Revising the methane cycling in lakes: sources and sinks in two German lakes with specific consideration of methane accumulation in oxic waters

修改湖泊中的甲烷循环：德国两个湖泊的源和汇，特别考虑含氧水域中的甲烷积累

• 批准号: 241479293
• 负责人: Professor Dr. Hans-Peter Grossart
• 金额: --
• 依托单位: Institut für Geowissenschaften
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/241479293?language=en
• 关键词: Revising; methane; cycling; lakes; sources

Recently, methane (CH4) accumulation in oxic waters has been found in freshwater and marine waters worldwide. In our Aquameth project (GR1540/21-1) we have reviewed and evaluated potential mechanisms for this phenomenon in meso-oligotrophic Lake Stechlin. By establishing an online CH4 measurement system, we could show a close spatio-temporal relationship between the dynamics of alga (e.g. cyanobacteria and cryptophytes) and CH4 in the oxic water layers of the lake. Whilst the recently established methyl phosphonate metabolism might be present in the lake we found first evidence that algae directly produce CH4 during photosynthesis. However, the possible mechanism and its contribution to CH4 produced in oxic waters to total CH4 fluxes remains largely unknown. By combining the expertise of two established research groups - that ideally complement each other including instrumental applications, we aim to evaluate the precise chemistry and biology of CH4 formation and oxidation processes to better understand the role of lakes in regional and global CH4 cycling. Therefore, the complete CH4 budget of two lakes in Germany will be quantified in detail, i.e. CH4 bulk sources and sinks will be evaluated by a detailed mass balance approach combined with in situ incubation experiments. Our contrasting field sites/lakes (oligo-mesotrophic Lake Stechlin and eutrophic Willersinnweiher) represent 2 main temperate lake types (deep /nutrient-poor and shallow /nutrient-rich) well studied and biogeochemically characterized by the two research institutes. In both lakes, the presence of specific processes of CH4 production, accumulation and its release to the atmosphere depend on a complicated interplay of physical, chemical and biological factors favoring certain organisms and related processes. Thus our main objectives are to entangle the complicated interplay between environmental variables and processes of CH4 formation, accumulation and release, and to provide a seasonal CH4 budget of the lake to determine the relevance of oxic CH4 formation for regional and global CH4 cycling. We hypothesize that (1) Methane production is directly linked to photosynthesis and CH4 can be directly formed by various photoautotrophic organisms at specific environmental conditions, e.g. nutrient limitation. (2) Methane formation is decoupled from oxidation due to spatial and/or temporal decoupling of methanotrophic activity in oxic waters. (3) Methane at the thermocline is the product of a complicated interplay between biological, chemical and physical processes. (4) Increased CH4 concentrations in the upper oxic water layer facilitate the gas exchange between water and atmosphere. Although CH4 accumulation in the upper water layers has been largely neglected, it may represent a major missing link in the global CH4 budget. To address these hypotheses, field measurements and lab experiments will be combined by close interactions between both teams.

最近，在世界范围内的淡水和海水中都发现了含氧水域中甲烷（CH4）的积累。在我们的 Aquameth 项目 (GR1540/21-1) 中，我们回顾并评估了中贫营养湖 Stechlin 中这种现象的潜在机制。通过建立在线CH4测量系统，我们可以显示湖泊含氧水层中藻类（例如蓝藻和隐藻）动态与CH4之间密切的时空关系。虽然最近建立的磷酸甲酯代谢可能存在于湖中，但我们发现了第一个证据表明藻类在光合作用过程中直接产生 CH4。然而，可能的机制及其对含氧水中产生的 CH4 对总 CH4 通量的贡献仍然很大程度上未知。通过结合两个已建立的研究小组的专业知识（包括仪器应用），这两个研究小组可以理想地相互补充，我们的目标是评估 CH4 形成和氧化过程的精确化学和生物学，以更好地了解湖泊在区域和全球 CH4 循环中的作用。因此，德国两个湖泊的完整 CH4 预算将被详细量化，即通过详细的质量平衡方法结合原位孵化实验来评估 CH4 散装源和汇。我们对比的野外地点/湖泊（寡营养-中营养湖 Stechlin 和富营养湖 Willersinnweiher）代表了 2 个主要温带湖泊类型（深水/营养贫乏和浅水/营养丰富），并由两个研究机构进行了充分研究和生物地球化学特征。在这两个湖泊中，CH4 产生、积累及其释放到大气中的特定过程的存在取决于有利于某些生物体和相关过程的物理、化学和生物因素的复杂相互作用。因此，我们的主要目标是解决环境变量与 CH4 形成、积累和释放过程之间复杂的相互作用，并提供湖泊的季节性 CH4 预算，以确定含氧 CH4 形成与区域和全球 CH4 循环的相关性。我们假设 (1) 甲烷的产生与光合作用直接相关，并且 CH4 可以由各种光合自养生物在特定的环境条件下直接形成，例如：营养限制。 (2)由于含氧水中甲烷氧化活性的空间和/或时间解耦，甲烷形成与氧化解耦。 (3) 温跃层的甲烷是生物、化学和物理过程之间复杂相互作用的产物。 (4)上层含氧水层CH4浓度增加有利于水与大气之间的气体交换。尽管上层水层的 CH4 积累在很大程度上被忽视，但它可能是全球 CH4 预算中一个重要的缺失环节。为了解决这些假设，现场测量和实验室实验将通过两个团队之间的密切互动结合起来。