Temporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbia

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dc.contributor.authorJi, Qixing
dc.contributor.authorJameson, Brett D.
dc.contributor.authorJuniper, S. Kim
dc.contributor.authorGrundle, Damian S.
dc.date.accessioned2021-07-18T16:26:28Z
dc.date.available2021-07-18T16:26:28Z
dc.date.copyright2020en_US
dc.date.issued2020
dc.description.abstractNitrous oxide (N2O) is a strong greenhouse gas and an ozone depleting agent. In marine environments, N2O is produced biologically via ammonium oxidation, nitrite, and nitrate reduction. The relative importance of these principle production pathways is strongly influenced by oxygen availability. We conducted 15N tracer experiments of N2O production in parallel with measurements of N2O concentration and natural abundance isotopes/isotopomers in Saanich Inlet, a seasonally anoxic fjord, to investigate how temporal and vertical oxygen gradients regulate N2O production pathways and rates. In April, June, and August 2018, the depth of the oxic‐anoxic interface (dissolved oxygen ¼ 2.5 μmol L−1 isoline) progressively deepened from 110 to 160 m. Within the oxygenated and suboxic water column, N2O supersaturation coincided with peak ammonium oxidation activity. Conditions in the anoxic deep water were potentially favorable to N2O production from nitrate and nitrite reduction, but N2O undersaturation was observed indicating that N2O consumption exceeded rates of production. In October, tidal mixing introduced oxygenated water from outside the inlet, displacing the suboxic and anoxic deep water. This oxygenation event stimulated N2O production from ammonium oxidation and increased water column N2O supersaturation while inhibiting nitrate and nitrite reduction to N2O. Results from 15N tracer incubation experiments and natural abundance isotopomer measurements both implicated ammonium oxidation as the dominant N2O production pathway in Saanich Inlet, fueled by high ammonium fluxes (0.6–3.5 nmolm−2 s−1) from the anoxic depths. Partial denitrification contributed little to water column N2O production because of low availability of nitrate and nitrite.en_US
dc.description.reviewstatusRevieweden_US
dc.description.scholarlevelFacultyen_US
dc.description.sponsorshipThe authors thank Roberta Hamme and Erinn Raftery (UVic) for their generous assistance in oxygen measurements. During field sampling, Catherine Stevens and Sarah Thornton (UVic), Shirley Lyons (Victoria Capital Regional District), and Lu Guan (Ocean Networks Canada) provided valuable technical guidance. Laboratory analyses of oxygen concentrations in sample vials at the end of incubation experiments were completed with help from Amy Maas (BIOS). We thank Captain Ken Brown and crew members of the R/V Strickland for their professional seamanship. Financial support for this study was provided by a grant from the cluster of excellence “The Future Ocean” to D. Grundle and C. Marandino (GEOMAR), the German Research Foundation Collaborative Research Centre 754 (www.sfb754.de), and a German Research Foundation grant to D. Grundle and C. Marandino (GR4731/2‐1 and MA6297/3‐1). B. Jameson was supported by the Canadian Healthy Oceans Network, University of Victoria, and NSERC CGS‐M. Q. Ji was additionally supported by the Grant‐In‐Aid program at the Bermuda Institute of Ocean Sciences.en_US
dc.identifier.citationJi, Q., Jameson, B.D., Juniper, S.K., & Grundle, D.S. (2020). Temporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbia, Journal of Geophysical Research: Biogeosciences, 125. http://doi.org/10.1029/2020JG005631en_US
dc.identifier.urihttp://doi.org/10.1029/2020JG005631
dc.identifier.urihttp://hdl.handle.net/1828/13127
dc.language.isoenen_US
dc.publisherJournal of Geophysical Research: Biogeosciencesen_US
dc.titleTemporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbiaen_US
dc.typeArticleen_US

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