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1.
238Pu,239Pu and137Cs in rain and dry fallout and90Sr in rain samples were measured at Woods Hole, Massachusetts, from June 1976 through December 1977. The dry fallout was estimated to be about 7.8% of the total deposition of239Pu and137Cs.239Pu/137Cs ratios, almost constant at about 0.011 in rain or dry fallout, February through December 1977, suggested that fractionation between the refractory and volatile radionuclides is insignificant in stratospheric fallout. This supports the idea of regional homogeneity of radionuclide ratios in fallout.  相似文献   

2.
Anthropogenic radionuclides have reached the Hudson estuary as global fallout from nuclear weapons testing and through local releases from commercial nuclear reactors. Significant activities of238Pu and239,240Pu (fallout-derived),134Cs and60Co (reactor-released), and137Cs (derived from both sources), have accumulated in the sediments throughout the estuary, with the primary zone of accumulation near the downstream end of the system in New York harbor. The estuary appears to have trapped nearly all of the239,240Pu delivered as fallout, and consequently, ocean dumping of dredged harbor sediment is currently the primary means for the net transport of these nuclides to coastal waters. In contrast, only 10–30% of the137Cs,134Cs and60Co delivered to the estuary have been retained on the fine particles which accumulate at a rapid rate in the harbor.The primary factors which have governed the distribution of anthropogenic radionuclides in Hudson sediments are: (1) spread of fine particles labeled with both fallout and reactor nuclides throughout the axis of the estuary, (2) differences in timing of the peak fallout years (1962–1964) and years of maximum reactor releases (1971–1972), (3) large variations in sediment accumulation rates, ranging from a few millimeters per year or less to many tens of centimeters per year, (4) appreciable desorption of137Cs and134Cs from particles at higher salinities, and (5) possible enhanced desorption of60Co at higher salinities (relative to134Cs and137Cs) which may be associated with the release of reduced manganese from the harbor sediments.  相似文献   

3.
Analyses are presented of137Cs,238Pu, and239,240Pu, in relation to depth in sediment, in 21 gravity cores. These cores span the ranges of times 1964–1975, and of water depths 12–2000 m; they come from three distinct sedimentation areas off the northeast coast of the United States. Although the ranges of total sediment inventories of239,240Pu and of137Cs from the various areas hardly overlap, the range of ratios of the inventories of these two nuclides is probably the same in all the areas. In the shallow-water cores the239,240Pu/137Cs ratio regularly diminishes with depth in the core, and a tendency is seen for curves of this function to have similar slopes in each area; ratios of238Pu/239,240Pu show no change with depth in these shallow-water cores. In the deeper-water cores, the239,240Pu/137Cs ratio shows no systematic change with depth, but sometimes the238Pu/239,240Pu ratio shows a minimum at the sediment surface, and is much higher deeper in the cores. We believe that these phenomena can be explained in terms of a complicated bioturbational process moving the nuclides, together, down into the sediments, of chemical resolubilization, at depth, of plutonium only, and of its subsequent upward translocation in the interstitial solution. Some re-immobilization of plutonium near the sediment surface is implied, and a mechanism is suggested for this, based on displacement of plutonium from organic complexes by the increasing concentrations, in upper layers of the sediment, of re-oxidized dissolved iron.  相似文献   

4.
Floodplains comprise geomorphologically important sources and sinks for sediments and associated pollutants, yet the sedimentology of large dryland floodplains is not well understood. Processes occurring on such floodplains are often difficult to observe, and techniques used to investigate smaller perennial floodplains are often not practical in these environments. This study assesses the utility of 137Cs inventory and depth‐profile techniques for determining relative amounts of floodplain sedimentation in the Fitzroy River, northeastern Australia; a 143 000 km2 semi‐arid river system. Caesium‐137 inventories were calculated for floodplain and reference location bulk soil cores collected from four sites. Depth profiles of 137Cs concentration from each floodplain site and a reference location were recorded. The areal density of 137Cs at reference locations ranged from 13 to 978 Bq m–2 (0–1367 Bq m–2 at the 95% confidence interval), and the mean value ± 2 (standard error of the mean) was 436 ± 264 Bq m–2, similar to published data from other Southern Hemisphere locations. Floodplain inventories ranged from 68 to 1142 Bq m–2 (0–1692 Bq m–2 at the 95% confidence interval), essentially falling within the range of reference inventory values, thus preventing calculation of erosion or deposition. Depth‐profiles of 137Cs concentration indicate erosion at one site and over 66 cm of deposition at another since 1954. Analysis of 239+240Pu concentrations in a depositional core substantiated the interpretation made from 137Cs data, and depict a more tightly constrained peak in concentration. Average annual deposition rates range from 0 to 15 mm. The similarity between floodplain and reference bulk inventories does not necessarily indicate a lack of erosion or deposition, due to low 137Cs fallout in the region and associated high measurement uncertainties, and a likely influence of gully and bank eroded sediments with no or limited adsorbed 137Cs. In this low‐fallout environment, detailed depth‐profile data are necessary for investigating sedimentation using 137Cs. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

