Soils of Valaam archipelago

In what concerns the substrate characteristics, soil profile structure and high natural fertility the soils of the Valaam archipelago are notably different from the soils forming on the granites and glacial deposits of the Karelian isthmus. Where the soil cover in Karelia is dominated by podzolic-type soils, Valaam soils are chiefly brown earth soils and podburs (Lazareva, Morozova, 1989; Matinjan, Urusevskaya, 1999).

Brown earth soils and podburs form on the bedrock in well-drained landscapes. Podzolic soils develop in depressions. Sod-gley, swamped-podzolic and swamped soils occupy poorly drained elements of the landscape.

Brown earth and podburs are shallow, with crushed stone profile, mineral horizons coloured rust-brown, high humus content, acidic reaction, considerable exchange capacity, high ferrum content. In contrast to brown earth podburs lack the humic horizon, and litter is replaced by the illuvial-metamorphic horizon changing into the parent material.

Podzolic soils are less common. The leaders among them are low-podzolic Fe-illuvial soils. The polimictic composition of the parent material, their richness in calcium and iron inhibit podzolization, and the grassy vegetation on the soil cover promotes humus accumulation in the eluvial horizon.

The soils are characterized by the accumulative distribution of the clay fraction, eluvial-illuvial differentiation of chemical elements, acidic reaction, are enriched with mobile phosphorus and poor in potassium. The typical features of podzolic soils are acidic reaction, low humus content, eluvial-illuvial distribution of silica and iron oxides. The soils are poor in nutrients, particularly potassium.

Sod-gley soils developing in depressions and hollows of the island are over-moistured due to retention of surface waters or the groundwaters lying close to the surface. The soils have a well-expressed humus horizon. They are potentially fertile, but the water regime needs to be controlled.

The distribution of swamped soils in Valaam is limited. They are mainly represented by low-lying peaty-gleyed types. Non-complete peaty soils lying on slightly weathered crystalline rocks occur as small patches in the midst of primitive soils and podburs. Their peaty horizon is not over 10-20 cm thick, it is easily separated from the underlying gabbro-diabase plate. These soils formed as a result of atmospheric precipitation accumulating in minor drainless sink holes. Alternating, the soils described above form a heavily differentiated soil cover with small areas of different components.

Alongside with natural soils Valaam has anthropogenic soils. Depending on the way of creation and impact degree the soils are divided into superficially-transformed and deeply-transformed. Deeply-transformed soils belong to agrozems.

Agrozems are noted for a thick humus horizon, neutral reaction and high phosphorus and potassium content (Matinjan et al., 1996). Agrozems include filled soils created in connection with land levelling. The filling was placed on the soil already existing on loose deposits or on gabbro-diabase plate.

Deeply-transformed soils are common in gardens and vegetable plots maintained by the principal church complexes. The largest gardens were established in the main premises of the monastery, where fruit, berries, vegetables, medicinal herbs were grown. Superficially-transformed soils are wide-spread in farmlands.

Farmlands in the island (meadows, pastures) are mainly located in depressions covered with thick deposits free of crushed stone. The soil cover is represented chiefly by drained sod-gley soils. Agricultural uses covered also a smaller share (normally in field margins or near friaries) of podzolic and brown earth soils.

Anthropogenic transformation of the Valaam soils is unstable, while many of their properties are maintained by man.

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