Environmental Engineering Reference
In-Depth Information
The process of ferric iron reduction to more mobile and grey ferrous iron compounds is
partially chemical, partially carried out by anaerobic micro-organisms and partially
carried out by the products of decomposing organic matter. The process is known as
gleying
. When the soil or horizon is permanently gleyed, it has a uniform grey or blue-
grey colour. Where the soil or horizon is only gleyed temporarily or seasonally, and
reoxidation can take place, the soil shows reddish-orange mottles, or segregations of
ferric oxides. In tropical and subtropical climates, dehydration often produces hard, black
iron-manganese concretions. Mottles and concretions are usually found in more porous
spots within the horizon or along root and faunal channels, where air can enter.
Plate 19.4
A humus-iron podzol (FAO: Orthic Podzol)
beneath acid heath on quartzite gravels. The horizon
sequence is L/F/Ea/Bh/Bf/C. Profile depth 1m.
Photo: Ken Atkinson.
