The disposal of industrial lime kiln waste at Harpur Hill, Buxton, since the 18th century has substantially altered the site’s geochemistry, producing a hyperalkaline lagoon with pH values of 11–13. Through interactions with rainwater and groundwater, these waste deposits have generated calcium carbonate tufas through atmospheric CO₂ sequestration resulting in a carbon sink. The resulting hyperalkaline and potentially anaerobic sediments present a significant challenge to microbial life. The presence of both organic carbon in the soil, and inorganic carbon in the form sequestered CO2 in anaerobic conditions presents the opportunity for a methanogenic population to develop. The presence of a methanogenic population in-situ presents an opportunity to understand methane evolution in-situ but may also provide further insights into the potential influence of methanogens in carbon capture technologies, and in geological radioactive waste disposal concepts. This study investigated the presence and activity methanogens at Harpur Hill through integrated biogeochemical characterisation, 16S rRNA gene sequencing, enrichment microcosms and metagenomic analyses. 16S rRNA gene sequencing of the site sediments revealed low abundances of Archaeal methanogens, notably Methanosarcina and Methanobacterium and dominance of Bacterial reads from Proteobacteria and Bacteroidetes. Shotgun metagenomics enabled the reconstruction of high-quality metagenome-assembled genomes, demonstrating diverse functional capacities related to carbon and nitrogen cycling. Minimal methanogenesis key functional genes, such as methyl-coenzyme M reductase, were detected through the research, however partial pathways consistent with hydrogenotrophic and acetoclastic methanogenesis were identified, suggesting the possibility of these processes in-situ despite their low archaeal biomass. The sediments recovered from Harpur Hill were used as inocula for microcosms that intended to enrich for hydrogenotrophic, and acetoclastic methanogens. Activity was limited to the inoculum from a single sediment sample. Methane generation via the hydrogenotrophic pathway was observed at pH 10 and 11, with Methanosaeta being the dominant methanogenic genus. Following a series of subcultures, the microcosm volume was scaled to allow a grater biomass to be obtained. After the successful detection of methane generation at 1.03 mmoles in the pH 11.0 microcosm, the increased volume allowed for DNA extraction methods and community profiling to be completed. This allowed for the identification and characterisation of the methanogens generating the methane within the site to be characterised. Analysis of the final site 6 soil microcosm at pH 11.0 revealed the presence of hydrogenotrophic methanogens within the microbial community, however, only a high-quality genome of a previously described acetoclastic methanogen, Methanocalculus chunghsingensis, was recovered. Community profiling and functional analysis suggested a potential syntrophic relationship between the methanogens and members of the Bacteroidales, which are known for their fermentative metabolism that provides substrates such as acetate and hydrogen for utilisation. The results have identified that hydrogenotrophic methanogenesis is likely to be the most prevalent metabolism in the sediments at Harpur Hill. These releases may merit further consideration to determine their impacts, such as enhancing the release of inorganic carbon from the tufa present on site. Further, the activity of these organisms has implications for carbon capture and geological disposal of radioactive wastes in which methane could be generated such that they impact upon respective safety cases.
| Date of Award | 16 Jan 2026 |
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| Original language | English |
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| Supervisor | Martin Carr (Main Supervisor) |
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