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1.
Long-term downward distribution of global fallout 137Cs was studied in different soil types, in natural and semi-natural environments of four Chilean climatic zones. The 137Cs soil content showed an exponential decrease with depth; relaxation depth ranged from 0.9 cm in the polar climate environment up to 6.8 cm in the mesothermal warm summer one. In the Antarctic and Westpatagonic ecosystems the long freezing periods delayed the 137Cs leaching. In temperate and tropical climate zones, primarily the rates of annual rainfall and volume of coarse soil pores control the radionuclide's distribution in the soil profiles.  相似文献   

2.
《CATENA》2001,43(2):81-99
Differences between measured 137Cs activity–depth profiles and idealised undisturbed profiles generated from an exponential model suggest that faunal turbation has redistributed 137Cs in mineral and organic upland soils in southern Scotland. Bioturbation is also demonstrated by the vertical displacement of other inputs to the soils of known age (non-native tree pollen and spheroidal carbonaceous particles, SCPs). The causes and mechanisms of bioturbation were further investigated by soil micromorphology. Well-drained mineral soils with active populations of earthworms are the most bioturbated, showing near-complete homogenisation to depths of about 20 cm. Enchytraeids also seem to remobilise 137Cs by the digestion of organic matter and may be the main cause of 137Cs redistribution in organic-rich upland soils. Relative rates of mixing are evaluated by comparing 137Cs depth profiles.  相似文献   

3.

Purpose

The area of southeastern Serbia, the P?inja 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.

Materials and methods

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.

Results and discussion

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.

Conclusions

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.
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4.
Radionuclide fallout during nuclear accidents on the land may impair the atmosphere, contaminate farmland soils and crops, and can even reach the groundwater. Previous research focused on the field distribution of deposited radionuclides in farmland soils, but details of the amounts of radionuclides in the plough layer and the changes in their proportional distribution in the soil profile with time are still inadequate. In this study, a lysimeter experiment was conducted to determine the vertical migration of 137Cs and 60Co in brown and aeolian sandy soils, collected from the farmlands adjoining Shidaowan Nuclear Power Plant(NPP) in eastern China, and to identify the factors influencing their migration depths in soil. At the end of the experiment(800 d), >96% of added 137Cs and 60Co were retained in the top 0–20 cm soil layer of both soils;very little 137Cs or 60Co initially migrated to 20–30 cm, but their amounts at this depth increased with time. The migration depth of 137Cs was greater in the aeolian sandy soil than in the brown soil during 0–577 d, but at the end of the experiment, 137Cs migrated to the same depth(25 cm) in both soils. Three phases on the vertical migration rate(v) of 60Co in the aeolian sandy soil can be identified: an initial rapid movement(0–355 d, v = 219 ± 17 mm year-1), followed by a steady movement(355–577 d, v = 150 ± 24 mm year-1) and a very slow movement(577–800 d, v = 107 ± 7 mm year-1). In contrast, its migration rate in the brown soil(v = 133 ± 17 mm year-1) was steady throughout the 800-d experimental period. The migration of both 137Cs and 60Co in the two soils appears to be regulated by soil clay and silt fractions that provide most of the soil surface area, soil organic carbon(SOC), and soil pH, which were manifested by the solid-liquid distribution coefficient of 137Cs and 60Co. The results of this study suggest that most 137Cs and 60Co remained within the top layer(0–20 cm depth) of farmland soils following a simulated NPP accident, and little reached the subsurface(20–30 cm depth). Fixation of radionuclides onto clay minerals may limit their migration in soil, but some could be laterally distributed by soil erosion and taken up by crops, and migrate into groundwater in a high water table level area after several decades.Remediation measures, therefore, should focus on reducing their impact on the farmland soils, crops, and water.  相似文献   

