Ninth International Conference on Permafrost ... - IARC Research

Cryological Status of Russian Soils: Cartographic AssessmentT.V. Ananko, D.E. Konyushkov, E.M. NaumovV.V. Dokuchaev Soil Science Institute, Russian Academy of Agricultural Sciences, Moscow, RussiaSoil maps contain valuable information on the cryologicalconditions encoded in the names of soils and in knowledgeof soil morphogenetic properties. In the new Russian soilclassification system (Shishov et al. 2004), the presence andcharacter of permafrost are not taken into account (exceptfor an order of the cryoturbated nongley soils, Cryozems).A separate classification of soil cryological regimes issuggested (Sokolov et al. 2006). The following criteria aretaken into account.(I) The presence/absence of permafrost and seasonalfreeze-thaw processes: (1) seasonally thawing soils (thedepth of winter freezing exceeds the depth of summerthawing, the freezing layer merges with the permafrosttable), (2) seasonally freezing soils (permafrost is absent oris below the depth of winter freezing), and (3) nonfreezingsoils (cryogenic processes are absent).(II) Duration of the thawed (group 1)/frozen (group 2)state of soils in the root zone (months): long-term (> 5),medium-term (3–5), short-term (1–3), and very short-term(< 1). The stability of soil freezing-thawing patterns ininterannual cycles (stable, unstable, episodic) is consideredas an additional criterion.(III) The ice content in the transient layer of permafrost(group 1) or in the seasonally frozen soil layer (group 2):ice-rich (ice schlieren > 2 mm, the ice volume exceedssoil porosity in the thawed state); medium-ice (fine icesegregations, ice volume is approximately equal to soilporosity); low-ice (separate ice crystals; ice volume is lessthan soil porosity); and dry frost (no visible ice crystals; soilmoisture after thawing is about maximum hygroscopy). Forgroup 2, the ice content in the frozen state can be judgedfrom the soil morphology and from the soil water contentbefore freezing.(IV) Depth of permafrost table (active layer thickness,seasonal thawing depth, cm) (group 1)/depth of seasonalfreezing (group 2): superficial (< 25), shallow (25–50),medium (50–100), medium deep (100–150), deep (150–250),and extremely deep (> 250). The criterion of stability of thethawing/freezing depth may also be introduced (see II).(V) The dynamics of phase transitions of soil water(freezing-thawing): Arctic type (in summer), Boreal type (inspring-early summer and in the late summer-fall), and Subborealtype (in winter). Additionally, the frequency of phasetransitions in the root zone is to be taken into account.A schematic pedocryological map of the FSU developedby us on a scale of 1:35 M (Fig. 1) contains informationon the depth of soil seasonal thawing/freezing, mean annualtemperature at the depth of zero seasonal temperaturefluctuations, soil temperature characteristics at the depthof 20 cm, duration of the frozen state of soils, merging ofpermafrost table with the layer of seasonal freezing, the onesided(from the top) or two-sided (from the top and fromthe bottom) character of soil freezing, etc. It is considered apart of the integral system of soil maps for the FSU (Anankoet al. 1998) developed for the cartographic assessment ofthe proper pedogenic, lithogenic, and regime (water andtemperature) soil characteristics. The initial soil informationwas obtained from the Soil Map of the Russian Federation(1:2.5 M; 1988) and from the State Soil Map (1:1 M). Inthe presented variant, soil polygons are renamed accordingto the WRB system (2006) with due account for the earlierelaborated correlation tables (Goryachkin et al. 2002).Estimates of soil cryological characteristics are based onthe Geocryology of the USSR (1988–1989), the monographsby Dimo (1972) and Romanovskii (1993), and numerousregional works. A fragment of the database to the map isshown in the table below; soil cryological characteristics forthe polygons along meridian 120°E are included in it. Theestimates are given for predominant soils. The real spatialand temporal variability of the cryological parameters withinthe polygons is much greater.Information about cryogenic soil processes (cracking,ice-wedging, heaving, cryoturbation, dehydration, icesegregation, migration of solutes to freezing fronts, etc.) isincluded in a separate database. Their character and intensitydepend on many factors—soil texture, water content, andfreezing intensity being the most important.Mean annual data reflected on the map were obtained from1950–1980. Since the 1990s, a tendency for some warmingof the climate (due to extremely warm winters or extremelywarm summers) has been registered in many regions. Climatechange results in a certain alteration of the soil cryologicalconditions (though its range is much less than the range ofchanges induced by anthropogenic impacts on soils andvegetation). Seasonally freezing soils beyond the permafrostzone become nonfreezing soils, and this phenomenon can betraced not only in the southern parts of European Russia butalso in its northern regions (Mazhitova 2008).In sharply continental regions with a shallow ice-rich andlow-temperature permafrost, the buffer role of the latter inregulation of the soil temperature increases. At the sametime, the upper layers of permafrost, being involved inseasonal freeze-thaw cycles, are subjected to degradation,which in enhanced by the development of thermokarst andthermal erosion in the case of ice-rich permafrost. A negativefeedback in this system may occur due to the more activedevelopment of moss layers on the surface of waterloggedsoils and a gradual increase in insulation properties of themoss and peat in the summer. In the areas of discontinuouspermafrost, soils with a deep active layer merging with thepermafrost table may lose their contact with permafrost. Ingeneral, the cryological response of soils to climate changesis as diverse and complicated as the diversity of differentcombinations of cryological parameters in the soil profiles.5