Temporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbia
Temporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbia
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DOI：
10.1029/2020jg005631
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发表时间：
2020-09-01
影响因子：
3.7
通讯作者：
Grundle, Damian S.
中科院分区：
文献类型：
--
作者：
Ji, Qixing;Jameson, Brett D.;Grundle, Damian S.
一氧化二氮（N2O）是一种强温室气体和臭氧消耗剂。在海洋环境中，N2O是通过氨氧化、亚硝酸盐和硝酸盐还原产生的。这些主要生产途径的相对重要性受到氧可用性的强烈影响。我们在Saanich Inlet（一个季节性缺氧峡湾）进行了N2O生成的N示踪实验，同时测量了N2O浓度和天然丰度同位素/同位素体，以研究时间和垂直氧气梯度如何调节N2O生成途径和速率。2018年4月、6月和8月，氧-缺氧界面深度（溶解氧= 2.5 μ mol L（-1）等值线）从110 m逐渐加深到160 m。在含氧水柱和缺氧水柱中，N2O过饱和与铵态氧化活性峰值一致。缺氧深水环境有利于硝酸盐和亚硝酸盐还原产生N2O，但N2O欠饱和表明N2O的消耗超过了生产速度。十月，潮汐混合从入口外引入了含氧水，取代了缺氧和缺氧的深水。这一氧化事件刺激了氨氧化产生N2O，增加了水柱N2O过饱和，同时抑制了硝酸盐和亚硝酸盐还原为N2O。（15）N示踪剂培养实验和天然丰度同位素测量结果都表明，在Saanich Inlet，缺氧深度的高铵通量(0.6-3.5 nmol m（-2) s(-1)）推动下，铵氧化是主要的N2O生成途径。部分反硝化作用对水柱N2O生成的贡献不大，因为硝酸盐和亚硝酸盐的有效性较低。
Nitrous 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(15)N 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 = 2.5 mu mol 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(15)N 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 nmol m(-2) s(-1)) from the anoxic depths. Partial denitrification contributed little to water column N2O production because of low availability of nitrate and nitrite.