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RESEARCH PRODUCT

Satellite survey of seasonal trophic status and occasional anoxic crises ?Malaigues? in the Thau lagoon using MeRIS images

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International audience; The Thau lagoon, located in southern France, suffers episodically from anoxic crises locally known as'malaigue'. Such crises mostly occur under warm conditions, low winds leading to a strongeutrophication of the lagoon. The development of a sulphur bacterium sometimes gives locally to thewaters a 'milky turquoise' appearance and leads to shellfish mortality. One of the indicators of theeutrophication status of the lagoon can be surveyed by the chlorophyll product provided by remotesensing images such as Medium Resolution Imaging Spectrometer (MERIS). In this paper wecompare chl2 (or algal2) estimations provided by MERIS level 2 products and the groundmeasurements of chlorophyll a concentrations in water and we propose a linear correction of the chl2MERIS product. The corrected chl2 estimations obtained over four years are analysed to understandthe seasonal evolution of the trophic status of the Thau lagoon. We also study the influence of theanoxic crises of summers 2003 and 2006 on the chl2 estimations and we find a strong correlationbetween chl2 and the oxygen percentage at 1 m depth (0.70 for measurements in summers 2003 and2006)