Unsupported 210Pb Research Articles

Application of Constant Rate of Supply Model for the Determination of Sediment Accumulation Rates and Chronology of Bukit Merah Reservoir Perak, Malaysia

The Constant Rate of Supply (CRS) model is used to measure the continuous influx of unsupported 210Pb into the sediment, allowing for the assessment of changes in the rate of sediment accumulation due to anthropogenic impacts over time. Thus, the CRS model was used to analyze a 25 cm bottom sediment core extracted from Bukit Merah Reservoir. Results revealed a high sedimentation rate in the reservoir, which ranged from 0.14 to 0.37 gcm-2 yr-1, with a mean sedimentation rate of 0.31 cm yr-1. The presence of 137Cs was not observed in the core, while the activity of 241Am was detected in two isolated samples but was insufficient for use as a marker. The constant rate of 210Pb supply (CRS) model dated the oldest sediments (22.5-24.5 cm) to AD 1985 ± 34 years of human influences. Overall, the sedimentation rate in the reservoir experienced a rapid increase from the 1980s to the 2000s and fluctuated to the top of the core indicating continuous anthropogenic impacts on the reservoir. The study identified continuous increases in agricultural activities, expansion in the tourism industry, population growth, and changes in land use, as the main cause of heightened sedimentation and sediment particles delivery into the reservoir. Therefore, urgent measures are needed to address the current siltation state of the reservoir.

Natural radionuclides as tracers of coastal sediment dynamics in El Confital Bay (Spain): Spatial distribution and relationships with sediment characteristics

Erosion and accumulation of coastal areas have become an increasing concern in recent years since they can result in important social and economic problems. In this framework, natural radionuclides have emerged as an alternative tool to study coastal sediment transport and help with the management of the littoral zone. However, there is still a lack of knowledge on how these radionuclides can be applied as tracers of coastal sediment dynamics and how the sediment characteristics can influence this use. Thus, a methodology is presented in this work to use natural radionuclides as tracers of coastal erosion, transport and accumulation of sediments. For this purpose, the spatial distributions of 226Ra, 228Ra, 40K and unsupported 210Pb (210Pbex) in two periods of time were analysed and compared in a coastal area with diverse marine dynamics. The results showed that 226Ra, 228Ra and 40K identified the different sediment erosion, transport and accumulation occurring in the study region. In addition, it was found that changes in the activity concentrations of the samples were mostly related to variations in their mineralogical composition. Finally, the activity concentration values of 210Pbex made it possible to trace the areas where accumulation due to the sedimentation of aerosol particles in the seabed is favoured. These results highlight the suitability of natural radionuclides to study coastal sediment transport.

Considerations on premises of recent (< 120 years) sedimentation rate models with unsupported 210Pb: a study case of sediment cores from mud shelf depocenters

Considerations on premises of recent (< 120 years) sedimentation rate models with unsupported 210Pb: a study case of sediment cores from mud shelf depocenters

210Pb-based dating of recent sediments with χ-mapping versions of the CFCS, CIC, CF and TERESA models

The 210Pb-based method allows for absolute age determination in recent sediments on the centennial scale. The most common sedimentary scenarios involve ideal deposition without any further redistribution. The conventional models apply to such conditions by adding specific assumptions that allow analytical formulations: constant flux (CF), constant initial concentration (CIC), and constant flux with constant sedimentation (CFCS). The χ-mapping models are presented as a novel methodological approach. They generate a large number (105 to 106) of potential solvers, consisting of sets of n (the number of slices in the core) values of initial activity concentrations, A0, and sedimentation rates, w. Empirical data serve to attract the solver that minimizes a χ function after encountering the best sorting along the core of the A0 and w values. The specific assumptions of the above models are reformulated in terms of the statistical distributions of A0 and w. The performance of the χ-mapping versions is demonstrated with a set of cores from the literature with independent chronologies. The main advantages compared to known analytical formulations are: i) χ-mapping provides a more robust fitting method. ii) It overcomes the problem of age reversals often found in the CIC model. iii) The CF model successfully applies to cores with unsteady and/or incomplete inventories. iv) The TERESA model (time estimates from random entries of sediments and activities), without analytical counterpart, is the only model that can manage continuous trends of change in the fluxes of unsupported 210Pb. The work discusses the conditions for compensating model errors in the chronologies, and the use of the palaeorecords of fluxes, A0 and w. The methodology can be extended to other assumptions (models) and provides novel and insightful views on the 210Pb-based dating of recent sediments.

