Saturday, 15 July 2006

Cambisols and Luvisols - “Zonal” Soils of East-European Tundra.

Valentine D. Tonkonogov, Dokutchaev Soil Institute, Russian Agricultural Academy, h. 7, Pyzhevskiy pereulok, Moscow, Russia and Sergey V. Goryachkin, Institute of Geography, Russian Academy of Sciences, Staromonetny, 29, Moscow, 119017, Russia.

It was widely accepted after Yu.Liverovsky and E.I.Ivanova that “zonal” soils of Eurasian tundra are mostly Gleysols (with deep permafrost) or Gleyi-Turbic Cryosols which are equivalent to Russian “Tundra gleyic soils”. Traditionally, “zonal” soils are loamy ones with perfect drainage. J.Tedrow (1977) criticized Russian colleagues for distinguishing of “zonal” soils with well-pronounced gleyzation within profiles. He proposed “Arctic brown soils” to be “zonal” for the most of territories to the north of the treeline. However, a lot of well-drained sandy and skeletic soils occurred in this group of soils - they were distinguished as “Podboors” in Russian literature (Targulian, 1971). So, the situation with understanding of “zonal” soils in tundra, and particularly, in the level and poorly drained East-European tundra is very intricate. We investigated the diversity of soils on silty loams with admixture of pebbles, which are widespread in tundra of East Europe. In rare cases they have permafrost within upper 1 or 2 m. Basing on genetic approach, the studied soils can be correlated as 5 soil (sub)units. 1. Gleysols (or Gleyi-Turbic Cryosols). They are characterized by bluish-olive gleyic horizon beneath litter and raw humus horizons. They may have thixotropic and cryoturbic features and rusty ferruginous local accumulations in profiles. Deep horizons are of brownish-olive color. These soils are widespread but they are not well drained and cannot be considered as “zonal” ones. 2. Cambisols. Profiles consist of litter or raw-humus horizons and cryometamorphic horizons, differed from parent material by subangular- and angular-blocky structure, caused by frost action. There are no pronounced gleyic features in profiles. Permafrost usually is deeper than 2 m. 3. Luvisols. Profiles consist of litter or raw-humus horizons, eluvial horizons with subangular- and angular-blocky structure also caused by frost action and argic horizon with clay coatings and increase of clay fraction content in middle horizons. Permafrost usually is deeper than 2 m. 4. Humic Cambisols or Haplic Phaeozems. They are soils with dark crumb-structured humus horizon with 3-4% of organic carbon in upper 10-cm and with 1.5-2% of C in next 10-15 cm. These horizons are underlain by cambic subangular- and angular-blocky horizon. These soils are formed in hollows under meadow vegetation. These soils are widespread but their areas are very small. They occupy very specific slope positions and therefore cannot be considered as “zonal” soils. 5. “Cambic” Stagnosols. Soils are characterized by combination of stagnic and cryometamorphic horizons. Stagnic features are in upper 20-25 cm. In often cases thixotropy takes place here. According to traditional definition of “zonal” soils Cambisols and Luvisols are “zonal” soils of East European tundra. They have only weakly pronounced stagnic or gleyic features, they are mostly well drained and they are developed from loamy materials. At the same time they are usually cryoturbated, however, the presence or absence of permafrost layer within 2 m does not play significant role, if any, in the horizon stratification of soil profiles. Thus, in spite of the fact that the most widespread soils in East European tundra are poorly drained Gleysols or Stagnosols for “zonal” soils cryometamorphic Cambisols and Luvisols should be recognized. They could be placed in the “Arctic brown soils” concept of J.Tedrow.

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