利用210Pb、137Cs和241Am计年法测算云南抚仙湖现代沉积速率

通过对云南抚仙湖沉积物柱芯样品的210Pb、137Cs和241Am测试表明,柱芯剖面上有明显的1963年和1986年137Cs蓄积峰,验证了1975年次级蓄积峰存在的可能性,这些峰形完好的蓄积峰对抚仙湖的现代沉积环境有明显的时标意义。利用137Cs计年法得到抚仙湖沉积物自1963年、1975年及1986年以来到2007年的平均沉积速率分别为0.063g/(cm2·a)、0.052g/(cm2·a)和0.039g/(cm2·a),说明了过去近五十年抚仙湖沉积速率整体上经历了一个由快到慢的过程。借助于241Am 的1963年蓄积峰可以提高137Cs计年的准确性。根据210PbCRS计年模式,计算出每个样品深度所对应的年代,与137Cs计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。通过质量深度和年代分析,抚仙湖的沉积速率变化幅度比较大,表明抚仙湖近129年来的沉积环境不稳定,可能与相应历史时期的人类活动有密切的关系。     

Estimation of suspended sediment sources using 137Cs and 210Pbex in unmanaged Japanese cypress plantation watersheds in southern Japan

To analyse suspended sediment sources in unmanaged Japanese cypress plantation watersheds, field measurements and fingerprinting of the suspended sediment was conducted in the Shimanto River basin in southern Japan. For sediment fingerprinting, ¹³⁷Cs and ²¹⁰Pb_ex were detected by means of gamma‐ray spectrometry in the surface soil of the forest floor, stream bank and truck trail and mobilized sediment by interrill erosion. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the forest floor materials were considerably higher than those of the stream bank and truck trail. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the suspended sediment were found to vary with the sampling period. Evidently, the suspended sediment can comprise materials generated from the forest floor by interrill erosion and those from the truck trail and/or stream bank. The multivariate sediment‐mixing model using ¹³⁷Cs and ²¹⁰Pb_ex showed that the contribution of the forest floor varied periodically, ranging from 23–56% in the Hinoki 156 subwatershed and from 18–85% in the Hinoki 155 subwatershed. The difference in the average contribution of the forest floor between Hinoki 156 (46%) and Hinoki 155 (69%) may relate to the presence of truck trail networks in the watershed. The truck trail network can play roles of sediment source and pathway for sediment from forest floor to stream channel due to the concentrated overland flow on the truck trail during heavy rainfall events. These results indicate that the forest floor should be recognized as a major source of suspended sediment in unmanaged Japanese cypress plantation watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Depositional history of artificial radionuclides in the Ross Ice Shelf,Antarctica

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.     

Sudden enhancement of sedimentation flux of <Superscript>210</Superscript>Pb<Subscript>ex</Subscript> as an indicator of lake productivity as exemplified by Lake Chenghai

The fundamental assumption of ²¹⁰Pb sediment dating is the stable flux of ²¹⁰Pb_ex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the ²¹⁰Pb_ex activity in sediments will be exponentially reduced with sedimentation age. ²¹⁰Pb_ex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly increased, ²¹⁰Pb_ex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of ²¹⁰Pb dating; on the other hand, the sudden enhancement of ²¹⁰Pb_ex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of ²¹⁰Pb_ex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of ¹³⁷Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of ²¹⁰Pb_ex activity displays a specific distribution of peaks, and is similar to the vertical profile of C_org. This phenomenon seems to be related to the mechanism of constraining the transfer of ²¹⁰Pb_ex into lake sediments. The average atomic ratios of H_org/C_org and C_org/N_org in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(C_org)) of organic carbon (C_org) since 1970 were calculated by modeling. The sedimentation fluxes of ²¹⁰Pb_ex (F(²¹⁰Pb_ex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(C_org)), especially in the years of 1972–1974 and 1986–1989. The variation of F(C_org) led to the variation of F(²¹⁰Pb_ex); the variation of F(²¹⁰Pb_ex) reflects, to some extent, the historical variation of lake productivity.     

