The relative mobility of natural (Th,Pb and Po) and fallout (Pu,Am, Cs) radionuclides in the coastal marine environment: results from model ecosystems (MERL) and Narragansett Bay

The relative mobility of nuclides of Pb, Th, Pu, and Cs, which are widely used as geochemical tracers for sedimentation and bioturbation. was investigated in artificial microcosm tanks (MERL) and in Narragansett Bay. Their mobility was characterized by their removal rates from the water column, their affinity toward particles and their degree of penetration into the surface sediments. Pb, Th, and Pu transport was controlled predominantly by the affinity of these elements to particles, and the transport parameters of the particles themselves (i.e. sediment resuspension and mixing rates). Because of its low distribution coefficient, transport of Cs was controlled by molecular diffusion through pore water in the winter, while in summer, Cs transport was enhanced due to bioturbation. The increase with depth of the $\text{Cs}\text{Pu}$ ratio in core profiles of MERL and Narragansett Bay sediments is thus caused primarily by the higher mobility of Cs.     

Determination of 210Pb, 226Ra and 137Cs in sediments

A method is described for bringing a sediment sample into solution and subsequently carrying out analysis for ²¹⁰Pb, ²²⁶Ra and ¹³⁷Cs. Silica is removed from the sample by cyclic HNO₃HF treatments. ¹³⁷Cs is separated from ²¹⁰Ra in a carbonate fusion, extracted by absorption on ammonium molybdophosphate, precipitated directly with BiI₃ in presence of citric acid, and β-counted. ²¹⁰Pb and ²²⁶Ra are separated out by 70–75% HNO³ precipitation. Further purification and mutual separation of the two radionuclides is achieved by solvent extraction and anion-exchange techniques. ²¹⁰Pb and ²²⁶Ra are determined by β- and α- counting of their chromate precipitates, respectively, after allowing suitable ingrowth periods for their daughters. The procedural steps effectively eliminate possible interference from other natural or fall-out radioactivities.     

Transport mechanism for Pb-210, Cs-137 and Pu fallout radionuclides through fluvial-marine systems

Pb-210, Cs-137 and Pu-239,240 sediment-depth profiles in an anoxic, unbioturbated, estuarine depositional regime at the head of the Saguenay Fjord, Que. exhibit a seasonally-modulated component caused by pulsed inputs of silts and sands during high energy, spring river discharge events superimposed on an ambient depositional pattern of finer grained clays and organic matter. A precise sediment timestratigraphy has been determined by the inverse correlation of the Pb-210 activity with the rate of river discharge during the period, 1963–1976. The historical record of Cs-137 and Pu-239,240 sediment fluxes has been reconstructed through the normalization of fallout radionuclide activities to the excess Pb-210 activity profile. Radionuclide flux geochronologies have been interpreted on the basis of a fluvial-marine transport model which distinguishes between inputs due to direct adsorption of radionuclides onto particles in the water column and inputs resulting from the erosion of particle-associated radionuclides from the drainage basin. Rate constants corresponding to residence times of one year for Cs-137 and Pu-239,240 in the water column and 1500 years for each radionuclide in the drainage basin provide reasonable agreement between the model and experimental results, although there is some evidence for a slightly longer drainage basin residence time for plutonium. Both the threshold for the initial appearance of Pu-238, derived from the atmospheric burnup of a SNAP-9A satellite reactor in 1964, and the magnitude of its isotopic dilution by drainage basin inputs of Pu-239,240 are also in agreement with model predictions.     

