PHOSPHORUS SPECIATION AND INPUTS TO THE E ASTERN BAY OF SEINE

The Bay of Seine receives the French river with the highest nutrient c oncentrations, especially phosphorus. Dissolved (phosphate) and partic ulate phosphorus fluxes have been determined from fortnightly serial d ata collected by the Port Autonome de Rouen. These determinants exhibi t behaviour opposite to that of the river flow: phosphate concentratio n decreases hyperbolically and particulate phosphorus increases linear ily. An approach based on the rate of domestic effluent treatment agre es well (20%) with the measured phosphate flux. The determination of t he main particulate phosphorus forms (adsorbed, apatite, non-apatite i norganic, organic) was undertaken over the whole estuarine salinity ra nge. The speciation of particulate phosphorus exhibits a great homogen eity, irrespective of the salinity and the time of the year. From this study, it may be concluded that some 50% of the particulate phosphoru s is potentially bioavailable. Heavy loads of particles expelled from the estuary during spring floods may therefore significantly contribut e to the enrichment of the bay at the time when phytoplankton is activ ely growing.