Evidence for anaerobic bacterial processes in the water column: Denitrification and dissimilatory nitrate ammonification in the northwestern Mediterranean Sea

Abstract

Bacterial anaerobic processes in particles in the water column of the northwestern Mediterranean Sea were investigated. Particles concentrated on a filter were incubated in oxygen-free sterile sea water. Results demonstrated that there is a weak but almost constant expression of bacterial nitrate-dissimilation processes [denitrification and dissimilatory nitrate ammonification (DAP)] associated with particles. Both activities were found from 30 m down to 615 m depth in coastal water off Marseilles, France, in autumn and from 100 to 700 m depth in spring and autumn in coastal water off Nice. In summer when oligotrophic conditions occurred, both activities were just detectable. In the other seasons, denitrification was the main process of nitrate dissimilation, with peak activity in autumn. This activity was associated with both large and small particles. In contrast, nitrate ammonification was associated only with large particles that were located in the upper layer in autumn and spread throughout the water column in spring.