Tracing depositional consequences of environmental radionuclides (137Cs and 210Pb) in Slovenian forest soils

Depth distribution profiles of environmental radionuclides (¹³⁷Cs and ²¹⁰Pb) have been investigated in soil to elucidate the underlying environment of semi-natural temperate deciduous and/or coniferous forest soils in Slovenia (?irovski vrh, Idrija, Ko?evski Rog, Pohorie, Gori?nica and Rakitna). Surface enrichment of both nuclides was observed at all the sites investigated in this study, suggesting that the soils had undergone little natural or anthropogenic disturbance for at least the last several decades. Apparent annual burial rates of ¹³⁷Cs (0.1–0.2 cm y^??1) were estimated to be about 1.3 times higher than those of ²¹⁰Pb at individual sites of different lithology, which suggests strong affinity of ²¹⁰Pb to soil organic matter. Variability of the vertical distribution profiles of these nuclides depends not only on “in situ” pedology but also on geographical and meteorological conditions, especially precipitation and wind direction.     

Sources and vertical distribution of 137Cs, 238Pu, 239+240Pu and 241Am in peat profiles from southwest Spitsbergen

This paper presents a detailed survey of the activities of selected man-made radionuclides in peat deposits located in SW Spitsbergen. Peat cores from the High Arctic (SW Spitsbergen) were analyzed by gamma spectrometry (¹³⁷Cs), alpha spectrometry (²³⁸Pu, ^239,240Pu, ²⁴¹Am activities) and by ICPMS (²⁴⁰Pu/²³⁹Pu atom ratios). Maximum activities evident in the peats correspond to the 1963/1964 global maximum fallout from atmospheric testing of nuclear weapons; some of the activity profiles have been altered post-deposition by water infiltration. Activity ratios of ²³⁸Pu/^239+240Pu, ²⁴¹Am/^239+240Pu, ^239+240Pu/¹³⁷Cs and ²⁴⁰Pu/²³⁹Pu atom ratios indicate mixing between global (stratospheric) and regional (tropospheric) sources of these radionuclides in the Svalbard area. The ²³⁸Pu/^239+240Pu activity ratios varied from 0.02 ± 0.01 to 0.09 ± 0.03, suggesting global fallout as the dominant source of Pu. The ^239+240Pu/¹³⁷Cs activity ratios varied from 0.01 ± 0.01 to 0.42 ± 0.11, which apparently arises from the post-depositional mobility of ¹³⁷Cs. The ²⁴¹Am/^239+240Pu activity ratios ranged between 0.10 ± 0.02 and 1.5 ± 0.3 and exceed the published global fallout ratio for Svalbard of 0.37 due to the relatively higher geochemical mobility of Pu vs. Am and/or ingrowth of Am from the decay of ²⁴¹Pu. The atom ratio ²⁴⁰Pu/²³⁹Pu ranged from 0.142 ± 0.006 to 0.241 ± 0.027; however, the vast majority of peat samples exhibited ²⁴⁰Pu/²³⁹Pu atom ratios similar to the stratospheric fallout (∼0.18).     

210Pb activities in and fluxes to sediments of the Washington continental slope and shelf

Surface sediments of the Washington coast have ²¹⁰Pb activites which average 104 ± 48dpm/g for submarine canyon and slope regimes and 18 ± 12dpm/g for the continental shelf regime. ²¹⁰Pb sedimentary fluxes are also higher in canyons, averaging 18 ± 13dpm/cm² per yr, compared to 5.2 ± 3.1 dpm/cm² per yr for slope and 4.8 ± 1.8dpm/cm² per year for shelf regions. These ²¹⁰Pb activities and fluxes are 2–7 times greater than those reported for other coastal regions. Inputs from the atmosphere and the Columbia River are not sufficient to supply the ²¹⁰Pb, but advection of seawater containing dissolved ²¹⁰Pb produced in situ from ²²⁶Ra provides an input several times larger than the sedimentary fluxes. The sedimentary ²¹⁰Pb flux is limited by scavenging reactions rather than by supply of dissolved ²¹⁰Pb.Calculations of maximum biological uptake and fluxes of ²¹⁰Pb and ‘selective’ chemical leaching experiments all show that the primary scavenging processes are due to hydrous Mn and Fe oxides rather than biological phases. The pattern of higher ²¹⁰Pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved ²¹⁰Pb near the sea floor, rather than by processes operating throughout the water column. Relatively rapid removal of dissolved ²¹⁰Pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer.     

