Schroll Moritz, Liu Liu, Einzmann Teresa, Keppler Frank, Grossart Hans-Peter
Laboratory of Plateau Geographical Processes and Environmental Changes, Faculty of Geography, Yunnan Normal University, 650500 Kunming, China; Institute of Earth Sciences, Heidelberg University, 69120 Heidelberg, Germany.
Laboratory of Plateau Geographical Processes and Environmental Changes, Faculty of Geography, Yunnan Normal University, 650500 Kunming, China; Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries, 16775 Stechlin, Germany.
Sci Total Environ. 2023 Dec 10;903:166205. doi: 10.1016/j.scitotenv.2023.166205. Epub 2023 Aug 10.
Methane (CH) supersaturation in oxygenated waters is a widespread phenomenon despite the traditional perception of strict anoxic methanogenesis. This notion has recently been challenged by successive findings of processes and mechanisms that produce CH in oxic environments. While some of the processes contributing to the vertical accumulation of CH in the oxygenated upper water layers of freshwater lakes have been identified, temporal variations as well as drivers are still poorly understood. In this study, we investigated the accumulation of CH in oxic water layers of two contrasting lakes in Germany: Lake Willersinnweiher (shallow, monomictic, eutrophic) and Lake Stechlin (deep, dimictic, eutrophic) from 2019 to 2020. The dynamics of isotopic values of CH and the role of potential precursor compounds of oxic CH production were explored. During the study period, persistent strong CH supersaturation (relative to air) was observed in the surface waters, mostly concentrated around the thermocline. The magnitude of vertical CH accumulation strongly varied over season and was generally more pronounced in shallow Lake Willersinnweiher. In both lakes, increases in CH concentrations from the surface to the thermocline mostly coincided with an enrichment in C-CH and H-CH, indicating a complex interaction of multiple processes such as CH oxidation, CH transport from littoral sediments and oxic CH production, sustaining and controlling this CH supersaturation. Furthermore, incubation experiments with C- and H-labelled methylated P-, N- and C- compounds clearly showed that methylphosphonate, methylamine and methionine acted as potent precursors of accumulating CH and at least partly sustained CH supersaturation. This highlights the need to better understand the mechanisms underlying CH accumulation by focusing on production and transport pathways of CH and its precursor compounds, e.g., produced via phytoplankton. Such knowledge forms the foundation to better predict aquatic CH dynamics and its subsequent rates of emission to the atmosphere.
尽管传统观念认为甲烷生成严格依赖缺氧环境，但含氧水体中甲烷（CH₄）过饱和却是一种普遍现象。最近，一系列关于在有氧环境中产生CH₄的过程和机制的发现对这一观念提出了挑战。虽然已经确定了一些导致CH₄在淡水湖含氧上覆水层中垂直积累的过程，但对其时间变化和驱动因素仍知之甚少。在本研究中，我们调查了2019年至2020年德国两个形成对比的湖泊——维勒斯辛魏尔湖（浅湖、单循环、富营养化）和施特克林湖（深湖、双循环、富营养化）——含氧水层中CH₄的积累情况。探讨了CH₄同位素值的动态变化以及有氧CH₄生成潜在前体化合物的作用。在研究期间，在表层水体中观察到持续强烈的CH₄过饱和（相对于空气），主要集中在温跃层附近。垂直CH₄积累的幅度随季节变化很大，并且在浅的维勒斯辛魏尔湖中通常更为明显。在两个湖泊中，从表层到温跃层CH₄浓度的增加大多与¹³C-CH₄和²H-CH₄的富集相吻合，这表明多种过程（如CH₄氧化、来自沿岸沉积物的CH₄输送和有氧CH₄生成）之间存在复杂的相互作用，维持并控制着这种CH₄过饱和。此外，用¹³C和²H标记的甲基化磷、氮和碳化合物进行的孵化实验清楚地表明，甲基膦酸酯、甲胺和蛋氨酸是积累的CH₄的有效前体，并且至少部分维持了CH₄过饱和。这突出表明需要通过关注CH₄及其前体化合物（例如通过浮游植物产生的）的生产和运输途径，更好地理解CH₄积累的潜在机制。这些知识是更好地预测水生CH₄动态及其随后向大气排放速率的基础。
