Cs contamination of the Techa river flood plain near the village of Muslumovo

The results of a radiometric survey of the Techa river flood plain near the village of Muslumovo in the Chelyabinsk region of Russia are presented. The observed territory extended 16.6 km along the riverbed, with a total area of 2.5 km². The collimated scintillation detector technique was applied to in situ field measurements of ¹³⁷Cs deposition on the soil. Maps of ¹³⁷Cs deposition and soil penetration depth were developed on the basis of approximately 5000 measurements. The total ¹³⁷Cs deposition within the surveyed territory has been estimated at 6.6 TBq. The means of the total ¹³⁷Cs soil depositions at half-kilometer sites on the flood plain and its distribution along the river have also been calculated. A maximum ¹³⁷Cs contamination above 7.5 MBq/m² is associated with a bank height up to 1 m above the usual water level. The data identify zones of intensive radionuclide sedimentation and transit zones.     

近期长江口南支河道洪季含沙量时间变化及床沙再悬浮研究

基于2011年洪季在南支河道从小潮至大潮连续8天现场定点观测所获得水沙观测数据(包括潮流、悬沙浓度、悬沙粒度和表层沉积物样品),通过对悬沙浓度、悬沙粒度和沉积物在不同时刻的组成分析,以及流速、悬沙和底床切应力的相互影响分析,对长江河口南支河道悬沙随时间变化特性和河床沙再悬浮作用进行了研究。结果表明:观测期间南支主槽下段落潮水动力强于涨潮;落潮悬沙浓度高于涨潮,并由小潮至大潮逐渐增加;落潮悬沙粒径粗于涨潮,并随小潮至大潮不断粗化;河床沉积物颗粒较粗,细砂类组成达到90%以上;流速、悬沙及底床切应力之间存在显著相关性;河床泥沙再悬浮强度较强,其量值有限。而近期研究区域悬沙浓度和水沙关系发生变化,与流域来沙出现锐减有关。     

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides ²¹⁰Pb and ¹³⁷Cs. The anthropogenic radionuclide, ¹³⁷Cs, originating from atmospheric nuclear weapons testing can provide an important “first appearance” horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with ²¹⁰Pb geochronology. However, while ¹³⁷Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of ¹³⁷Cs in the southern hemisphere was only 25% that of the north and the low activities of ¹³⁷Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low ¹³⁷Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator.This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding ¹³⁷Cs profiles and ²¹⁰Pb geochronologies. We find that Pu has significant advantages over ¹³⁷Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to ¹³⁷Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the ²³⁸Pu/^239+240Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over ¹³⁷Cs due to its enrichment in bottom sediment relative to ¹³⁷Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.     

Sediment accumulation rate and radiological characterisation of the sediment of Palmones River estuary (southern of Spain)

Chemical analyses and radioecological methods were combined in order to estimate the sediment accumulation rate in the upper 20 cm depth of the Palmones River estuary. Organic matter, total carbon, C:N and (137)Cs vertical profiles showed changes at 13 cm depth. These changes could be associated with the decrease in river input since 1987 when a dam situated in the upper part of the estuary started to store water. Using 1987 as reference to date the sediment, accumulation rate was 1.2 cm yr(-1). As alternative method, two layer model of (210)Pb(xs) vertical distribution showed a sedimentation rate of 0.7 cm yr(-1) with a surface mixing layer of 7 cm thickness. The high ammonium, potassium and sodium content in pore water and the strong correlation between (137)Cs activities and organic matter in dry sediment suggests that (137)Cs (the only anthropogenic product detected) is mainly accumulated in the estuary associated with the particulate organic material from the catchment area.     