5.
The vertical distribution and bioavailability of 137Cs in Histosols and mineral soils with different physicochemical properties from the southeast of Bavaria (Germany) more than ten years after the Chernobyl accident were the focus of this study. The vertical distribution of 137Cs was low in the investigated soils. About 85–98 % of the total 137Cs was located in the upper 10 cm of the mineral soils. Slightly higher 137Cs percentages were observed in deeper soil layers of the peat soils. Although the organic matter is assumed to enhance 137Cs mobility in soils, 137Cs was also located in the upper 10 cm of the peat soils (73–85 %). The highest 137Cs‐activities were found in the humus layers of forest soils, where 45–93 % of the total 137Cs soil inventories were observed. To determine the bioavailability of radiocesium, the soil‐to‐plant transfer of 137Cs and additionally added 134Cs was investigated under controlled conditions. The results revealed that the 134+137Cs soil‐to‐plant transfer factors as well as the percentages of NH4‐exchangeable 134+137Cs were much higher for the peat soils and humus layers than for the mineral soils. Nevertheless, the migration of 137Cs from the humus layers to the underlying soils was low. Considering the high bioavailability and low migration of radiocesium in the humus layers, it is suggested that radiocesium is involved in a shortcut element cycle in the system humus layer‐plant uptake‐litter. Furthermore, the organic matter has to be taken into account for radiocesium immobilization.  相似文献   

6.
Data on the concentrations of natural (226Ra, 232Th and 40K) and artificial (137Cs) radionuclides and on the physicochemical properties of chernozems sampled in different years are presented. In 1952, upon the creation of the Penza-Kamensk state shelterbelt, three deep (up to 3 m) soil pits were examined within the former arable field under two-year-old plantations of ash and maple along the transect crossing the territory of the Beloprudskaya Experimental Station of the USSR Academy of Sciences in Volgograd oblast. The samples from these pits were included into the collection of dated soil samples of the Dokuchaev Central Soil Science Museum. Five pits were examined along the same transect in 2009: three pits under shelterbelts (analogues of the pits studied in 1952) and two pits on arable fields between the shelterbelts. In the past 57 years, certain changes took place in the soil structure, bulk density, and the content and composition of humus. The salt profile of soils changed significantly under the forests. The comparison of distribution patterns of natural soil radionuclides in 1952 and 2009 demonstrated their higher contents at the depth of 10–20 cm in 2009 (except for the western shelterbelt). Background concentrations of natural radionuclides in parent materials and relationships between their distributions and the salt profiles of soils have been determined; they are most clearly observed is the soils under shelterbelts. Insignificant contamination with 137Cs (up to 34 Bq/kg) has been found in the samples of 2009 from the upper (0–20 cm) horizon. The activity of 137Cs regularly decreases from the east to the west; the highest concentrations of this radionuclide are found in the topmost 10 cm. This allows us to suppose that 137Cs was brought with aerial dust by eastern winds, and the shelterbelts served as barriers to the wind flow.  相似文献   

7.
Caesium-137 (137Cs) has been widely used for the determination of soil erosion and sediment transport rate. However, depth distribution patterns of 137Cs in the soil profile have not been considered. As a result, the erosion rates may be over-estimated or underestimated. This paper presents the depth distribution of 137Cs fallout in different soil profiles using published data. Three types of depth distribution functions of 137Cs are given by using statistical regression methods, the exponential type, the peak type and the decreasing type (including uniform distribution). Relationships between 137Cs loss and soil erosion rate are given by introducing the regression functions. The influence of depth distribution of 137Cs on the estimation of the soil erosion rate was simulated. Simulation results showed that very different soil erosion rates could be deduced for different depth distributions when 137Cs loss is the same, which indicates that the depth distribution pattern should be considered when soil erosion is estimated by using 137Cs. Simulation results also suggested that it is most important to determine the depth distribution of 137Cs near the soil surface and the annual relative loss of 137Cs by using the depth distribution of 137Cs as a criterion to estimate the soil erosion rate.  相似文献   