Recent accretion in mangrove ecosystems based on137Cs and210Pb

Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides²¹⁰Pb and¹³⁷Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr^?1, with an average rate of 1.6 mm yr^?1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr^?1, with an average of 2.4 mm yr^?1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr^?1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.     

松花湖沉积物~(137)Cs和~(210)Pb分布及沉积速率

松花湖沉积物柱心中存在3个明显的137Cs蓄积峰,分别是37 cm处的1964年蓄积峰、27 cm处的1971年蓄积峰和23 cm处的1975年蓄积峰.利用137Cs核素1964年和1975年对应蓄积峰计算的沉积速率分别为0.86 cm/a和0.71 cm/a.采用210Pb计年的常量初始浓度模式(CIC)计算的平均沉积速率为0.71 cm/a,两者估算的沉积速率吻合.松花湖1964-1975年间的沉积速率明显高于1975-2006年间的沉积速率.137Cs和210Pb计年方法的结合有助于提高沉积速率估算的准确性.     

新疆乌伦古湖的210Pb、137Cs测年与现代沉积速率

通过对乌伦古湖2个沉积柱样的²¹⁰Pb和¹³⁷Cs剖面的观测,运用²¹⁰Pb过剩法和¹³⁷Cs时标法估算了近几十年来的平均沉积速率。研究结果表明：²¹⁰Pb过剩法的CRS模式测定的沉积速率的变化范围为0.018～0.071 g/(cm²·a),137Cs时标法测定沉积速率的变化范围为0.034～0060 g/(cm²·a),两者具有较高的一致性。20世纪60年代以前,人类活动对本区影响相对较小,湖泊的沉积速率主要受自然因素的影响;20世纪60年代以后,随着乌伦古河中、下游农业的发展和调水工程的实现,人类活动逐渐成为主导湖泊演化的因素,从而影响乌伦古湖沉积速率。     

Geochronology of a surface core in the northern basin of Lake Qinghai： Evidence from ^210pb and ^137Cs radionuclides

1 Introduction The radionuclides 210Pb and 137Cs are of particularimportance for estimating the dates of recentsediments. It was Goldberg (1963) who firstlysuggested that the disequilibrium between 210Pb and226Ra could serve as a geochronometer applicable…     

吉林小龙湾沉积速率的210Pb和137Cs年代学方法测定

吉林省辉南县、靖宇县境内有很多小型湖泊(人称龙湾),属火山成因,也可称作玛珥湖^[1]。其中小龙湾(42°18′N,126°22′E),位于辉南县境内,湖面海拔655m,近椭圆形,湖泊长、宽分别约400m和250m,是该区最小的一个积水玛珥湖,湖泊周围无地表径流输入,湖泊面积基本等同流域面积。周围山体海拔约700m,植被茂盛,主要由多旋回、互层的玄武质火山碎屑岩组成,包括火山角砾岩和凝灰岩。2001年6月在湖泊中心部位水深14.41m处,用重力取样器钻取湖泊沉积岩心,岩心长49cm。该孔沉积岩性均一,     

Sedimentary environment change in northwestern of Lake Qinghai Based on the ~(137)Cs and ~(210)Pb

正Lake Qinghai is located in the northeastern margin of qinghai-tibet plateau.It’s very sensitive to climate change.Through the research of modern sedimentary environmental change in Lake Qinghai,We expect to gain the information about its response to global environmental change.Our study collected three sedimentary columns of Lake Qinghai in the northwestern,Column samples’length     

Plutonium, 241Am and 137Cs ratios,inventories and vertical profiles in Washington and Oregon continental shelf sediments

