Arctic and Alpine tundra environments Soils

Tundra soils The limited plant growth in this biome only produces a small amount of litter and as there are few soil biota in the cold soil, organic matter decomposes very slowly to give a thin layer of peat – a very acidic humus or mor. When water percolates downwards, usually as meltwater in late spring, the humic acid within it (pH less than 4.5) releases iron. Underlying the soil, often at a depth of less than 50cm, is permafrost. This impermeable layer restricts moisture percolation causing extreme waterlogging and gleying. Few mixing agents can survive in the cold, wet soil which are thin and without developed horizons. Where bedrock is close to the surface the parent material is weathered by freeze thaw action. The shattered fragments are raised to the surface by frost heave preventing horizon development.

Gleying The waterlogged conditions do not allow the oxidation of iron minerals into reddish brown ferrous salts. Instead reduction is the main process, resulting in bluish-grey ferric compounds. Where air bubbles occur reddish mottles may occur. This process is called gleying and the sort of soil produced a gley.

Gelisols are an order in USA soil taxonomy Gelisols are an order in USA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two metres of the soil surface. The word "Gelisol" comes from the Latin gelare meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing characteristic of Gelisols. In the United Nations Food and Agriculture Organization soil classification system, Gelisols are known as Cryosols. Structurally, Gelisols have no B horizon and have an A horizon resting on the permafrost. Because soil organic matter accumulates in the upper layer, most Gelisols are black or dark brown in soil colour, followed by a shallow mineral layer. Despite the influence of glaciations in most areas where Gelisols occur, chemically they are not highly fertile because nutrients, especially calcium and potassium, are very easily leached above the permafrost. The permafrost greatly restricts the engineering use of Gelisols, as large structures (e.g. buildings) subside as the frozen earth thaws when they are put in place. Gelisols are found chiefly in Siberia, Alaska and Canada. Smaller areas are found in the Andes (mainly near the intersection between Chile, Bolivia and Argentina), Tibet, northern Scandinavia and the ice-free parts of Greenland and Antarctica. Fossil Gelisols are known from as far back as Precambrian ice ages 900 million years ago. Gelisols

In USDA soil taxonomy, Gelisols are subdivided into: Histels: organic soils similar to Histosols except that they have permafrost within 2 meters below ground surface. They have 80 % or more organic materials from the soil surface to a depth of 50 cm or to a glacial layer or contact with the bedrock, whichever is shallowest. These soils occur predominantly in Subarctic and Low Arctic regions of continuous or widespread permafrost. Less than one-third of the active layer (the soil between the ground surface and a permafrost table) or an ice layer which is at least 30-cm thick has been cryoturbated . Turbels: soils that show marked influence of cryoturbation (more than one-third of the depth of the active layer) such as irregular, broken, or distorted horizon boundaries and involutions and areas with patterned ground. They commonly contain tongues of mineral and organic horizons, organic and mineral intrusions and oriented rock fragments. Organic matter is accumulated on top of the permafrost and ice wedges are a common features. Turbels occur primarily in the zone of continuous permafrost. Orthels: soils that show little or no cryoturbation (less than one-third of the depth of the active layer). Patterned ground (except for polygons) generally is lacking. Orthels occur primarily within the zone of discontinuous permafrost, and in alpine areas.

Alpine soils Alpine soils are characterized by their shallowness, stoniness and lack of horizon development. These sorts of soils are called lithosols. No subsoil or B horizon is present and the rudimentary A horizon or topsoil can only be distinguished from the weathered parent rock by the presence of organic material. Lithosols can be subdivided into rendzinas which develop on calcareous parent rocks and rankers on non-calcareous parent materials. Different types of soil may be expected to develop at different heights with different climatic conditions. This sequence is called a soil catena (chain in Latin).

Decomposition Decomposition rates are low in the cold temperatures. Some specialised bacteria are psychrophilic (cold tolerant). In wet areas partially decomposed material may collect on the surface as a layer of peat. Mostly this will be a raw, acid peat called mor, rather than the more decomposed neutral moder or mull varieties. In these wet areas bacteria may be anaerobic.