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

The envisaged future dihydrogen (H 2 ) economy requires a H 2 gas grid as well as large deep underground stores. However, the consequences of an unintended spread of H 2 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 H 2 into a shallow aquifer at the TestUM test site and monitored the subsequent biogeochemical processes in the groundwater system. At elevated H 2 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 H 2 oxidation was indicated by temporally higher abundances of taxa known for aerobic or anaerobic H 2 oxidation. After H 2 concentrations diminished below the detection limit, α- and β-diversity approached baseline values. In summary, the emulated H 2 leakage resulted in a temporally limited change of the groundwater microbiome and associated geochemical conditions due to the intermediate growth of H 2 consumers. The results confirm the general assumption that H 2 , being an excellent energy and electron source for many microorganisms, is quickly microbiologically consumed in the environment after a leakage.