Chemical availability of fallout radionuclides in cryoconite

Atmospheric deposition on glaciers is a major source of legacy fallout radionuclides (FRNs) accumulating in cryoconite, a dark granular material with surface properties that efficiently bind FRN contaminants (specifically 137Cs; 210Pb; 241Am). Cryoconite-bound FRNs in glaciers can be released when they interact with and are transported by glacial meltwater, resulting in the discharge of amassed particulate contaminants into aquatic and terrestrial environments downstream. The environmental consequences of FRN release from the cryosphere are poorly understood, including impacts of cryoconite-sourced FRNs for alpine food chains. Consequently, there is limited understanding of potential health risks to humans and animals associated with the consumption of radiologically-contaminated meltwater. To assess the chemical availability of cryoconite-adsorbed FRNs we used a three-stage sequential chemical extraction method, applied to cryoconite samples from glaciers in Sweden and Iceland, with original FRN activity concentrations up to 3300 Bq kg−1 for 137Cs, 10,950 Bq kg−1 for unsupported 210Pb (210Pbun) and 24.1 Bq kg−1 for 241Am, and orders of magnitude above regional backgrounds. Our results demonstrate that FRNs attached to cryoconite are solubilized to different degrees, resulting in a stage-wise release of 210Pbun involving significant stepwise solubilization, while 137Cs and 241Am tend to be retained more in the particulate phase. This work provides an insight into the vulnerability of pristine glacial environments to the mobilization of FRN-contaminated particles released during glacier melting, and their potential impact on glacial-dependent ecology.

210Pb-based dating of recent sediments with the χ-mapping version of the Constant Sediment Accumulation Rate (CSAR) model

The 210Pb-based method aims at determining the absolute age of recent sediments on the centennial scale. A family of models assumes that at the sediment-water interface the flux of unsupported 210Pb (210Pbexc), F, relates to its initial activity concentration, Ao, and the mass sedimentation rate, w, as: F=Aow. Additional specific assumptions that allow for analytical formulations of the models are: i) constant Ao (CIC), constant F (CF), and constant F with constant w (CFCS). A model with constant w (CSAR) was suggested for completeness but never used because of the lack of a suitable analytical formulation. The TERESA model assumes random and independent variability for Ao and w, described by normal distributions. It systematically generates a large number (∼105) of potential solutions, whose performance for fitting the empirical 210Pbexc profile is quantified through the χ-function. This work aims to adapt the above methodology to formulate the χ-mapping version of the CSAR model. The performance of the model is evaluated with a set of synthetic and real cores for which an independent chronology is available. CSAR is able to capture the mean sedimentation rate from the 210Pbexc data and provides reliable chronologies and paleorecords of Ao, useful for tracking past changes in sedimentary conditions. CSAR provides an interesting different perspective for researchers working with 210Pb-based dating of recent sediments.

Distribution and storage of uranium, and its decay products, in floodplain sediments

Industrialised rivers contain legacy contaminants stored in their sediments and floodplain soils which may inhibit attainment of environmental quality criteria. The River Fal catchment, SW England, is impacted by inputs from uranium mining and clay production and serves as an exemplar for understanding the consequences of medium-term process dynamics in contaminated basins. Radionuclides were determined, by gamma spectroscopy, in six cores from the river floodplain with the aim of quantifying the activities of 238U, and its decay products, and the bomb fallout radionuclides137Cs and 241Am. Activity concentrations of 238U implied inputs from mining, accentuated by flood events and historic industrial accidents, whereas 210Pb activities included a significant input of unsupported 210Pb linked to processed mine spoil. The radionuclide inventories did not decrease systematically downstream revealing evidence of attenuation of particulate radionuclides within the river floodplain sediment column. Storage of legacy contaminants in fluvial systems, at levels in excess of contemporary environmental quality guidelines, emphasises the challenges posed by changing climatic conditions. This scenario raises significant consequences for the management of uranium-contaminated, fertile riverine floodplains within Europe.

