Abstract form

Salt-affected soils in the permafrost zone of Central Yakutia
Galina I. CHERNOUSENKO
V.V. Dokuchaev Soil Science Institute, Russian Academy of Agricultural Sciences,
Pyzhevskiy per. 7/2, Moscow, 119017 Russia
Contact e-mail: chergi@mail.ru
Yakutia occupies 3 103 200 km 2 in the permafrost zone of Central and East Siberia. The
permafrost thickness in Central Yakutia is about 400 m. Salt-affected soils occupy only
0.13% of the total area of Yakutia. In the agricultural zone of Central Yakutia, their role
is more significant: 421 600 ha (38.4%), including 56 600 ha (50.3%) of cropland. They
are developed in thermokarst depressions (alases) within the ancient alluvial plain and
on river floodplains and low terraces in the area of 60º–64º N and 120º–135º E. This is
the area of sharply continental and arid climate. Annual precipitation is about 200–250
mm, and the potential evaporation reaches 350–450 mm/yr. The mean January
temperature is –43.2ºC, and the mean July temperature is 18–19ºC.
The chemistry and genesis of salinization in river valleys and alases of Yakutia are
different. In alases within the ancient alluvial plain, the accumulation of salts took place
in the Early Pleistocene with water flows from the adjacent denuded plateaus composed
of the Palaeozoic calcareous rocks with interlayers of gypsum and soluble salts. In the
middle Pleistocene, these salts were immobilized in the frozen deposits of the Ice
Complex. Permafrost in this area contains 0.1–0.3% of salts with a predominance of
sulphates and bicarbonates of sodium and magnesium. The development of thermokarst
is accompanied by the release of relict salts from thawing rocks and their concentration
in the water of thermokarst lakes upon drying of the latter. At a certain stage of lake
drying, the talik zone beneath it is subjected to freezing. The migration of water to the
freezing front results in the development of hydrolaccoliths (pingo). The freezing is
accompanied by the differentiation of salts due to the precipitation of calcium and
magnesium carbonates, so that sodium salts remain in the solution. In mature alases, an
association of specific alas soils is formed, including salt-affected soda-sulphate and
soda-saline solonchaks, solonetzes, and mucky gley solonchakous soils.
Within river valleys, salt-affected soils—solonchaks, solonetzes, and various variants of
solonchakous soils (meadow-chernozemic, meadow alluvial, and meadow-swampy
alluvial soils) occur on floodplains and on the first and second terraces. The chloridesulphate
and sulphate-chloride salinization predominates; in some soils, soda is also
present. River valleys are the areas of recent salt accumulation. Salts are delivered with
floodwater; partly, they originate from anthropogenic wastes. Several factors favour soil
salinization: (a) the lack of drainage because of the presence of permafrost; (b)
evaporative concentration of flood water under arid climate conditions (the moistening
factor is 0.44); (c) the presence of mesodepressions, in which the stagnation and
evaporation of flood water occurs, (d) the widespread development of technogenic
cryopegs in the alluvial deposits of the Lena River terraces with the salt content of 3–25
g/l and with a predominance of sulphates and chlorides of magnesium and sodium; and
(e) the presence of outcrops of saline Lower Cambrian rocks at the flanks of the valley.
Thus, the geography and genesis of salt-affected soils in Central Yakutia are related to
the local climatic, palaeohydrological, lithological and geomorphic conditions and to
the presence of permafrost.
Key words: soil genesis, soil geography, salt-affected soils, permafrost zone, Yakutia
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