Solute Concentrations Influence Microbial Methanogenesis in Coal-bearing Strata of the Cherokee Basin, USA

Abstract

Microorganisms have contributed significantly to subsurface energy resources by converting organic matter in hydrocarbon reservoirs into methane, the main component of natural gas. In this study, we consider environmental controls on microbial populations in coal-bearing strata of the Cherokee basin, an unconventional natural gas resource in southeast Kansas, USA. Pennsylvanian-age strata in the basin contain numerous thin (0.4–1.1 m) coalbeds with marginal thermal maturities (0.5–0.7% Ro) that are interbedded with shale and sandstone. We collected gas, water, and microbe samples from 16 commercial coalbed methane wells for geochemical and microbiological analysis. The water samples were Na–Cl type with total dissolved solids (TDS) content ranging from 34.9 to 91.3 g L−1. Gas dryness values [C1/(C2 + C3)] averaged 2640 and carbon and hydrogen isotope ratios of methane differed from those of carbon dioxide and water, respectively, by an average of 65 and 183‰. These values are thought to be consistent with gas that formed primarily by hydrogenotrophic methanogenesis. Results from cultivation assays and taxonomic analysis of 16S rRNA genes agree with the geochemical results. Cultivable methanogens were present in every sample tested, methanogen sequences dominate the archaeal community in each sample (avg 91%), and few archaeal sequences (avg 4.2%) were classified within Methanosarcinales, an order of methanogens known to contain methylotrophic methanogens. Although hydrogenotrophs appear dominant, geochemical and microbial analyses both indicate that the proportion of methane generated by acetoclastic methanogens increases with the solute content of formation water, a trend that is contrary to existing conceptual models. Consistent with this trend, beta diversity analyses show that archaeal diversity significantly correlates with formation water solute content. In contrast, bacterial diversity more strongly correlates with location than solute content, possibly as a result of spatial variation in the thermal maturity of the coalbeds.

Influence of pH on the balance between methanogenesis and iron reduction

“…However, many microbial traits are phylogenetically conserved (Martiny, Jones, Lennon, & Martiny, ; Martiny, Treseder, & Pusch, ), particularly at lower taxonomic ranks (e.g., genus; Philippot et al., ). Furthermore, although it is not always the case, direct relationships between relative abundance and reaction chemistry have been observed previously (Akob, Mills, & Kostka, ; Anderson et al., ; Flynn et al., ; Kirk et al., , ; Roling, Van Breukelen, Braster, Lin, & Van Verseveld, ; Tischer et al., ). Thus, a semi‐quantitative assessment of abundance does not preclude direct relationships between abundance and reaction extent.…”

“…Specific taxa included in each sum are noted in the main text. Complete results from our taxonomic analysis are available in Supporting Information not always the case, direct relationships between relative abundance and reaction chemistry have been observed previously (Akob, Mills, & Kostka, 2007;Anderson et al, 2003;Flynn et al, 2013;Kirk et al, 2013Kirk et al, , 2015Roling, Van Breukelen, Braster, Lin, & Van Verseveld, 2001;Tischer et al, 2013). Thus, a semi-quantitative assessment of abundance does not preclude direct relationships between abundance and reaction extent.…”

Impact of Land Use on Microbial Communities in the Great Bend Prairie Aquifer

“…Growing evidence shows dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (Anammox) as important alternative nitrogen transformation pathways that are also microbially mediated (Burgin and Hamilton 2007;Nelson et al 2016). Because microbial activities drive many redox reactions in aquifers, they can have a major influence on groundwater chemistry and quality (Puckett et al 2011;Kirk et al 2015;Ham et al 2017). As a result, aquifer microbial communities are important to consider when seeking to understand the quality of groundwater.…”

“…Microorganisms were collected using autoclave-sterilized materials (120º C for 30 min). We used 60 mL sterile syringes to take up water and filtered each sample through mixed cellulose ester (MCE) membranes (0.22 microns) until the membranes clogged (Kirk et al 2015). Filters used for Well 50B became clogged after 240 mL groundwater, and filters used for Well 50C became clogged after 720 mL groundwater.…”

“…O. Nriagu et al 2007;Richard et al 2014;Zheng and Ayotte 2015). Microbially-driven redox reactions in groundwater can increase or decrease proportions of mobile and bioavailable compounds like arsenic and nitrate (Khan and Hoque 2003;Weber et al 2006;Wallenstein et al 2006;Kirk et al 2015;Whaley-Martin et al 2016;Kumar et al 2017). Thus, understanding controls on the composition and function of aquifer microbial communities is important because microorganisms can strongly influence the chemistry of aquifers.…”