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

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.