Inventories, profiles and deposition fluxes of 210Pbex in mineral and organic (peatlands) Southern Hemisphere soils

Unsupported 210Pb (210Pbex) activity profiles have been determined in both mineral soils from Argentina (La Plata region) and organic soils from Brazil (Serra do Espinhaço Meridional). For the Argentine mineral soils, no significant differences in the 210Pbex inventories are found (ranging from 2920 ± 560 to 4570 ± 460 Bq/m2). The measured activity profiles are properly fitted by the one-dimensional transport model by effective diffusion and migration developed by He and Walling and the resulting parameters were analyzed considering the soil properties. It was observed that the migration rate is inversely proportional to the illite content, that the soils with higher amounts of smectite exhibit higher migration rates, and that the higher the pH, the higher the migration rate. These results agree with the higher Pb sorption capacity of smectite than illite, at identical conditions, and the Pb speciation with pH, that gives raise to different interactions between Pb and soil components. For organic soils, 210Pbex accumulates in superficial layers (5 cm depth) and the 210Pbex inventories (ranging from undetectable value to 5100 ± 200 Bq/m2) depend on the altitude of the sampling points. The activity values of 210Pbex and 137Cs (previously reported) are not significantly correlated, probably because the 137Cs fallout occurred more than 50 years ago, allowing the 137Cs profiles to develop. Finally, the deposit fluxes were determined for both regions studied and were incorporated into the global curve elaborated in previous works, contributing to a better definition of the general trend reported for the Southern Hemisphere.

Using environmental tracers to understand soil organic carbon and soil erosion on a steep slope hillslope in south-east Australia

Context It is well recognised that soil organic carbon (SOC) can be transported and deposited along the same pathways as those of soil erosion and deposition. Aims To examine the viability of environmental tracers 137Cs and unsupported 210Pb (210Pbex) as tools to inform soil erosion and deposition patterns as well as that of the distribution of SOC. Methods Multiple soil cores were collected along two transects of similar length and aspect in a steep-slope soil mantled environment in south-east Australia. Key results Average SOC concentration was high for both transects (~6% and 4%). SOC decreased moving downslope suggesting loss of SOC by erosion. There were strong and significant positive relationships of SOC with 137Cs and 210Pbex (both r > 0.77, P < 0.0001). At this site, SOC concentration appears related to erosion and deposition patterns. Conclusion The hillslope distribution of 137Cs and 210Pbex were very similar, indicating that both tracers were viable in this environment (r = 0.9, P < 0.0001). The different origins and half-lives of 137Cs and 210Pbex also demonstrate that the patterns of erosion and deposition are consistent at decadal time scales. Implications The use of 210Pbex provides an alternative method for understanding erosion and deposition patterns as well as that of SOC, given that the viability of 137Cs (half-life of 30.1 years) is now questionable due to no new replenishment.

Lessons Learnt from the Revitalisation of Chemical Factory in Marktredwitz and River Banks Downstream: When ‘Renaturation’ Can Be Harmful

Our study addressed mercury contamination hotspots that originated from Chemical Factory Marktredwitz, Germany. The factory was abandoned in 1985 but its legacy has been persistently endangering the river ecosystem of the Ohře River, a Labe (Elbe) River tributary in the Czech Republic. We identified the timing for the peak contamination of fine sediments entering the Skalka Reservoir located on the Ohře River downstream of the Czech German boundary. Age constraints for the reservoir sediments were obtained using gamma spectrometry analyses of 137Cs and unsupported (excess) 210Pb. We also summarised historical and current Hg concentrations in suspended particulate matter in the Kössein–Röslau–Ohře river system and recent Hg concentrations in aquatic plants. Secondary contamination and its transfer to the Czech stretch of the Ohře River and the Skalka Reservoir through severely contaminated suspended material peaked during the period of factory closure and the start of remediation. The Hg contamination import to the Czech Republic is not likely to improve if the river is left without traditional management of bank reinforcement. This case study highlights a gap in safety regulations for the management of severely contaminated rivers and demonstrates the need to consider the role of historical contamination in river ‘renaturation’.

