Distribution Of 137Cs In Soils Research Articles

Features of the modern distribution of 137Cs in soils under overmoistened growth conditions of black alder forests in Zhytomyr Polissia, Ukraine

Research on the modern distribution of 137Cs in soils of different forest site types in black alder (Alnus glutinosa (L.) Gaerth.) stands was conducted. In forest litter, there is not a high percentage of its total activity in soil: in moist fairly fertile site type (C3) – 13.4 %, damp fairly fertile site type (C4) – 16.3 %, and wet fairly fertile site type (C5) – 3.8 %. The mineral part of the soil in moist and damp fairly fertile site type is characterized by decreased density of radioactive contamination of soil layers with depth. In wet fairly fertile site type, this indicator increases to a depth of 6 - 8 cm and decreases with further deepening. A 10-cm layer of moist fairly fertile site type (C3) contains 61.8 % of the total radionuclide activity in soil, damp fairly fertile site type (C4) – 68.1%, and wet fairly fertile site type (C5) – 70.1 %, correspondingly; a 20-cm layer has 75.4, 78.3, 91.9 % and a 30-cm layer – 80.9, 82.2, 96.0 % of the total radionuclide activity.

Modeling long-term transfers of radiocesium in farmland under different tillage and cover crop treatments

The 2011 nuclear accident at Japan's Fukushima Daiichi Nuclear Power Plant (FDNPP) prompted inquiries about the long-term transfer of Cesium-137 (137Cs) from soil to agricultural plants. In this context, numerical modeling is particularly useful for the long-term evaluation of the consequences of agroecosystem contamination. Agricultural practices, such as tillage and cover cropping, play key roles in 137Cs recycling in agroecosystems. In this study, we used 10-year monitoring data to develop a dynamic model to predict 137Cs redistribution (via uptake, litterfall, translocation, and percolation) under different tillage (no-tillage, NT; rotary cultivation, RC; moldboard plow, MP) and cover crop (rye; hairy vetch; fallow weed) treatments. The verification exercise and assessment results indicated the model's reliability, as the temporal dynamics of predicted values agreed with observed values. Tillage significantly influenced the 137Cs distribution in soil, thereby decreasing plant uptake of 137Cs, whereas cover crop exerted a minimal effect on 137Cs cycling. Furthermore, while the 137Cs concentrations in soybean grain under RC and NT treatments were comparable 62 years after the FDNPP accident, the concentration under MP treatment remained consistently the lowest. Despite natural decay being the main cause of the decreased global 137Cs level in the agroecosystem, with minimal losses from percolation to deeper soil layers and soybean harvesting, adopting an appropriate tillage practice was shown to promote a long-term reduction of 137Cs concentration in crops. Finally, to improve the model's accuracy, further research should consider incorporating the effects of soil properties and extreme weather events on 137Cs flow into the model, as these factors are essential for realizing improved agroecosystem predictions.

Long-term study (1987-2023) on the distribution of 137Cs in soil following the Chernobyl nuclear accident: a comparison of temporal migration measurements and compartment model predictions.

After the Chernobyl accident, a designated area of ~1000m2 within the University farm of Aristotle University of Thessaloniki in Northern Greece was utilized as a test ground for radioecological measurements. The profile of 137Cs in the soil was monitored from 1987 to 2023, with soil samples collected in 5-cm-thick slices (layers) down to a depth of 30cm. The mean total deposition of 137Cs in the area, backdated to the time of the Chernobyl accident, was determined to be 18.6±1.8kBqm-2 based on four follow-up profile measurements of 137Cs in the soil for the years 2022 and 2023. It is noteworthy that this value is similar the total deposition at the site, which was independently measured to be about 20kBqm-2 during the first year after the Chernobyl accident. The fractional contribution of each soil layer (e.g., 0-5cm, 5-10cm, 10-15cm, etc.) to the total deposition of 137Cs (0-30cm) is presented and analyzed. A compartment model was utilized to forecast the temporal evolution of fractional contributions of the different soil layers to the total deposition of 137Cs (0-30cm). In this model, each soil layer is represented as a separate compartment. The model assumes that the transfer rates between adjacent compartments are equal. The agreement between the measured fractional contributions and the model predictions suggests that the compartment model with equal transfer rates can capture the broad patterns of 137Cs migration within the soil layers over the long period of 1987-2023. However, the use of a second compartment model with increasing transfer rates between consecutive soil layers did not align with the observed outcomes. This indicates that diffusion may not be the primary migration mechanism over the 36-y period covered by our study.

