Soils

Рубрикатор / City Topography/Nature and Natural Phenomena
SOILS, topsoils and subsoils have retained their original composition outside city residential areas, and partly transformed in the city's gardens and parks. The soil cover of St. Petersburg has a characteristic multilayer texture conditioned by the climate, parent rocks, drainage, microclimate, and vegetation. There are also soils of various mechanical compositions: medium and light loamy moraine soils and glaciolacustrian loam soils; clay sand and sandy soils, as well as sandy soils on a loam glaciolacustrian bedding and alluvial sands. Inclusions of boulders are common (in the course of agricultural development they were discarded thus one can observe hummocky boulder piles collected by hand). Soil stoniness amounts to 60-80 cubic meters per hectare, and around the Karelian Isthmus - up to 200-500 cubic meters per hectare. Medium and light loamy soils are more common, and have a higher potassium and calcium content in comparison to sandy loam and sandy soils. Loam sandy soils on a carbonate bedding are the most fertile ones and are found in the area of Izhora Plateau. Loam sandy and sandy soils are typical for the landscape of the Karelian Isthmus, Neva Lowland, in the pre Baltic Glint part of the coast of the Gulf of Finland, in the Luga River basin. As for genesis, most of the encountered soils are podzolic, developing under forests, mostly coniferous. Moisturized forest bedding supplies the emerging soil with nutritious elements, at the same time the lower strata are washed out alongside with humus. Thus podzols are characterized by a light upper level (podzolized) and illuviation in the lower horizons, usually of a fulvous colour. The degree of podzolization depends on the washout intensity and the composition of the parent rocks. Here the medium and light podzol soils dominate; are poor in humus content and have high acidity content. Rich podzolic soils develop usually in lows on loam sands, under fir woods; medium podzolic soils - on the upland. Places with high drainage density such as sands and loam sands with a low moisture-trapping ability (mostly under pine woods) amidst a hilly environment create conditions for the development of more fertile light podzolic soils, which are abundant on the Karelian Isthmus. Soddy-podzolic soils emerging in herbaceous vegetation are common in felled areas, as well as in places with thin mixed and small-leaved forests. Within Izhora Upland it is rendzina soils that are most frequently to encounter, displaying the best qualities. The lowland and plain, usually characterised by a poor drainage capacity and sometimes a high ground water level create conditions for the development of swamp-like soils common for the surroundings of St. Petersburg and its territory prior to its residential development. Presently they are found in the South-West and around Lake Dolgoe and the Kamenka River. The superfluous moisture and poor oxygen supply prevent a complete decomposition of organic substances which results in the formations of peat in the upper stratum of the specific soil. Another typical characteristic of this kind of soil is a grey rusty unstructured gley with low porosity, which hampers vegetation growth. As to the peat accumulation rate and gleyness in swamp-like soils there are podzol gleys, peat podzol gleys, peat gleys and swamp peat soils. Many of these soil types became quite fertile after drainage, like those occurring in Neva Lowland and Ladoga Lowland. Alluvial soils with high humus content develop on intertidal meadow terraces develop from river drifts, however, the area is limited and they rarely occur in the lower course of the Volkhov River, Luga River, and Svir River. Most of the soils in the surroundings of St. Petersburg provide favourable conditions for forest vegetation growth, yet their natural fertility is insufficient for good agricultural crops: it requires additional fertilization and drainage. The soil under urban plantation is heavily contaminated by heavy metals.

References: Природа Ленинграда и окрестностей. Л., 1964.

Y. P. Seliverstov.