The element‐release mechanisms of two pyrite‐bearing siliciclastic rocks from the North German Basin at temperatures up to 90 °C under oxic and anoxic conditions

Background Over the last few decades, shallow geothermal systems (< 400 m depth) have been increasingly utilized as renewable energy sources and storage systems for heating and cooling for domestic and public use (e.g., Bayer et al. 2012; Blum et al. 2010; Fridleifsson et al. 2009; Lund et al. 2011). Aquifer thermal energy storage (ATES) facilities directly use aquifers for seasonal storage of thermal energy. In summer, groundwater is produced from the storage aquifer, heated up with excess energy, and reinjected into the aquifer. In winter, the stored thermal energy is withdrawn from the water by reversing the process. That way, storage of cooling energy is possible as well (Hähnlein et al. 2010; Kranz and Bartels 2009; Kranz and Frick 2013). The reliability and efficiency of ATES systems can be affected by fluid mixing and changes in temperature and pressure in the storage Abstract