8.
A study of the downward movement of 137Cs in an undisturbed forest soil is presented. Seasonal variations and depth profiles of 137Cs activities were measured in seepage water, which is the transport medium for the downward movement of anthropogenic substances in soils. Furthermore the correlation of 137Cs mobilization and production of dissolved organic carbon (DOC) was investigated. Seasonal variations of both 137Cs and DOC fluxes in the seepage water in a depth of 5 cm depth were observed, where the maximum fluxes in the summer months were about one order of magnitude higher than the minimum fluxes in the winter months. 137Cs fluxes are found to be correlated with DOC fluxes with a correlation coefficient of r = 0.63, and both are highly correlated with soil temperature. This indicates that cesium is bound to soil organic material. The production of DOC is controlled by microbial decomposition of soil organic matter and we assume that this holds true for the 137Cs release as well. The actual transport velocity (0.2 ± 0.14 mm/a) of 137Cs (calculated by the weighed mean of 137Cs concentration in the seepage water and the total 137Cs content of the soil) is about one order of magnitude less than the mean transport velocity (1.2 ± 0.3 mm/a) over the past 25 years (calculated from the 137Cs depth profile). It is possible that the transport velocity of 137Cs in undisturbed soils decreases with time as it binds to aged organic material which is less easily decomposable than fresh organic material.  相似文献   

9.
中国南方红壤地区的137Cs基准点的选取   总被引：1，自引：0，他引：1  
The ^137Cs vertical distributions in uncultivated and cultivated soils, developed from Quaternary red clay, granite, argillaceous shale, and red sandstone, were studied to develop reliable guidelines for selecting reference sites in southeastern China, which is dominated by strong acidic and/or clay-textured soils, and examine their reliability by comparing them to the reported ^137Cs reference inventory data to see whether they agreed with the global distribution pattern. It was observed that a relatively high proportion of ^137Cs was concentrated in the surface layers of soils with relatively high clay content. In the paddy soils developed from granite more ^137Cs penetrated to depths below the plow layer （about 45.3%）, when compared to those from the other three parent materials. The relatively low soil ^137Cs inventories on crests excluded using the crest as the ^137Cs reference site; instead the paddy field on the hillock plain was selected. Furthermore, within a specific county characterized by great systematic spatial variations of rainfall and topography across the landscape, a significant （P 〈 0.01） and positive linear relationship （r^2 = 0.81） between local ^137Cs inventory and corresponding local annual rainfall was observed. Thus, for areas with large variations in rainfall, a single uniform value of local ^137Cs reference inventory should be used with caution.  相似文献   

10.
Migration and chemical availability of 137Cs and90Sr in the long-term was studied on a36-yr-old deposition experiment on pastureconsisting of a sandy soil and a clay soil,contaminated in 1961 with radionuclides in aqueoussolution. Comparisons were made with a study of thesame soils in 1967. Soil samples to 55 cm depth wereanalysed for 137Cs and 90Sr to establish thevertical distribution. Chemical availability wasstudied using sequential extractions with H2O,NH4Ac, NH2OH·HCl, H2O2 andHNO3. Both 137Cs and 90Sr were found atall depths in both soil types. Cs-137 waspredominantly retained within the upper 10 cm (70%)in both soils. For 90Sr, the soils differedsignificantly, retention within the upper 10 cm was27% in sandy soil and 47% in clay soil. Migrationsince 1967 was faster in the sandy soil for bothnuclides. More than 95% of 137Cs was bound inthe acid-digestible and residual fractions in bothsoils. The residual fraction was larger in clay soil.90Sr was highly available in both soils. Noresidual fraction was found, and the easilyexchangeable fraction was 63–75%.  相似文献   