Continental shelf sediments from nine locations off Washington and Oregon have ^239,240Pu inventories which average 8.0 ± 2.6 mCi/km². The Columbia River and seawaters advecting over the shelf supply Pu which is removed to underlying sediments, principally through scavenging by inorganic paniculate matter. Mass balance calculations argue that less than 20 percent of the advected Pu need be scavenged from the water column to balance river input and total shelf sediment inventories. The percentage of the Pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment/water distribution coefficients.No marked separation of Pu from ¹³⁷Cs is observed with depth in Pacific shelf sediments as has been reported in Atlantic coastal sediments. This interocean distinctness can be explained by differences in particle mixing and downward diffusion of Cs in sediments of varying porosities. The transuranic inventories and Pu/Cs ratios in the Pacific sediments do not support the hypothesis of Livingston and Bowen that Pu is remobilized within the sediment column by ‘complexone’ formation with (principally) organic substances.Excess ²¹⁰Pb/^239,240Pu inventory ratios in eight representative cores from the Washington shelf average 100 ± 19, even though absolute values of both inventories vary by much larger factors. This reasonably constant ratio, for a given water depth, permits estimation of total Pu inventories and prediction of sites of unusual Pu accumulation from data on the more easily measured natural radionuclide.     

Transport and sediment accumulation of210Pb and137Cs in two Southeast Alaskan fjords

Sediment profiles of²¹⁰Pb and¹³⁷Cs in cores collected at increasing distances from the heads of Smeaton Bay and Boca de Quadra fjords indicate that watersheds influence the inventories of radioisotopes present and that the steep topographies of the fjords enhance sediment redistribution. Episodic deposition of terrestrially derived sediment was responsible for roughly 50% of the¹³⁷Cs and 45% of the²¹⁰Pb inventories in shallower (less than 180 m) locations in Wilson and Bakewell arms of Smeaton Bay.²¹⁰Pb sedimentation rates at shallower sites when corrected for episodic deposition were less than sedimentation rates obtained in the deep basins of the fjords where sediment focusing and increased primary productivity in the overlying water column occur. Higher fluxes of dissolved Mn from surficial sediments and subsequent reoxidation in the overlying water may have enhanced scavenging of²¹⁰Pb in basin locations, resulting in higher inventories. Episodic events have occurred frequently in Smeaton Bay and Boca de Quadra suggesting that steady-state conditions with respect to sedimenting particles can be achieved only when averaged over long time periods approaching the time over which¹³⁷Cs and²¹⁰Pb are useful.     

渤海地区^210Pb、^137Cs同位素测年的研究现状

近百年来环渤海地区的沉积作用是影响该区近现代地质环境变化的重要因素。本文收集了该区迄今公开发表的用于确定现代沉积速率的84组^210Pb、^137Cs柱状剖面（包括210Pb样柱52组，^210Pb、^137Cs样柱32组），其中海区39组，潮间带及沿海低地地区45组。环渤海地区的^210Pb放射性活度的深度分布曲线主要表现为3种形式：理想指数衰变型、近等幅摆动型和海洋特殊动力事件影响型。根据由陆向海方向沉积速率的变化，可初步划分为沿岸低沉积速率带、开放潮坪高沉积速率带及海区低沉积速率区；区域性差异则表现为渤海湾开放潮坪区上部由北（蓟运河口）向南（老狼坨子）沉积速率表现为高-低-高，辽东湾从其西侧的锦州湾向东至辽河河口的开放潮坪地区，沉积速率递减，黄河三角洲地区及其附近海域属于间歇式快速沉积区，莱州湾西部为高速沉积区。     

Determination of diffusion coefficients associated with the transport of210Pb radionuclides in lake bed sediments

An iterative least-squares optimization technique is utilized in conjunction with a one-dimensional representation of the mass transport equation to generate theoretical²¹⁰Pb concentration/depth profiles beneath the water-sediment interface that are best-fit approximations to directly measured²¹⁰Pb concentration/depth profiles at various locations within the Great Lakes system. The outputs of such an optimization analysis are the diffusion coefficientsD _M (molecular) andD _B (bioturbation) associated with the transport of²¹⁰Pb radionuclides in lake bed sediments. For all stations studied, the estimated values ofD _B are consistently larger than the estimated values ofD _M , emphasizing the importance of accounting for the effects of bioturbation in the modelling of contaminant transport through lake bed sediments.     

