Gley

Gley is a soil term used to describe a set of hydromorphic conditions that develop in soils when they are saturated with water for prolonged periods. The defining feature of gley soils is a gray to bluish-gray matrix color produced by reduction reactions that occur under anaerobic conditions. When iron and other elements are reduced, ferric oxides are removed from the solid phase, giving the soil a characteristic pale or blue-gray hue. If drainage returns and oxidation recurs, mottling with yellow or brown spots often forms as iron oxides are re-precipitated.

The color characteristics of gley soils are typically low in chroma and can range from grayish to bluish-gray. A gley horizon, or gleyic horizon, is the part of the soil profile that shows the gley color. Mottling—interspersed zones of contrasting colors—frequently accompanies gleying, reflecting alternating periods of reduction and oxidation as water tables rise and fall.

Gley soils commonly occur in wetlands, floodplains, depressions, and other poorly drained landscapes where the water table remains near the surface for extended periods. They are often associated with clay-rich or otherwise impeded drainage layers that limit aeration. In modern soil classification, gleyic properties are the basis for identifying hydromorphic soils, and soils exhibiting these features are classified as Gleysols (or gley soils) in many systems.

In summary, gley denotes a characteristic hydromorphic soil condition marked by gray-blue colors due to reduction in saturated soils, frequently accompanied by mottling from periodic drainage and oxidation.