Cs, Pu concentrations and the Pu/Pu atom ratio in a sediment core from the sub-aqueous delta of Yangtze River estuary

A sediment core collected from the sub-aqueous delta of the Yangtze River estuary was subjected to analyses of ¹³⁷Cs and plutonium (Pu) isotopes. The ¹³⁷Cs was measured using γ-spectrometry at the laboratories at the Nanjing University and Pu isotopes were determined with Accelerator Mass Spectrometry (AMS), measurements made at the Australian National University. The results show considerable structure in the depth concentration profiles of the ¹³⁷Cs and ^239+240Pu. The shape of the vertical ¹³⁷Cs distribution in the sediment core was similar to that of the Pu. The maximum ¹³⁷Cs and ^239+240Pu concentrations were 16.21 ± 0.95 mBq/g and 0.716 ± 0.030 mBq/g, respectively, and appear at same depth. The average ²⁴⁰Pu/²³⁹Pu atom ratio was 0.238 ± 0.007 in the sediment core, slightly higher than the average global fallout value. The changes in the ²⁴⁰Pu/²³⁹Pu atom ratios in the sediment core indicate the presence of at least two different Pu sources, i.e., global fallout and another source, most likely close-in fallout from the Pacific Proving Grounds (PPG) in the Marshall Islands, and suggest the possibility that Pu isotopes are useful as a geochronological tool for coastal sediment studies. The ¹³⁷Cs and ^239+240Pu inventories were estimated to be 7100 ± 1200 Bq/m² and 407 ± 27 Bq/m², respectively. Approximately 40% of the ^239+240Pu inventory originated from the PPG close-in fallout and about 50% has derived from land-origin global fallout transported to the estuary by the river. This study confirms that AMS is a useful tool to measure ²⁴⁰Pu/²³⁹Pu atom ratio and can provide valuable information on sedimentary processes in the coastal environment.     

Determining floodplain sedimentation rates using Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

Fallout ¹³⁷Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of ¹³⁷Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total ¹³⁷Cs inventories calculated from the detailed profile data. Information on the rates of ¹³⁷Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of ¹³⁷Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for ¹³⁷Cs being known and without having to assume that ¹³⁷Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total ¹³⁷Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, ¹³⁷Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.     

C, δC and total C content in soils around a Brazilian PWR nuclear power plant

Nuclear power plants release ¹⁴C during routine operation mainly as airborne gaseous effluents. Because of the long half-life (5730 years) and biological importance of this radionuclide (it is incorporated in plant tissue by photosynthesis), several countries have monitoring programs in order to quantify and control these emissions. This paper compares the activity of ¹⁴C in soils taken within 1 km from a Brazilian nuclear power plant with soils taken within a reference area located 50 km away from the reactor site. Analyses of total carbon, δ¹³C and ¹³⁷Cs were also performed in order to understand the local soil dynamics. Except for one of the profiles, the isotopic composition of soil organic carbon reflected the actual forest vegetation present in both areas. The ¹³⁷Cs data show that the soils from the base of hills are probably allocthonous.     

Origin and transport of U and Ra in riverine,estuarine and marine sediments of the Krka River,Croatia

Spatial distribution of ²³⁸U and ²²⁶Ra activities in sediment columns along the Krka River and estuary, were studied using gamma spectrometry. Markedly different ²³⁸U and ²²⁶Ra activities between riverine, estuarine and marine sediments were observed. Distribution of these radionuclides, as well as their anthropogenic and natural origin, was evaluated by activity measurements, taking into account sedimentation rates estimated by ¹³⁷Cs distribution in sediment columns.     