5.
The nature of sedimentation and mixing are examined in abyssal red clay sediments from the North Central Pacific using three types of indicators: 230Th/232Th, organic14C, and137Cs and 239.240Pu.230Th/232Th analysed revealed that the clay sedimentation rate in three box cores collected within a 50 km radius was less than 1.0 mm/103 yr. However, analyses of the organic carbon in thin layers of sediment revealed that radiocarbon was present much deeper in the cores (down to 20 cm) than was expected from the 230Th/232Th distribution. In addition, both the stratigraphy and inventory of radiocarbon was significantly different between box cores. The distributions and inventories of137Cs and239.240Pu were similar to that found for radiocarbon, further illustrating the spatial variability of radionuclides in oligotrophic North Pacific red clays. These data suggest that bioturbational processes are important for transporting organic carbon down into the sediment column.  相似文献   

6.
The anthropogenic radionuclides, 137Cs, 90Sr, 108mAg, 239+240Pu, were measured in two Chionoecetes species, red queen crab (Chionoecetes japonicus) and snow crab (Chionoecetes opilio) collected around Japan during 1996–2007. There was no increase in the concentrations of these radionuclides and no large variation of the atom ratio of 240Pu/239Pu during this research period. These results indicated that the source of the radionuclides was not the radioactive wastes dumped by the former USSR and Russia and originated from past nuclear weapon tests. The higher atom ratio in the crab species than that from global fallout would be contributed by the Pacific Proving Grounds close-in fallout. The variability of the concentration of radionuclides in the crab species would result from the variability of the composition and quantity in the diet. However, the decrease in the concentration of radionuclides with sampling depth would depend on the concentration in the seawater and diet.  相似文献   

7.
We have used in-situ pumps which filter large volumes of sea water through a 1 μm cartridge prefilter and two MnO2-coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans. Two sites in the northwest Atlantic show subsurface maxima of the fallout radionuclides137Cs,239,240Pu and241Am. Although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions, comparison of predicted and measured water column inventories suggests that at least 35–50% of the Pu and241Am are supplied to the deep water by advection.The depth distributions of the naturally occurring radionuclides232Th,228Th and230Th reflect their sources to the oceans.232Th shows high dissolved concentrations in surface waters, presumably as a result of atmospheric or riverine supply. Activities of232Th decrease with depth to values 0.01 dpm/1000 l.228Th shows high activities in near surface and near bottom water, due to the distribution of its parent,228Ra. Dissolved230Th, produced throughout the water column from234U decay, increases with depth to 3000 m. Values in the deep water (> 3000 m) are nearly constant ( 0.6–0.7 dpm/1000 l), and the distribution of this tracer (and perhaps other long-lived particle-reactive tracers as well) may be affected by the advection inferred from Pu and241Am data.The ratio of particulate to dissolved activity for both230Th and228Th is 0.15–0.20. This similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium. Moreover, in mid-depths228Th tends to have a higher particulate/dissolved ratio than230Th, suggesting uptake and release of230Th and228Th by different processes. This could occur if228Th, produced in surface water, were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking.230Th, produced throughout the water column, may more closely approach a sorption equilibrium at all depths.230Th,241Am and239,240Pu are partitioned onto particles in the sequence Th > Am > Pu with 15% of the230Th on particles compared with 7% for Am and 1% for Pu. Distribution coefficients (Kd) are 1.3–1.6 × 107 for Th, 5–6 × 106 for Am and 7–10 × 105 for Pu. The lower reactivity for Pu is consistent with analyses of Pu oxidation states which show 85% oxidized (V + VI) Pu. However, theKd value for Pu may be an upper limit because Pu, like228Th, may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase.  相似文献   

