[en] ⁹⁰Sr and ¹³⁷Сs content in soil and unplanted wood of small size has been measured along the southern fuel trace of Chernobyl fallout, in Ivankov region of Kiev Oblast during 2012 - 2013. At present, due to biogenic and vertical ⁹⁰Sr migration in soil of forests, is reserved in 20-cm rooting-layer, containing less than 0.25 mg-eq of exchangeable calcium per 100 g of soil, reduced by 67 ± 18 % in average. Therefore, contamination of fuel wood with ⁹⁰Sr today is depended weakly on exchangeable calcium content in soil (up to 1 mg-eq/100 g), considering the equal levels of the initial soil contamination with ⁹⁰Sr. Values of ⁹⁰Sr transfer factor (TF) to unplanted wood of deciduous trees and pine mounted to 34 ± 20 and 61 ± 56 (Bq/kg/(kBq/m²), in average, that is in dozens exceeded the values, recommended by IAEA. In practice, at total area of Ivankov region there exist a risk to overrun hygienic norm value of ⁹⁰Sr content in fuel wood, and brushwood. (authors)

[en] ⁹⁰Sr and ¹³⁷Cs content in soil and unplanted wood of small size has been measured along the southern fuel trace of Chernobyl fallout, in Invok region of Kiev Oblast during 2012 - 2013. At present, due to biogenic and vertical ⁹⁰Sr migration in soil of forests, is reserved in 20-cm rooting-layer, containing less than 0.25 mg-eq of exchangeable calcium per 100 g of soil, reduced by 67 ± 18 % in average. Therefore, contamination of fuel wood with ⁹⁰Sr today is depended weakly on exchangeable calcium content in soil (up to 1 mg-eq/100 g), considering the equal levels of the initial soil contamination with ⁹⁰Sr. Values of ⁹⁰Sr transfer factor (TF) to unplanted wood of deciduous trees and pine mounted to 34 ± 20 and 61 ± 56 (Bq/kg/(kBq/m2), in average, that is in dozens exceeded the values, recommended by IAEA. In practice, at total area of Ivankov region there exist a risk to overrun hygienic norm value of ⁹⁰Sr content in fuel wood, and brushwood

[en] Statistical and graphical interpretation of ⁹⁰Sr vertical distributions in soil profiles up to a depth of 1.0 m was presented based on the study of the typical Scots pine stands forest at 14 experimental sites within the Chernobyl exclusion zone. Significant differences were found between ⁹⁰Sr activity distribution in soil profiles collected at different sites. The part of ⁹⁰Sr activity below of a depth of 30 cm varied from 15 to 71 %. ⁹⁰Sr transfer factors from soil to anatomical structures of the stem wood were estimated based on values of soil contamination density, which were calculated for the depth of 0.3 and 1.0 m. The statistically significant correlation between the transfer factors of ⁹⁰Sr to stem wood (heartwood, sapwood) and its vertical distributions in soil profiles have not been observed. Among the forest inventory parameters for pine stands only the average diameter of trees significantly correlated with ⁹⁰Sr transfer factors to stem wood. (authors)

[en] This paper presents a developed mathematical model of biogenic fluxes and depots of ⁹⁰Sr for pine stands (Pinus sylvestris L.) of the Chernobyl Exclusion Zone. We separated 26 compartments of the mathematical model including ten-centimeter soil layers - 10 pcs (up to a depth of 1.0 m), 3 layers of forest litter (undecomposed vegetable matter, fragmented organic materials, humus), 12 components of live aboveground and underground biomass (stem: outer bark, inner bark, sapwood, heartwood; crown: 1 year needle, 2+3 year needle, twigs, branches < 1.0 cm, branches > 1.0 cm; roots: < 0.2 cm, 0.2-2.0 cm, >2.0 cm); and coarse woody debris. During the period of 2016-2019, we obtained observational data on the pine experimental plot on the activity concentration and inventories of ⁹⁰Sr in just listed ecosystem compartments as well as upstream and downstream fluxes of the stand that allowed to find the optimal parameters for equation system of radionuclide fluxes in simulation mathematical model using a minimization of the sum squares of deviations the objective function by the stochastic gradient descent method. The analysis of previous studies on the redistribution of hot particles and their leaching during the first years after the Chernobyl accident allowed us to establish the probable frequency distribution of the studied radioisotope between compartments in 1987. We have used these indicators as starting points for the developed model. The output results of the simulation made an estimate of the dynamics of the ⁹⁰Sr inventories redistribution between the elements of biocenosis in the interval 1990-2035. The time series of radioisotope aggregated transfer factors from soil to stem wood and stem with bark have been identified. The increase of ⁹⁰Sr aggregated transfer factors calculated based on soil contamination density up to a depth of 0.2 m and ^stabilization of aggregated transfer factors of study radionuclide obtained during their calculation using the density of soil contamination at a depth to 1 m are revealed. This indicates a significant impact of vertical migration on the values of the parameters mentioned above. Therefore, the estimation of ⁹⁰Sr content in biomass components using aggregated transfer factor which have been calculated on recent observations according to standard accepted radioecological monitoring approaches, where radionuclide contamination density was measured only at a depth of 0.2 m, and also by applying early geo data of contamination (to 2000), may contain significant systematic errors toward overestimation of ⁹⁰Sr content in the elements of the pine stem. (authors)