DYNAMICS OF CS-137 IN THE FORESTS OF THE 30-KM ZONE AROUND THE CHERNOBYL NUCLEAR-POWER-PLANT

Dynamics of the Cs-137 content in the components of the forests in the 30-km zone around the Chernobyl nuclear power plant (NPP) in 1986-199 4 are associated mainly with such factors as the size of radioactive p articles in the fallout, ecosystem humidification and soil type, tree age. The influence of particle size was especially noticable between 1 986-1987 and was displayed by low biological availability of radionucl ides in the near part of the zone (within the 10-km radius circle arou nd the NPP) in comparison with more distant regions (within the 30-km radius circle). Later, the expression of this influence decreased and transfer factor (the ratio of Cs-137 content in overground phytomass t o the soil contamination density) became approximately the same for al l plots with similar ecological and fallout characteristics. Humidity of landscape and soil type determined the velocity of radionuclide ver tical migration in the soil and Cs-137 biological availability. These parameters were maximum for the hydromorphic soils of wet landscapes e nriched in organic substance and poor clayey minerals. Differences of Cs-137 accumulation in overground phytomass of trees caused by tree ag e are displayed in the higher Cs-137 concentration in structural parts of young trees as compared with old ones. Copyright (C) 1997 Elsevier Science B.V.