11.
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.  相似文献   

12.
Profiles of vertical 137Cs distribution in alluvial meadow soils on the low and medium levels of the Lokna River floodplain (central part of the Plavsk radioactive spot in Tula oblast) 28 years after the Chernobyl fallout have been studied. A significant increase in the 137Cs pool is revealed on the low floodplain areas compared to the soils of interfluves due to the accumulation of alluvium, which hampers the reduction of the total radionuclide pool in alluvial soils because of radioactive decay. The rate of alluvium accumulation in the soil on the medium floodplain level is lower by three times on average. An imitation prognostic model has been developed, which considers the flooding and climatic conditions in the region under study. Numerical experiments have quantitatively confirmed the deciding role of low-mobile forms in the migration of maximum 137Cs content along the soil profile in the absence of manifested erosion–accumulation processes.  相似文献   

13.
利用137Cs示踪农业耕作土壤侵蚀速率的定量模型   总被引：32，自引：4，他引：28  
建立了一个根据农业耕作土壤剖面中^137Cs的损失量与土壤侵蚀量之间关系的定量模型,在假设^137Cs在耕层中得到充分的混合而变得均一的基础上,根据质量平衡模型推导而成,模型显示^137Cs的衰变常数,年沉降分量,耕层厚和采样年份对年平均土壤侵蚀速率都有重大影响,模型结果还说明,^137Cs的损失量与年平均土壤侵蚀量之间的关系既非线性关系亦非指数关系,而是一种复杂的曲线关系。  相似文献   

14.
《CATENA》2004,57(1):15-34
Concentrations in the soil of anthropogenic and natural radionuclides have been investigated in order to assess the applicability of the 137Cs technique in an area of typical Mediterranean steep slopes. This technique can be used to estimate net soil redistribution rates but its potential in areas with shallow and stony soils on hard rock lithology have not been evaluated so far. In this research, the validity of using this technique in stony shallow soils at very steep slopes is discussed together with the relations between radionuclide concentrations and other soil properties, lithology, slope morphology and land use in a Mediterranean environment. Both natural Potassium-40 (40K), Uranium-238 (238U), Thorium-232 (232Th) and anthropogenic Caesium-137 (137Cs) radionuclides have been determined in samples taken along slope transects on uncultivated serpentinite soils and cultivated gneiss soils. In addition to the radionuclide concentrations, parameters such as slope position, slope angle, aspect, soil depth, surface stone cover, moss, litter, vegetation cover, soil crust, stone content and bulk density have been quantified.All the natural radionuclides 40K, 238U, 232Th show significantly higher concentrations in the gneiss than in the serpentinite soils, opposed to the 137Cs concentration, which is found significantly higher in the serpentinite soils probably because of the difference in clay mineralogy. The exponential decreasing depth distribution of 137Cs and its homogeneous spatial distribution emphasise the applicability of the 137Cs technique in this ecosystem.Lithology determines the concentration of natural and anthropogenic radionuclides. Land use determines the relations between 137Cs concentration/inventory and some soil characteristics. Higher 137Cs concentration and inventory are associated with higher percentages of vegetation cover, higher percentage of stones in the soil and higher values of soil bulk density in cultivated gneiss soils. Slope morphology and land use influence the soil redistribution at slope scale. The gneiss slopes show a zonation of four to five areas of differential erosion/accumulation processes corresponding with more regular slopes and soil redistribution due to water erosion and to tillage translocation and erosion. The serpentinites, as an example of a more unstable slope type, show more erosion areas with less accumulation downslope and soil redistribution due to water erosion.  相似文献   

15.
The concentrations and distribution of 137Cs in alluvial soils (Fluvisols) of the upper and middle reaches of the Markha River in the northwest of Yakutia and 226Ra and 238U in alluvial soils within the El’kon uranium ore deposit in the south of Yakutia have been studied. It is shown that the migration of radiocesium in the permafrost-affected soils of Yakutia owing to alluviation processes extends to more than 600 km from the source of the radioactive contamination. The migration of 137Cs with water flows is accompanied by its deposition in the buried horizons of alluvial soils during extremely high floods caused by ice jams. In the technogenic landscapes of southern Yakutia, active water migration of 238U and 226Ra from radioactive dump rocks. The leaching of 238U with surface waters from the rocks is more intense than the leaching of 226Ra. The vertical distribution patterns of 238U and 226Ra in the profiles of alluvial soils are complex. Uranium tends to accumulate in the surface humus horizon and in the buried soil horizons, whereas radium does not display any definite regularities of its distribution in the soil profiles. At present, the migration of 238U and 226Ra with river water and their accumulation in the alluvial soils extend to about 30 km from the source.  相似文献   

