ABSTRACT: 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) between November and June 1993. The 2 dissimilatory pathways of nitrate reduction, denitrification and nitrate ammonification, were measured using a combination of the acetylene inhibition and ¹⁵N techniques. Irrespective of the sampling site, denitrification and nitrate ammonification rates, measured without nitrate and glucose amendment, ranged from 1.0 to 4.3 µmol l^-1 d^-1 and 0.7 to 2.5 µmol l^-1 d^-1, respectively. 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 that the mechanism of reduction was dissimilatory. The dissimilatory character of nitrate ammonification was unequivocally confirmed in experiments using a bacterial community isolated from a natural water sample.

KEY WORDS: Nitrate ammonification · Denitrification · ¹⁵N · Water column · Mediterranean Sea

Published in MEPS Vol. 141 (1996) on October 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996