Natural and manmade (137Cs) radioisotopes in Holocene sequence of the Sherstobitovsky 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 the winter period. It has been established that the main concentrator of the 7Be radioisotope is a fine fraction of suspended matter (colloidal particles <0.45 μm in size and dissolved component). For 210Pb, it is a coarse-grain fraction (dust particles >3 μm in size). The first data on the distribution of natural (238U, 210Pb, 226Ra, and 40K) and manmade (137Cs) radioisotopes have been obtained for raised bogs in the forest-steppe zone of Western Siberia. Migration of 137Cs deep down the peat deposit is largely governed by the magnitude of peat water level fluctuations during both the seasonal and long-term cycles and is closely related to the surface microrelief of the bog surface. Moreover, 137Cs, being the geochemical analogue of the biophilic 40K, is absorbed by plant roots from underlying peat horizons and transferred to the upper horizons during the dry seasons. An additional contribution to the high activity of 137Cs in the upper horizons is probably conditioned by its deposition on the surface of the Sherstobitovsky peat bog during its atmospheric transport as a result of peat and forest fires.