Vertical distribution of Sr90 and Cs137 in the bottom sediments of rivers and lakes

It is shown that the maximum concentrations of caesium-137 are observed at the surface of bottom sediments in sections of rivers with a very weak current because sorption processes predominate over desorption processes. The processes of caesium-137 desorption from the surface layer of bottom sediments predominate in sections of rivers with a strong current, so that the concentration of the isotope in the surface layer diminishes. Strontium-90 is washed off the surface of bottom sediments more easily than caesium-137; as a result, the caesium-137/strontium-90 ratio rises. The maximum concentrations of these isotopes are observed at the bottom sediment surface in lakes with no drainage and in the water at some depth in lakes with drainage, as the isotopes are washed off the bottom sediment surface. A second caesium-137 and strontium-90 concentration maximum was observed at a depth of about 0.5 m; in the opinion of the authors, it is associated with the period of intensive radioactive fall-out in 1963. (V.A.P.)