The history of the Chernobyl 137Cs contamination of the flood plain soils and its relation to physical and chemical properties of the soil horizons (a case study)

A study of the 137Cs distribution and mobility in alluvial soil profiles was performed in the basin of the Iput river (Bryansk region) to reveal peculiarities of the flood plain contamination after the accident at the Chernobyl NPP. Four study plots have been located on the medium and low-level riverside flood plain of the rivers Iput and its right tributary Buldynka. Soil profiles were sampled manually and continuously in the increasing increments of 2 to 5 cm down to 50 cm below the soil surface. Soil profiles have been analysed for the 137Cs specific activity, organic matter content, granulometric composition, absorbed bases, exchangeable potassium and 137Cs, mobile iron and manganese and mineral composition of the clay fraction (< 0.001 mm).Performed case study showed that modern distribution of the Chernobyl radiocesium in natural alluvial soils is closely connected to the history of contamination of the particular geomorphological elements of the flood plain and the physical and chemical properties of the hosting soil horizons. Dynamic processes of the alluvial soils development under flooding conditions are believed to cause periodical enhanced mobilization of radiocesium supporting the relatively stable values of radiocesium transfer factor to local vegetation and food chains observed in the region since 1988–1992.