Using ²¹⁰Pb measurements to estimate sedimentation rates on river floodplains

Growing interest in the dynamics of floodplain evolution and the important role of overbank sedimentation on river floodplains as a sediment sink has focused attention on the need to document contemporary and recent rates of overbank sedimentation. The potential for using the fallout radionuclides ¹³⁷Cs and excess ²¹⁰Pb to estimate medium-term (10-10² years) sedimentation rates on river floodplains has attracted increasing attention. Most studies that have successfully used fallout radionuclides for this purpose have focused on the use of ¹³⁷Cs. However, the use of excess ²¹⁰Pb potentially offers a number of advantages over ¹³⁷Cs measurements. Most existing investigations that have used excess ²¹⁰Pb measurements to document sedimentation rates have, however, focused on lakes rather than floodplains and the transfer of the approach, and particularly the models used to estimate the sedimentation rate, to river floodplains involves a number of uncertainties, which require further attention. This contribution reports the results of an investigation of overbank sedimentation rates on the floodplains of several UK rivers. Sediment cores were collected from seven floodplain sites representative of different environmental conditions and located in different areas of England and Wales. Measurements of excess ²¹⁰Pb and ¹³⁷Cs were made on these cores. The ²¹⁰Pb measurements have been used to estimate sedimentation rates and the results obtained by using different models have been compared. The ¹³⁷Cs measurements have also been used to provide an essentially independent time marker for validation purposes. In using the ²¹⁰Pb measurements, particular attention was directed to the problem of obtaining reliable estimates of the supported and excess or unsupported components of the total ²¹⁰Pb activity of sediment samples. Although there was a reasonable degree of consistency between the estimates of sedimentation rate provided by the ¹³⁷Cs and excess ²¹⁰Pb measurements, some differences existed and the various models used to interpret excess ²¹⁰Pb measurements could produce different results. By using the ¹³⁷Cs measurements to provide independent validation of the estimates of sedimentation rate provided by the different models used with the excess ²¹⁰Pb measurement it was shown that the CICCS and Composite CRS models appeared to generally provide the best results.     

Occurrence and behaviour of radionuclides in the Moselle River-Part II: Distribution of radionuclides between aqueous phase and suspended matter

Most of the radionuclides released from nuclear power plants ( NPPs) into rivers are primarily adsorbed onto suspended matter. To describe this nuclide transfer, a model was used which takes the total suspended matter load as solid phase into account. The necessary partition factors of various radionuclides were determined in river water/suspended matter of the Moselle in laboratory investigations. By use of this model, a conservative estimate of the radionuclide concentration of the solid phase could be obtained which proved to be more realistic than the results based on the distribution law.Furthermore, the influence of grain-size on the specific activity of single fractions of a Moselle sediment was demonstrated using ¹³⁷Cs, ¹⁰⁶Ru and ¹⁴⁴Ce from the Chernobyl nuclear accident as tracers. The grain-size pattern is considered to be a main factor which may seriously distort the determination of distribution coefficients and concentration factors that are needed in applying the model based on the distribution law.     

Simulation of 137Cs Migration over the Soil–Plant System of Peat Soils Contaminated after the Chernobyl Accident

A mathematical model was constructed to simulate the processes of ¹³⁷Cs migration in peat soils and its uptake by vegetation. Model parameters were assessed and the pattern of ¹³⁷Cs distribution over soil profile was predicted in case of peat soils, which are typical of the Russian regions contaminated after the Chernobyl accident. The ecological half-life of ¹³⁷Cs in the plant-root soil zone was calculated, and a long-term prognosis of the radionuclide uptake by plants was made.     

210Pb as a tool for establishing sediment chronologies: examples of potentials and limitations of conventional dating models

For aquatic sediments, the use of ²¹⁰Pb originating from the decay of atmospheric ²²²Rn is a well-established methodology to estimate sediment ages and sedimentation rates. Traditionally, the measurement of ²¹⁰Pb in soils and sediments involved laborious and time-consuming radiochemical separation procedures. Due to the recent development of advanced planar (‘n-type’) semi-conductors with high efficiencies in the low-energy range which enable the gamma-spectrometric analysis of the 46.5 keV decay line of ²¹⁰Pb, sediment dating using this radionuclide has gained renewed interest.In this contribution, potentials and limitations of the ²¹⁰Pb methodology and of the models used for estimating sediment ages and sedimentation rates are discussed and illustrated by examples of freshwater and marine sediments. Comparison with the use of ¹³⁷Cs shows that the information which may be gained by these two tracers is complementary. As a consequence, both radionuclides should be used in combination for dating of recent sediments. It is shown that for various sedimentation regimes additional information from other sources (e.g. sediment lithology) may be needed to establish a reliable chronology. A strategy for sediment dating using ²¹⁰Pb is recommended.     

