Infiltration of water from the River Elbe into the unconfined Torgau aquifer has resulted in the following sequence of biogeochemical reactions, driven by the presence of both dissolved and particulate organic carbon: aerobic respiration, denitrification, reduction of manganese and iron oxide, and sulphate reduction. Computer-based geochemical modelling suggests that the waters are out of redox equilibrium, namely that the waters are supersaturated with respect to Fe(III) minerals and undersaturated with respect to Fe(II) minerals. Levels of Fe(II) are controlled by the rate at which Fe is produced from Fe oxide rather than by mineral precipitation reactions.