利用~(210)Pb、~(137)Cs和~(241)Am计年法测算云南抚仙湖现代沉积速率

通过对云南抚仙湖沉积物柱芯样品的~(210)Pb、~(137)Cs和~(241)Am测试表明,柱芯剖面上有明显的1963年和1986年~(137)Cs蓄积峰,验证了1975年次级蓄积峰存在的可能性,这些峰形完好的蓄积峰对抚仙湖的现代沉积环境有明显的时标意义。利用~(137)Cs计年法得到抚仙湖沉积物自1963年、1975年及1986年以来到2007年的平均沉积速率分别为0.063g/(cm~2·a)、0.052g/(cm~2·a)和0.039g/(cm~2·a),说明了过去近五十年抚仙湖沉积速率整体上经历了一个由快到慢的过程。借助于~(241)Am的1963年蓄积峰可以提高~(137)Cs计年的准确性。根据~(210)Pb CRS计年模式,计算出每个样品深度所对应的年代,与~(137)Cs计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。通过质量深度和年代分析,抚仙湖的沉积速率变化幅度比较大,表明抚仙湖近129年来的沉积环境不稳定,可能与相应历史时期的人类活动有密切的关系。     

Use of fallout radionuclides as indicators of erosion processes

The different depth penetration characteristics of ¹³⁷Cs, ⁷Be and ²¹⁰Pb excess in undisturbed soils can be used to identify erosion processes by analysis of sediments derived from surface erosion. Caesium-137 concentrations (half-life 30 years) typically decrease to half the surface value at between 30 and 50 mm. Beryllium-7 (half-life 53 days) has half-penetration depths of between 0.7 and 10 mm, whereas ²¹⁰Pb excess (half-life 20.2 years) has half-penetration depths between 10 and 30 mm. Experiments designed to determine the applicability of these depth penetration characteristics to soil erosion studies are reported. Surface runoff was artificially generated at two locations in a grazed paddock using a rainfall simulator. Suspended sediment was extracted from runoff and analysed for natural and artificial gamma emitting radio-nuclides. Suspended sediment derived from sheet flow contained initially high values of ¹³⁷Cs, ⁷Be and ²¹⁰Pb excess. As the experiment continued ¹³⁷Cs concentrations remained high, but ⁷Be and ²¹⁰Pb excess value decreased with time. This is interpreted as indicating a change from sheet dominated erosion to rill dominated erosion. During a second experiment artificial rain was allowed to fall onto an eroded gully wall. The derived suspended sediment contained no detectable ¹³⁷Cs, ⁷Be or ²¹⁰Pb excess. Overland flow from above the gully wall was then allowed to run down the gully face and mix with the water falling directly onto the gully wall. There was no detectable change in the radionuclide signature, showing that the gully wall was the predominant source of sediment. This was tested independently by mass balance and ²²⁶Ra to ²³²Th ratios. The good correlation between ²¹⁰Pb excess and ⁷Be at this site suggests that the differential technique described here may be applicable over time-scales longer than are possible with ⁷Be. It may therefore be practical to examine catchment erosion history through analysis of ²¹⁰Pb excess and ¹³⁷Cs in sediment cores.     

Spatial variability in sedimentation rates and artificial radionuclide storage in alluvial banks of the lower Rh?ne River

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.     

Floodplain sedimentation rates in an alpine watershed determined by radionuclide techniques

Vertical profiles of the activities of ¹³⁷Cs and ²¹⁰Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm^?2 yr^?1 and were in good agreement with sedimentation rates calculated from the inventories of ¹³⁷Cs and ²¹⁰Pb. Sedimentation rates calculated from the position of the ¹³⁷Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of ¹³⁷Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the ¹³⁷Cs and ²¹⁰Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.     