Assessment of secondary radioactive contamination of a decontaminated land plot located on the territory of a recreation base in a wooded area

The article presents results of a long-term (1998–2021) radiological monitoring survey of a recreation base located in a wooded area in the zone of radioactive contamination after the accident at the Chernobyl nuclear power plant. Local mechanical decontamination of the soil had been made on the territory of the base in 1997. The evaluation of the secondary radioactive contamination of the decontaminated territory was performed by comparing dynamics of the radiological situation at the treated plot and the control, nondecontaminated, part of the base according to four main criteria: 1) dose rate of gamma radiation in the air from cesium radionuclides; 2) inventory of 137Cs in soil; 3) vertical distribution of 137Cs in soil; 4) activity concentration of 137Cs in plants and fungi. In 1998, the value of the 137Cs inventory in the upper 20 cm of soil in the control part of the territory of the base and in the decontaminated plot was 930 kBq/m2 and 143 kBq/ m2, respectively. By 2015, the value of the 137Cs inventory in the control area and the decontaminated plot had significantly decreased: by 35% and 36%, respectively. A decrease in the dose rate of gamma radiation in the air at the decontaminated plot and control area proceeded at the same rate, which is currently mainly determined by the decay of 137Cs. There was a gradual self-restoration of the forest ecosystem at the plot subjected to decontamination. Activity concentration of 137Cs in biota (pine, edible mushrooms) in the treated plot was many times lower than that in the control part of the recreation base. In general, there was no significant secondary radioactive contamination of the decontaminated plot in the 24 years after the intervention.

<sup>137</sup>Cs Pollution in Soils and Plants of Urban Ecosystems Near the Elektrostal Heavy Machinery Plant

In urban ecosystems to the west of the Elektrostal Heavy Machinery Plant, 6 years after the radiation incident, local areas with a total area of 0.2 km2 with an increased equivalent dose rate of γ radiation of 0.15–0.40 μSv/hour and a high specific activity of 137Cs reaching 8328–8740 Bq/kg in the upper soil horizons were identified. Statistically significant direct correlations were noted between the specific activity of 137Cs in a layer of 0–10 cm of soil and the equivalent dose rate of γ radiation at the surface and height of 1 meter. The types of vertical distribution of 137Cs in soils of polluted urban ecosystems, including those on which earth decontamination works were carried out, have been determined. The calculated 137Cs transfer coefficients increase in row of tree: Salix alba Sórbus aucupária Ácer platanoídes Malus domestica Alnus incana Ácer negúndo; and grassy vegetation: Týpha angustifólia Artemísia vulgáris Tussilágo fárfara Cirsium arvense Urtíca dióica.

Soil technogenic radioactivity in the vicinity of the Morzhovets Lighthouse (the Morzhovets Island, Archangelsk region)

