Investigating the chemical and isotopic kinetics of aerobic methane oxidation

研究有氧甲烷氧化的化学和同位素动力学

• 批准号: 1318102
• 负责人: John Kessler
• 金额: $ 52.39万
• 依托单位: University of Rochester
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-12-10 至 2016-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1318102&HistoricalAwards=false
• 关键词: Investigating; chemical; isotopic; kinetics; aerobic

Roughly 8 billion moles of methane (CH4) were emitted in 83 days during the Deepwater Horizon disaster in the northern Gulf of Mexico in 2010. Interestingly, none of this CH4 was emitted to the atmosphere, but instead stayed dissolved and suspended as "plume" or "intrusion" layers approximately 1000m below the ocean surface. Based on measurements of CH4 concentration and oxidation rates, dissolved oxygen anomalies, and microbial community structure as well as a CH4 geochemical model, it was determined that all the CH4 emitted during this disaster was respired within 120 days of the initial well blowout. In addition, the methanotrophic bacteria responsible for the oxidation of this CH4 appeared to experience all stages of microbial growth, limited only by the availability of CH4. This finding suggests that releases of CH4 into deepwater, be them anthropogenic or natural, will have minimal direct influence on the radiative budget of the atmosphere. The major weakness in these previous investigations is that CH4 related parameters were only measured at the beginning (May - June 2010) and end (September - October 2010) of this massive CH4 feast, primarily because the rapid demise of CH4 was unanticipated. Thus, the time- and growth phase-dependent understanding of the kinetics of this bloom response is only based on model interpolation between endpoints. A more complete, and measurement-based, understanding of the chemical kinetics is necessary to predict an oceanographic environment's ability to respire large CH4 perturbations. And while measurements of CH4 stable isotopes in theory can be used to assess the extent that the released CH4 has been oxidized, this kinetic isotope effect can only be used in a quantitative fashion if it is known how the isotopic fractionation factor changes with varying chemical and temperature conditions and throughout all stages of the microbial bloom. In this study, researchers at the Texas A & M University will test two fundamental hypotheses relating to aerobic CH4 oxidation and ultimately produce a thorough characterization of the time-, growth phase-, and temperature-dependency of CH4 oxidation rates, oxidation rate constants, and isotopic fractionation factors. Hypothesis 1: Excluding mixing processes, the bacterial response to a large CH4 perturbation will be limited primarily by the availability of CH4 or dissolved oxygen. Hypothesis 2: Without knowing the stage of microbial growth, measurements of natural stable isotopes of CH4 and dissolved carbon (organic and/or inorganic) cannot be used to assess the extent of CH4 oxidation in situations of large CH4 perturbations. In order to test these hypotheses, with the goal of disproving hypothesis 2, a suite of mesocosm and pure culture incubations will be conducted. Throughout these incubations, concentrations of CH4 and dissolved inorganic carbon as well as their 13C isotopes will be measured in extremely high resolution with new equipment and experimental designs. In addition, dissolved oxygen, nutrient concentrations, trace metals, CH4 oxidation rates, and microbial community structure will be measured. Broader Impacts. In addition to the normal dissemination of results in publications, meeting presentations, and on a project web site, this work will have strong educational and research impacts with close interactions between the PIs, postdoctoral scholar, graduate student, and undergraduate researchers with collaborations between Texas A&M University and the University of California Santa Barbara. The students will have extended visits at each lab for skill development, knowledge transfer, and general academic growth. During 2010, an informal collaboration was established with Ms. Vicki Soutar, a high school science teacher in Watkinsville, GA, to develop high school science laboratory exercises using real scientific data. This proposed project will involve Ms. Soutar to formalize, enhance, extend, and disseminate the products of this collaboration

在2010年墨西哥湾北方的深水地平线灾难期间，大约80亿摩尔的甲烷（CH 4）在83天内排放。有趣的是，这些甲烷没有一个被排放到大气中，而是在海洋表面以下约1000米处溶解和悬浮为“羽流”或“侵入”层。基于测量的甲烷浓度和氧化速率，溶解氧异常，微生物群落结构以及甲烷地球化学模型，它被确定为所有的甲烷排放在这场灾难中的120天内的初始井喷呼吸。此外，甲烷氧化菌负责的CH 4的氧化似乎经历了微生物生长的所有阶段，仅限于CH 4的可用性。这一发现表明，甲烷释放到深水中，无论是人为的还是自然的，对大气辐射收支的直接影响都很小。这些先前调查的主要弱点是，仅在这场大规模甲烷盛宴开始（2010年5月至6月）和结束（2010年9月至10月）时测量了与甲烷有关的参数，主要是因为甲烷的迅速消亡是意料之外的。因此，依赖于时间和生长阶段的理解的动力学，这种盛开的反应是唯一的基础上端点之间的模型插值。一个更完整的，和测量为基础的，化学动力学的理解是必要的，以预测海洋环境的能力，呼吸大CH 4扰动。虽然理论上CH 4稳定同位素的测量可以用来评估释放的CH 4被氧化的程度，但这种动力学同位素效应只能以定量的方式使用，如果知道同位素分馏因子如何随着不同的化学和温度条件以及微生物水华的所有阶段而变化的话。在这项研究中，研究人员在得克萨斯州A M大学将测试两个基本假设有关有氧甲烷氧化，并最终产生一个彻底的表征的时间，生长阶段，和温度依赖性的甲烷氧化速率，氧化速率常数，和同位素分馏因素。 假设1：排除混合过程，细菌对大的CH 4扰动的反应将主要受到CH 4或溶解氧的可用性的限制。 假设二：在不知道微生物生长阶段的情况下，测量甲烷和溶解碳（有机和/或无机）的天然稳定同位素不能用来评估甲烷大扰动情况下甲烷氧化的程度。为了检验这些假设，以反驳假设2为目标，将进行一系列围隔和纯培养物孵育。在整个培养过程中，CH 4和溶解无机碳及其13 C同位素的浓度将通过新设备和实验设计以极高的分辨率进行测量。此外，还将测量溶解氧、营养物浓度、微量金属、甲烷氧化率和微生物群落结构。更广泛的影响。除了在出版物，会议演示文稿和项目网站上正常传播的结果，这项工作将有强大的教育和研究的影响与PI之间的密切互动，博士后学者，研究生和本科生研究人员与德克萨斯州A M大学和加州大学圣巴巴拉之间的合作。学生将在每个实验室进行扩展访问，以进行技能开发，知识转移和一般学术成长。2010年期间，与佐治亚州沃特金斯维尔的高中科学教师Vicki Soutar女士建立了非正式合作，利用真实的科学数据开发高中科学实验室练习。Soutar女士将参与这一拟议项目，以正式确定、加强、扩大和传播这一合作的产品。