Nitrate elimination and regeneration as evidenced by dissolved inorganic nitrogen isotopes in Saanich Inlet, a seasonally anoxic fjord
| Type | : | ACL |
|---|---|---|
| Nature | : | Production scientifique |
| Au bénéfice du Laboratoire | : | Non |
| Statut de publication | : | Publié |
| Année de publication | : | 2013 |
| Auteurs (5) | : | BOURBONNAIS A LEHMANN M,f HAMME Roberta,c MANNING C,c JUNIPER S,k |
| Revue scientifique | : | Marine Chemistry |
| Volume | : | 157 |
| Fascicule | : | |
| Pages | : | 194-207 |
| DOI | : | 10.1016/j.marchem.2013.09.006 |
| URL | : | - |
| Abstract | : | In this study, we used natural abundance isotope measurements of dissolved inorganic nitrogen (N) species to evaluate the effect of different oxygenation regimes on N transformation and elimination in Saanich Inlet, a seasonally anoxic fjord in British Columbia, Canada. We analyzed dissolved nutrient concentrations and the N (and O) isotope composition of nitrate (NO3-) and ammonium (NH4+) at different depths throughout the water column near the mouth of the inlet between April 2008 and April 2009. A gradual increase in both the NO3- delta N-15 and delta O-18, associated with a decrease in NO3- concentration and an increase in biological excess N-2, was observed after bottom water renewal events in August-October 2008, indicating NO3- consumption by denitrifying bacteria in an expanding suboxic water column. An increase in the delta N-15 of NH4+, with depth toward the suboxic/hypoxic transition, indicated net consumption of NH4+, most likely by micro-aerobic or anaerobic NH4+ oxidation and dissimilatory consumption by microorganisms. Deviations from a 1:1 correlation between the NW delta N-15 and delta O-18 (Delta(15,18)) that appears characteristic for both assimilatory and dissimilatory NW consumption in the ocean, were observed in surface waters and close to the hypoxic/suboxic transition. Lowered Delta(15, 18) values can most plausibly be explained by aerobic nitrification of newly remineralized NH4+ and/or low delta N-15-NO3- inputs from atmospheric precipitation in the surface mixed layer, and NO3- regeneration through NH4+ oxidation and/or the reoxidation of nitrite (NO2-) in deeper waters. Closed and open system model-derived N isotope effects for NO3- consumption calculated from time-series samples collected near the sediments in anoxic bottom waters were significantly lower (as low as similar to 11 parts per thousand) than the biological N isotope effects of similar to 20-30 parts per thousand for water column denitrification reported in other studies. We argue that the reduced N isotope effect is mainly due to the combined effects of water column and sediment denitrification, the latter occurring with a highly suppressed N isotope fractionation at the ecosystem level. We estimated that similar to 40-60% of the denitrification occurs within the sediments of the inlet. (C) 2013 Elsevier B.V. All rights reserved. |
| Mots-clés | : | ANAEROBIC AMMONIUM OXIDATION; Anoxic basin; British Columbia; Dissolved inorganic nitrogen isotopes; Fixed nitrogen loss; FRESH-WATER; MARINE-SEDIMENTS; N-2 FIXATION; Nitrate isotope anomalies; Nitrogen cycle; Northeast Pacific Ocean; OCEANIC FIXED NITROGEN; OXIDIZING BACTERIA; OXYGEN ISOTOPES; PARTICULATE ORGANIC-MATTER; Saanich Inlet; SANTA-BARBARA BASIN; Sedimentary denitrification; TROPICAL NORTH PACIFIC; Water-column denitrification |
| Commentaire | : | Times Cited in Web of Science Core Collection: 15 |
| Tags | : | - |
| Fichier attaché | : | - |
| Citation | : |
Bourbonnais A, Lehmann MF, Hamme RC, Manning CC, Juniper SK (2013) Nitrate elimination and regeneration as evidenced by dissolved inorganic nitrogen isotopes in Saanich Inlet, a seasonally anoxic fjord. Mar Chem 157: 194-207 | doi: 10.1016/j.marchem.2013.09.006
|