Application of the ERICA Assessment Tool to freshwater biota in Finland

In recent years there has been growing international interest in the assessment of doses and risks from ionising contaminants to biota. In this study the ERICA Tool, developed within the EC 6th Framework Programme, was applied to estimate incremental dose rates to biota in freshwater ecosystems in Finland mainly resulting from exposure to the Chernobyl-derived radionuclides ¹³⁷Cs, ¹³⁴Cs and ⁹⁰Sr. Data sets consisting of measured activity concentrations in fish, aquatic plants, lake water and sediment for three selected lakes located in a region with high ¹³⁷Cs deposition were applied in the assessment. The dose rates to most species studied were clearly below the screening level of 10 μGy h⁻¹, indicating no significant impact of the Chernobyl fallout on these species. However, the possibility of higher dose rates to certain species living on or in the bottom sediment cannot be excluded based on this assessment.     

Distribution of 137Cs in the Tree Layer of Forest Ecosystems in the Zone of the Accident at the Chernobyl Nuclear Power Plant

Trends in ¹³⁷Cs distribution over the parts of coniferous (Pinus sylvestrisL.) and deciduous (Betula pendula Rocht.) trees are described. The trees have been selected in the stationary experimental plots located in southwestern Bryansk oblast, Russian Federation. The distribution of ¹³⁷Cs in the wood along the trunk height is shown to be nonuniform. The effects of ¹³⁷Cs content in the xylem sap on the accumulation of this radionuclide in the leaves and needles are assessed. The factors controlling ¹³⁷Cs accumulation in the components of woody plants are revealed, and their significance is estimated.     

The Role of Floodplain Soils as a Barrier to Radionuclide Migration: An Example of the Techa–Iset' River System

The contents of ⁹⁰Sr and ¹³⁷Cs and the pattern of their redistribution in the soil and plant cover of floodplain ecosystems have been assessed. It is shown that the radionuclide distribution across the floodplain and along the river flow is determined by the formation of a barrier to their migration near the river channel, at which less mobile ¹³⁷Cs accumulates. The soil and plant cover of the central floodplain are enriched with ⁹⁰Sr. Differences in radionuclide migration in floodplain soils and their input into plants are determined by the relationship between the processes of their immobilization and migration with soil water.     

长江口溢油数值模拟及对水源地影响

首先建立了一套基于非结构网格的长江口-杭州湾二维垂向平均潮流数学模型,又基于最新的实测资料重点对南支水域流速、流向和水位进行验证,充分证实了模型的可靠性。在潮流模型可靠的基础上为MIKE21 SA(溢油模块)提供水动力基础数据,建立了一套基于欧拉 拉格朗日体系的“油粒子”追踪技术,综合考虑油膜扩展、输移和风化过程的长江口溢油行为与归宿预测模型。并对长江口夏季和冬季大潮溢油事故发生后取水口油膜厚度的变化及油膜运动路径进行了模拟预测。研究表明：油膜在长江口受到往复流形式的涨落潮交替作用,油膜沿深槽向下游震荡漂移;〖JP2〗油膜在纵向上逐渐被拉伸,形成窄长的油带,覆盖面积逐渐增大;油膜的运动轨迹除了受到涨落潮流的主控外还易受风况和长江口水下地形等影响;夏季溢油对3个水库均有不同程度的影响,冬季溢油只威胁到陈行水库的取水;夏季油膜蒸发量大于冬季     

Migration of Cs in tributaries,lake water and sediment of Lago Maggiore (Italy,Switzerland) – analysis and comparison with Lago di Lugano and other lakes