In Depth Analysis of a Sediment Core from North Aegean Sea

In this work a thorough analysis of the vertical distribution of natural and artificial radionuclides and trace elements in a sediment core sample was conducted. A sediment core of 39 cm length was grabbed from the deep-sea trench (1540 m depth) southern of Samothrace Island, Aegean Sea. The sediment core was then treated at the Hellenic Centre for Marine Research, separated at 1cm increment samples, ranging from 0cm to 39 cm, dried, and milled. A first analysis of the samples was also conducted at HCMR using gamma spectroscopic techniques. Further spectroscopic analysis continued at Nuclear Engineering Department of the National Technical University of Athens (NED-NTUA) using an Extended Range Germanium Detector. The following radionuclides were determined 210Pb, 234Th, 226Ra, 228Ra, 228Th, 137Cs and 40K. Additionally, Instrumental Neutron Activation Analysis was used and the following major and trace elements were identified and quantified: Al, V, La, Sc, Mn, As, Ga, Cr, Zn, Co, Rb, Fe, K, Na and Ce. Based on the analysis of each sample, the vertical distribution of most natural radionuclides showed no significant variation. The vertical distribution of anthropogenic 137Cs was very low and almost constant. Unsupported 210Pb activity was about six times higher than 226Ra, indicating high radon fluxes. Furthermore, neutron activation analysis results indicate that almost all elements are within the expected range based on literature, while K and Na show a slightly increased concentration. For the area, these findings indicate steady and calm sedimentation processes.

226Ra, 228Ra and 40K as tracers of erosion and accumulation processes: A 3-year study on a beach with different sediment dynamics

The aim of this study is to analyse the role of natural radionuclides 226Ra, 228Ra, 40K and unsupported 210Pb (210Pbex), as erosion and accumulation process tracers. For this purpose, a complex system, including both the characteristic dynamics of a closed beach and those associated with a beach open to wave action, was studied. A 3-year study of monthly variation of 226Ra, 228Ra, 40K and 210Pbex was carried out at Las Canteras beach, on the Island of Gran Canaria (Spain), covering several erosion and accumulation periods. A correlation analysis, ANOVA test and Tukey’s Honestly Significant Difference (HSD) Test proved that the marine erosion and accumulation agents influenced the activity concentration values found for the different radionuclides. Moreover, the geochemical analysis of samples from maximum and minimum activity concentration values showed that the natural radionuclides studied could be suitable tracers for studying beach sediment dynamics in erosion and accumulation periods.

Reconstruction of sedimentation rates based on the chronological framework of Lake Pykara, Tamil Nadu, India.

This work presents a piece of initial information about the estimation of the sedimentation rate for Lake Pykara. In this investigation, a chronological sequence of sediment core was set up dependent on 137Cs and 210Pbex analysis to study sediment accumulation rates in Lake Pykara. Caesium-137 (Cs) is an artificial radionuclide and is regularly utilized in building up the chronology of lake sediments in the Anthropocene period. The unsupported 210Pb profile shows a non-exponential decline of 210Pb activity with sediment depth. Sedimentation rates dependent on global atmospheric nuclear weapon maximum fallout of 137Cs (1963) bolster the utilization of the consistent rate of 210Pb supply (CRS) model in core sediments. The geochronology studies of the core were performed using the 137Cs method, to evaluate the model of time changes in the sediment. The 137Cs radioactivity was resolved directly by gamma spectrometry and fluctuated from 13.11 ± 1.3Bqkg-1 for top layers to 1.21 ± 0.1Bqkg-1 for the bottom of the core. Two trademark peaks of 137Cs radioactivity identified with the global fallouts after atomic weapons testing and the Chernobyl mishap were observed and used to affirm the 210Pb dating method. Radioactivity of 210Pbex ranged from 8.00 ± 1.0 to 1.40 ± 0.1Bqkg-1. The mean sedimentation rate evaluated from both models was 0.71 ± 0.06cmyear-1, while the estimated age of Lake Pykara was 514.08years (137Cs) and 521.43years (210Pbex), respectively.

Deeper snow increases the net soil organic carbon accrual rate in moist acidic tussock tundra: 210Pb evidence from Arctic Alaska

ABSTRACT The net change in the carbon inventory of arctic tundra remains uncertain as global warming leads to shifts in arctic water and carbon cycles. To better understand the response of arctic tundra carbon to changes in winter precipitation amount, we investigated soil depth profiles of carbon concentration and radionuclide activities (7Be, 137Cs, 210Pb, and 241Am) in the active layer of a twenty-two-year winter snow depth manipulation experiment in moist acidic tussock tundra at Toolik Lake, Alaska. Depth correlations of cumulative carbon dry mass (g cm−2) vs. unsupported 210Pb activity (mBq g−1) were examined using a modified constant rate of supply (CRS) model. Results were best fit by two-slope CRS models indicating an apparent step temporal increase in the accumulation rate of soil organic carbon. Most of the best-fit model chronologies indicated that the increase in carbon accumulation rate apparently began and persisted after snow fence construction in 1994. The inhomogeneous nature of permafrost soils and their relatively low net carbon accumulation rates make it challenging to establish robust chronologic records. Nonetheless, the data obtained in this study support a decadal-scale increase in net soil organic carbon accumulation rate in the active layer of arctic moist acidic tussock tundra under conditions of increased winter precipitation.