16.
Soil organic carbon (SOC) has considerable spatial and temporal variability both at the hillslope and catchment scale as well as down the soil profile. In recent years the distribution of SOC down the soil profile has become an area of interest in the understanding of the carbon sequestration potential of soils. Most studies however have concentrated on highly disturbed agricultural sites with little data available for untilled locations. In this study the vertical distribution of SOC is examined at a grassland site in the Young River area of Western Australia that has remained undisturbed by human activity for 50 years. Soil physical properties (texture, rock content) as well as the distribution of the environmental tracers 137Cs and 210Pb were assessed with the aim of better understanding the transport processes which produce the observed vertical distribution of SOC. While no consistent relationship was found between SOC and soil physical properties significant relationships were found between the distribution of SOC and the environmental tracers, 137Cs and 210Pb. Finite element simulations based on a diffusion/convection/decay model showed that the transport of 137Cs and 210Pb down the soil profile is likely to be driven by the same (primarily diffusive) processes. The same model used in conjunction with plant input and decay data generated from the RothC-26.3 soil carbon model revealed that transport of SOC down the soil profile, while also a diffusion process, was significantly slower indicating that different processes and/or pathways are involved in SOC transport at this site.  相似文献   

17.
The results of the extensive measurements ofCesium-137 (137Cs) in virgin soils, plants,forest litter and lake bottom sediments of AltayRegion in 1992–1995 are presented. Analyses of thevertical soil profiles indicate that 137Cs ispresent in the upper 5–20 cm of the soil. Crops andthe majority of wild plants show no signs ofcontamination with 137Cs even in areas where soilis contaminated. A regional map of 137Csconcentration is presented, which shows a highlyirregular pattern of radio-cesium deposition from thenuclear tests on the Semipalatinsk Nuclear Polygonbetween 1949 to 1962. This kind of lateraldistribution of 137Cs in Altay virgin topsoilscannot be accounted for only by the distance from thenuclear testing site, on the contrary, it seems to bepredominantly dependent on the weather conditions anda pattern of rainfall at the time of Semipalatinskexplosions. The article discusses the factors causingthe post-precipitation redistribution of 137Cs inthe soil column and demonstrates that forest litter,lichen and lake bottom sediments can be used assensitive indicators of the historical and currentradioactive contamination.  相似文献   

18.
Increasing concern for problems of soil degradation and the off‐site impacts of accelerated erosion has generated a need for improved methods of estimating rates and patterns of soil erosion by water. The use of environmental radionuclides, particularly 137Cs, to estimate erosion rates has attracted increased attention and the approach has been shown to possess several important advantages. However, the use of 137Cs measurements to estimate erosion rates introduces one important uncertainty, namely, the need to employ a conversion model or relationship to convert the measured reduction in the 137Cs inventory to an estimate of the erosion rate. There have been few attempts to validate these theoretical conversion models and the resulting erosion rate estimates. However, there is an important need for such validation, if the 137Cs approach is to be more widely applied and reliance is to be placed on the results obtained. This paper reports the results of a study aimed at validating the use of two theoretical conversion models, namely the exponential depth distribution model and the diffusion and migration model, that have been used in several recent studies to convert measurements of 137Cs inventories on uncultivated soils to estimates of soil erosion rates. The study is based on data assembled for two small catchments (1.38 and 1.65 ha) in Calabria, southern Italy, for which measurements of sediment output are available for the catchment outlet. The two catchments differ in terms of the steepness of their terrain, and this difference is reflected by their sediment yields. Because there is no evidence of significant deposition within the two catchments, sediment delivery ratios close to 1.0 can be assumed. It is therefore possible to make a direct comparison between the estimates of the mean annual erosion rates within the two catchments derived from 137Cs measurements and the measured sediment outputs. The results of the comparison show that the erosion rate estimates provided by both models are reasonably consistent with the measured sediment yields at the catchment outlets. However, more detailed assessment of the results shows that the validity of the erosion rate estimates is influenced by the magnitude of the erosion rates within the catchment. The exponential depth distribution model appears to perform better for the catchment with higher erosion rates and to overestimate erosion rates in the other catchment. Similarly, the basic migration and diffusion model performs better for the catchment with lower erosion rates and overestimates erosion rates in the other catchment. However, the improved migration and diffusion model appears to perform satisfactorily for both catchments. There is a need for further studies to extend such independent validation of the 137Cs technique to other environments, including cultivated soils, and to other conversion models and procedures. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

