Rapid Consumption of Dihydrogen Injected into a Shallow Aquifer by Ecophysiologically Different Microbes

The envisaged future dihydrogen (H₂) economy requires a H₂ gas grid as well as large deep underground stores. However, the consequences of an unintended spread of H₂ through leaky pipes, wells, or subterranean gas migrations on groundwater resources and their ecosystems are poorly understood. Therefore, we emulated a short-term leakage incident by injecting gaseous H₂ into a shallow aquifer at the TestUM test site and monitored the subsequent biogeochemical processes in the groundwater system. At elevated H₂ concentrations, an increase in acetate concentrations and a decrease in microbial α-diversity with a concomitant change in microbial β-diversity were observed. Additionally, microbial H₂ oxidation was indicated by temporally higher abundances of taxa known for aerobic or anaerobic H₂ oxidation. After H₂ concentrations diminished below the detection limit, α- and β-diversity approached baseline values. In summary, the emulated H₂ leakage resulted in a temporally limited change of the groundwater microbiome and associated geochemical conditions due to the intermediate growth of H₂ consumers. The results confirm the general assumption that H₂, being an excellent energy and electron source for many microorganisms, is quickly microbiologically consumed in the environment after a leakage.