An alternative methodology to determine 210Pb activity soil profiles

Unsupported 210Pb (Pbexc) is generated in air and is subsequently deposited on soil surface. The Pbexc can be used for sediment dating, soil erosion/sedimentation and air mass studies.In many cases, 210Pb activity determination (gamma ray 46.5 keV) cannot be performed due to the lack of efficiency calibration curve, especially when radioactive patron source is not available.This work presents an alternative methodology to obtain the 210Pb activity values, based on the activity definition and the attenuation coefficient determinations and assuming that soil samples coming from depth higher than 25 cm only contain 210Pb generated in the soil (Pbexc free, i.e., for those soil layers the 210Pb activity is equal to the 226Ra activity, at secular equilibrium).The proposed methodology was evaluated using soils from La Plata region, Argentina. The same soil samples were also analyzed in a second laboratory by the conventional methodology. The obtained results indicated that the proposed procedure can be used as a good alternative in cases where a calibration sample is not available.

Disequilibrium of uranium series radionuclides in soil and plants of South India

Soil and plants of South India were analysed using standard methods for equilibrium state between radionuclides 226Ra, 210Pb, and 210Po of uranium series. A disequilibrium state was observed, with mean 210Pb/226Ra, 210Po/226Ra, and 210Po/210Pb as 21.71, 5.52, and 0.40; 10.01, 4.21, and 0.43; and 30.86, 9.34, and 0.35 in Coastal Karnataka, Malnad Karnataka, and Malnad Kerala, respectively. 210Po/210Pb in soil was 0.29, 0.30, and 0.49 respectively, for the three regions. Unsupported 210Pb and 210Po might have caused the observed disequilibrium state. The investigation helps to monitor radionuclide distribution and dynamics in soil and plants of the study area.

Radiometric dating of recent sediments: On the performance of 210Pb-based CRS chronologies under varying rates of supply

Abstract Radiometric dating was a revolutionary contribution to the study of sedimentary processes. Empirical data from varved sediments show that unsupported 210Pb (210Pbexc) fluxes vary over time while they statistically correlate with sediment accumulation rates (SAR). This contradicts the basic assumption of the Constant Rate of Supply (CRS) model, which is the most widely used technique for recent sediments. This work is aimed at assessing the CRS model-errors by quantifying the effects on chronologies of various patterns of temporal variability of fluxes. Results are discussed through applications with synthetic and real cores for which and independent varve chronology or a set of reference dates are available. Periodic harmonic and random fluctuations in fluxes tend to cancel out positive and negative deviations in CRS ages, but they produce spurious variability in SARs. Persistent changes in fluxes lead to cumulated and unacceptable deviations of the CRS ages, which cannot be satisfactorily compensated by the use of a piecewise CRS model. The raw and piecewise CRS models can still be powerful tools of widespread use when the conditions for their applicability are well understood. The paper shows how the analysis of clusters in the 210Pbexc vs mass depth profile, along with the estimation of equivalent constant fluxes pre and post-dating a known reference date, are powerful methods to prevent misapplications of the CRS model.

Determination of geochronology and sedimentation rates of shallow lakes in the middle Yangtze reaches using 210Pb, 137Cs and spheroidal carbonaceous particles

