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: 1623899
• 负责人: Ruth Varner
• 金额: $ 15.12万
• 依托单位: University of New Hampshire
• 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 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1623899&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.

泥炭地仅占地球土地面积的约3％，但在产生强烈的温室气体的甲烷方面非常重要。泥炭地估计，估计所有甲烷的5-10％为大气中，也被认为是全球碳循环中的重要储层，约占全球土壤碳的33％。该项目通过促进对调节这种有效温室气体释放到大气的机制的科学理解的进步来为国家利益和NSF的使命服务。该项目解决的基本问题与调节气态甲烷突然（情节性）向大气的机制和水文因素有关。这些释放是由水位和大气压力的变化驱动的，这鼓励了甲烷的向上气泡运输/释放。该项目将对水位的变化，大气压和泥炭织物的变化产生新的了解，从而导致甲烷突然释放，这远远超过了以前在甲烷释放中持有的理论。尽管该项目集中在北方泥炭地上，但它将影响我们对其他气候中甲烷动力学的理解，包括诸如大沼泽地和货币系统的亚热带系统。该项目包括为少数族裔学生参与现场地球科学研究的夏季研究经验。这项项目将涉及两名全日制研究生和一名博士后科学家。这项工作的结果将通过学生LED在国际/国际会议上的演讲进行传播，并提交给国际期刊的文章。泥炭地对大气CH4负担的贡献在很大程度上还不清楚，这在很大程度上不清楚，因为对戒烟途径的了解不完全。溶解甲烷的氧化可通过扩散减少甲烷的释放，但是通过戒断释放的气泡的过境时间太短了，无法发生大量氧化，即戒断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连，从而提高对潮流的理解。这种测量和建模的整合将允许向更定量地了解泥炭地的CH4戒断迈出基本的一步。将测试两个假设：H1：可以预测，与泥炭结构（和强度）相关的可测量性能中，可以预测CH4的生产率和泥炭柱中的压力变化的频率和大小。 H2：来自泥炭地的戒断受与累积气体体积，与泥炭强度相关的可测量的物理特性以及泥炭柱中的气体结合（例如分散气泡与一些大型“气泡”）的阈值调节。测量值将在位于缅因州的多单元泥炭地（Caribou Bog）中进行。将使用接地穿透雷达来监测体积气体含量，而使用声学戒断传感器，气体陷阱的延时成像，在压力仪和室内测量中的液压头的延时成像，使用快速甲烷分析仪来监测弹药通量。孔隙水CH4样品将使用小型压电仪巢获取。描述气泡膨胀的现有戒断模型将与一种入侵渗透方法相结合，以描述CH4在多个泥炭层之间的运输，这是通过在孔隙水中的扩散和层之间的消除。 尽管所提出的模型未明确结合泥炭的地质力学特性，但最大气体含量的模型预测将与可能控制戒断的关键可测量的地质力学特性进行比较。