Changes in microbial communities and associated water and gas geochemistry across a sulfate gradient in coal beds: Powder River Basin, USA

Hannah Schweitzer; Daniel Ritter; Jennifer McIntosh; Elliott P. Barnhart; Alfred B. Cunningham; David Vinson; William H. Orem; Matthew W. Fields

doi:10.1016/j.gca.2018.11.009

USGS · 70201455

Changes in microbial communities and associated water and gas geochemistry across a sulfate gradient in coal beds: Powder River Basin, USA

Hannah Schweitzer·Daniel Ritter·Jennifer McIntosh·Elliott P. Barnhart·Alfred B. Cunningham·David Vinson·William H. Orem·Matthew W. Fields

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Abstract

Competition between microbial sulfate reduction and methanogenesis drives cycling of fossil carbon and generation of CH 4 in sedimentary basins. However, little is understood about the fundamental relationship between subsurface aqueous geochemistry and microbiology that drives these processes. Here we relate elemental and isotopic geochemistry of coal-associated water and gas to the microbial community composition from wells in two different coal beds across CH 4 and SO 4 2− gradients (Powder River Basin, Montana, USA). Areas with high CH 4 concentrations generally have higher alkalinity and δ 13 C-DIC values, little to no SO 4 2− , and greater conversion of coal-biodegradable organics to CH 4 (based on δ 13 C-CH 4 and δ 13 C-CO 2 values). Wells with SO 4 2− concentrations from 2 to 10 mM had bacterial populations dominated by several different sulfate-reducing bacteria and archaea that were mostly novel and unclassified. In contrast, in wells with SO 4 2− concentrations <1 mM, the sequences were dominated by presumptive syntrophic bacteria as well as archaeal Methanosarcinales and Methanomicrobiales . The presence of sequences indicative of these bacteria in low SO 4 2− methanogenic wells may suggest a syntrophic role in coal biodegradation and/or the generation of methanogenic substrates from intermediate organic compounds. Archaeal sequences were observed in all sampled zones, with an enrichment of sequences indicative of methanogens in low SO 4 2− zones and unclassified sequences in high SO 4 2− zones. However, sequences indicative of Methanomassiliicoccales were enriched in intermediate SO 4 2− zones and suggest tolerance to SO 4 2− and/or alternative metabolisms in the presence of SO 4 2− . Moreover, sequences indicative of methylotrophic methanogens were more prevalent in an intermediate SO 4 2− and CH 4 well and results suggest an important role for methylotrophic methanogens in critical zone transitions. The presented results demonstrate in situ changes in bacterial and archaeal population distributions along a SO 4 2− gradient associated with recalcitrant, organic carbon that is biodegraded and converted to CO 2 and/or CH 4 .

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Hannah Schweitzer, Daniel Ritter, Jennifer McIntosh, Elliott P. Barnhart, Alfred B. Cunningham, David Vinson, William H. Orem, Matthew W. Fields. 2019. Changes in microbial communities and associated water and gas geochemistry across a sulfate gradient in coal beds: Powder River Basin, USA. https://doi.org/10.1016/j.gca.2018.11.009

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