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: 1623895
• 负责人: Lee Slater
• 金额: $ 21.96万
• 依托单位: Rutgers University Newark
• 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=1623895&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.

泥炭地仅占地球陆地面积的 3% 左右，但在产生甲烷（一种强温室气体）方面却异常重要。据估计，泥炭地向大气中释放的甲烷占所有甲烷的 5-10%，也被认为是全球碳循环的重要储库，约占全球土壤碳的 33%。该项目通过促进对调节这种强效温室气体向大气释放的机制的科学认识的进步，服务于国家利益和 NSF 的使命。该项目解决的基本问题涉及调节气态甲烷突然（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，从而促进气泡向上输送/释放甲烷。该项目将对水位、大气压力和泥炭结构的变化如何导致甲烷突然释放产生新的认识，这种释放远远超出了之前关于甲烷释放的理论。尽管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态的理解，包括大沼泽地等亚热带系统和北极系统。该项目包括少数民族学生参与实地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。这项工作的结果将通过学生在国家/国际会议上主导的演讲以及提交给国际期刊的文章来传播。泥炭地对大气中 CH4 负荷的贡献仍然不清楚，这在很大程度上是由于对沸腾路径的不完全了解。溶解甲烷的氧化减少了通过扩散释放的甲烷，但通过沸腾释放的气泡的传输时间太短，不足以发生广泛的氧化，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、创新的测量策略与物理模型开发结合起来，增进对沸腾的理解。这种测量和建模的结合将在更加定量地了解泥炭地甲烷沸腾方面迈出根本性的一步。将测试两个假设： H1：当与泥炭结构（和强度）相关的可测量特性纳入模型拟合参数时，可以根据泥炭柱内的 CH4 生产率和压力变化来预测泥炭地沸腾事件的频率和规模； H2：泥炭地的沸腾受到与累积气体体积相关的阈值、与泥炭强度相关的可测量物理特性以及泥炭柱内气体如何聚结（例如分散的气泡与一些大的“气泡”）相关的阈值的调节。测量将在位于缅因州的驯鹿沼泽（Caribou Bog）进行，这是一个多单元泥炭地。体积气体含量将使用探地雷达进行监测，而沸腾通量将使用声学沸腾传感器、气体捕集器的延时成像、压力计中的液压头以及使用快速甲烷分析仪进行室测量的组合来监测。孔隙水 CH4 样品将使用微型压力计巢采集。描述气泡膨胀的现有沸腾模型将与侵入渗透方法相结合，通过孔隙水中的扩散和层间沸腾来描述多个泥炭层之间的 CH4 传输。 尽管所提出的模型没有明确纳入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沸腾的关键可测量地质力学特性进行比较。

项目成果

Evidence for glacial geological controls on the hydrology of Maine (USA) peatlands

冰川地质控制缅因州（美国）泥炭地水文的证据

• DOI: 10.1130/g46844.1
• 发表时间: 2020-05
• 期刊: Geology
• 影响因子: 5.8
• 作者: Chen, Xi;Comas, Xavier;Reeve, Andrew;Slater, Lee
• 通讯作者: Slater, Lee

A Lumped Bubble Capacitance Model Controlled by Matrix Structure to Describe Layered Biogenic Gas Bubble Storage in Shallow Subtropical Peat

矩阵结构控制的集总气泡电容模型描述浅亚热带泥炭层状生物气体气泡储存

• DOI: 10.1029/2018wr022573
• 发表时间: 2018-08
• 期刊: Water Resources Research
• 影响因子: 5.4
• 作者: Chen, Xi;Comas, Xavier;Binley, Andrew;Slater, Lee
• 通讯作者: Slater, Lee

Methane emission through ebullition from an estuarine mudflat: 2. Field observations and modeling of occurrence probability: EBULLITION FROM AN ESTUARINE MUDFLAT

河口泥滩沸腾产生的甲烷排放：2. 现场观测和发生概率建模：河口泥滩沸腾

• DOI: 10.1002/2016wr019720
• 发表时间: 2017-08
• 期刊: Water Resources Research
• 影响因子: 5.4
• 作者: Chen, Xi;Schäfer, Karina V.;Slater, Lee
• 通讯作者: Slater, Lee