NITROGEN UPTAKE AND REGENERATION IN A FRO NTAL REGION OF THE ALGERIANCURRENT (WESTERN MEDITERRANEAN-SEA) - NEW EVALUATION OF NEW PRODUCTION

The uptake and regeneration of four forms of nitrogen NO3-, NO2-, NH4 and urea) have been studied, in the euphotic layer of a frontal area (Algerian current), in relation with hydrological, chemical and biolog ical parameters. Ln this area vertical stratification is pronounced; a deep chlorophyll maximum at the bottom of the euphotic layer is prese nt. Results show the importance of measuring urea uptake and regenerat ion in the study of nitrogen cycling, because this component can be re generated as rapidly as ammonia, and is a source of nitrogen for phyto plankton. Other results show the oxidation of ammonia to nitrate in th e euphotic layer, and particularly at the base of this layer. This nit rification is a source of in situ regenerated nitrate, and could lead to a wrong estimation of the new production estimation.