The influence of the River Rhone upon the nutrient fluxes of the Golfe du Lion

The five major dissolved nutrients were measured during December and
January, 1988/89, for the Golfe du Lion and the plume of the River
Rhone. Deep water stations exhibited some thermal stratification,
with nitrate depletion In the upper mixed layer, and deeper nutrient
rich water below the thermocline. The high nutrient concentrations
from the river (90 umoles/1 Nitrate), were the major influence for
the mixed inshore water column. The inshore profiles showed the low
salinity, nutrient enriched river water flowing over the saline
Mediterranean water, and the effect of this plume was seen up to 18
Km from its source. Secondary nutrient source were observed,
possibley the Petit Rhone or sewage inputs, and areas of nitrate
removal were identified probably due to sedimentary denitrlfication
processes. Within the plume, there was potential phosphate
limitation for the lower salinity samples, but the majority of the
area exhibited the potential for nitrogen limitation. Considering
the N/P ratio for ammonia alone, (Instead of all nitrogen species),
there was a lower salinity at which there could be phosphate
limitation, and this would be ecologically significant for the whole
area influenced by the River Rhone.