8.
In sediments deposited in the coastal basins off the western North American continent since the early 1960's, there is more241Am activity than one would predict if its presence was solely due to the decay of241Pu that was produced during the testing of weapons in 1961–1962 (taken as July 1, 1962 for calculations). This excess can be accounted for by the decay of241Pu, if pre-1962 fallout (fallout from the pre-moratorium testing) has been continuously introduced into the recent sediments along with fallout from post-moratorium testing. This hypothesis is supported by the plutonium depth profiles which do not reflect direct fallout from the atmosphere, as characterized by two peaks corresponding to the two major weapons testing periods, but continuously increasing plutonium and americium concentrations from 1954 to 1974. Thus, the nuclides may be coming from a large reservoir that has accumulated and mixed fallout since 1952. Such a concentration gradient for all of the nuclides requires their immobilization in the sediment after deposition.  相似文献   

9.
137Cs湖泊沉积年代学方法应用的局限——以Crawford湖为例   总被引：17，自引：5，他引：12  
项亮 《湖泊科学》1995,7(4):307-313
＾１３７Ｃｓ湖泊沉积年代学方法是测定现代湖泊沉积物沉积年代和沉积速率的重要同位素年代学方法之一。对加拿大Ｃｒａｗｆｏｒｄ湖采集的沉积孔柱内＾１３７Ｃｓ垂直分布的研究发现,该方法给出时的标有明显偏差。比较＾２１０Ｐｂ和纹层等年代方法的结果,其１９６３年时标蓄积峰值所在位置明显移向表层,而作为１９５４年时标的该核素出现蓄积的层位则远早于该年沉积物蓄积层位。研究还表明,孔柱中较高的间隙水含量、缺少足以吸  相似文献   

10.
The concentrations of 239+240Pu and 137Cs in zooplankton and nekton in the Northwest Pacific and Southern Oceans were measured during the period 1993-1996. The object of the sampling was to assess the potential impacts of existing submerged anthropogenic-radioactive materials in the western North Pacific as well as the East China Sea. Samples from the Bransfield Strait of the Antarctic Ocean provided a control source impacted by only atmospheric bomb fallout. No particularly elevated levels of 239+240Pu were found in zooplankton samples from the Northwest Pacific, although significantly lower levels of 239+240Pu were found in three mixed zooplankton samples from the Bransfield Strait. The body burden of 239+240Pu in zooplankton appears to reflect concentrations in ambient seawater with some variation. Some additional measurements of 137Cs in fish are also reported here to complement existing databases and for future reference in the regional marine environmental radioactivity monitoring effort.  相似文献   

11.
The annual fluxes of artificial radionuclides (238Pu,239+240Pu,241Am,137Cs,90Sr and3H) from the atmosphere to the Ross Ice Shelf in Antarctica were determined from measurements in strata dated by210Pb. Recognizable sources include the U.S. tests (Mike-Ivy and Castle Hill) in the early 1950s, the U.S.S.R. tests of the early 1960s, the SNAP-9A burnup of 1964 and the French and Chinese tests in the late 1960s and 1970s. There are several problems still awaiting resolution: the differences in atmospheric chemistries of fission products and of transuranics produced in weapons tests and the anomalous fluxes of238Pu to the ice shelf which do not appear to reflect a one-year stratospheric residence. There is no evidence for a smearing of the fallout record as a consequence of diffusion of these radionuclides in the glacial column.  相似文献   

12.
The state of radioactive pollution of Lake Ladoga has been studied. The purification half-life of lake water from 90Sr was found to be 21.7 year. The ratio of 90Sr storage in lake water volume to its storage in silts (0?C10 cm layer) was 2: 1. Lake water purification from global 137Cs was slower than that from 137Cs originating from Chernobyl emergency emission because of the chronic supplement of global 137Cs reserve by atmospheric fallouts. The behavior of 90Sr, 137Cs, and 239,240Pu in bed soils was in agreement with the geochemical nature of the elements. By the distribution of 239, 240Pu in bed soils, the sedimentation of substances of non-radiation nature was estimated at 0.3 and 0.5 mm/year at denting and flat relief, respectively.  相似文献   

