Anaerobic subsurface environments, microbial activities

Ward, T.E. (1985) Characterizing the aerobic and anaerobic microbial activities in surface and subsurface soils. Environ Toxicol. Chem. 4, 727-737. 

In addition to dilution of acid rock/mine drainage under oxidizing conditions, neutralization can occur under mildly or highly anaerobic conditions. This will create distinctive environments in which microorganisms thrive and nanoparticles form as a result of their activity. We describe two examples of such subsurface systems below. However, before turning to these topics, we note that Fe-based microbial ecosystems are not only found in association with metal sulfide deposits, but may be broadly relevant in the subsurface where Fe-rich minerals (biotite, olivine, pyroxenes, etc.) are present in reasonable abundance and dissolve, releasing aqueous ferrous iron. 

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