The Quaternary cover and soil cover

The Quaternary cover largely determines the features the outlook of Estonian landscapes. It is the primary origin of the soil cover and an important factor influencing the water condtitions and the chemical composition of waters.

The Quaternary cover of Estonia, covering the bedrock, was formed during and after the last glaciation. The usual thickness of the Quaternary cover in the plateaus of North and Central Estonia is 2–3 m, in South Estonia 5–10 m. Parts of the limestone plateaus, where the Quaternary cover is absent or only a few centimetres thick, are called alvars. The maximum thickness of the Quaternary cover, exceeding 100 m, occurs in ancient valleys and in the accumulative heights in southern Estonia.

The main constituent of the Quaternary cover is till. The limestone in North and North-West Estonia is covered by a gray till, rich in boulders. The sandstone in South Estonia is covered by a brown till, rich in clay and poor in boulders. Except for tills, the Quaternary cover includes sediments of gravel, sand, varved clay, peat and mud. The fluvioglacial sediments are usually composed of cross-bedded gravel and sand, used in road and building construction. The fine-grained limnoglacial sediments include varved clays, used as a raw material for bricks, drainage pipes and roof stones.

After the retreat of the ice margin, the Quaternary cover in the lowlands of Estonia was largely formed by the sea. In the uplands, untouched by the sea and large lakes, the Quaternary cover was formed by the erosion and accumulation caused by temporary water currents, weathering and wind. The sediments formed after the glaciation are of different origin. The sand, gravel and pebbles are of marine origin. The lake sediments include lake mud, sand and lacustrine lime; the river sediments, gravel, sand and clay. The occurrences of travertine are rare.

Soil cover
The soil cover of Estonia is characterised by high diversity due to the varied composition of parent material and diverse water conditions, a large share of peatland and peaty soils (ca 50%), abundance of calcareous soils (especially in North and West Estonia), and the high rock content of soils. About ten types of soil are distinguished in Estonia, differing from one another in their distribution, structure, properties and the ways they are used.

Limestone rendzinas (Rendzic Leptosols) on alvars occur in North and West Estonia, where limestone bedrock lies close to the land surface. These soils have a high humus and nutrient content but are very stony and sensitive to drought. Therefore attempts are made to be maintain these soils under natural vegetation instead of tilling them. The most common natural vegetation types on such soils are alvar forests and alvar meadows.

Ryhk and pebble rendzinas (Rendzic Leptosols and Calcaric Regosols) on calcareous sceletal till can also be found mainly in North and West Estonia, although in areas of thicker quaternary cover. Such soils are characterised by a high humus and nutrient content and a high content of sharp-edged pieces of weathered limestone (ryhk). These soils have been largely cultivated. In places where natural vegetation still remains, these soils are covered with species-rich wooded meadows and fresh boreo-nemoral forests.

Brown typical and lessive soils (Cambisols and Luvisols) occur mainly on the till plains of Central Estonian and Pandivere Uplands. These are the most productive agricultural soils in Estonia and their area of distribution therefore coincides with the main agricultural regions.

Sod-podzolic soils and podzols (Podzols) have formed primarily in areas of sandy quaternary cover. Podzols usually occur under pine forests without herbaceous vegetation. No humus horizon forms in such soils. Sod-podzolic soils have formed on a relatively richer parent material, which supports herbaceous vegetation whose decomposition yields a thin humus horizon in the soil profile. A common feature of both soils is the existence of a greyish-white eluvial horizon, beneath which there is a reddish-brown illuvial horizon rich in mobile humus substances, aluminium and iron.

Pseudopodzolic soils (Stagnic Luvisols and Planosols) occur on the till plains of South and Central Estonia. Their formation is conditioned on the presence of a clayey or two-layered parent material, where a compact layer with low permeability underlies the upper layer. Seasonal stagnation of perched water is characteristic of these soils, especially in spring, resulting in the formation of a whitish layer resembling a podzolic horizon in the soil profile. Pseudopodzolic soils are, for example, South Estonian soils of medium humus content, which have largely been cultivated. Where the natural vegetation still remains, fresh boreo-nemoral and boreal forests grow on such soils.

Sod-gley soils (Gleysols) represent a large association of waterlogged soils with highly variable composition and properties. They prevail in the soil cover of Estonia. The common feature of Gleysols is a bluish-grey or greenish-grey gley horizon formed in the conditions of either high ground water level or prolonged surface and perched water. Their surface horizon consists of only partly transformed organic matter — raw humus. Some sod-gley sandy soils may have undergone podzolisation. Paludified pine forests grow on such soils. Sod-gley soils, formed in a calcareous environment, support paludified deciduous forests. In West Estonia, cultivated grasslands and fields can often be found on sod-gley soils.

Peatland soils (Histosols) occupy about one-fourth of the territory of Estonia and are divided into lowland mires (Terric Histosols), transitional and raised bogs (Fibric Histosols). These soils are characterised by an at least 30-cm peat layer with underlying gleyic and podzolic profiles, respectively.

Alluvial soils (Fluvisols) form in the bank and shore zones of inland water bodies in conditions of periodic floods. Relatively few of them have been preserved in Estonia, as the frequency and scope of floods have considerably decreased due to dredging and damming of rivers and drainage. On low seacoasts, in the influence zone of saline seawater, slightly saline littoral soils (Salic Fluvisols) occur. These are, as a rule, young soils still in their developing stage.

South Estonian uplands with a hillocky relief host soil communities typical of eroded areas. The slopes and tops of hills are covered with eroded soils where the humus horizon has thinned significantly due to erosion, or is entirely absent. At the foot of hillocks, however, deluvial soils with an extremely thick (up to 1 m) humus horizon accumulate. Such soil communities can be found in cultivated areas exposed to rain-water erosion. In exhausted open pits, artificial soils can be found.

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