Natural and Manmade (137Cs) Radioisotopes In Holocene Sequnce of The Sheresrtobitovsky Raised Bog In The Barabinsk Forest Steppe (West Siberia)

Abstract The specific activities of natural (7Be, 210Pb) and manmade (137Cs) radioisotopes in a suspended matter of snow water have been determined and the density of their fallouts on the surface of the Sherstobitovsky and Ubinsky raised bogs in the Barabinsk forest-steppe has been assessed at the points of snow sampling during winter period. It has been established that the main concentrator of 7Be radioisotope is a fine fraction of suspended matter (particle size < 0.45 µm) consisting of colloid and dissolved component, 210Pbatm is a coarse-grain fraction composed of dust particles (> 3 µm in size). As an example of the vertical profile of the Sherstobitosky peat bog, the first data on the distribution of natural (238U, 210Pb, 226Ra, and 40K) and manmade (137Cs) radioisotopes have been obtained for raised bogs of the forest-steppe zone in Western Siberia. The pattern for 226Ra and 238U in the nature of their vertical distribution is the same that is traced for 137Cs and 40K. According to our assumption, some increase in activities of these radionuclides is observed in horizons 6–12 cm, as well as in the lower part of the sequence (25–35 cm) is due to the same processes. Migration of 137Cs deep down the peat deposit is largely governed by the magnitude of peat water level fluctuations in both the seasonal and long-term cycle and it is closely related to the surface microrelief of the bog surface. Alongside this, 137Cs, being geochemical analog of the biophilic 40K, is absorbed by plant roots from underlying peat horizons during the dry season of a year. An additional contribution to the high activity of 137Cs in the upper horizons is probably conditioned by input of 137Cs to the surface of Sherstobitosky peat bog involved into atmosphere as a result of peat and forest fires.