Enhancement of anammox by the excretion of diel vertical migrators
Enhancement of anammox by the excretion of diel vertical migrators
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DOI：
10.1073/pnas.1410790111
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发表时间：
2014-11-04
影响因子：
11.1
通讯作者：
Galbraith, Eric D.
中科院分区：
文献类型：
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作者：
Bianchi, Daniele;Babbin, Andrew R.;Galbraith, Eric D.
测量表明，亚硝酸盐厌氧氨氧化（厌氧氨氧化）是公海缺氧区固定脱氮的主要途径。厌氧氨氧化需要铵源，在缺氧条件下，可以通过异养反硝化分解下沉的有机物来提供铵源。然而，在许多测量厌氧氨氧化的地点，反硝化率很小或无法检测到。已经提出了铵的替代来源来解释这一悖论，例如通过硝酸盐的异化还原为铵并从缺氧沉积物中运输。然而，这些来源在公海缺氧区的相关性仍存在争议。在这里，我们注意到铵的另一个来源，即浮游动物和微游生物从表面迁移到缺氧水域的白天排泄。我们综合声学数据表明，当水柱内出现缺氧水域时，大多数迁徙者都会在其中度过白天。尽管洄游者仅从地表输出初级产物的一小部分，但它们将排泄集中在缺氧水的有限深度范围内，其中颗粒输入很小。使用简单的生物地球化学模型，我们建议，在这些深度，来自经历昼夜垂直迁移的生物体的铵来源可能超过颗粒再矿化的释放，从而提高原位厌氧氨氧化速率。这一先前被忽视的过程的贡献以及围绕它的众多不确定性，要求进一步努力评估动物在最低氧区生物地球化学中的作用。
Measurements show that anaerobic ammonium oxidation with nitrite (anammox) is a major pathway of fixed nitrogen removal in the anoxic zones of the open ocean. Anammox requires a source of ammonium, which under anoxic conditions could be supplied by the breakdown of sinking organic matter via heterotrophic denitrification. However, at many locations where anammox is measured, denitrification rates are small or undetectable. Alternative sources of ammonium have been proposed to explain this paradox, for example through dissimilatory reduction of nitrate to ammonium and transport from anoxic sediments. However, the relevance of these sources in open-ocean anoxic zones is debated. Here, we bring to attention an additional source of ammonium, namely, the daytime excretion by zooplankton and micronekton migrating from the surface to anoxic waters. We use a synthesis of acoustic data to show that, where anoxic waters occur within the water column, most migrators spend the daytime within them. Although migrators export only a small fraction of primary production from the surface, they focus excretion within a confined depth range of anoxic water where particle input is small. Using a simple biogeochemical model, we suggest that, at those depths, the source of ammonium from organisms undergoing diel vertical migrations could exceed the release from particle remineralization, enhancing in situ anammox rates. The contribution of this previously overlooked process, and the numerous uncertainties surrounding it, call for further efforts to evaluate the role of animals in oxygen minimum zone biogeochemistry.