The aim of the study was to assess soil technogenic radioactivity in the vicinity of the Morzhovets Lighthouse and surrounding areas by measuring radio caesium (137Cs) specific activity. Location and time of the study. Field work was performed in the area around the Morzhovets Lighthouse (the Morzhovets Island, Archangelsk region) in summer 2022. Methods. Soil samples were collected at 26 sites from the 0-5 cm layer, of which at 12 sites soil samples were collected also from 5-10 и 10-20 cm layers. Aboveground phytomass was sampled as well. In the laboratory the soil samples were air-dried and placed in the Marinelli vessel for measuring 137Cs specific activity by gamma-spectrometry. Registration of the gamma-radiation from the measured soil sample, as well as processing of the obtained spectra were performed using the Progress-gamma software and hardware complex FVKM.412131.002-03. The energy calibration of the gamma spectrometer to control the safety of the setup parameters was carried out after each measurement using a combined control source OISN-137-1 in a Marinelli vessel. The minimal exposure time of the study sample was 3600 sec; however, the time was increased for some samples with low activity. Results. The territory of the Morzhovets Island is occupied by the lowland seaside terraced plane landscapes with tundra vegetation on the peaty podsolised illuvial humus soils, alternating with mires. Caesium specific radioactivity in the top 0-5 cm soil layer, represented by poorly decomposed peat horizon, was found to vary from 9.4 to 144.5 Bq/kg in the peaty illuvial-humus podzol (Gleyic Histic Entic Podzol) and from 12.2 to 139.4 Bq/kg in the bog peat gley soils (Fibric Histosols (Gleyic)). The radio caesium specific activity was shown to decrease sharply with soil depth, reaching the 3 Bq/kg detection limit of the gamma-spectrometer. Comparative analysis of the data showed that in the West Arctic sector 137Cs specific activity decreases from the east to the west, with increasing distance from the Novaya Zemlya, from 80.2 Bq/kg (the Novaya Zemlya Archipelago) and 80.7 Bq/kg (Bolshezemelskaya Tundra) to 19. 2 Bq/kg (the Svalbard Island). Conclusions. The 137Cs distribution in soil of the Morzhovets Island showed the persistent fixation of the element by the upper 5 cm-thick organic part of the soil profile, representing the primary biogeochemical barrier. The vegetation does not accumulate technogenic radioactivity. Overall, the 137Cs distribution in soils around the Morzhovsky Lighthouse displays a medley pattern. The maximal 137Cs specific activity values were measured both in the peaty illuvial-humus podzol and bog peat gley soils.

In situ determination of 137Cs inventory in soil using a field-portable scintillation gamma spectrometer-dosimeter

A new empirical method for in situ determination of the inventory of 137Cs in soil (ACs, kBq m−2) at grasslands and forests using a field-portable NaI(Tl) scintillation spectrometer-dosimeter was developed. The method is based on evaluation of the ambient dose equivalent build-up factor. The practical implementation of the new method with the spectrometer-dosimeter does not require a priori knowledge of the vertical distribution of 137Cs in soil. Moreover, the method allows assessing a value of the mean migration depth of 137Cs in soil (Z) in terms of g cm−2. The 95% confidence interval for the mean value of the conversion coefficients from the ambient dose equivalent build-up factor to ACs and to Z is less than 10%. The new method has been developed and verified using published data that where obtained at territories in Russia and Belarus heavily contaminated with 137Cs (ACs > 37 kBq m−2) due to the Chernobyl accident. Therefore, the survey of less contaminated areas requires additional validation of this method.

Distribution of 137Cs in different soil particle sizes in the vicinity of the Qianshan nuclear power plant

We investigated the size distribution of 137Cs in soils in the vicinity of the Qinshan nuclear power plant. The soil samples were separated into five fractions, namely coarse sand (2000–250 μm), fine sand (250–53 μm), silt (53–20 μm and 20–2 μm), and clay (< 2 μm). The results show that 137Cs was concentrated in the clay and silt fractions. X-ray diffraction analysis of size-fractionated samples showed that micaceous minerals such as chlorite and muscovite are critical in the fixation of 137Cs in the soil. No significant relationship was observed between 137Cs concentrations and organic carbon content in the soil.

Temporal dynamics of 137Cs distribution in soil and soil-to-crop transfer factor under different tillage systems after the Fukushima Daiichi Nuclear Power Plant accident in Japan

