Efflux of methane (CH4) to the atmosphere from northern peatlands via ebullition: the role of plants and peat structure.

甲烷 (CH4) 通过沸腾从北部泥炭地流出到大气中：植物和泥炭结构的作用。

• 批准号: NE/F004958/1
• 负责人: Andrew Binley
• 金额: $ 22.14万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF004958%2F1
• 关键词: Efflux; methane; CH4; atmosphere; northern

Large areas of the northern hemisphere's land mass are covered with peat soils. Peats form in waterlogged conditions. When peatland plants die and start to decay they form peat. Over many thousands of years, peat deposits have built up and may exceed 5-10 m in thickness. It is commonly thought that the decay of plant material cannot take place in waterlogged conditions. However, decay does occur below the water table and produces a gas called methane. Methane is an important greenhouse gas / that is, it contributes to the greenhouse effect / and northern peatlands are one of the largest global sources of this gas. Scientists are interested in predicting how much methane enters the atmosphere so that they are better able to predict climate change. As part of this effort, they have written computer models that simulate the production of methane in peat soils and the escape of this gas to the atmosphere. In the computer models it is assumed that methane can escape from peats to the atmosphere in three main ways: (i) by slow diffusion through the spaces between peat fibres, (ii) by diffusion and sometimes mass flow through vascular wetland plants like sedges, and (iii) as bubbles rising through the peat, a process called ebullition. A problem with applying these computer models is that we have very little understanding of how much methane escapes via bubbles and the factors involved in bubble loss, so it has not been possible to simulate accurately the process of ebullition. Some recent studies have shown that ebullition may be much more important than previously thought. Indeed, some researchers have suggested (i) that ebullition can account for more loss of methane to the atmosphere than the other two pathways combined (diffusion and plant-mediated transport) and (ii) that previous measurements of methane losses from northern peatlands are gross underestimates. However, that ebullition is the dominant pathway for transport of methane to the atmosphere in peatlands currently has the status of hypothesis and more work is urgently needed on characterising bubble build up and losses in northern peatlands. The purpose of our study is to gain a better understanding of both processes in one important class of peatland / bogs. We will take samples of peat (including the growing surface of the bog) back to the laboratory and keep them in state-of-the-art environmental cabinets where the light, temperature and humidity can be set to realistic values. We aim to answer three key research questions: 1. In bogs, how do the magnitude of the methane efflux and the relative importance of the mechanisms of that efflux (i.e. diffusion, plant-mediated, and ebullition) vary according to peat type? 2. How is bubble buildup and release affected by peat structure? 3. How does the presence of vascular plants, especially common types of sedge, affect bubble build up and loss from bog peats? Having the peat in the laboratory makes it possible to take sophisticated measurements of gas bubble dynamics that are not possible in the field. We will measure how gas bubbles accumulate in the peat during the onset of spring/summer conditions (when most methane is produced) and also how they are released from the peat. New technologies involving measuring the electrical properties of the peat will allow us to map where most bubbles form and how the volume of bubble accumulations changes in response to more methane being produced and the loss of bubbles to the surface of the peat. After the experiments, we will analyse the structure of the peat using an x-ray scanner. Using the x-rays we will be able to reconstruct the 'skeleton' of the peat and will be able to identify the plant remains that make up the peat, like stems of Sphagnum mosses and roots of sedges. With our knowledge of bubble build up in our samples, we will be able to identify which structures within the peat are most effective at trapping bubbles.

