ABSTRACT
Iron and manganese represent the 4th and 12th most abundant elements, respectively, in the Earth’s crust. Iron and manganese are both key elements involved in oxidation–reduction reactions in biosphere soils and sediments, and they are essential trace elements for living organisms. Solid phases of Mn(IV) are more common in soils including wetlands, and subsequent discussion on this metal will focus on only two oxidation states: Mn(II) and Mn(IV). Transitions between these two forms in soils and sediments are mediated by a range of oxidation and reduction reactions and pH and associated biotic and abiotic processes. Iron and manganese are widely distributed in soils and sediments. Owing to a lack of gaseous and minimal soluble phases, both iron and manganese cycles are largely uncoupled from hydrologic and atmospheric cycles. However, within Earth’s surface layers, iron and manganese play a significant role in various other biogeochemical cycles.
