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 these regions Gleysolic soils are the dominant wetland soil.
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)
Gleysolic Great Groups
The three great groups of the Gleysolic order all have well-developed gley features within 50 cm of the soil's surface. They differ based on the presence of a B horizon enriched in clay (Btg horizon, Luvic Gleysols), anAhhorizon (Humic Gleysols), or an absence of both of these features (Gleysol).
Luvic Gleysolic Great Group
Soils of this great group have aBtghorizon and often have an eluvialAeghorizon overlying the clay-enriched horizon. (Humic Luvic Gleysol)
Humic Gleysolic Great Group
These soils have an organically enriched A horizon (Ah) greater than 10 cm thick or a ploughed A horizon (Ap) greater than 15-cm thick, and have a least 3.5% organic matter in the surface horizon. These soils also result from the translocation of A horizon from upper slopes to depressions due to water erosion or tillage translocation. (Humic Gleysol)
Gleysolic Great Group
These soils lack either aBtgor an Ah horizon. In some cases, these soils develop in pond sediments created by the organisms that live in the wetlands (biogenic sediments). (Fera Gleysol)
Gleysolic Subgroups
|
Subgroup |
Great Groups of the Gleysolic Order |
||
|
|
Luvic |
Humic |
Gleysol |
|
Vertic |
X |
X |
X |
|
Solonetzic |
X |
X |
X |
|
Fragic |
X |
Not applicable |
Not applicable |
|
Humic |
X |
Not applicable |
Not applicable |
|
Fera |
X |
X |
X |
|
Orthic |
X |
X |
X |
|
Rego |
Not applicable |
X |
X |
Vertic
These soils develop in parent materials high in clay (> 60%) and are properties in common with the Vertisolic order. Specifically they have a slickenside horizon (Btgss or Cgss) within 1 m of the soil surface. They are primarily found in the Prairies and Boreal Plain Ecozones.
Solonetzic
These soils are transitional between the Gleysolic and Solonetzic orders and are found in the Prairies and Boreal Plain Ecozones. They have a Solonetzic B horizon (Bng). The Luvic great group also has clay enrichment in the B horizon (Bntg).
Fragic
Soils of this subgroup have a fragipan within or below the gleyed B horizon (Btgx or Bxg). They are most commonly found in forested or previously landscapes.
Humic
This subgroup of the Luvic great group occurs where an Ah horizon at least 10 cm thick or an Ap horizon great than 15 cm thick is found at the surface of the soil. In cultivated landscapes, these soils can result from the translocation of A horizon from upper slopes to depressions due to water erosion or tillage translocation. (Humic Luvic Gleysol 2)
Fera
Soils of this subgroup are found in association with Podzolic soils in Boreal regions. They have a Btgf horizon or both Bfg and Btg horizons where the f suffix is associated with deposition of iron oxides from higher in the profile. (Fera Gleysol)
Orthic
Orthic subgroups lack any of the horizons listed for the subgroups above but do have Aeg and Btg horizons. If cultivated the Aeg may be truncated. (Orthic Humic Gleysol)
Rego
Soils of the Rego subgroup lack a gleyed B horizon that is at least 10 cm thick. They may have an Ah (Humic great group) or O horizon (Gleysol great group) overlying the Cg horizon. (Rego Humic Gleysol)