Nephtys cirrosa. Ecologie, Environnement. Université de Caen Basse-Normandie, 2013. Français. ⟨NNT : 2013CAEN2071⟩. ⟨tel-01922183⟩

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