Increased rates of dissimilatory nitrate reduction to ammonium (DNRA) under oxic conditions in a periodically hypoxic estuary
Increased rates of dissimilatory nitrate reduction to ammonium (DNRA) under oxic conditions in a periodically hypoxic estuary
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DOI：
10.1016/j.gca.2014.02.042
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发表时间：
2014-05
影响因子：
5
通讯作者：
K. Roberts;Adam J. Kessler;M. Grace;P. Cook
中科院分区：
文献类型：
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作者：
K. Roberts;Adam J. Kessler;M. Grace;P. Cook
亚拉河河口是一个盐楔口，在低流量时期，底部水域容易缺氧。用15n对氧、硝态氮和有效还原剂对反硝化和异化硝态氮还原速率（DNRA）的影响进行了定量研究。反硝化是所有氧条件下硝酸盐还原的主要途径，然而，在完整的核心培养中，DNRA从缺氧条件下（<50 μmol L−1O2）的<1%增加到氧饱和条件下水柱中硝酸盐还原总量的~ 18%。利用薄层（DET）凝胶扩散平衡分析完整岩心中硝酸盐还原途径的微剖面显示，只有在Fe2+存在的氧化条件下，DNRA才会发生显著的速率。在缺氧条件下培养的岩心，在孔隙水中产生了游离硫化物，Fe2+浓度非常低，DNRA率也很低。不同NO3−浓度的水泥浆培养表明，反硝化细菌对反硝化和DNRA的亲和力分别高于km值为49 μmol L−1和86 μmol L−1的硝酸氨化细菌，但这并不能解释DNRA的速率相对于反硝化的变化。进一步的浆液培养研究DNRA和Fe2+氧化之间的关系是不确定的，并且由于非常高的吸附（HCl可萃取）Fe2+背景而变得复杂。与对照组（不添加Fe2+）相比，向浆体中添加Fe2+并没有促进反硝化作用，然而，在Fe2+添加处理中发生DNRA期间，Fe2+浓度显著降低，而对照处理中没有显著降低。Fe2+处理和对照处理的DNRA与Fe2+消耗量之比分别为15±6和7±3。我们认为缺氧条件下DNRA速率的降低可以通过Fe2+与游离硫化物的结合和FeS的形成来解释，FeS去除了DNRA的可用Fe2+。
The Yarra River Estuary is a salt wedge estuary prone to hypoxia in the bottom waters during low flow periods. Rates of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were quantified using15N in relation to oxygen, nitrate and available reductants. Denitrification was the dominant nitrate reduction pathway under all oxygen conditions, however, DNRA increased from <1% under hypoxic conditions (<50 μmol L−1O2) to ∼18% of total nitrate reduction under oxygen saturation in the water column in intact core incubations. Microprofiles of nitrate reduction pathways in intact cores using diffusive equilibrium in thin layer (DET) gels showed significant rates of DNRA only occurred under oxic conditions in the presence of Fe2+. Cores incubated anoxically, developed free sulfide within the porewater, had very low concentrations of Fe2+and low rates of DNRA. Slurry incubations with varying concentrations of NO3−showed that denitrifying bacteria had a higher affinity than nitrate ammonifying bacteria withKmvalues of 49 and 86 μmol L−1for denitrification and DNRA, respectively, however, this could not explain the change in the rates of DNRA relative to denitrification observed. Further slurry incubations to investigate the relationship between DNRA and Fe2+oxidation were inconclusive and complicated by very high backgrounds of sorbed (HCl extractable) Fe2+. Addition of Fe2+to the slurry did not stimulate denitrification compared to a control (no Fe2+addition), however, there was a significant decrease in the Fe2+concentration over the period where DNRA occurred in the Fe2+addition treatment, and no significant decrease in the control treatment. The ratio of DNRA to Fe2+consumption was 15 ± 6 and 7 ± 3 for the Fe2+and control treatments, respectively. We suggest reduced rates of DNRA under anoxic conditions can be explained by the binding of Fe2+with free sulfides and the formation of FeS removing available Fe2+for DNRA.