Influence of water column stratification and mixing patterns on the fate of methane produced in deep sediments of a small eutrophic lake
Influence of water column stratification and mixing patterns on the fate of methane produced in deep sediments of a small eutrophic lake
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水柱分层和混合模式对小型富营养化湖泊深层沉积物中产生的甲烷的影响
DOI：
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发表时间：
2019
影响因子：
4.5
通讯作者：
D. McGinnis
中科院分区：
文献类型：
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作者：
D. Vachon;Timon Langenegger;D. Donis;D. McGinnis
甲烷 (CH4) 是一种强效温室气体，湖泊的产生和排放速度在全球范围内都很高。然而，控制所产生的甲烷进入大气的比例的驱动因素仍不清楚。我们于 2016 年至 2017 年对一个小型富营养化湖泊（瑞士索彭湖）进行了采样，了解 CH4 浓度分布和排放情况，并结合水柱流体动力学研究了低浅层沉积物中产生的 CH4 的命运。采用质量平衡方法，对两年的 4 月至 10 月期间的情况进行分析，低浅层沉积物中 CH4 的净生产率在 11.4 至 17.7 mmol m−2 d−1 之间，其中 66-88% 储存在低浅层中，13-27% 扩散到浅层，6-7% 通过沸腾离开沉积物。将这些结果与基于过程的模型相结合，我们发现水柱湍流扩散率 (K z) 对沉积物中产生的 CH4 的命运有重大影响，其中较高的 K z 值可能导致更大的比例被氧化，而较低的 K z 导致更大的比例被储存。在秋季水柱混合时，我们发现，如果湖泊快速混合，则释放出更大比例的储存的CH4，而如果水柱混合缓慢，则更大比例的CH4将被氧化。这项工作强调了湖泊水动力学在调节 CH4 动力学中的核心作用，并进一步表明 CH4 生产和排放对气候驱动的湖泊混合机制和分层变化敏感的潜力。
Methane (CH4), a potent greenhouse gas, is produced in and emitted from lakes at globally significant rates. The drivers controlling the proportion of produced CH4 that will reach the atmosphere, however, are still not well understood. We sampled a small eutrophic lake (Soppensee, Switzerland) in 2016–2017 for CH4 concentrations profiles and emissions, combined with water column hydrodynamics to investigate the fate of CH4 produced in hypolimnetic sediments. Using a mass balance approach for the periods between April and October of both years, net CH4 production rates in hypolimnetic sediments ranged between 11.4 and 17.7 mmol m−2 d−1, of which 66–88% was stored in the hypolimnion, 13–27% was diffused to the epilimnion, and 6–7% left the sediments via ebullition. Combining these results with a process‐based model we show that water column turbulent diffusivity (K z) had a major influence on the fate of produced CH4 in the sediments, where higher K z values potentially lead to greater proportion being oxidized and lower K z lead to a greater proportion being stored. During fall when the water column mixes, we found that a greater proportion of stored CH4 is emitted if the lake mixes rapidly, whereas a greater proportion will be oxidized if the water column mixes more gradually. This work highlights the central role of lake hydrodynamics in regulating CH4 dynamics and further suggests the potential for CH4 production and emissions to be sensitive to climate‐driven alterations in lake mixing regimes and stratification.