Collaborative Research: Towards a mechanistic prediction of methane ebullition fluxes from northern peatlands

合作研究：北部泥炭地甲烷沸腾通量的机械预测

• 批准号: 1623882
• 负责人: Xavier Comas
• 金额: $ 6.1万
• 依托单位: Florida Atlantic University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2021-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1623882&HistoricalAwards=false
• 关键词: Collaborative; Research; Towards; mechanistic; prediction

Peatlands cover only about 3% of the Earth's land area, but are disproportionately important in producing methane, a strong greenhouse gas. Peatlands yield an estimated 5-10% of all methane to the atmosphere and are also recognized as an important reservoir in the global carbon cycle, accounting for about 33% of the global soil carbon. This project serves the national interest and NSF's mission by promoting the progress of scientific understanding of the mechanisms that regulate the release of this potent greenhouse gas to the atmosphere. The fundamental issue addressed by this project relates to the mechanisms and hydrological factors that regulate the sudden (episodic) release of gaseous methane to the atmosphere. These releases are driven by changes in water level and atmospheric pressure that encourages upward bubble transport/release of methane. This project will generate new understanding of how changes in water level, atmospheric pressure and peat fabric lead to sudden releases of methane that far exceed previously held theories on methane release. Although the project is focused on a boreal peatland it will impact our understanding of methane dynamics in other climates, including sub-tropical systems such as the Everglades, and Artic systems. The project includes summer research experiences for the participation of minority students in field geoscience research. Two full-time graduate students and one postdoctoral scientist will be involved this project. Results of the work will be disseminated through student led presentations at national/international meetings and articles submitted to international journals.The contribution of peatlands to the atmospheric CH4 burden remains unclear in large part due to incomplete understanding of the ebullition pathway. Oxidation of dissolved methane reduces the release of methane by diffusion, but the transit time of bubbles released via ebullition is too short for extensive oxidation to occur, i.e. ebullition releases increase the greenhouse gas potential of peatlands. This project will advance understanding of ebullition by coupling new, innovative measurement strategies to physical model development. This integration of measurement and modeling will permit a fundamental step forward towards a more quantitative understanding of CH4 ebullition from peatlands. Two hypotheses will be tested: H1: The frequency and size of ebullition events from peatlands can be predicted from CH4 production rates and pressure changes within the peat column when measurable properties related to the peat structure (and strength) are incorporated into model fitting parameters; H2: Ebullition from the peatland is regulated by a threshold related to the accumulated gas volume, measurable physical properties related to the peat strength, and how gas coalesces within the peat column (e.g. dispersed bubbles versus a few large 'bubbles'). Measurements will be performed in Caribou Bog, a multi-unit peatland located in Maine. Volumetric gas content will be monitored using ground penetrating radar, whereas ebullition fluxes will be monitored using a combination of acoustic ebullition sensors, time-lapse imaging of gas traps, hydraulic heads in piezometers and chamber measurements using a fast methane analyzer. Pore water CH4 samples will be acquired using mini piezometer nests. An existing ebullition model describing gas bubble expansion will be combined with an invasion percolation approach to describe the transport of CH4 between multiple peat layers by both diffusion in the pore water and ebullition between layers. Although the proposed model does not explicitly incorporate the geomechanical properties of peat, model predictions for maximum gas contents will be compared with key measurable geomechanical properties that may control ebullition.

泥炭地只占地球陆地面积的3%，但在产生甲烷（一种强烈的温室气体）方面却不成比例地重要。据估计，泥炭地产生的甲烷占大气中甲烷总量的5-10%，也被认为是全球碳循环中的重要储存库，约占全球土壤碳的33%。该项目服务于国家利益和国家科学基金会的使命，通过促进科学认识的机制，调节释放到大气中的这种强大的温室气体的进展。该项目所处理的基本问题涉及到调节甲烷气体突然（间歇性）释放到大气中的机制和水文因素。这些释放是由水位和大气压力的变化驱动的，这些变化鼓励甲烷向上气泡运输/释放。该项目将产生新的认识，了解水位，大气压力和泥炭结构的变化如何导致甲烷的突然释放，远远超过以前关于甲烷释放的理论。虽然该项目的重点是北方泥炭地，但它将影响我们对其他气候中甲烷动力学的理解，包括亚热带系统，如大沼泽地和北极系统。该项目包括让少数民族学生参加野外地球科学研究的暑期研究经验。两名全日制研究生和一名博士后科学家将参与该项目。工作的结果将通过学生主导的国家/国际会议上的演讲和提交给国际journals. The大气CH 4负担的泥炭地的贡献仍然不清楚，在很大程度上是由于不完全理解的沸腾途径。溶解的甲烷的氧化减少了甲烷通过扩散的释放，但是通过沸腾释放的气泡的通过时间太短而不能发生广泛的氧化，即沸腾释放增加了泥炭地的温室气体潜力。 该项目将通过将新的创新测量策略与物理模型开发相结合来促进对沸腾的理解。这种测量和建模的集成将允许一个基本的一步，朝着更定量的了解甲烷沸腾泥炭地。将检验两个假设：H1：当可测量的性质与泥炭结构相关时，泥炭地的沸腾事件的频率和大小可以从泥炭柱内的CH 4产生速率和压力变化来预测（和强度）被纳入模型拟合参数; H2：泥炭地的沸腾由与积聚的气体体积相关的阈值、与泥炭强度相关的可测量的物理性质以及气体如何在泥炭柱内聚结（例如，分散的气泡相对于一些大的“气泡”）。将在驯鹿沼泽（位于缅因州的多单元泥炭地）进行测量。将使用探地雷达监测气体体积含量，而将使用声学沸腾传感器、气体收集器的延时成像、压力计中的液压头和使用快速甲烷分析仪的腔室测量相结合来监测沸腾通量。孔隙水CH 4样品将使用微型测压管巢采集。现有的描述气泡膨胀的沸腾模型将结合入侵渗流的方法来描述多个泥炭层之间的运输甲烷在孔隙水和沸腾层之间的扩散。 虽然所提出的模型没有明确纳入泥炭的地质力学性质，模型预测的最大气体含量将与关键的可测量的地质力学性质，可能控制沸腾。