Benthic ecosystems have come under intense pressure, due to eutrophication-driven oxygen decline and industrial metal contamination. One of the most toxic metals is Cadmium (Cd), which is lethal to many aquatic organisms already at low concentrations. Denitrification by facultative anaerobic microorganisms is an essential process to transform, but also to remove, excess nitrate in eutrophied systems. Cd has been shown to decrease denitrification and sequester free sulfide, which is available when oxygen is scarce and generally inhibits complete denitrification (i.e. N2O to N2). In polluted sediments, an interaction between oxygen and Cd may influence denitrification and this relationship has not been studied. For example, in the Baltic Sea some sediments are double exposed to both Cd and hypoxia. In this study, we examined how the double exposure of Cd and fluctuations in oxygen affects denitrification in Baltic Sea sediment. Results show that oxygen largely regulated N2O and N2 production after 21 days of exposure to Cd (ranging from 0 to 500 μg/L, 5 different treatments, measured by the isotope pairing technique (IPT)). In the high Cd treatment (500 μg/L) the variation in N2 production increased compared to the other treatments. Increases in N2 production are suggested to be an effect of 1) enhanced nitrification that increases NO3- availability thus stimulating denitrification, and 2) Cd successfully sequestrating sulfide (yielding CdS), which allows for full denitrification to N2. The in situ field sediment contained initially high Cd concentrations in the pore water (∼10 μg/L) and microbial communities might already have been adapted to metal stress, making the effect of low Cd levels negligible. Here we show that high levels of cadmium pollution might increase N2 production and influence nitrogen cycling in marine sediments.

中文翻译：

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在波罗的海沉积物中反硝化对镉暴露增加的响应。

由于富营养化驱动的氧气下降和工业金属污染，底栖生物生态系统承受着巨大的压力。毒性最高的金属之一是镉（Cd），它对许多浓度很低的水生生物都是致命的。兼性厌氧微生物的反硝化是转化但也去除富营养化系统中过量硝酸盐的重要过程。事实表明，镉可减少反硝化作用和螯合游离硫化物，这在缺氧的情况下可用，并且通常会抑制完全反硝化作用（即N2O至N2）。在受污染的沉积物中，氧气和Cd之间的相互作用可能会影响反硝化作用，这种关系尚未得到研究。例如，在波罗的海，一些沉积物被双重暴露于Cd和低氧。在这项研究中，我们研究了镉的二次暴露和氧气的波动如何影响波罗的海沉积物中的反硝化作用。结果表明，氧气在暴露于Cd 21天后（在0至500μg/ L范围内，通过同位素配对技术（IPT）进行了5种不同的处理），在很大程度上调节了N2O和N2的产生。在高Cd处理（500μg/ L）下，与其他处理相比，N2产生的变化增加。建议增加N2的产生是以下方面的作用：1）增强硝化作用，从而增加NO3-的利用率，从而刺激反硝化作用； 2）Cd成功地螯合硫化物（产生CdS），从而使N2完全反硝化。原位田间沉积物最初在孔隙水中含有高浓度的Cd（〜10μg/ L），微生物群落可能已经适应了金属胁迫，因此低Cd含量的影响可以忽略不计。在这里，我们显示出高水平的镉污染可能会增加N2的产生并影响海洋沉积物中的氮循环。