AUTHOR=Mu Andre , Boreham Chris , Leong Henrietta X., Haese Ralf , Moreau John W.

TITLE=Changes in the deep subsurface microbial biosphere resulting from a field-scale CO2 geosequestration experiment

JOURNAL=Frontiers in Microbiology

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2014.00209

DOI=10.3389/fmicb.2014.00209

ISSN=1664-302X

ABSTRACT=<p>Subsurface microorganisms may respond to increased CO<sub>2</sub> levels in ways that significantly affect pore fluid chemistry. Changes in CO<sub>2</sub> concentration or speciation may result from the injection of supercritical CO<sub>2</sub> (scCO<sub>2</sub>) into deep aquifers. Therefore, understanding subsurface microbial responses to scCO<sub>2</sub>, or unnaturally high levels of dissolved CO<sub>2</sub>, will help to evaluate the use of geosequestration to reduce atmospheric CO<sub>2</sub> emissions. This study characterized microbial community changes at the 16S rRNA gene level during a scCO<sub>2</sub> geosequestration experiment in the 1.4 km-deep Paaratte Formation of the Otway Basin, Australia. One hundred and fifty tons of mixed scCO<sub>2</sub> and groundwater was pumped into the sandstone Paaratte aquifer over 4 days. A novel U-tube sampling system was used to obtain groundwater samples under <italic>in situ</italic> pressure conditions for geochemical analyses and DNA extraction. Decreases in pH and temperature of 2.6 log units and 5.8°C, respectively, were observed. Polyethylene glycols (PEGs) were detected in the groundwater prior to scCO<sub>2</sub> injection and were interpreted as residual from drilling fluid used during the emplacement of the CO<sub>2</sub> injection well. Changes in microbial community structure prior to scCO<sub>2</sub> injection revealed a general shift from <italic>Firmicutes</italic> to <italic>Proteobacteria</italic> concurrent with the disappearance of PEGs. However, the scCO<sub>2</sub> injection event, including changes in response to the associated variables (e.g., pH, temperature and salinity), resulted in increases in the relative abundances of <italic>Comamonadaceae</italic> and <italic>Sphingomonadaceae</italic> suggesting the potential for enhanced scCO<sub>2</sub> tolerance of these groups. This study demonstrates a successful new <italic>in situ</italic> sampling approach for detecting microbial community changes associated with an scCO<sub>2</sub> geosequestration event.</p>