RADIOECOLOGICAL RESEARCH OF LANDSCAPES IN THE NATIONAL PARK «SMOLNY»

Abstract

A study of radiation level in the recreational areas is of scientific and practical interest.  For this reason, the goal of the paper is to assess the distribution of radionuclides ¹³⁷Cs, ²²⁶Ra, ²³²Th and ⁴⁰K and to calculate the irradiation level in the major types of  locality of western cluster in the national park “Smolny”. In such a case, the following tasks were to be solved: to carry out radio ecological studies on the index plots and along the landscape profiles; to determine the vertical and horizontal distribution of radionuclides in soil cover and to define the intensity of accumulation in vegetation; to calculate the rate and  the structure of gamma-radiation intensity in the considered geosystems. The study was carried out on the basis of a landscape approach using field and laboratory methods of gamma-ray spectrometry. Results. It was determined that the level of  surface contamination of soil with ¹³⁷Cs varied within 6.1–6.8 kBq /m² in the ridge and its slopes, 11,2–15,6 kBq /m² - in the bottom-land, and up to 22.7 kBq /m²  - in the terrace above flood-plain  in south-eastern outskirts of  first terrace rising above the floodplain of the cluster. At that, the content of ¹³⁷Cs in the upper 0-5 сm layer of forest soils is 83-90 % ¹³⁷Cs, but the content of ¹³⁷Cs in floodplain soil is 48-50 %. The terrain and the nature of geological substrate in the moment of radiological fallout in spring-1986 had a major impact on the horizontal distribution of ¹³⁷Cs. Volume activity of terrigenous radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K in the soils is determined with the mineral composition of  parent rock materials: it is minimum in the sandy forest soils (thus, it is 3-17, less than 8 and 40-100 Bq/kg), maximum - in the floodplain soils (thus, it is 17-28, 33-37 and 490-600 Bq /kg). Distribution of terrigenous radionuclides in depth is of steady rate, except for ²³²Th, which is  recognized with biota and is not accumulated in the organic horizon. Gamma background in the considered geosystems meets the norms of radiation security. Contribution of soil nuclides (¹³⁷Cs, ²²⁶Ra, ²³²Th and ⁴⁰K) in formation of the equivalent dose  rate of gamma radiation is 37-62 % in forest plots,  up to 100 % - in the agricultural bottomland plot, thence, it is possible to define the contribution of radionuclides in vegetation. Maximum intensity of accumulation of ¹³⁷Cs (for air-dry weight) is revealed in fruit bodies of mushrooms (Tf  = 78 10^-3m²/kg), male shield fern (Tf = 49 10^-3m²/kg) and true mosses (Tf = 1-9 10^-3m²/kg). Accumulation of ¹³⁷Cs in vegetation is minimum (Tf < 1 10^-3m²/kg) in rich in mineral nutrition soils (river basin soil) and in close deposit of underlying mudrock (ridge).