Chronology of Holocene lacustrine sediments in Co Ngoin, central Tibetan Plateau

Lake sediments, in which abundant, continuous and high resolved signals are preserved, have the potential to recover the history of terrestrial environmental variation. The value of such paleo-environment signals depends firstly on tying them to accurate …     

Comparative dating of recent peat deposits using natural and anthropogenic fallout radionuclides and Spheroidal Carbonaceous Particles (SCPs) at a local and landscape scale

Proxy records from recently accumulated peats provide valuable information about past environmental change, but they depend on high quality chronological information to calculate rates and timing of change. However, there is uncertainty in the accuracy and consistency of the methodologies used for dating recent peats. This study compares results from Spheroidal Carbonaceous Particles (SCPs) and natural and anthropogenic fallout radionuclides (²¹⁰Pb, ¹³⁷Cs and ²⁴¹Am) used to date three replicate cores from three contrasting sites. Data are used to test the consistency of dating techniques within and between sites, and to assess the impact of local conditions on geochronological results.There is broad consistency in results, but there is also a significant disagreement between dates in a number of cores, both within and between sites. A relatively dry site that had been affected by past burning and erosion showed the greatest consistency between methods and replicate cores. Wetter, less degraded sites showed least consistency. Using patterns of (dis)agreement between dating techniques we assess the potential causes of dating inaccuracy. The data support previous suggestions that ²¹⁰Pb is mobile in wetter conditions, and suggests that ²⁴¹Am can be considered an increasingly valuable radionuclide. Finally, our data suggest the current estimates for SCP-based ages in the region maybe incorrect and require further regional calibration.Using several techniques on replicate cores from three sites in the same area has provided a more robust evaluation of the likely reliability of individual techniques and the processes that may adversely affect them. We conclude that until advances are made in understanding the processes behind the variable quality of SCP and fallout radionuclide dating, using two or more dating techniques will greatly improve understanding of the validity of a peatland chronology, especially in wetter locations.     

Multiple dating of varved sediments from Lake Łazduny,northern Poland: Toward an improved chronology for the last 150 years

On two short sediment cores from Lake Łazduny (northeastern Poland) different methods for age estimation were applied including varve counting, ²¹⁰Pb, ¹³⁷Cs and OSL dating. The investigated sediment consists of finely laminated, organic-rich calcareous gyttja interrupted by a sand layer. For ²¹⁰Pb we tested the CFCS, CIC, CRS and SIT models and compared the results with the established varve chronology and the ¹³⁷Cs distribution. The total ²¹⁰Pb activity distribution is consistent between cores and shows a regular decrease with depth. However, the total inventory of unsupported ²¹⁰Pb was significantly different and indicates varying rates of sediment focusing. Our results show that all ²¹⁰Pb dating models used in this study produced different results, while the SIT model performed best in comparison with varve counts and ¹³⁷Cs peaks. The CFCS model produced a realistic age-depth trend but obtained ages were too old compared to the varve time scale. The age estimates provided by the CRS model were too old as well with an increasing offset downcore and the CIC model failed completely by producing an unrealistic chronology with age inversions. This confirms that only systematic testing of different ²¹⁰Pb dating models and routine validation using independent time markers produces reliable ²¹⁰Pb chronologies. OSL dating of two samples from the sand layer provided much too old results which indicate incomplete bleaching during deposition of the analyzed quartz grains. This multiple dating approach demonstrates the considerable potential but also potential pitfalls of dating such young sediments.     