The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan in 2011 released a large amount of radionuclides, primarily radiocesium-137 (137Cs; half-life: 30 years), resulting in long-term contamination of soil and consequently crops. Tillage is a common agricultural management practice that alters the vertical distribution of nutrients in the soil. However, the effect of tillage on 137Cs contamination in soil and crops over time remains unclear. In this study, we investigated the temporal changes in the vertical distribution of 137Cs in the soil, concentration of 137Cs in soybean and cover crops, and the transfer factor (TF) of 137Cs from the soil to crops under three tillage systems (rotary cultivation [RC], moldboard plow [MP], and no tillage [NT]; main factors) using three cover crops (hairy vetch, winter rye, and fallow weeds; side factors). The amount of 137Cs in the soil decreased exponentially with soil depth under the NT and RC treatments. By contrast, 137Cs showed uniform distribution at each soil depth tested under the MP treatment since 2012. The exchangeable 137Cs demonstrated a similar tendency as 137Cs. The 137Cs concentration in soybean (including grain and residue) and cover crops decreased exponentially with time. Consistently higher 137Cs concentration was observed in soybean grains under the NT treatment, suggesting that tillage continuously reduced the concentration of 137Cs in soybean over 7 years since the FDNPP accident. The TF of 137Cs from soil to soybean and cover crops decreased continuously over time; however, 137Cs concentration of soybean grain showed a positive linear correlation with its annual variation rate. Additionally, TF showed a positive logarithmic correlation with 137Cs relaxation depth in the soil. These results enhance our understanding of the long-term behavior and radioecology of 137Cs in agroecosystems in Japan since the radionuclide accident.

Effect of mass of organic layers on variation in 137Cs distribution in soil in different forest types after the Fukushima nuclear accident

ABSTRACT Forests over a wide area were contaminated with radiocesium following the Fukushima nuclear accident in March 2011. Most radiocesium in the forests migrated into the soil a year after the accident and it is therefore necessary to clarify the distribution pattern of radiocesium in soil to evaluate the actual state and possible future changes of the radiocesium cycle in forest ecosystems. We investigated the stock and vertical distribution patterns of 137Cs in soil under evergreen and deciduous tree species from 2012 to 2014 in a mountainous area in Fukushima Prefecture. The 137Cs stock in soil was higher in evergreen forests than in deciduous forests. This was likely caused by the difference in tree leaf biomass at the time of the initial deposition, when deciduous trees were defoliated. The organic layer (particularly the humified layer) retained 137Cs in high concentration and stock, indicating limited migration of 137Cs into the mineral layer during the study period. This may reflect the incorporation of 137Cs into organic matter and the retention of fungi in the organic layer. Analyses of these data and those from other studies conducted in regions contaminated by the accident showed that the ratio of radiocesium stock in the organic layer to the total amount in soil was positively correlated with the mass of the organic layer (organic layers with a mass of >2.0 kg/m2 retained more than 50% of total radiocesium). Thus, the status of the organic layer is an important factor regulating the downward migration of radiocesium.

Distribution characteristics of 137Cs in soil profiles under different land uses and its implication

This paper presents a study of the distribution of 137Cs in soils under three different land uses in a semiarid watershed. The results showed the average inventory of 137Cs in the cultivated land, woodland and grassland was 888, 1489 and 1650 Bq/m2, respectively. The pattern of depth distribution of 137Cs in the soil profiles with cultivated land, woodland and grassland was disturbed, eroding and aggrading, and normal profiles, respectively. The coefficient of variation of 137Cs inventory varied from 8.9 to 38.8 % for different land uses.

Spatial and vertical distribution of 137Cs in soils in the erosive area of southeastern Serbia (Pčinja and South Morava River Basins)

The area of southeastern Serbia, the Pcinja and South Morava River Basins, is under the influence of very strong erosion, and the aim of this study was to investigate the vertical and spatial distribution of the 137Cs in the eroded soils of this area. Vertical soil profiles were collected with 5-cm increments from the uppermost layer down to 20, 25, 30, 40, and 50 cm of depth, depending on the thickness of the soil layers, i.e., down to the underlying parent rocks. Measurements of 137Cs activity concentration were performed by using the HPGe gamma-ray spectrometer ORTEC-AMETEK (34 % relative efficiency and high resolution 1.65 keV at 1.33 MeV for 60Co), from its gamma-ray line at 661.2 keV. The mean 137Cs activity concentration across all 18 soil profiles (for all soil layers) was found to be 20 Bq kg−1. In the greatest number of soil profiles, the 137Cs activity concentration was generally highest in the first soil layer (0–5 cm) and decreased with soil depth, while in a few soil profiles, the peak of either the 137Cs activity concentration occurred in the second soil layer (5–10 cm) or the 137Cs activity concentration was almost equal throughout the entire soil profile. The mean 137Cs activity concentration in the first soil layer (0–5 cm) was found to be 61 Bq kg−1, and the high coefficient of variation of 92 % pointed out high spatial variability and large range of the 137Cs activity concentrations in the study area. The obtained results indicate that in the greatest number of soil profiles, 137Cs is present in the upper layers, with concentration decreasing with depth, as is typical in uncultivated soil. Its spatial distribution was very uneven among the surface soil layers of the investigated sites. One of the main reasons for such pattern of 137Cs in the study area may be soil erosion. Additional investigations which would support this hypothesis are required.

