Shallow geothermal energy production leads to temperature perturbations in aquifers. Matthijs Bonte, KWR Watercycle Research Institute, Nieuwegein, The Netherlands, and colleagues investigated the effect of temperature variations from 5−80 °C on the kinetics and competition of redox processes and associated changes in microbial communities in anoxic unconsolidated subsurface sediments.

An in situ temperature increase from 11−25 °C caused a shift from iron-reducing to sulfate-reducing and methanogenic conditions. A temperature increase to above 45 °C caused the emergence of a thermophilic microbial community specialized in fermentation and sulfate reduction.
Sulfate-reducing functionality can withstand a substantial temperature rise, whereas other key biochemical processes appear more temperature sensitive.

The results can be used in hydrochemical computer models dealing with temperature changes due to aquifer thermal energy storage (ATES).

• Impacts of Shallow Geothermal Energy Production on Redox Processes and Microbial Communities,
  Matthijs Bonte, Wilfred F. M. Röling, Egija Zaura, Paul W. J. J. van der Wielen, Pieter J. Stuyfzand, Boris M. van Breukelen,
  Environ. Sci. Technol. 2013.
  DOI: 10.1021/es4030244