19.
Little is known on the hydrological behavior of the volcanic ash soils, which are characterized by extremely high porosities and hydraulic conductivities. In this study the occurrence and hydrological effects of water repellency were investigated at a plot scale for different types of land use and volcanic soils in Mexican volcanic highlands from Michoacan, Mexico: [1] fir, pine and oak mixed forest soils developed from lavas, [2] soils developed from volcanic ashes and pyroclastic sediments under sparse fir, pine and oak forest and shrubland, [3] pine and oak forested soils developed from lavas and pyroclastic sediments, and [4] bare soils on recent ash sediments in plain surfaces. Soil water repellency was assessed using the water drop penetration time test and rainfall simulations were performed on circular plots (50 cm in diameter) during 30 min and at an intensity of 90 mm h− 1 in order to study the hydrological response of each area. The return period for storms with a similar intensity in the area is 10 years. The shape and depth of the wetting front after simulated rainfall was also analyzed. Soil water repellency showed a high variability among the different studied zones. Organic matter content, soil texture and acidity were the most important factors for developing hydrophobicity. A wide range of soil water repellency classes (hydrophilic to severely water-repellent soils) has been found in soils under dense fir, pine and oak mixed forests or shrubland, while inexistent or slight water repellency has been observed in soils under sparse forest or at bare ash-covered areas. At a plot scale, marked differences in the hydrological behavior of the studied land use and soil zones were observed after the rainfall simulations. Soil water repellency contributes to fast ponding and runoff generation during the first stages of rainstorms. Runoff was enhanced in water-repellent forested soils (average runoff coefficients between 15.7 and 19.9%), in contrast to hydrophilic or slightly water-repellent soils, where runoff rates were lower (between 1.0 and 11.7%). Shallow and irregular wetting fronts were observed at water-repellent zones, reducing the soil water storage capacity. The implications of soil water repellency in soil hydrology and erosion risk in the area shed light on the soil hydrology of the studied ecosystems, and can contribute to develop better management policies.  相似文献   

20.
Accumulation and distribution of 137Cs by the root systems of forests in the radioactive contamination zone of Bryansk oblast have been discussed. It has been found that the phytomass and distribution of roots of pine and birch trees along the soil profile in the studied BGCs differ considerably. The specific activity of 137Cs in the roots changes depending on their diameter: the lowest specific activity is observed in small fractions of the roots, and the highest one in large fractions. It has been shown that the contribution of roots in the total reserves of 137Cs in the soil layer of 0–50 cm of various biogeocenoses is different: the largest contribution is characteristic for birch forests (1.66%) with variation of this parameter in separate soil layers from 1.12 to 3.53%, while the contribution for pine forests is lower (0.97%) with the variation from 0.82 to 7.5%. The contribution of roots to the overall contamination of soils in the studied plant communities increases with depth.  相似文献   

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