Bacterial production in the Rhone River plume: effect of mixing on relationships among microbial assemblages

Abstract

We examined inorganic nutrients and microbial assemblages in the Rhone River plume during January 1987. When wind speed is low the plume forms a transient layer of high nutrient-low salinity water overlaying the Mediterranean Sea. The vertical thickness of the plume was on the order of 100 cm, and during one horizontal transect surface density decreased 2-fold within 1 km. Ammonium, nitrate, and phosphate concentrations were at least 10-fold higher in the thin plume compared with sea values. Bacterial production was higher by about 2-fold at plume-sea boundaries. Although bacterial biomass and production peaked with chlorophyll at plume-sea boundaries, the correlation between these bacterial parameters and chlorophyll concentrations was low.