Investigating the chemical and isotopic kinetics of aerobic methane oxidation

2010年墨西哥湾北部深水地平线灾难期间，83天内排放了大约80亿摩尔的甲烷(CH4)。有趣的是，这些甲烷都没有排放到大气中，而是以“羽流”或“入侵”层的形式溶解并悬浮在海面下约1000米处。根据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的测量，确定在这场灾难中排放的所有甲烷在最初井喷后120天内都得到了呼吸。此外，负责氧化甲烷的甲烷营养细菌似乎经历了微生物生长的所有阶段，仅受甲烷的可用性限制。这一发现表明，甲烷排放到深水中，无论是人为的还是自然的，对大气的辐射收支的直接影响都将微乎其微。这些先前调查的主要弱点是，甲烷相关参数仅在这场大规模的甲烷盛宴开始(2010年5月至6月)和结束(2010年9月至10月)时测量，主要是因为甲烷的迅速消亡是意想不到的。因此，对这种水华响应动力学的依赖于时间和生长阶段的理解仅基于端点之间的模型内插。对化学动力学有一个更完整的、基于测量的理解对于预测海洋环境呼吸大的CH4扰动的能力是必要的。虽然理论上对CH4稳定同位素的测量可以用来评估释放的CH4被氧化的程度，但只有在知道同位素分馏系数随着不同的化学和温度条件以及在微生物繁殖的所有阶段发生变化的情况下，这种动态同位素效应才能以定量的方式使用。在这项研究中，德克萨斯农工大学的研究人员将测试两个与甲烷好氧氧化有关的基本假设，并最终得出甲烷氧化速率、氧化速率常数和同位素分馏系数随时间、生长阶段和温度变化的全面特征。假设1：排除混合过程，细菌对大的CH4扰动的反应将主要受到CH4或溶解氧的可用性的限制。假设2：在不知道微生物生长阶段的情况下，不能使用对CH4和溶解碳(有机和/或无机)的天然稳定同位素的测量来评估在CH4大扰动的情况下CH4的氧化程度。为了检验这些假说，为了反驳假说2，将进行一套中胚层和纯培养孵化。在整个孵化过程中，将使用新的设备和实验设计以极高的分辨率测量甲烷和溶解的无机碳及其13C同位素的浓度。此外，还将测量溶解氧、营养物质浓度、痕量金属、甲烷氧化速率和微生物群落结构。更广泛的影响。除了在出版物、会议演示和项目网站上正常传播结果外，这项工作还将产生强大的教育和研究影响，因为在德克萨斯农工大学和加州大学圣巴巴拉分校的合作下，PI、博士后学者、研究生和本科生之间的密切互动将产生强大的教育和研究影响。学生们将在每个实验室进行长期访问，以获得技能发展、知识传授和一般学术成长。2010年，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制定高中科学实验室练习。这个拟议的项目将使苏塔尔女士正式确定、加强、扩展和传播这种合作的产品。

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