Features of 137Cs distribution and dynamics in the main soils of the steppe zone in the southern European Russia

Data are presented on the concentration and vertical distribution of the artificial isotope 137Cs in soils (chestnut soils, chernozems, solonetzs, solonchaks, meadow soils and alluvial soils) of the steppe zone in the southern Russia. The work has been focused on the study of radiocesium distribution in undisturbed virgin lands. It has been shown that the mean concentration of the radionuclide in the upper (0 to 15cm) soil layer is 20.5Bq/kg. The proportions of adsorbed 137Cs in the soils increase with increasing humus content and decreasing pH level. Two types of the profile distribution of radiocesium were distinguished: (1) with the maximum concentration in the upper soil layer and a relatively abrupt decrease with depth (the majority of 137Cs is concentrated in the upper 0 to 15cm soil layer) and (2) with the maximum concentration of 137Cs shifted into the soil profile down to a depth of 45–55cm. This difference is related to the soil type, humus content, pH value, and regional climatic conditions. Long-term (2000–2013) studies of the vertical distribution of 137Cs in soil profiles have revealed a decrease in its total activity by 1.5 to 2.0 times. It has been shown that the migration of radiocesium in soil profiles depends on the soil type and the diffusion of the radionuclide itself, as well as on convective transfer, transpiration, infiltration, and colmatage.

Spatial distribution of 137Cs in surface soil under different land uses in Chao Phraya watershed: Potential used as sediment source tracing

Sediment fingerprinting techniques involves the discrimination of sediment sources based on differences in source material properties and quantification of the relative contributions from these sources to sediment delivered downstream to the river catchments. Results of the previous study indicated that fallout radionuclides (FRNs); 137Cs and excess 210Pb (210Pbex) are the most suitable radionuclides to be used as sediments sources tracers. This study investigated the spatial distribution of 137Cs in soil under different land uses in Chao Phraya watershed; the most significant watershed in Thailand. Emphasis was placed on discriminating among potential sediment sources including the cultivated (upland crops), pasture field, uncultivated (swamp, forest, and grass field), and channel erosion (stream and river bank). One hundred and twenty four soil samples were collected from all sources and determining for 137Cs. The 137Cs mass activities in pasture areas varied from the limit of detection (LLD) to 1.22±0.05 with the average of 0.64±0.14 Bq kg-1. In cultivated areas the 137Cs mass activities varied from LLD to 1.41±0.04 with the average of 0.38±0.04 Bq kg-1. The 137Cs mass activities were higher in uncultivated areas varied from 0.12±0.03 to 1.73±0.05 with the average of 0.76±0.15 Bq kg-1. The 137Cs mass activities in channel bank varied from LLD to 1.16±0.04 with the average of 0.39±0.05 Bq kg-1.GIS and geospatial interpolations revealed pattern in the spatial concentrations of 137Cs and indicated important differences in its distributions showing the differences behaviour of 137Cs in different land uses.

Analysis of 134Cs and 137Cs distribution in soil of Fukushima prefecture and their specific adsorption on clay minerals

We collected surface soil samples within 60 km from the Fukushima Daiichi Nuclear Power Plants (FDNPP) and analyzed spatial and temporal radiocesium distributions. No large change in vertical distribution pattern of radiocesium has been observed on the samples collected in April 2011 and April 2012 at the same sampling points, suggesting strong adsorption of 134Cs and 137Cs on soil. Cesium is known to be adsorbed specifically on clay minerals in soil. To confirm the specific adsorption of Cs on clay minerals in these samples, we divided the soil into different particle sizes and measured the activity in each size fraction. The activity was highest in the clay fraction (<2 μm) and tended to decrease as the particle size increases. The radiocesium interception potential (RIP), which is defined by the product of the frayed edge sites (FES) capacity and Cs-K selectivity coefficient, was measured using carrier-free 137Cs. No correlation between the value of RIP and the penetration depth of radiocesium was observed, probably suggesting other important physicochemical factors.