内蒙古乌梁素海~(210)Pb和~(137)Cs测年与现代沉积速率

对乌梁素海沉积物柱心样品进行210Pb、137Cs测年分析表明,柱心剖面上有明显的1963年蓄积峰,这个蓄积峰对乌梁素海的现代沉积有明显的时标意义。根据210Pb的CRS模式,可以计算出每个样品深度所对应的年代,在该沉积柱心中与137Cs时标吻合较好。乌梁素海的沉积速率并不稳定,变化比较大,表明乌梁素海近113 a来沉积环境不稳定。210Pb、137Cs两种计年方法的结合有助于认识沉积速率变化较大的沼泽的沉积状况,也有助于对核素计年方法的理解。     

Radionuclide dating(~(210)Pb,~(137)Cs) of recent inter-dune saline lake sediment cores in the Badain Jaran Desert,Inner Mongolia,Northwest China

正Inter-dune lake sediment cores are ideal and unavailable materials for study climate and environmental changes of arid region.The precious dating of lake sediment cores is required for carrying out high resolution climate and environmental changes with these cores.The Badain Jaran inter-dune lake group embedding in the sand sea is the     

Accretion and canal impacts in a rapidly subsiding wetland. I.137Cs and210Pb techniques

The influence of canals on vertical marsh accretion, including mineral sediment and organic matter accumulation, was evaluated at three locations along the Louisiana coast representing different geographic regions. The isotopes²¹⁰Pb and¹⁵⁷Cs were used to determine vertical accretion along transects representing a canal and a control site. Rapid rates of vertical accretion were measured at all sites and ranged from 0.47 cm yr^?1 to 0.90 cm yr^?1. Results indicated that there was no measurable effect of canals on marsh accretionary processes. In general, greater variation in vertical accretion, including mineral sediment deposition and organic matter accumulation, was observed between geographical regions than between canal and control sites within a region. Statistical analysis of data suggest that any difference between canal and control site would be less than 0.20 cm yr^?1. Such a change in marsh surface-water level relationships as a result of any canal influence on marsh accretionary processes would be less than reported eustatic sea-level rise for the Gulf of Mexico. Results suggest that any change in the marsh surface-water level relationship could be the influence of canals on local hydrology, resulting in increased water level rather than any appreciable reduction in accretionary processes. Such changes in hydrology under certain conditions could stress vegetation, resulting in marsh deterioration.     

210Pb and 137Cs measurements in the Circum Bohai Sea coastal region: sedimentation rates and implications

The representative ²¹⁰Pb and ¹³⁷Cs age-depth profiles were selected from more than 100 sites in the Circum Bohai Sea (CBS) coastal region to examine the sedimentation rates and associated environmental changes. There are three unique ²¹⁰Pb_exc distribution patterns: 1) ideal-decaying type, representing relatively constant sediment supply and quieter environmental setting; 2) wiggling type, but with approximately equivalent amplitude, representing coarser sediments and associated stronger flow current environment; and 3) episodic-eventinfluencing type, each representing typhoon storm-influenced depositional environment. Our results also show that there is a lower sedimentation rate (ca. 0.1 cm/a) in the coastal lowlands, a higher sedimentation rate (ca. 0.5–3 cm/a) in the intertidal flat and an intermediate rate of ca. 0.58 cm/a in the subtidal zone near the Huanghua Harbor. The interbedded silt layer occurring in the core sediment reveals lower ²¹⁰Pb activities, indicating a discontinuous sedimentation mostly due to typhoon events which dwarfs against ²¹⁰Pb and ¹³⁷Cs applicability. Overall, the ²¹⁰Pb and ¹³⁷Cs measurements of the present study provide physical insight into the evaluation of the coastal-marine ecological environment and associated management.