Ninth International Conference on Permafrost ... - IARC Research

Differential Estimates of Organic Carbon Poolsin Permafrost-Affected Soils of RussiaD.E. Konyushkov, D.I. Rukhovich, N.V. Kalinina, E.A. DolininaV.V. Dokuchaev Soil Science Institute, Russian Academy of Agricultural Sciences, Moscow, RussiaAt present, a challenge for Russian cryopedologists is toperform differential estimates of organic carbon pools inpermafrost-affected soils of Russia on the basis of digitizedversions of the 1:2.5 M and 1:1 M scale soil maps. Thiswork is hampered by the absence of adequate databases.For permafrost regions, along with data on the thickness andbulk density of soil horizons and the organic carbon contentin them, the databases should include information on the realsoil cover complexity, differentiation of thawing depths, theice content in the soil and the presence of massive ice bodies;the content of gravel and coarser fragments (particularly, forCentral and East Siberia); and the depth to the lithic contact.It is important to distinguish between the organic carbon inmineral horizons, the organic carbon in peat layers, and theorganic carbon in litter horizons. The organic carbon pool inthe transient permafrost layer is a separate problem, as thereare little data on the carbon content in it.Permafrost regions occupy nearly two-thirds of Russiaand encompass a wide range of ecosystems with differenttypes of carbon turnover and soil organic carbon (C org) pools:(a) surface accumulation of organic matter in litter, peat, andraw-humus horizons; (b) soil humus accumulation in situdue to the decomposition of root residues; and (c) illuviationof mobile humic substances into humus-illuvial horizons.The real distribution of C orgis a result of variouscombinations of these processes. A specific feature ofpermafrost-affected soils is the cryosequestration of C orgdueto (a) cryoturbation and (b) the rise of permafrost table uponthe surface accumulation of organic matter, so that the lowerpart of organic horizons becomes frozen. Another specificfeature is the high spatial variability of soil horizons andtheir intermittent character. In Siberia, these soils are oftendeveloped from the residuum of hard bedrock and have highpebble content. The high ice content and the presence of icewedges are typical of heavy-textured and peat soils. Thesefeatures should be taken into account in calculations of C orgreserves in permafrost regions.Three major works on carbon reserves in Russian soils arebased on different cartographic sources. Orlov et al. (1996)used the Soil Map of the USSR (1984, 1:16 M); only majorzonal soils were considered. Rozhkov et al. (1996) used amore detailed Soil Map of Russia and Contiguous Countries(Gerasimova et al. 1995; 1:4 M); the carbon stored in surfaceorganic horizons and the carbon of soil carbonates wereseparately calculated. Nilsson et al. (2000) and Stolbovoi(2002) used a generalized version of the Soil Map of theRussian Federation (Fridland et al. 1989; 1:2.5 M). Thegeneralized version (1:5 M) contains 168 mapping units and1300 soil polygons.In fact, the original map contains 35,000 soil polygons;its legend includes 205 names of individual soils and nearlyFigure 1. Soil polygons on the 1:2.5 M scale map over the Circum-Arctic Map of Permafrost and Ground-Ice Conditions (fragment).100 names of unique soil combinations (soil complexes).The latter are especially typical of the permafrost regions ofRussia. The soil cover complexity in the permafrost zone isconsiderable. Thus, within the permafrost zone of EuropeanRussia, 1055 soil polygons encompassing 55 differentsoils can be found on the 1:2.5 M scale map (Fig. 1). Tocalculate the reserves of C orgon the basis of this map, theattribute database to the digitized version of the map has tobe developed.At present, such a database exists for the upper (20 cmthick) soil horizons and, separately, for litters. On thisbasis, the organic carbon density values used for modelingpurposes have been calculated for the European part ofRussia (Rukhovich et al. 2007). Figures 2 and 3 illustrate thedistribution of C orgreserves in the 20 cm thick soil horizons(both mineral and peat soils have been taken into account)and in mineral horizons + litters, respectively. It is seen thatthe reserves of C orgstored in litter horizons play a significantrole in the total organic carbon pool within the permafrostzone of European Russia.However, the database is still incomplete; information onthe organic carbon contents and bulk density of the deepersoil horizons is insufficient for final calculations. Informationon the content of gravel and coarser fragments is also to becompleted for the particular polygons. Finally, in order tocalculate C orgreserves in the active layer, information onthawing depths is essential.These problems become more complicated in the case ofcalculations for the entire permafrost zone of Russia. Thedatabase for the map is being developed. The great variabilityin the soil properties within this vast territory has to be takeninto account. A given genetic soil unit may be developed141