13.
The deposition record of 137Cs was traced in the SE Black Sea sediments adjacent to the Coruh river mouth in comparison with the earlier studied chronology of 137Cs deposition in front of the Danube delta (NW Black Sea). In both cases, the 137Cs profiles showed two subsurface peaks attributable to maximum fallout of ‘bomb’ and Chernobyl radionuclides. The Coruh profile revealed a larger contribution of ‘bomb’ 137Cs in comparison with the Chernobyl input, suggesting different coverage of NW and SE Black Sea regions with the Chernobyl fallout. The 137Cs-derived dating showed that maximum deposition of particulate bound 137Cs in sediments adjacent to the Coruh river mouth was delayed for 14 yr relative to date of Chernobyl accident, reflecting a buffer effect of the watershed soils. This transit time is 3 times longer than in the Danube catchment area, indicating a difference in retention processes in these mountainous (Coruh) and lowland (Danube) river basins. The 137Cs profile in Coruh sediments showed penetration of 137Cs to much greater depth than would be expected from 137Cs fallout chronology, suggesting the sediment mixing rate of 1.3 cm2 yr−1. This value was used to evaluate deposition chronology of 137Cs, applying the model developed for pulse fallout case. Comparing the measured and modelled data has allowed differentiation of the flood-induced discharge of the 137Cs-containing suspended matter and the slower transit of eroded soil particles from the contaminated catchment areas. The obtained results may be used for the prediction of period when the pollutants, deposited over the river basins, can reach the Black Sea.  相似文献   

14.
Surface sediment samples in the Laptev Sea have average 137Cs content of 7.1 Bq kg(-1), a value intermediate between that of the western Kara Sea (23 Bq kg(-1) and the East Siberian Sea (4.2 Bq kg-'). Both surface sediment content and sediment inventory of 137Cs in the Laptev Sea sediments show significant variability, and the influence of a variety of environmental factors.137Cs concentrations in the Laptev Sea surface sediments range from 0.8 to 16 Bq kg(-1). There is a marked increase in 137Cs content of surface sediment samples collected near the Lena River delta, and a local enrichment in the 137Cs inventories at these sites is also evident. Fine-grained mixed-layer illite/ smectite rich sediments in the estuary provide effective adsorption sites to fix 137Cs, in spite of desorption processes associated with low salinities in estuarine mixing. The Lena River-Laptev Sea mixing zone is a major site of sea-ice production. River and shelf sediments are incorporated into sea-ice formed in this region (Holmes and Creager, 1974). The irregular 137Cs activity profiles of the Lena River estuary cores indicate disturbance or removal of 137Cs-laden sediments via sea-ice related processes. Lena River and Estuary sediments may have served as a secondary source (i.e. other than direct fallout) of 137Cs in sea-ice. North-east of the Lena River estuary, sediment contains a thin layer of 137Cs-bearing material over an erosion surface. The 137Cs-laden surface layer may be the result of transient deposition of estuarine sediments being delivered by sea-ice or spring floods.  相似文献   

15.
137Cs和241Am在滇池、剑湖沉积孔柱中的蓄积分布及时标意义   总被引：16，自引：2，他引：14  
项亮  吴瑞金  吉磊 《湖泊科学》1996,8(1):27-34
自70年代以来,对湖泊沉积物中核试验散落核素的研究已成为研究现代湖泊沉积过程和沉积年代及沉积速率的一个重要方面,本文通过对分别采自云南省滇池、剑湖的两个沉积孔柱中~(137)Cs和~(241)Am蓄积分布的研究,测定了它们60、70年代以来的沉积速率分别是42.1和28.7mg/(cm~2·a)。研究发现,虽然~(241)Am的含量远低于~(137)Cs,但~(241)Am具有沉积后迁移能力较小,半衰期长等特点,因而随着时间的推移,在未来湖泊现代沉积作用的研究中将会显示出越来越重要的作用。  相似文献   

