No abstract

No abstract

Sediment-water dissolved inorganic nitrogen fluxes were measured monthly between November 1997 and January 1999 at two sites on the continental shelf in the Gulf of Lions. Exchanges of ammonium, nitrate and nitrite were measured using whole core incubations performed in the laboratory at in situ temperature and in the dark. Stations were located on the shelf and near the shelf break. Nitrate release represented the major part of total dissolved inorganic nitrogen fluxes (52-98%). At station Sofi, nitrate flux doubled from winter-early spring to August (4 to 10 µmol m-2 h-1). At station R, a large increase (2 to 14 µmol m-2 h-1) was recorded between December 1997 and January 1998, after which flux tended to decrease. Ammonium flux was generally directed out of the sediment, and was lower at station Sofi than at station R. Nitrite flux was always less than 1 µmol m-2 h-1. A large part of the temporal variability observed at station R could be attributed to the input of organic matter associated with the discharge of the Rhône River. On the contrary, the influence of the Rhône River is limited at station Sofi, and the spring phytoplankton bloom deposition was probably the major cause of temporal variability. Comparisons of total fluxes with diffusive fluxes suggested a high nitrification rate in the upper centimetre of the sediment. Annual dissolved inorganic nitrogen release from sediments, equivalent to 20-34% of the Rhône River inputs, may contribute 4-8% of the requirements for primary production in the Gulf of Lions. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Résumé − Variabilité temporelle des flux d'azote inorganique dissous à l'interface eau-sédiment et bilan annuel sur un plateau continental (Méditerranée nord occidentale). Afin de décrire la variabilité temporelle des flux d'azote inorganique dissous sur le plateau continental du golfe du Lion, un suivi mensuel (novembre 1997-janvier 1999) a été effectué à deux stations. Les flux de NH 4 + , NO 3-, NO 2 ont été mesurés par incubation de carotte. Le flux de nitrate hors

No abstract