Phosphorus dynamics and bioavailability in sediments of the Penzé Estuary (NW France): in relation to annual P-fluxes and occurrences of Alexandrium Minutum |
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Authors: | F Andrieux-Loyer X Philippon G Bally R Kérouel A Youenou J Le Grand |
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Institution: | (1) DYNECO Pelagos, IFREMER, B.P. 70, 29280 Plouzane, France |
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Abstract: | The macrotidal estuary of Penzé (Brittany, Western part of the Channel, France) has been subjected to recurrent annual toxic
blooms of Alexandrium minutum since 1988. This study aims to specify the phosphorus dynamics and bioavailability in sediments in order to improve our understanding
of Alexandrium occurrences. Sediment-P pools and diffusive phosphate fluxes were studied under similar hydrodynamic conditions, in the intermediate
estuary in May, June and July 2003 and along the salinity gradient from August 2004 to June 2005. The results highlight a
decrease in bioavailable phosphorus (iron and organic bound) from the inner part of the estuary seaward. The ratio of iron-bound
phosphorus to iron-oxyhydroxides is lower in the inner and intermediate estuaries (5–8) than in the outer site (15), suggesting
a saturation of sorption sites and greater phosphorus bioavailability in this area. Pools of bioavailable phosphorus in surficial
sediments are about eight times higher than the annual net-export of P (7 ton year−1). Phosphate releases from sediments are always lower than 5 μmol m−2 d−1 in March. The highest supplies occur in June and August in the intermediate area (up to 400 μmol m−2 d−1) where they represent up to 50% of river loadings. These results further suggest that phosphate pulses coincide with occurrences
of Alexandrium reported in June. |
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Keywords: | Alexandrium minutum Estuary Phosphate fluxes Pore water Sediment phosphorus Sequential extraction |
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