This paper describes the behaviour of ¹³⁷Cs in Lago Maggiore and other pre-alpine lakes as a consequence of atmospheric nuclear weapons testing fallout and the fallout from the nuclear accident in Chernobyl. It presents data on the ¹³⁷Cs distribution in tributaries, lake water, bottom sediments and reveals the role of ¹³⁷Cs as a marker of the sedimentation processes. The run-off of ¹³⁷Cs from the watershed to the lake is described with a simple compartment model. Measurements of the activity concentration of ¹³⁷Cs in sediments are compared with the output of a model (diffusion–convection type) which describes the input of ¹³⁷Cs into and its vertical distribution within the sediment. Varying sedimentation rates (0.05–0.90 g (cm² y)⁻¹) in Lago Maggiore are compared with data of other authors. Sedimentation rates and total distribution coefficients (of about 10⁵ L kg⁻¹) in Lago Maggiore are discussed and compared with those of Lago di Lugano, Lake Constance, and Lake Vorsee.     

Migration of Cs and Sr in undisturbed soil profiles under controlled and close-to-real conditions

Migration of ¹³⁷Cs and ⁹⁰Sr in undisturbed soil was studied in large lysimeters three and four years after contamination, as part of a larger European project studying radionuclide soil–plant interactions. The lysimeters were installed in greenhouses with climate control and contaminated with radionuclides in an aerosol mixture, simulating fallout from a nuclear accident. The soil types studied were loam, silt loam, sandy loam and loamy sand. The soils were sampled to 30–40 cm depth in 1997 and 1998. The total deposition of ¹³⁷Cs ranged from 24 to 45 MBq/m², and of ⁹⁰Sr from 23 to 52 MBq/m². It was shown that migration of ¹³⁷Cs was fastest in sandy loam, and of ⁹⁰Sr fastest in sandy loam and loam. The slowest migration of both nuclides was found in loamy sand. Retention within the upper 5 cm was 60% for both ¹³⁷Cs and ⁹⁰Sr in sandy loam, while in loamy sand it was 97 and 96%, respectively. In 1998, migration rates, calculated as radionuclide weighted median depth (migration centre) divided by time since deposition were 1.1 cm/year for both ¹³⁷Cs and ⁹⁰Sr in sandy loam, 0.8 and 1.0 cm/year, respectively, in loam, 0.6 and 0.8 cm/year in silt loam, and 0.4 and 0.6 cm/year for ¹³⁷Cs and ⁹⁰Sr, respectively, in loamy sand. A distinction is made between short-term migration, caused by events soon after deposition and less affected by soil type, and long-term migration, more affected by e.g. soil texture. Three to four years after deposition, effects of short-term migration is still dominant in the studied soils.     

Radiocesium in North San Francisco Bay and Baja California coastal surface waters

Radiocesium, 137Cs, and rare earth elements (REEs) were determined in suspended material and dissolved fractions of waters across the salinity gradient in North San Francisco Bay (estuary). We describe the variation of this conservative isotope tracer with salinity and sediment load. REE data are used to differentiate marine and terrigenous source terrains for suspended material and dissolved fractions. We estimate that about 1-4 x 10(10) Bq of 137Cs migrates annually on suspended material through the North Bay. In addition, 137Cs concentrations were measured in surface waters off Baja California. Combined in situ water density (sigma(t)) and 137Cs data distinguish between California Current and Gulf of California water, and delineate areas of upwelling, where nutrient-rich, deep Pacific Intermediate water, with little or no 137Cs, is brought to the surface off promontories along Baja California.     

Long-term dynamics of technogenic radionuclide concentrations in moss-lichen cover

Ample factual data has been used to analyze the long-term dynamics of ⁹⁰Sr and ¹³⁷Cs concentrations in moss-lichen cover. The stocks of radionuclides in lichens, mosses, and the moss-lichen cover of northern regions of the Urals and Siberia has been estimated for the first time. The data on recent ranges of ⁹⁰Sr and ¹³⁷Cs concentrations in lichens and mosses can serve as a basis for determining the background levels of radionuclide contamination for long-term monitoring and prognostic radioecological studies.