INSIGHTS INTO THE MICROBIOLOGICAL RESPONSE TO CO2 LEAKAGE FROM BROAD-SCALE GEOCHEMICAL DATA

How aquifer microbial populations respond to an increase in CO2 abundance will influence the environmental impact and fate of CO2 that leaks from geological sequestration reservoirs. In this study, we use geochemical data from the U.S. Geological Survey National Water Information System to assess how variation in CO2 abundance affects interactions between iron and sulfate-reducing microorganisms, two of the most common groups of microbes in anoxic aquifers. Thermodynamic calculations and bioreactor experiments indicate that an increase in CO2 abundance can increase the ability of iron reducers to compete with sulfate reducers. Variation in water chemistry with CO2 abundance is consistent with that trend. Alkalinity, iron, and the iron-sulfide ratio of groundwater share a statistically significant positive correlation with CO2 abundance (P <0.0001). Thermodynamic calculations show that iron reducers gain an increasing energetic advantage over sulfate reducers with rising CO2 abundance. Hence, the balance between each group may vary in response to bioenergetics. These findings imply that shifts in microbiology in response to CO2 leakage can negatively affect groundwater quality but enhance CO2 trapping.