Investigation of radionuclides in the Yenisey River floodplain systems: Relation of the topsoil radionuclide contamination to landscape features

• 137Cs short-distance heterogeneity was analyzed in the middle Yenisey floodplain
• 60Co and 152,154Eu depth distribution in different landscape positions was analyzed.
• Radionuclide burial patterns depend upon contamination history, elevation, and lithology.

Landscape–radiometric survey and soil sampling performed in the islands of Beriozovy and Balchug (20 km downstream the Krasnoyarsk Mining and Chemical Combine), and in the Mikhin Island (180 km downstream) showed that the distribution of technogenic radionuclides depends upon the history of contamination and landscape features of the floodplain. Contamination densities of 137Cs appeared to be significantly higher than could be expected from global fallout (1.75–2.5 kBq/m2): in 2000 the maximum value for 137Cs in the Beriozovy Island equaled 663 kBq/m2, in the Balchug site — 577 kBq/m2 and in the Mikhin Island — 518 kBq/m2). 137Cs contamination density was practically independent of the remoteness from the KMCC that proved its considerable migration in the water-soluble or fine particulate forms. Vertical distributions of man-made nuclides in soil cores depended upon the different half-life of the studied radionuclides, the soil profile relative altitude, its structure and texture. The two main burial depths of 137Cs activity depended upon the intensity of sedimentation and varied from 5 cm to 20–25 cm. In 2000 maximum contamination by 60Co and 152,154Eu isotopes was associated with the top layer and decreased exponentially with depth.Obtained data is believed to be important for ecological monitoring of the flood plains subjected to radionuclide contamination.