Nitrification contributes to winter oxygen depletion in seasonally frozen forested lakes
Nitrification contributes to winter oxygen depletion in seasonally frozen forested lakes
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DOI：
10.1007/s10533-017-0382-1
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发表时间：
2017-10
期刊：
影响因子：
4
通讯作者：
S. Powers;H. Baulch;S. Hampton;S. G. Labou;N. Lottig;E. Stanley
中科院分区：
文献类型：
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作者：
S. Powers;H. Baulch;S. Hampton;S. G. Labou;N. Lottig;E. Stanley
在经历季节性冰盖的湖泊中，对氮氧耦合和硝化作用的了解主要是在开阔水域、无冰条件下进行的观察。为了解决冰下氮氧联系的知识空白，我们研究了美国威斯康星州北部森林覆盖的7个温带湖泊的长期冬季数据(30多年，每个冬季2-3个样本事件)。在湖泊和深度上，溶解氧(DO)与自冰上以来的天数之间存在着强烈的负相关关系，反映了冰下一致的DO消耗率。在两个经常经历漫长冬季DO浓度低于1.0mgL−1的沼泽湖中，硝酸盐主要在冬末在冰面附近积累，这表明硝化作用可能依赖于光合作用产生的生物氧。相比之下，在五个富营养化-中营养化湖泊中，硝酸盐在冬季积累得更稳定，通常是在整个水柱中，特别是在中等深度。与硝酸盐累积速率相比，这些湖泊的外源硝酸盐输入微乎其微。要通过湖内硝化作用生产硝酸盐，需要氨氧化微生物消耗大量的氧气。在冬季DO耗竭严重的湖泊和深度中，化学计量硝化细菌的需氧量在DO耗竭速率的1%到25%之间。这些对硝化菌驱动的DO下降的估计可能是保守的，因为我们没有考虑藻类吸收或反硝化所消耗的硝酸盐。我们的结果提供了一个例子，说明在温度低于5摄氏度的情况下，硝化作用对季节性冻结的北部森林湖泊的生态系统层面的氮和氧的有效性有很大影响。因此，可以通过考虑硝化作用，更广泛地说，耦合氮和氧循环来推进冰下溶解和氧气动力学的模型。
In lakes that experience seasonal ice cover, understanding of nitrogen–oxygen coupling and nitrification has been dominated by observations during open water, ice-free conditions. To address knowledge gaps about nitrogen–oxygen linkages under ice, we examined long-term winter data (30 + years, 2–3 sample events per winter) in 7 temperate lakes of forested northern Wisconsin, USA. Across lakes and depths, there were strong negative relationships between dissolved oxygen (DO) and the number of days since ice-on, reflecting consistent DO consumption rates under ice. In two bog lakes that routinely experience prolonged winter DO concentrations below 1.0 mg L−1, nitrate accumulated near the ice surface mainly in late winter, suggesting nitrification may depend on biogenic oxygen from photosynthesis. In contrast, within five oligotrophic-mesotrophic lakes, nitrate accumulated more consistently over winter and often throughout the water column, especially at intermediate depths. Exogenous inputs of nitrate to these lakes were minimal compared to rates of nitrate accumulation. To produce the nitrate via in-lake nitrification, substantial oxygen consumption by ammonium oxidizing microbes would be required. Among lakes and depths that had significant DO depletion over winter, the stoichiometric nitrifier oxygen demand ranged from 1 to 25% of the DO depletion rate. These estimates of nitrifier-driven DO decline are likely conservative because we did not account for nitrate consumed by algal uptake or denitrification. Our results provide an example of nitrification at temperatures < 5 degrees C having a substantial influence on ecosystem-level nitrogen and oxygen availability in seasonally-frozen, northern forested lakes. Consequently, models of under-ice dissolved oxygen dynamics may be advanced through consideration of nitrification, and more broadly, coupled nitrogen and oxygen cycling.