Accurate chronologies for recent sediments of shallow lakes in the Yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century. This study presents the results of detailed 210Pb analysis from eight lake sediment cores collected from the middle Yangtze reaches, southeast China. Unsupported 210Pb activities generally declined exponentially with mass depth in the eight cores. The chronologies and sedimentation rates for the sediment cores were calculated using different 210Pb-based mathematical models. The 137Cs chronomarker (i.e. the 1963 fallout peak) and the spheroidal carbonaceous particle (SCP) chronomarker (i.e. the start of the rapid increase in 1970 CE) were selected to validate the 210Pb dating. Sedimentation rates derived from different models were validated using historical data including lake area, arable land area, sediment discharge and reservoir volume in the Yangtze basin. The SCP-corrected CRS (constant rate of supply) model performs better than other models, based on validation using historical documents in the Yangtze basin. The 137Cs chronomarker might be erroneous due to catchment-driven 137Cs inputs from soil erosion and post-depositional diffusion. Both SCPs and 137Cs are susceptible to inputs from catchment soil erosion, but SCPs show no apparent degradation and post-depositional changes in lake sediments. The SCP profile provides a relatively reliable chronomarker, which can be used for validating 210Pb chronologies in these floodplain lakes. Generally, sedimentation rates in the eight lakes were <0.2 g cm−2 yr−1 before the 1930s, and then increased to a peak in the 1960s. Afterwards, sedimentation rates decreased and remained low after the 1980s.

Evidence for a recent increase in delivery of atmospheric 210Pb to Oualidia lagoon, coastal Morocco.

Two sediment cores were collected from the Oualidia lagoon, on the Atlantic coast of Morocco, and analyzed for 210Pb and 137Cs activity by gamma spectrometry. The 210Pb profiles were characterized by high activity at specific depths in each core, which were attributed to substantial increases in atmospheric 210Pb input to the sediment. A modified CRS model was applied to develop age-depth relations (chronologies) for the cores and calculate sediment accumulation rates, taking into account changing unsupported 210Pb delivery and specifying the year when the increase began. Calculated 210Pb inventories (activity/area) and fluxes (activity/area/time) depend strongly on sedimentation rates and were much higher than mean values in similar coastal systems worldwide. We attempted to use 137Cs as a time marker to support the modified CRS chronologies for both cores. The 137Cs profiles, however, were affected by post-depositional cesium migration in the sediment which made it difficult to identify the 1963 atmospheric bomb-testing peak, especially in the core with low sedimentation rate. We conclude that the high activities of 210Pb detected at specific depths in the Oualidia lagoon sediment cores are a consequence of decay of radioactive 222Rn, which displayed periodic high concentrations in the overlying atmosphere.

Quantifying geostatistical properties of 137Cs and 210Pbex at small scales for improving sampling design and soil erosion estimation

Knowledge of spatial structures of the radionuclides 137Cs and unsupported 210Pb (210Pbex) is vital for developing sound sampling designs that are crucial for deriving quantitative soil erosion estimates. The objectives are to characterize spatial structures of 137Cs and 210Pbex inventories at small spatial scales under different land uses, and to quantify the effects of core sizes on (1) estimated sample means and variances of the 137Cs and 210Pbex inventories and (2) sample numbers required for estimating the mean inventories at a given confidence level. Three different core sizes were used to take soil samples along three 10-m transects at 0.25-m or 0.5-m intervals for each land use. Land uses included cropland, grassland, forestland, and rangeland. 330 samples were analyzed for 137Cs and 210Pbex inventories. Semivariograms were obtained by plotting empirical semivariances with sample separation distances. The spatial correlation distances ranged from 0.2 to 0.75 m for most cases. The semivariances at the separation distances of >0.75 m were close to the variances of the fields for all four land uses, indicating that the spatial distributions of 137Cs and 210Pbex were nearly stationary and had little spatial dependence at scales between 0.75 and 5 m. The overall results suggested that samples taken at a separation distance of >0.75 m would be largely independent and could be composited to form a representative sample for the sampling location for most cases. Given the large spatial variability at such a small scale, quantitative soil erosion rates cannot be estimated for a single soil core, because remarkably different soil erosion rates can be estimated for soil cores taken within a meter. Core size variation between 38 mm and 86 mm has no apparent effect on estimating sample means and sample standard deviations of 137Cs and 210Pbex inventories, except for gravely soils. In general, 15–30 samples are needed to estimate 137Cs reference inventory on reference sites, but may be more for gravely soils. More samples are required for forest and cultivated sites than for uncultivated grassland sites. On measuring sites, it is strongly recommended that 5–15 samples be taken for a grid point and measured individually if feasible or as a combined sample to allow reliable estimation of the mean 137Cs inventory for the location for most soils and land uses. If samples are taken for each of uniformly eroded land form units, the same number of individual samples as on the reference site are recommended. This work will be useful to improving sampling designs and consequently the accuracy of soil erosion estimation of the 137Cs technique.