Reductosols: Natural soils and Technosols under reducing conditions without an aquic moisture regime

According to the German soil classification, Reductosols (German: Reduktosole) are soils with a redoximorphic color pattern, but without water saturation for lengthy periods. They are formed by reducing conditions due to oxygen deficiency caused by the accumulation of reduct gases such as CH4, CO2, NH3, or H2S in the soil atmosphere. Soil oxygen may have been displaced by the ascent of CO2 from post-volcanic mofettes or by CH4 from sanitary landfills. Furthermore, a lack of oxygen causing redoximorphism can occur in unsaturated soils if they contain or receive large quantities of easily decomposable organic matter (i.e., organic urban waste or sludge). Under such circumstances, a gleyic color pattern (e.g., an oxidized Bg horizon above a Cr horizon with strongly reducing conditions) forms without the influence of an aquic moisture regime. Waste-water and petrol infiltration in soil can form a stagnic color pattern without the stagnation of surface water. Such more or less well-drained but strongly redoximorphic horizons should be named as Yg instead of Bg. In some cases, such soils only exist for a short time due to the loss of reduct gases or termination of infiltration of organic liquids. Reductosols are ecotops with oxygen deficiency. Natural Reductosols dominate in recent and former volcanic areas, whereas Reductic Technosols are formed in urban-industrial agglomerations. Their morphology, chemistry, dynamics, genesis, and ecology is summarized and discussed in this paper. Natural gas and CO2 gas are deposited in deeper zones of the earth crust since some time. Leakages of these depots let form reductosols as well.