temperature effects on aquifer microbial communities

High-temperature aquifer thermal energy storage (HT-ATES) is a promising technique to reduce the CO2 footprint of heat supply in the frame of transitioning to renewable energies. However, HT-ATES causes temperature fluctuation in groundwater ecosystems and affects indigenous microbial communities that mediate important ecosystem services under natural conditions. Hence, assessing the impact of increasing temperatures on the structure and function of aquifer microbiomes is crucial to evaluate potential environmental risks associated with HT-ATES. In this study, we investigated the effects of temperature variations (12-80°C) on microbial communities and their capacity to mineralize acetate in aerobically incubated sediments sampled from a pristine aquifer. Compared to natural conditions (12°C), increased acetate mineralization rates were observed at 25°C, 37°C and 45°C, whereas mineralization was decelerated at 60°C and absent at 80°C. Sequencing of 16S rRNA genes revealed that the bacterial diversity in acetate-amended and non-acetate-amended sediments decreased with rising temperatures. Distinct communities dominated by bacterial groups affiliated with meso- and thermophilic bacteria established at 45°C and 60°C, while the number of archaeal phylotypes decreased. In conclusion, the changes in microbial composition and diversity above 37°C indicate an increasing loss of ecosystem functioning and resilience. Nevertheless, acetate mineralization was sustained until 60°C, but collapsed at 80°C together with the microbial community.