DISSOLVED AND PARTICULATE ORGANIC-CARBON IN THE WATER COLUMN AND AT THE SEDIMENT-WATER INTERFACE IN THE ESTUARINE BAY OF MARENNES-OLERON - INFLUENCE OF OYSTER FARMING

At the sediment-water interface with and without oyster farming (Crassostrea gigas), the accumulation and redistribution of different forms of dissolved and particulate carbon were studied. Particulate and dissolved organic carbon fluxes between the water column, the sediment and the biodeposits were measured. The annual flux of dissolved organic carbon is 178,3 10(3) g m-2 yr-1, while that of particulate organic carbon is less than half this amount: 71,4 10(3) g m-2 yr-1. Organic carbon with a detrital origin accounts for 84% of particulate organic carbon. Organic accumulation is 0,1 10(3) g m-2 yr-1 in the control zones; in the oyster cultivation areas, the accumulation is six times higher (0,6 10(3) g m-2 yr-1). Resuspension can be important, with release of dissolved organic carbon and redistribution of particulate organic carbon in the water column. An enrichment of humic acids in the sediment is linked with phytobenthic biomasses, increased by the presence of oysters.