Microbial Stimulation and Succession following a Test Well Injection Simulating CO₂ Leakage into a Shallow Newark Basin Aquifer

Abstract

In addition to efforts aimed at reducing anthropogenic production of greenhouse gases, geological storage of CO2 is being explored as a strategy to reduce atmospheric greenhouse gas emission and mitigate climate change. Previous studies of the deep subsurface in North America have not fully considered the potential negative effects of CO2 leakage into shallow drinking water aquifers, especially from a microbiological perspective. A test well in the Newark Rift Basin was utilized in two field experiments to investigate patterns of microbial succession following injection of CO2-saturated water into an isolated aquifer interval, simulating a CO2 leakage scenario. A decrease in pH following injection of CO2 saturated aquifer water was accompanied by mobilization of trace elements (e.g. Fe and Mn), and increased bacterial cell concentrations in the recovered water. 16S ribosomal RNA gene sequence libraries from samples collected before and after the test well injection were compared to link variability in geochemistry to changes in aquifer microbiology. Significant changes in microbial composition, compared to background conditions, were found following the test well injections, including a decrease in Proteobacteria, and an increased presence of Firmicutes, Verrucomicrobia and microbial taxa often noted to be associated with iron and sulfate reduction. The concurrence of increased microbial cell concentrations and rapid microbial community succession indicate significant changes in aquifer microbial communities immediately following the experimental CO2 leakage event. Samples collected one year post-injection were similar in cell number to the original background condition and community composition, although not identical, began to revert toward the pre-injection condition, indicating microbial resilience following a leakage disturbance. This study provides a first glimpse into the in situ successional response of microbial communities to CO2 leakage after subsurface injection in the Newark Basin and the potential microbiological impact of CO2 leakage on drinking water resources.

Thermodynamic and Kinetic Response of Microbial Reactions to High CO2

“…The aforementioned field experiments of O'mullan et al (2015) also support the role of CO 2 in microbial competition. Specifically, in their two push-pull tests, the CO 2 injection increased the relative abundance of 16S rRNA genes associated with iron reducers, including Geothrix and Geobacter .…”

“…The predicted benefit to hydrogenotrophic methanogenesis is supported by the field experiments of O'mullan et al (2015). O'mullan et al (2015) carried out two push-pull tests in a shallow aquifer in the Newark Basin, USA.…”

“…O'mullan et al (2015) also detected an increase of genes associated with Desulfosporosinus in the second push-pull test. Members of Desulfosporosinus can use sulfate as an electron acceptor, but some members are also capable of reducing ferric minerals under acidic conditions (Senko et al, 2009; Bertel et al, 2012).…”

“…Specifically, in their two push-pull tests, the CO 2 injection increased the relative abundance of 16S rRNA genes associated with iron reducers, including Geothrix and Geobacter . The increase in these genes overlapped in time with the increase in the concentration of groundwater ferrous iron (O'mullan et al, 2015, their Figures 1, 7). These observations suggest that the CO 2 injection may have stimulated microbial reduction of ferric minerals.…”

“…O'mullan et al (2015) carried out two push-pull tests in a shallow aquifer in the Newark Basin, USA. During the tests, they first injected CO 2 -enriched solution into the aquifer through a test well, and then extracted the groundwater from the same well.…”