16.
Abstract

The caesium-137 technique affords both an alternative to conventional measurement methods and an effective quantitative estimate of soil redistribution at the basin scale. Among the available calibration relationships which link the degree of increase or depletion of the 137Cs activity relative to the baseline 137Cs input and sediment yield, the mass balance approach has received increased application for its physical basis. First, the applicability of the refined simplified point-based mass balance (RSPMB) model of Zhang et al. (1999) at the scale of the morphological unit is proposed herein. The 137Cs spatial distribution measured in a small Sicilian basin and the spatial distribution of the sediment yield calculated by a sediment delivery distributed approach are used to estimate values of the two key parameters of the RSPMB model, φ1 and φ2, the fraction of 137Cs fallout incorporated into soil and a particle size correction factor, respectively. Finally, the best procedure for experimental testing of a distributed sediment yield model by using caesium-137 measurements is investigated.  相似文献   

17.
The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify 137Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured 137Cs levels were found to be very low (usually <1 Bq kg−1 wet wt) 137Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.  相似文献   

18.
At two locations in southern Lake Huron (U.S.A.), twelve 35.5-cm diameter cores of fine-grained sediments were taken for comparison of the vertical distributions of210Pb and falllout137Cs with the distributions of benthic macroinvertebrates, mainly oligochaete worms (Tubificidae) and the amphipod,Pontoporeia affinis. Locations were selected on the basis of210Pb distributions measured a year earlier which indicated contrasting depths of mixing of surface sediments. At one location the activity of210Pb is uniform down to about 6 cm and 95% of total invertebrates occur within this zone; at the other location the zone of constant activity is only 3 cm deep but 90% of the invertebrates occur within it. Comparison of published tubificid defecation rates with sediment accumulation rates based on210Pb shows that oligochaetes alone can account for mixing in one case while the effects of amphipods may be required in the case of shallower mixing. If mixing is represented as a diffusional process, eddy diffusion coefficients are at least 5.8 and 3.3 cm2 yr?1 at respective locations. In comparison with bioturbation, molecular diffusion is of minor importance in the post-depositional mobility of137Cs. The necessity for introducing a diffusion coefficient varying continuously with depth is indicated by characteristics of the distribution of137Cs. Biological reworking of near-surface sediments is an important process affecting radioactivity and chemical profiles in profundal deposits of this and probably other Great Lakes.  相似文献   

19.
This paper analyzes the relationship between bank sediment storage and radionuclide content in six alluvial sites located in different geomorphic contexts along the lower Rh?ne River. The 137Cs, 238Pu, 239+240Pu, 241Am and 210Pb profiles show different patterns, which indicates a differential storage of contaminated sediment in the banks. Three sites record historical nuclear releases in the river and give evidence for long-term retention of particle-reactive long-lived radionuclides. Two sites record only atmospheric global fallout. Only one site, connected to the river groundwater, provides some evidence for desorption of particle-bound contaminants, with a low and constant 137Cs activity profile. The history of the releases from the Marcoule spent-fuel reprocessing plant—the main source of artificial radioactivity—provides a reliable chronology of the last 50?years. Sediment grain size and bank topography are important factors in determining where artificial radionuclides are stored, but these two parameters cannot be used alone to determine variations in high concentrations of radionuclides. The chronology of fluvial geomorphic “metamorphosis” during the twentieth Century, especially after 1960, is also a critical factor affecting the spatial variability in sedimentation rates and artificial radionuclide storage; the timing of channel deepening and bank sedimentary accretion interfere with the chronology of major floods and the short period of low discharge during the height of contamination from nuclear liquid effluents. The reach-scale adjustment described in this paper can contribute to determining what the local history may have been. This result has important implications for river management decisions.  相似文献   

20.
The 137Cs radioactivity of soils was used as a tracer of soil erosion in a catchment in the Netherlands: 143 samples were analysed to map the 137Cs redistribution using geostatistical interpolation methods. Caesium-137 activities on grassland are significantly higher than on arable land. Also, 137Cs activities on waning slopes are higher and activities on steep slopes are lower. The soil erosion estimates, derived from the 137Cs data, are used to validate the USLE erosion model. The recent Chernobyl nuclear accident also contributed to the 137Cs activity. However, the Chernobyl input of 137Cs, with a constant ratio of 1.765:1 to 134Cs, cannot be used as a tracer of soil erosion. Because of the rapid decay of 134Cs, we will not be possible to separate the sources of 137Cs in the near future in areas significantly influenced by Chernobyl fallout and in these areas 137Cs can no longer be used as a soil erosion tracer.  相似文献   

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