ARE THE PEDOGENIC CARBONATE THE SOURCE OR THE SINK FOR CO2 IN RUSSIAN SOILS?

The role of soil carbonate as a buffer reservoir for atmospheric CO2 is not clear. Some scientists suggested that pedogenic carbonates can serve as a one of the possible sink of the CO2. In the present study, the temporal dynamics of pedogenic carbonate formation during the last 5000 years was examined using buried palaeosoils under archaeological barrows of different ages. Carbon isotope composition ranged from -2,5 ‰ to-10,3 ‰ which suggested the carbonates comprised lithogenic fragments and pedogenic components. In general, the concentration of pedogenic carbonates depends on the type, age and the parent material of the soils. Two carbonate accumulation phases during 4000-3500 and 2300 radiocarbon years B.P. occurred during the aridization of a climate. Earlier we demonstrated that in general, the bulk carbonate was leached from the profile and entered the carbon cycle. On the other hand, the dissolved lithogenic fragments served as a source of calcium-ion for formation of pedogenic carbonate. Demkin (1997) demonstrated that during the last 3500 years a considerable amounts of gypsum was leached from these soils and that the calcium-ions of this gypsum served as a source for pedogenic carbonate formation. The bulk carbonate formation in soils reached a value of 46 kg/m2 in chernozems, 57 kg/m2 in dark chestnut soils, 77 kg/m2 in light-chestnut soils. Contrastively, in the same time period, the formation of pedogenic carbonate reached only 6,6; 3,4; 2,6 kg/m2 respectively. This implies that dissolution and leaching of bulk carbonate was significantly higher compared to accumulation of pedogenic carbonate. Consequently, the Russian soils have served as an additional source of CO2, in spite of some of the CO2 being locked in as pedogenic carbonate. The soil carbonates are the source of CO2 and provide about 2,6% of common emission of CO2 from the soils.