北半球的大片土地被泥炭土覆盖。泥炭在浸水的条件下形成。当泥炭地植物死亡并开始腐烂时，它们会形成泥炭。经过数千年的发展，泥炭沉积物不断积累，厚度可能超过 5-10 m。人们普遍认为植物材料的腐烂不会在浸水的条件下发生。然而，腐烂确实发生在地下水位以下，并产生一种称为甲烷的气体。甲烷是一种重要的温室气体/也就是说，它会加剧温室效应/而北部泥炭地是这种气体的全球最大来源之一。科学家们有兴趣预测有多少甲烷进入大气，以便他们能够更好地预测气候变化。作为这项工作的一部分，他们编写了计算机模型来模拟泥炭土中甲烷的产生以及这种气体逃逸到大气中。在计算机模型中，假设甲烷可以通过三种主要方式从泥炭逃逸到大气中：（i）通过泥炭纤维之间的空间缓慢扩散，（ii）通过扩散，有时是通过莎草等维管束湿地植物的质量流， (iii) 当气泡通过泥炭上升时，这一过程称为沸腾。应用这些计算机模型的一个问题是，我们对有多少甲烷通过气泡逃逸以及气泡损失的因素知之甚少，因此无法准确模拟沸腾的过程。最近的一些研究表明，沸腾可能比以前想象的要重要得多。事实上，一些研究人员认为（i）沸腾可以解释比其他两种途径（扩散和植物介导的运输）加起来更多的甲烷损失，以及（ii）之前对北部泥炭地甲烷损失的测量是粗略的低估了。然而，沸腾是泥炭地甲烷向大气输送的主要途径，目前还处于假设状态，迫切需要开展更多工作来表征北部泥炭地气泡的形成和损失。我们研究的目的是为了更好地了解一类重要的泥炭地/沼泽中的这两个过程。我们将把泥炭样本（包括沼泽生长的表面）带回实验室，并将它们保存在最先进的环境柜中，其中光线、温度和湿度可以设置为实际值。我们的目标是回答三个关键的研究问题： 1. 在沼泽中，甲烷外流的大小以及外流机制（即扩散、植物介导和沸腾）的相对重要性如何根据泥炭类型而变化？ 2. 泥炭结构如何影响气泡的形成和释放？ 3. 维管束植物，尤其是常见类型的莎草的存在，如何影响沼泽泥炭中气泡的形成和损失？在实验室中拥有泥炭可以对气泡动力学进行复杂的测量，而这在现场是不可能的。我们将测量在春季/夏季条件开始时（产生大部分甲烷时）气泡如何在泥炭中积聚以及它们如何从泥炭中释放。涉及测量泥炭电特性的新技术将使我们能够绘制大多数气泡形成的位置，以及气泡积累的体积如何随着更多甲烷的产生和气泡流失到泥炭表面而变化。实验结束后，我们将使用 X 射线扫描仪分析泥炭的结构。利用 X 射线，我们将能够重建泥炭的“骨架”，并能够识别构成泥炭的植物残骸，例如泥炭藓的茎和莎草的根。凭借我们对样品中气泡形成的了解，我们将能够确定泥炭内的哪些结构最能有效地捕获气泡。

项目成果

The effect of peat structure on the spatial distribution of biogenic gases within bogs

泥炭结构对沼泽内生物气空间分布的影响

• DOI: 10.1002/hyp.10056
• 发表时间: 2014-10-30
• 期刊: Hydrological Processes
• 影响因子: 3.2
• 作者: X. Comas;N. Kettridge;A. Binley;L. Slater;A. Parsekian;A. J. Baird;M. Strack;J. Waddington
• 通讯作者: J. Waddington

Efficient multi-scale imaging of subsurface resistivity with uncertainty quantification using ensemble Kalman inversion

使用集合卡尔曼反演对地下电阻率进行不确定性量化的高效多尺度成像

• DOI: 10.1093/gji/ggab013
• 发表时间: 2021-01-11
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: A. Binley;M. Tso;M. Iglesias;P. Wilkinson;O. Kuras;J. Chambers
• 通讯作者: J. Chambers

Efficient multiscale imaging of subsurface resistivity with uncertainty quantification using ensemble Kalman inversion

使用集合卡尔曼反演进行地下电阻率的高效多尺度成像和不确定性量化

• DOI: http://dx.10.1093/gji/ggab013
• 发表时间: 2021
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: Tso C

X-ray computed tomography of peat soils: measuring gas content and peat structure

泥炭土的 X 射线计算机断层扫描：测量气体含量和泥炭结构

• DOI: http://dx.10.1002/hyp.7097
• 发表时间: 2008
• 期刊: Hydrological Processes
• 影响因子: 3.2
• 作者: Kettridge N

Characterization of peat structure using X-ray computed tomography and its control on the ebullition of biogenic gas bubbles

利用 X 射线计算机断层扫描表征泥炭结构及其对生物气泡沸腾的控制

• DOI: http://dx.10.1029/2010jg001478
• 发表时间: 2011
• 期刊: Journal of Geophysical Research
• 作者: Kettridge N