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首页> 外文期刊>Marine Chemistry >Nitrate elimination and regeneration as evidenced by dissolved inorganic nitrogen isotopes in Saanich Inlet, a seasonally anoxic fjord
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Nitrate elimination and regeneration as evidenced by dissolved inorganic nitrogen isotopes in Saanich Inlet, a seasonally anoxic fjord

机译：季节性缺氧峡湾萨尼奇湾中溶解的无机氮同位素证明了硝酸盐的消除和再生

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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 (NO_3~(1-)) and ammonium (NH_4~(1+)) 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 NO_3~(1-) δ~(15)N and δ~(18)O, associated with a decrease in NOf concentration and an increase in biological excess N_2. was observed after bottom water renewal events in August-October 2008, indicating NO_3~(1-) consumption by denitrifying bacteria in an expanding suboxic water column. An increase in the δ~(15)N of NH_4~(1+) with depth toward the suboxic/hypoxic transition, indicated net consumption of NH_4~(1+), most likely by micro-aerobic or anaerobic NH_4~(1+) oxidation and dissimila-tory consumption by microorganisms. Deviations from a 1:1 correlation between the NO_3~(1-) δ~(15)N and δ~(18)O (△(15,18)) that appears characteristic for both assimilatory and dissimilatory NOf consumption in the ocean, were observed in surface waters and close to the hypoxic/suboxic transition. Lowered △(15, 18) values can most plausibly be explained by aerobic nitrification of newly remineralized NH_4~(1+) and/or low δ~(15)N-NO_3~(1-) inputs from atmospheric precipitation in the surface mixed layer, and NO_3~(1-) regeneration through NH_4~(1+) oxidation and/ or the reoxidation of nitrite (NO_2~(1-)) in deeper waters. Closed and open system model-derived N isotope effects for NOf consumption calculated from time-series samples collected near the sediments in anoxic bottom waters were significantly lower (as low as ~1 l‰) than the biological N isotope effects of ~20-30‰ for water column de-nitrification 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 frac-tionation at the ecosystem level. We estimated that ~40-60% of the denitrification occurs within the sediments of the inlet.
机译：在这项研究中，我们使用了溶解的无机氮（N）物种的自然丰度同位素测量，以评估不同氧合作用方式对加拿大不列颠哥伦比亚省季节性缺氧峡湾Saanich Inlet中N转化和消除的影响。我们分析了从2008年4月开始在进水口附近水柱不同深度处的溶解营养物浓度以及硝酸盐（NO_3〜（1-））和铵盐（NH_4〜（1+））的N（和O）同位素组成和2009年4月。NO_3〜（1-）δ〜（15）N和δ〜（18）O逐渐增加，与NOf浓度降低和生物过量N_2增加有关。在2008年8月至10月的底部水更新事件后观察到了这一现象，这表明在不断膨胀的亚氧水柱中反硝化细菌会消耗NO_3〜（1-）。 NH_4〜（1+）的δ〜（15）N随向次氧/低氧过渡的深度增加而增加，表明NH_4〜（1+）的净消耗量最可能是微需氧或厌氧的NH_4〜（1+） ）微生物的氧化和异化消耗。 NO_3〜（1-）δ〜（15）N与δ〜（18）O（△（15,18））之间的1：1相关性偏差似乎是海洋中同化和异化NOf消耗的特征，在地表水和接近低氧/过硫酸盐的过渡过程中观察到。降低的△（15，18）值可以用新矿化的NH_4〜（1+）和/或低δ〜（15）N-NO_3〜（1-）的输入进行有氧硝化来解释通过深层水体中的NH_4〜（1+）氧化和/或亚硝酸盐（NO_2〜（1-））的再氧化来再生NO_3〜（1-）。由封闭和开放系统模型得出的氮氧化物的氮同位素消耗效应，是从缺氧底水中沉积物附近的时间序列样本中计算得出的，其NOf消耗量远低于生物氮同位素效应（约20-30）（低至约1 l‰）。在其他研究中报道了用于水柱脱氮的‰。我们认为减少的N同位素效应主要归因于水柱和沉积物反硝化的综合作用，后者在生态系统水平上被高度抑制的N同位素分解发生。我们估计，约40-60％的反硝化作用发生在进口的沉积物中。

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