Monte Carlo modelling of human body for dose conversion coefficients of 137Cs in soil of the Eastern Black Sea region of Turkey

Absorbed dose conversion coefficients for a human body standing on the soil surface were calculated for 137Cs in the soil of Eastern Black Sea region of Turkey using the Monte Carlo simulation method. The results were given in nGy h−1 per Bq cm−2 as a function of depth. Simple numerical integration of this function multiplied with the known specific activity as a function of depth gives the absorbed dose conversion coefficients for any distribution of 137Cs in soil. Gaussian distribution of 137Cs in the soil was considered for calculations.

Investigation of spatial distribution of 137Cs in soil in area of location of the Armenian NPP

Problem of evaluation of spatial distribution of 137Cs in soil and of direct radiation impact of the Armenian NPP on population dwelling in the region of its location, on the background of global radioactive fallouts and aftermaths of the Chernobyl accident is solved. Content of radiationdangerous radionuclide 137Cs in soil on the territory with radius 50 km including the NPP area has been investigated. Points of monitoring have been chosen on the basis of analysis of meteorological data and calculation of the distance where emissions from NPP have maximal concentration in air. The obtained results agree well with the data of UN Scientific Committee of Radiation Action.

MODELLING VERTICAL MIGRATION OF 137CS IN LITHUANIAN SOILS/137CS VERTIKALIOSIOS MIGRACIJOS LIETUVOS DIRVOŽEMIUOSE MODELIAVIMAS/МОДЕЛИРОВАНИЕ ВЕРТИКАЛЬНОЙ МИГРАЦИИ 137CS В ПОЧВАХ ЛИТВЫ