Use of fallout tracers 7Be, 210Pb and 137Cs to distinguish the form of sub‐surface soil erosion delivering sediment to rivers in large catchments

Fallout radionuclides (FRNs) ¹³⁷Cs and ²¹⁰Pb are well established as tracers of surface and sub‐surface soil erosion contributing sediment to river systems. However, without additional information, it has not been possible to distinguish sub‐surface soil erosion sources. Here, we use the FRN ⁷Be (half‐life 53 days) in combination with ¹³⁷Cs and excess ²¹⁰Pb to trace the form of erosion contributing sediment in three large river catchments in eastern Australia; the Logan River (area 3700 km²), Bowen River (9400 km²) and Mitchell River (4700 km²). We show that the combination of ¹³⁷Cs, excess ²¹⁰Pb and ⁷Be can discriminate horizontally aligned sub‐surface erosion sources (rilled and scalded hillslopes and the floors of incised drainage lines and gully ‘badland’ areas) from vertical erosion sources (channel banks and gully walls). Specifically, sub‐surface sources of sediment eroded during high rainfall and high river flow events have been distinguished by the ability of rainfall‐derived ⁷Be to label horizontal soil surfaces, but not vertical. Our results indicate that in the two northern catchments, erosion of horizontal sub‐surface soil sources contributed almost as much fine river sediment as vertical channel banks, and several times the contribution of hillslope topsoils. This result improves on source discrimination provided previously and indicates that in some areas erosion of hillslope soils may contribute significantly to sediment yield, but not as topsoil loss. We find that in north‐eastern Australia, scalded areas on hillslopes and incising drainage lines may be sediment sources of comparable importance to vertical channel banks. Previous studies have used the combination of ¹³⁷Cs, excess ²¹⁰Pb and ⁷Be to estimate soils losses at the hillslope scale. Here, we show that with timely and judicious sampling of soil and sediment during and immediately after high flow events ⁷Be measurements can augment fallout ¹³⁷Cs and ²¹⁰Pb to provide important erosion source information over large catchments. Copyright © 2013 John Wiley & Sons, Ltd.     

Radioactivity in sediments of the Great Lakes: Post-depositional redistribution by deposit-feeding organisms

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.     

Transport of the environmental radionuclides in an alpine watershed

The radionuclides¹³⁷Cs,²¹⁰Pb and⁷Be have been examined in the alpine Rhoˆne watershed (Switzerland) during a period of two years in order to evaluate their usefulness as tracers of the removal and transport rate of top-soil particles and particle-reactive contaminants of atmospheric origin. The specific activities of the radionuclides in fluvial suspension show a distinct seasonal pattern which depends on the hydrologic regime of the stream and the sources of the suspended matter. Input-output budgets based on the atmospheric deposition and fluvial removal of three radionuclides in the alpine Rhoˆne watershed are used to estimate their erosional residence times. The simplest one box model yields mean residence times of about 800 and 1400 years for¹³⁷Cs and²¹⁰Pb, respectively. The removal rate of short-lived⁷Be suggests that a part of the watershed (0.6–2.3% of the total surface) is exposed to a rapid erosion, in which the mean residence time of the radionuclides is in the range of 1–220 days. This has little influence on the calculated residence time of¹³⁷Cs but increases the estimated residence time of²¹⁰Pb in soil to over 1800 years. The use of²¹⁰Pb-⁷Be pair in fluvial output may be very helpful in the assessment of the impact of atmospheric pollutants on the water quality in rivers and lakes.     

Quantifying hillslope erosion rates and processes for a coastal California landscape over varying timescales

The Earth's surface erodes by processes that occur over different spatial and temporal scales. Both continuous, low‐magnitude processes as well as infrequent, high‐magnitude events drive erosion of hilly soil‐mantled landscapes. To determine the potential variability of erosion rates we applied three independent, field‐based methods to a well‐studied catchment in the Marin Headlands of northern California. We present short‐term, basin‐wide erosion rates determined by measuring pond sediment volume (40 years) and measured activities of the fallout nuclides ¹³⁷Cs and ²¹⁰Pb (40–50 years) for comparison with long‐term (>10 ka) rates previously determined from in situ‐produced cosmogenic ¹⁰Be and ²⁶Al analyses. In addition to determining basin‐averaged rates, ¹³⁷Cs and ²¹⁰Pb enable us to calculate point‐specific erosion rates and use these rates to infer dominant erosion processes across the landscape. When examined in the context of established geomorphic transport laws, the correlations between point rates of soil loss from ¹³⁷Cs and ²¹⁰Pb inventories and landscape morphometry (i.e. topographic curvature and upslope drainage area) demonstrate that slope‐driven processes dominate on convex areas while overland flow processes dominate in concave hollows and channels. We show a good agreement in erosion rates determined by three independent methods: equivalent denudation rates of 143 ± 41 m Ma^?1 from pond sediment volume, 136 ± 36 m Ma^?1 from the combination of ¹³⁷Cs and ²¹⁰Pb, and 102 ± 25 m Ma^?1 from ¹⁰Be and ²⁶Al. Such agreement suggests that erosion of this landscape is not dominated by extreme events; rather, the rates and processes observed today are indicative of those operating for at least the past 10 000 years. Copyright © 2006 John Wiley & Sons, Ltd.     

