Small boreal lakes are known to contribute significantly to global CH₄ emissions. Lake Lovojärvi is a eutrophic lake in southern Finland with bottom water CH₄ concentrations up to 2 mM. However, the surface water concentration, and thus the diffusive emission potential, was low (< 0.5 µM). We studied the biogeochemical processes involved in CH₄ removal by chemical profiling and through incubation experiments. δ¹³C-CH₄ profiling of the water column revealed a methane-oxidation hotspot just below the oxycline and zones of CH₄ oxidation within the anoxic water column. In incubation experiments involving the addition of light and/or oxygen, CH₄ oxidation rates in the anoxic hypolimnion were enhanced 3-fold, suggesting a major role for photosynthetically fueled aerobic CH₄ oxidation. We observed a distinct peak in CH₄ concentration at the chlorophyll-a maximum, caused by either in situ CH₄ production or other CH₄ inputs such as lateral transport from the littoral zone. In the dark anoxic water column at 7 m depth, nitrite seemed to be the key electron acceptor involved in CH₄ oxidation, yet additions of Fe(III), anthraquinone-2,6-disulfonate and humic substances also stimulated anoxic CH₄ oxidation. Surprisingly, nitrite seemed to inhibit CH₄ oxidation at all other depths. Overall, this study shows that photosynthetically fueled CH₄ oxidation can be a key process in CH₄ removal in the water column of humic, turbid lakes, thereby limiting diffusive CH₄ emissions from boreal lakes. Yet, it also highlights the potential importance of a whole suite of alternative electron acceptors, including humics, in these freshwater environments in the absence of light and oxygen.

中文翻译：

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受光合作用，亚硝酸盐，Fe（III）和腐殖质刺激的富含腐殖质的北方湖泊水域中的甲烷氧化

众所周知，小型的北方湖泊是全球CH ₄排放的重要来源。Lovojärvi湖是芬兰南部的富营养化湖泊，其底水CH ₄浓度高达2  mM。但是，地表水的浓度很低，因此扩散势很低（<  0.5  µM）。我们研究了通过化学概况分析和温育实验去除CH ₄的生物地球化学过程。δ ¹³ Ç - CH ₄仿形水柱揭示了甲烷氧化热点只是的oxycline和区域下面CH ₄在缺氧水柱内被氧化。在涉及添加光和/或氧的温育实验中，缺氧性水ion留中的CH ₄氧化速率提高了3倍，这表明光合作用的需氧CH ₄氧化具有重要作用 。我们观察到在具有明显的峰CH ₄在叶绿素浓度一最大，原位而导致的任何 CH ₄生产或其他CH ₄输入，诸如从沿海区域侧向传送。在深度为7 m的黑暗缺氧水柱中 ，亚硝酸盐似乎是参与CH ₄的关键电子受体氧化，但添加Fe（III），蒽醌-2,6-二磺酸盐和腐殖质也刺激了缺氧CH ₄氧化。出人意料的是，亚硝酸盐似乎在所有其他深度都抑制 CH ₄氧化。总体而言，这项研究表明，光合作用的CH ₄氧化可能是去除腐殖质浑浊湖泊水柱中CH ₄的关键过程，从而限制了北方湖泊扩散CH _4的排放。然而，它也强调了在没有光和氧气的情况下，在这些淡水环境中，包括腐殖质在内的整套替代电子受体的潜在重要性。