Ecological features of radionuclide accumulation by components of ground ecosystems of the exclusion zone

Abstract

The studies were carried out 30 years after the Chernobyl accident on the lands of the former land use subject to natural successional changes. The patterns of the lateral distribution of 137Cs, 90Sr, 241Am in the upper 20-cm soil layer of various biogeocenoses, including those depending on the height fluctuations of the relief, have been studied. The values of the coefficient of variation (V) of the content of radionuclides in the upper soil layer decrease with the time that has passed since the accident. The highest value of the coefficient of variation (75.2 %) was obtained for 90Sr in the soil in the pine forest. The influence of various soil conditions on the entry of radionuclides into birch sap, cap mushrooms, and meadow grasses was studied. Despite the significant excess of the density of soil contamination with 137Cs of all the studied communities (up to 9.1 times), its volumetric activity in the juice is significantly lower than 90Sr, which indicates a lower availability of 137Cs compared to 90Sr. Dynamic processes of accumulation of radionuclides during the entire period of the movement of sap are studied. With increase in extent of moistening of the soil, accumulation of radionuclides in mushrooms tends to decrease. At the same time differences between types is established that connected with feeding habits of mushroom and variability of microclimatic conditions. The effect of soil moisture content, the ratio of 137Cs mobility forms in the soil on the biological availability of the radionuclide by meadow grasses was studied. A decrease in the specific activity of radionuclides in the plant components of ecosystems was found as the phytocenoses moved away from the epicenter of the accident at an identical density of soil contamination. A relationship has been established between the accumulation of radionuclides and the agrochemical parameters of the soil: maintenance of humus, absorption capacity, cation exchange capacity, hydrolytic acidity, content of exchange phosphorus, concentration of mobile calcium, magnesium and potassium on post-agrogenic lands. The analysis of the soil-to-plant transfer factors (Cf) and aggregated transfer factors (Tag), the discrimination coefficient (DF) of 137Cs by a chemical analog element (potassium) was carried out. Species features of plants associated with the transport of K+ - Cs+ cations make significant adjustments to the mechanisms of 137Cs accumulation. Attention is drawn to the significant increase in the concentration of 90Sr in all components in recent years.