137Cs vertical migration in soil was evaluated using two methods: evaluating migration parameters using the quasi‐diffusion model, and modelling vertical migration using VS2DI software package, which is intended for simulating transport of pollution in different types of soil. 137Cs distribution in soil was compared in elevated contamination “spots” in 1992 and 1999–2000. It was determined that 137Cs vertical distribution in soil has two maxima caused by the 137Cs global fallout due to nuclear weapon tests and by the fallout due to the ChNPP accident. 137Cs concentration simulated by VS2DI software package is close to the measured 137Cs concentration, especially to values measured in 1992. This shows that the software is able to simulate 137Cs vertical migration due to a single fallout. The quasi‐diffusion model is adequate for description of long‐term 137Cs vertical migration, and the results of measurements and calculations agreed within error limits. Parameters of long‐term vertical migration of 137Cs in soil, the transfer rate w and the diffusion coefficient Dwere found for each region: in the western region of Lithuania (mainly sandy loam) D = 0.12 cm2/year−1, w =0,26 cm/year−1, in the southern region of Lithuania (mainly loam) D = 0.13 cm2/year−1, w = 0.29 cm/year−1, and on the Curonian Spit (mainly fine sand) D = 0.1 cm2/year−1, w = 0.22 cm/year−1. Santrauka 137Cs vertikalioji migracija dirvožemyje buvo įvertinta, matuojant jo savitąjį aktyvumą dirvožemyje ir taikant du metodus: radionuklido vertikaliosios migracijos įvertinimas pagal kvazidifuzinį modelį ir jos modeliavimas, naudojant VS2DI kompiuterinę programą, kuri skirta taršos sklidimui įvairių tipų dirvose modeliuoti. 137Cs pasiskirstymas dirvožemyje buvo palygintas su 137Cs didelės užtaršos plotuose („karštose dėmėse“) 1992 ir 1999–2000 m. Buvo nustatyta, kad 137Cs vertikalusis pasiskirstymas turi dvi smailes, pirmoji atsirado dėl 137Cs globalios iškritos, sukeltos branduolinio ginklo bandymais, antroji – dėl Černobylio avarijos iškritos. 137Cs savitasis aktyvumas, sumodeliuotas naudojant VS2DI kompiuterinę programą, yra artimas išmatuotam 137Cs savitajam aktyvumui, ypač išmatuotam 1992 m. Tai rodo, kad ši programa tinka vienkartinės taršos 137Cs vertikaliajai migracijai modeliuoti. Tačiau ilgalaikei 137Cs vertikaliajai migracijai aprašyti labiau tinka kvazidifuzinis modelis, ir jo rezultatai bei matavimo rezultatai sutampa neviršydami paklaidų ribų. Ilgalaikės 137Cs vertikaliosios migracijos dirvožemyje parametrai, kryptingos pernašos greitis w ir kvazidifuzinės pernašos koeficientas D buvo nustatyti kiekviename regione: Vakarų Lietuvos regione (vyrauja priesmėlis) D = 0,12 cm2 /m–1, w = 0,26 cm/m–1, Pietų Lietuvos regione (vyrauja priemolis) D = 0,13 cm2 /m–1, w = 0,29 cm/m–1, o Kuršių nerijoje, kur vyrauja smulkus smėlis, D = 0,1 cm2 /m–1, w = 0,22 cm/m–1. Резюме Вертикальная миграция 137Cs в почве была исследована при измерении его концентрации в почве, а также при помощи двух методов: оценки параметров миграции с помощью квазидиффузионного метода и с использованием компьютерной программы VS2DI, предназначенной для моделирования переноса загрязнения в различных типах почв. Cравнивается распределение 137Cs в областях повышенной загрязненности („горячих пятнах“) в 1992 г. и 1999–2000 гг. Установлено, что вертикальное распределение 137Cs имеет два максимума, обусловленных глобальным выпадением 137Cs в результате ядерных испытаний и вследствие Чернобыльской аварии. Концентрация 137Cs, смоделированная с помощью программы VS2DI, близка к измеренной, особенно к значениям, измеренным в 1992 г. Это свидетельствует о том, что программа может быть использована для моделирования вертикальной миграции одиночного выпадения 137Cs. Квазидиффузионная модель приемлема для описания долгосрочной вертикальной миграции, причем результаты измерений и вычислений совпадают в пределах погрeшности. Были найдены параметры долгосрочной вертикальной миграции 137Cs, направленная скорость переноса w и коэффициент диффузии D для каждого из регионов: в Западной Литве (преобладает супесчаная почва) D = 0.12 см2 г–1, w = 0,26 см г–1, в Южной Литве (преобладает суглинок) D = 0.13 см 2 г–1, w = 0.29 см г–1 и на Куршской косе (преобладает мелкий песок) D = 0.1 см2 г–1, w = 0.22 см г–1.

Determination and spatial distribution of 137Cs in soils, mosses and lichens near Kavanayen, Venezuela

The activity of 137Cs was determined in soils, mosses, lichens and other vegetation along the Caruay River and near the town of Kavanayen. The range of values for the soils was from <1.2 Bq·kg−1 of 137Cs (our detection limit) to 14.1 Bq·kg−1. The range of 137Cs activities in the mosses ranged from 9.9 to 17.9 Bq·kg−1 with a mean value of 13.4±4 Bq·kg−1; all the moss samples were found along the river. While the 137Cs activities in the lichens ranged from 9.1 to 29.8 Bq·kg−1; the two values along the river were about three factors higher than the one near Kavanayen. It was concluded that the 137Cs activities in the soils, mosses and lichens are much higher along the river in respect to the nearby town of Kavanayen.

Dynamics of Chernobyl 137Cs contamination fields at long distances

Structural changes in the 137Cs contamination fields in natural and agroecosystems of the northern forest steppe (the remote zone of the Chernobyl accident) were studied. It was shown that the lateral and vertical distribution of 137Cs in soils of different biogeocenoses depends on the features of functioning biogeocenoses and the spatial variation of the initial fallout. The effect of biogeocenosis on the spatial variation of the contaminant distribution increases with time. At present, the variation of primary distribution in soils of agrocenoses is changing. The soils of forest biogeocenoses have retained the features of primary distribution, particularly in the upper 0-to 5-cm sublitter layer. The 137Cs penetration depth is greatest in the soils of layland and functioning agrocenosis and least in the soils of forest biogeocenoses.