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Temporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbia
Journal of Geophysical Research: Biogeosciences ( IF 3.7 ) Pub Date : 2020-08-28 , DOI: 10.1029/2020jg005631
Qixing Ji 1, 2, 3 , Brett D. Jameson 4 , S. Kim Juniper 4, 5, 6 , Damian S. Grundle 3
Affiliation  

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 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 = 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 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.

中文翻译:

时间和垂直氧气梯度调节季节性缺氧峡湾中一氧化二氮的产生:不列颠哥伦比亚省Saanich入口

一氧化二氮(N 2 O)是一种强温室气体,是一种臭氧消耗剂。在海洋环境中,N 2 O是通过铵氧化,亚硝酸盐和硝酸盐还原而生物产生的。这些主要生产途径的相对重要性受到氧气供应的强烈影响。我们进行了15次N 2 O产生的示踪实验,并同时测量了季节性缺氧峡湾萨尼奇(Saanich)入口中的N 2 O浓度和自然丰度同位素/同位素,以研究时间和垂直氧梯度如何调节N 2。O生产途径和速率。在2018年4月,6月和8月,含氧-缺氧界面的深度(溶解氧= 2.5μmolL -1等值线)从110 m逐渐加深到160 m。在含氧和低氧的水塔中,N 2 O过饱和与铵氧化活性峰值同时发生。在缺氧深水条件潜在有利到N 2从硝酸盐和亚硝酸盐还原ö生产,但Ñ 2中观察到,表明N 2 O欠饱和2 ö消耗超过生产的速率。十月份,潮汐混合从进口外部引入了氧化水,取代了低氧和缺氧的深水。该氧化事件刺激了N 2从氧化铵ö生产和增加的水N列2 ö过饱和,同时抑制硝酸盐和亚硝酸盐还原成N 2从O.结果15个Ñ示踪剂培养试验和天然丰度同位素测量都牵连铵氧化为主导Ñ 2在萨尼奇ö生产途径进水口由缺氧深度的高铵通量(0.6–3.5 nmol m -2  s -1)提供燃料。由于硝酸盐和亚硝酸盐的利用率低,部分反硝化对水柱N 2 O的生产几乎没有影响。
更新日期:2020-09-11
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