Turning down the gas: what is the potential for microbial mitigation of methane leakage from soils

页岩气水力压裂开采的潜在环境影响是公众、监管机构和行业关注的主要问题。其中一个担忧是甲烷泄漏的可能性。甲烷是一种温室气体，如果在密闭空间积聚，有潜在的爆炸危险。量化甲烷泄漏的影响需要对自然系统中甲烷循环所涉及的化学、物理和生物过程有很好的理解。NERC最近的ESIOS科学计划强调了提高关键区域（包括土壤）自然生物过程知识的必要性，以及它们对页岩气开采等工业活动污染物的反应。该项目将使用实验室实验、实地考察和建模来了解微生物对土壤系统中一系列尺度上CH4源/汇行为的控制。烃类污染土壤将被用来确定环境因素对CH4运移的影响，以及生物、地球化学和物理因素如何影响地表排放。主要目的是：-评估土壤微生物群落对新的或增加的甲烷泄漏水平作出反应的潜力。需要解决的问题包括：同步甲烷生产（产甲烷）和氧化（产甲烷）如何影响土壤中CH4的运输和平均停留时间？微生物对甲烷浓度增加的反应有多迅速和持续？这种反应是由于微生物活性、数量或群落组成的变化引起的吗？-在实验室条件下，确定土壤中微生物活动对防止甲烷逸入大气至关重要的地球化学和物理条件。-调整和测试微生物油气勘探技术，作为区分页岩气作业泄漏、预先存在的碳氢化合物渗漏和生物甲烷循环自然变化的潜在工具。研究方案：本项目将利用一系列微生物、地球化学和气体输送技术，结合实验和实地数据的数值模拟，以确定控制地表甲烷排放的环境条件，并提出减缓战略。将提供以下方面的培训：基于分子和培养的微生物学技术、使用低压管采样器的气体采样（在最近研究unon的13c标记甲烷迁移过程中开发的）、气相色谱、数值模拟和模型拟合方法（用于气体输送和生物地球化学）。最初的9-12个月将用于掌握采样，分析和建模方法，并计划初始实验和现场采样。在此之后，学生将开始一系列的实验室实验，以评估不同的土壤特征和条件对微生物活动和原位气体扩散的影响。这些实验将在联合国进行，微生物分析将在英国地质调查局进行。在进行实验工作的同时，将在已知的碳氢化合物渗漏或废弃井周围进行现场采样，以确定土壤和环境特征的变化如何影响甲烷通过土壤的运输，以及预先存在的碳氢化合物泄漏如何反映在微生物活动和群落组成中。英国地质调查局可以进入几个合适的地点，并将领导实地取样和随后的微生物分析，并在联合国进行气体分析。使用PHREEQC和BGS内部代码的生物地球化学建模将用于估计微生物群落中观察到的变化的热力学优势；实验和现场数据将使用多相反应输运建模方法进一步模拟。

The potential environmental impacts of hydraulic fracturing for shale gas extraction are a major concern for the general public, regulators and industry. One concern is the possibility of methane leakage. Methane is a greenhouse gas and a potential explosion hazard if it accumulates in enclosed spaces. Quantifying the impacts of methane leakage requires a good understanding of chemical, physical and biological processes involved in methane cycling in natural systems. The need for improved knowledge of natural biological processes in the critical zone, including soils, and their response to pollutants from industrial activities such as shale gas extraction was highlighted in NERC's recent ESIOS Science Plan. This project will use laboratory experiments, fieldwork and modelling to understand the microbial controls on source/sink behaviour of CH4 at a range of scales in the soil system. Hydrocarbon-contaminated soils will be used to establish the influence of environmental factors on CH4 transport and how biological, geochemical and physical factors affect surface emissions. The key aims are:- To assess the potential of the soil microbial community to respond to new or increased levels of methane leakage. Questions to be addressed include: How does synchronous methane production (methanogenesis) and oxidation (methanotrophy) affect transport and mean residence times of CH4 in soils? How rapid and sustained is the microbial response to increased methane concentrations? Is the response due to changes in microbial activity, number or community composition? - To identify, under laboratory conditions, the geochemical and physical conditions under which microbial activity in soils is critical for the prevention of methane escapes to the atmosphere. - To adapt and test techniques used in microbial oil and gas prospecting as potential tools for discriminating between leakages from shale gas operations, pre-existing hydrocarbon seeps and natural variations in biological methane cycling. Programme of Research:This project will use a range of microbiological, geochemical and gas transport techniques, coupled to numerical simulations of experimental and field data, in order to identify the environmental conditions that control surface methane emissions and to propose mitigation strategies. Training will be provided in molecular- and culture-based microbiology techniques, gas sampling using low-tension tube samplers (developed during recent research into the migration of 13C-labelled methane at UoN), gas chromatography, numerical modelling and model fitting methods (for gas transport and biogeochemistry).An initial period of 9-12 months will be spent mastering sampling, analytical and modelling methods and planning initial experiments and field sampling. Following this the student will begin a series of laboratory experiments to evaluate the impact of varying soil characteristics and conditions on microbial activity and in situ gas diffusion. These experiments will be carried out at UoN, with microbiological analysis being carried out at BGS. Concurrent with experimental work, field sampling will be carried out around known hydrocarbon seeps or abandoned wells to establish how variation in soil and environmental characteristics affects the transport of methane through soils and how pre-existing hydrocarbon leakage is reflected in microbial activity and community composition. BGS has access to several suitable sites and will lead the field sampling and subsequent microbiological analysis, with gas analysis carried out at UoN. Biogeochemical modelling using PHREEQC and in-house codes at BGS will be used to estimate the thermodynamic favourability of the observed changes in microbial communities; experimental and field data will be further simulated using a multiphase reactive transport modelling approach.