Distribution and reactivity of O2-reducing components in sediments from a layered aquifer.

The redox status of subsurface aqueous systems is controlled by the reactivity of solid redox-sensitive species and by the inflow of such species dissolved in groundwater. The reactivity toward molecular oxygen (O2) of solid reductants present in three particle size fractions of sediments from a pristine aquifer was characterized during 54 days. The stoichiometric relationships between carbon dioxide (CO2) production and O2 consumption was used in combination with sulfate production to discriminate between the contributions of sedimentary organic matter (0-87%), pyrite (6-100%), and siderite (0-43%) as the dominant reductants.