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Title: Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures
Authors: Iverach, CP
Beckmann, S
Cendón, DI
Manefield, M
Kelly, BFJ
Keywords: Aquifers
Carbon 14
Ground water
Fresh water
Issue Date: 26-Apr-2017
Publisher: European Geosciences Union
Citation: Iverach, C. P., Beckmann, S., Cendón, D. I., Manefield, M., & Kelly, B. F. J. (2017). Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures. Oral presentation to the European Geoscience Union General Assembly 2017, Vienna, Austria, 23-28 April 2017. Retrieved from:
Abstract: Geochemical and microbiological indicators of methane (CH4) production, oxidation and migration processes in groundwater are important to understand when attributing sources of gas. The processes controlling the natural occurrence of CH4 in groundwater must be characterised, especially when considering the potential impacts of the global expansion of unconventional gas production on groundwater quality and quantity. We use geochemical and microbiological data, along with measurements of CH4 isotopic composition ( 13C-CH4), to determine the processes acting upon CH4 in a freshwater alluvial aquifer that directly overlies coal measures targeted for unconventional gas production in Australia. A combination of geochemical and microbiological groundwater samples were collected from private irrigation boreholes. The groundwater was analysed for the major ions, water stable isotopes ( 2H and 18O), the isotopic composition of dissolved organic carbon ( 13CDOC) and dissolved inorganic carbon ( 13CDIC). Quantitative realtime PCR was used to determine abundances of bacterial and archaeal 16S rRNA gene targets and functional gene targets in the groundwater. Measurements of CH4 indicate that there is biogenic CH4 in the aquifer, however microbial community analysis indicates that there are no methanogenic archaea in the groundwater. In addition, geochemical data, particularly the isotopes of DIC and, as well as the concentration of SO2-4 , indicate limited potential for methanogenesis insitu. Microbial community analysis also showed that aerobic oxidation of CH4 is occurring in the alluvial aquifer despite the absence of a microbial pathway to produce the CH4. The combination of microbiological and geochemical indicators suggests that the most likely source of CH4, where it was present in the freshwater aquifer, is the upward migration of CH4 from the underlying coal measures. © Author(s) 2016. CC Attribution 3.0 License.
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