210Pb和137Cs定年技术在湖泊沉积物中的应用与问题

湖泊沉积记录研究对了解流域侵蚀、揭示区域气候环境变化及人类活动影响、建立外生地球化学循环模式等均具有重要意义.放射性同位素~(210)Pb和~(137)Cs组合定年法是百年尺度湖泊沉积记录研究的首选方法,在过去几十年中得到了广泛应用,大力推动了湖泊沉积记录的高分辨率气候环境变化研究的开展.然而,如何理解和选择适用的计算模式来尽可能地提高定年准确度目前仍存在争议,这在一定程度上限制了该方法的应用.鉴于上述问题,本文基于本实验室近年来从青藏高原获取的若干支代表性湖芯的定年结果,从样品前处理、仪器及测试、数据分析及计算等全过程对~(210)Pb、~(137)Cs定年原理和方法进行了较为系统的阐述;在此基础上,提出了~(210)Pb定年样品封装原则,探讨了高纯锗γ谱仪在放射性活度测量中的影响因素,并建立了准确有效的比活度校正方法;明确指出了恒定初始浓度模式(constant initial concentration,CIC)可用于计算沉积物每层的年龄,而不是部分研究中认为的平均沉积速率,这对于深刻理解该定年模式并提供准确的定年结果具有重要的参考意义.同时,通过对比两种放射性核素的分布特征发现,相对于~(210)Pb而言,~(137)Cs更容易发生垂向迁移进而影响其时标准确性,这需引起研究者的充分重视,因此,当二者定年结果出现明显差异时,建议以~(210)Pb定年结果为准.     

137Cs湖泊沉积年代学方法应用的局限——以Crawford湖为例

＾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     

210pb as a chronometer and tracer,Burrinjuck Reservoir,Australia

Cores taken at Burrinjuck Reservoir in southeastern New South Wales have been dated using the first appearance of ¹³⁷Cs, charcoal/bushfire correlations, and annual grass pollen peaks. None of the main ²¹⁰Pb dating models reproduced the ‘known’ chronology. Correlation analysis shows no significant relationship between original ²¹⁰Pb (unsupp.) concentration and grain-size, sedimentation rate or loss on ignition. Differences in sediment source may explain the variations in ²¹⁰Pb. A simple provenance model has been used to interpret the ratio of original ²¹⁰Pb (unsupp.)/²²⁶Ra as a tracer of topsoils and subsoils. High ratios in the reservoir sediments probably indicate eroded topsoils and low ratios eroded subsoils.     

Sedimentation rates in the central lake constance determined with210Pb and137Cs

Sediment cores from central Lake Constance were dated with²¹⁰Pb and¹³⁷Cs. A sedimentation rate of (0.11±0.02) g·cm⁻²·y⁻¹ was determined with the²¹⁰Pb method.¹³⁷Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm⁻²·y⁻¹ and (0.08±0.01) g·cm⁻²·y⁻¹ respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the¹³⁷Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30–125 days residence times for suspended particulate matter were calculated from⁷Be measurements.     

137Cs和241Am在滇池、剑湖沉积孔柱中的蓄积分布及时标意义

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。