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Orders: Gleysolic

Gleysolic soils result from prolonged water saturation of the soil profile. In regions such as the St. Lawrence Lowlands or the Clay Belt in northern Ontario, landscapes with clay-dominated soil textures have very slow rates of water movement through the soil, which causes period of water saturation. In the grassland and non-boreal regions of the Prairies, saturated conditions result from both concentration of surface water flows (runoff) into depressions or from the groundwater table rising to an elevation where it intersects with soil forming processes. In this region Gleysolic soils are the dominant wetland soil (GLEYSOLIC CANADA MAP).

Water saturation leads to depletion of oxygen in the soil and soil features associated with oxygen-depleted (also called anaerobic or anoxic) conditions. Anaerobic conditions cause the transformation of metals such as iron and (to a lesser degree) manganese and lead to changes in the dominant colour of soil horizons. When oxygen is present, iron is oxidized and has a reddish colour; when oxygen becomes depleted (due to water saturation) the iron is reduced and takes on a blue-grey hue and this dominates the colour of the horizon. (Blue Grey Hue) Reduced iron is also mobile, and it can concentrate in the profile and re-oxidize, producing reddish or brown mottles. (Mottling)

These features are collectively referred to as gley features, and the diagnostic criteria for Gleysolic soils in the presence of well-developed gley features within 50 cm of the soil surface. Horizons with these features are labeled with the subscript g (e.g. Bg, Aeg).

Often gley features are observed in soils but are not well-developed - for example, the colour contrast between the mottles and the rest of the soil horizon they are found in may be low. This contrast is assessed using Munsell colour contrast, and horizons which fail to meet the criteria for true Gleysolic soils are assigned a j suffix in addition to the g (e.g., Bgj, Aegj). These soils are recognized in as Gleyed subgroups in the other soil orders (e.g. Gleyed Dark Brown Chernozem).

The water-saturated conditions also reduce the rate of transformation of organic matter in the soil. This can lead to the build up of organic matter on the surface of the mineral Gleysolic soils. Where the rate of decomposition is greatly reduced, organic matter inputs from plants build up over centuries and peat forms. In the transition to the boreal forest, Gleysolic soils are often overlain by layer of peat. If the peat is less than 60-cm thick (if fibrous) or 40-cm thick (if more decomposed), the Gleysolic soils are referred to as a Peaty Phase Gleysol. If the peat deposits are thicker than this the soils are classified as Organic.

As water moves from the soil surface to greater depths in the soil dispersed clay in the water may be carried by the water (lessivage). This dispersed clay may be deposited along the walls of the pores at depth, leading to clay skins on the surfaces of pores and peds. This transfer of clay leads to a clay-depleted layer in the upper soil and a clay-enriched layer deeper in the soil. The clay enriched layer is a B horizon and is assigned a t suffix (e.g. Btg). (Orthic Luvic Gleysol)

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