P. Omnes et al., EVIDENCE OF DENITRIFICATION AND NITRATE AMMONIFICATION IN THE RIVER-RHONE PLUME (NORTHWESTERN MEDITERRANEAN-SEA), Marine ecology. Progress series, 141(1-3), 1996, pp. 275-281
Water samples were collected from the turbid plume water of the River
Rhone at 2 stations (near the river mouth and at the plume front) betw
een November and June 1993. The 2 dissimilatory pathways of nitrate re
duction, denitrification and nitrate ammonification, were measured usi
ng a combination of the acetylene inhibition and N-15 techniques. Irre
spective of the sampling site, denitrification and nitrate ammonificat
ion rates, measured without nitrate and glucose amendment, ranged from
1.0 to 4.3 mu mol l(-1) d(-1) and 0.7 to 2.5 mu mol l(-1) d(-1), resp
ectively. The percentage of nitrate reduced to ammonium varied between
12 and 33% of the total nitrate dissimilated. Both processes occurred
simultaneously and competed for nitrate as an electron acceptor. The
reduction of nitrate to ammonium was inhibited by oxygen, indicating t
hat the mechanism of reduction was dissimilatory. The dissimilatory ch
aracter of nitrate ammonification was unequivocally confirmed in exper
iments using a bacterial community isolated from a natural water sampl
e.