HR: 0800h
AN: B51A-0189    [Abstracts]
TI: Ammonium Oxidation by Ferric Compounds in Continuous-Flow Microcosms and Verification Using Batch Experiments with 15N-NH4 Tracer
AU: * Shrestha, J
EM: jshresth@princeton.edu
AF: Dept of Civil and Environmental Engineering, Princeton University, E-Quad, Prospect Avenue, Princeton, NJ 08544 United States
AU: Rich, J R
EM: jjrich@princeton.edu
AF: Department of Geosciences, Guyot Hall, Washington Rd, Princeton, NJ 08544 United States
AU: Jaffe, P R
EM: jaffe@princeton.edu
AF: Dept of Civil and Environmental Engineering, Princeton University, E-Quad, Prospect Avenue, Princeton, NJ 08544 United States
AB: The possibility of ammonium oxidation by ferric hydroxides under anaerobic conditions was studied in riparian wetland sediment from New Jersey. Flow-through microcosms containing iron rich sediment from the site were operated by feeding either a control solution or an ammonium chloride solution for six months. After, four months of incubation under anaerobic conditions, nitrite was detected in pore water collected from different depths in both microcosms. Increase in nitrite concentrations was detected between the fourth and the fifth months of incubation in the microcosms containing ammonium chloride whereas the concentrations in the controls remained unchanged. In order to explain this appearance of nitrite under anoxic conditions, we propose that, under anaerobic conditions, there are biological processes that transfer electrons from ammonium to ferric hydroxides, producing nitrite and ferrous compounds as byproducts. Separate anaerobic batch experiments performed with the same sediment amended with 15N-NH4 produced labeled dinitrogen gas, indicating the presence of processes that could convert ammonium into nitrate or nitrite and then into dinitrogen gas by denitrification. No such activity was observed in the control batch experiment with the sediment containing completely reduced ferric compounds amended with 15N-NH4. This ammonium oxidation under iron reducing anaerobic conditions is thermodynamically feasible and is potentially a critical component of the N cycle in saturated sediments.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0469 Nitrogen cycling
DE: 0471 Oxidation/reduction reactions (4851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005