It is well known that submergence makes the pH values of soils to increase to about 7 due to iron reduction reactions that consume protons. Surprisingly, pH stabilizes at this neutral value despite continuous reduction reactions.

Here we report on a laboratory experiment with five synthetic soils aimed at understanding the elementary processes that govern pH regulation in soils induced by flooding. The synthetic soils were placed in a glove box under a N₂ atmosphere in the presence of Shewanella Putrefaciens, and submerged with rainwater for 15 weeks. Eh, pH, concentrations of Fe²⁺, Mn²⁺, cations and anions concentration in the soil solution were regularly measured. Synthetic soil samples were analyzed before and after submergence by X-Ray diffraction, Mössbauer Spectroscopy and Transmission Electron Microscopy.

Our results indicate that the geochemical control on pH might be exerted by Green Rusts minerals, the importance of which has only been invoked recently in soils.