A dual nitrite isotopic investigation of chemodenitrification by mineral-associated Fe(II) and its production of nitrous oxide
A dual nitrite isotopic investigation of chemodenitrification by mineral-associated Fe(II) and its production of nitrous oxide
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DOI：
10.1016/j.gca.2016.10.026
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发表时间：
2017-01-01
影响因子：
5
通讯作者：
Wankel, Scott D.
中科院分区：
文献类型：
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作者：
Grabb, Kalina C.;Buchwald, Carolyn;Wankel, Scott D.
在厌氧条件下，环境中硝酸盐(NO3(-))和亚硝酸盐(NO2-)还原为更还原的形式被广泛认为是微生物催化的。然而，还原铁(Fe(II))对氧化氮物种的化学还原，无论是矿物结合的还是表面结合的，也可能在与环境有关的条件下发生。在这里，我们研究了氮(N)和氧(O)稳定同位素动力学的化学还原NO2-矿物伴生Fe(II)(化学反硝化)及其产生的有效温室气体一氧化二氮(N2O)。通过揭示控制反应动力学的因素及其在反应物NO2-和产物N2O中的相应双重同位素表达，这项工作有助于提高我们在环境中识别化学脱氮作用的能力。与先前的研究一致，我们发现虽然NO2-和Fe(II)之间的均相反应动力学缓慢，但涉及含Fe(II)矿物的多相反应经常催化相当大的亚硝酸盐损失。尤其是富铁蒙脱石粘土矿物非硝石以及Fe(II)-Fe(III)混合氢氧化物相绿锈对NO2-的快速还原具有催化作用。这些矿物既是矿物结构中还原铁的来源，也是促进Fe(II)反应活性的表面。然而，即使在Fe(II)存在的情况下，低铁和非含铁矿物的实验表明NO2-几乎没有损失，这可能表明结构铁在化学反硝化过程中起着更主要的作用。在非硝石和绿锈的催化下，化学反硝化反应的N和O同位素效应((15)epsilon(CDNF)和(18)epsilon(CDNF))分别在2~11%和4~10%之间，反应速度越快，N和O同位素效应越低。更高的反应速度也与更高的N2O摩尔产率(高达31%)有关，这突出了化学反硝化产生N2O的强大潜力-特别是相对于微生物途径产生的N2O，通常表现出1%的产率。对于绿锈催化的化学反硝化过程中产生的N2O，还测量了反映不同生成机制的线性N2O分子的分子内15N位偏好(中心原子和外部原子之间的增量N-15的差异)。与最近其他化学脱氮研究中测得的值相比，SP值一直很高(+26.5‰+/-0.8‰)，特别是相对于细菌反硝化产生的N2O(SP类似于0%)。最后，在绿锈催化的化学脱氮作用中，(18)epsilon(CDNF)和(15)epsilon(CDNF)以类似于1的比例耦合，这与最近描述的细菌亚硝酸盐还原形成了鲜明的对比，这可能使两个过程在良好的约束条件下解开。这项研究有助于更广泛地理解矿物来源的Fe(II)促进亚硝酸盐的还原和N2O的产生的潜在相关性，特别是在富铁系统中，包括潜水带、河口沉积物和地下水含水层。(C)2016爱思唯尔有限公司。保留所有权利。
Under anaerobic conditions, the environmental reduction of nitrate (NO3(-)) and nitrite (NO2-) to more reduced forms is widely regarded as being microbially catalyzed. However, the chemical reduction of oxidized nitrogen species by reduced iron (Fe(II)), whether mineral-bound or surface-associated, may also occur under environmentally relevant conditions. Here we examine the nitrogen (N) and oxygen (O) stable isotope dynamics of the chemical reduction of NO2- by mineral associated Fe(II) (chemodenitrification) and its production of the potent greenhouse gas nitrous oxide (N2O). By shedding light on factors controlling kinetics of the reaction and its corresponding dual isotopic expression in the reactant NO2- and product N2O, this work contributes to a growing body of work aiming to improve our ability to identify chemodenitrification in the environment.Consistent with previous studies, we find that while homogenous reactions between aqueous NO2- and Fe(II) were kinetically slow, heterogeneous reactions involving Fe(II)-containing minerals often catalyzed considerable nitrite loss. In particular, rapid reduction of NO2- was catalyzed by the Fe-rich smectite clay mineral nontronite as well as the mixed Fe(II)-Fe(III) oxyhydroxide phase green rust. These minerals serve as both a source of reduced iron within the mineral structure as well as a surface for promoting the reactivity of Fe(II). However, even in the presence of aqueous Fe(II), experiments with low-Fe and non-Fe containing minerals showed little to no NO2- loss, perhaps suggesting a more dominant role for structural iron during chemodenitrification. When catalyzed by nontronite and green rust, N and O isotope effects for chemodenitrification ((15)epsilon(cDNF) and (18)epsilon(cDNF)) ranged from 2 to 11% and 4 to 10%, respectively, with lower values generally observed at higher reaction rates. Higher reaction rates were also linked to higher molar yields of N2O (up to 31%), highlighting a strong potential for chemodenitrification to produce N2O-especially relative to its production by microbial pathways, which typically exhibit yields < 1%. The intramolecular 15 N site preference (SP) of the linear N2O molecule (the difference in delta N-15 between the central and outer atoms), reflective of different production mechanisms, was also measured for N2O produced during green rust catalyzed chemodenitrification. Relative to values measured in other recent studies of chemodenitrification, SP values were consistently high (+ 26.5 parts per thousand +/- 0.8 parts per thousand), especially relative to N2O produced via bacterial denitrification (SP similar to 0%). Finally, the coupling of (18)epsilon(cDNF) and (15)epsilon(cDNF) at a ratio of similar to 1 during green rust catalyzed chemodenitrification contrasts distinctly with recently characterized bacterial nitrite reduction, potentially permitting disentangling of both processes under well-constrained conditions. This study contributes to the broader understanding of the potential relevance for mineral-derived Fe(II) to promote the reduction of nitrite and consequent production of N2O, especially in iron-rich systems hosting dynamic redox oscillations, including hyporheic zones, estuarine sediments and groundwater aquifers. (C) 2016 Elsevier Ltd. All rights reserved.