Plutonium aided reconstruction of caesium atmospheric fallout in European topsoils

Global nuclear weapon testing and the Chernobyl accident have released large amounts of radionuclides into the environment. However, to date, the spatial patterns of these fallout sources remain poorly constrained. Fallout radionuclides (137Cs, 239Pu, 240Pu) were measured in soil samples (n = 160) collected at flat, undisturbed grasslands in Western Europe in the framework of a harmonised European soil survey. We show that both fallout sources left a specific radionuclide imprint in European soils. Accordingly, we used plutonium to quantify contributions of global versus Chernobyl fallout to 137Cs found in European soils. Spatial prediction models allowed for a first assessment of the global versus Chernobyl fallout pattern across national boundaries. Understanding the magnitude of these fallout sources is crucial not only to establish a baseline in case of future radionuclide fallout but also to define a baseline for geomorphological reconstructions of soil redistribution due to soil erosion processes.

Lateral mobilization of soil carbon induced by runoff along karstic slopes

Soil erosion induced by runoff is a main hydrological pathway for lateral transport of carbon in terrestrial landscapes. More information about how water erosion influences the carbon gains and losses at different erosional and depositional landform positions is critical, especially in fragile agroecosystems with a variety of land uses and ephemeral hydrological and sedimentological pulses, typical of Mediterranean environments. The purpose of this study is to characterize the lateral mobilization of soil organic and inorganic carbon (SOC and SIC) along topographically driven transects over a period of four decades in a sub-humid karstic area in northern Spain. The ¹³⁷Cs inventories and the characterization of terrain attributes of the study area were used to identify whether erosional or depositional processes have been predominant in the 58 sampling sites. Average soil losses and gains varied between -4 and +4 mm ha^-1 yr^-1, and the carbon patterns obtained are discussed in the context of the dominant hydrological processes in the study area. Results indicate that SOC and SIC losses were related to an increase in water flow accumulation, while the highest SOC gains were recorded at concave positions. Soil erosion processes and the content of SOC and SIC in soils are the two main factors controlling carbon budgets. The topographical and geomorphological characteristics of the transects, the spatial distribution of land uses and the presence of landscape linear elements such as terraces or paths, affect runoff and determine the sediment connectivity and carbon dynamics along the slopes. The combined use of ¹³⁷Cs and the perceptual model provides reliable SDR estimates benefiting the appraisals of the redistribution of eroded carbon. The knowledge of processes involved in the lateral carbon movement induced by runoff along karstic hillslopes provides a better understanding of the role of soil erosion as carbon source or sinks in the global carbon cycle.

A deconvolutional Bayesian mixing model approach for river basin sediment source apportionment

Increasing complexity in human-environment interactions at multiple watershed scales presents major challenges to sediment source apportionment data acquisition and analysis. Herein, we present a step-change in the application of Bayesian mixing models: Deconvolutional-MixSIAR (D-MIXSIAR) to underpin sustainable management of soil and sediment. This new mixing model approach allows users to directly account for the ‘structural hierarchy’ of a river basin in terms of sub-watershed distribution. It works by deconvoluting apportionment data derived for multiple nodes along the stream-river network where sources are stratified by sub-watershed. Source and mixture samples were collected from two watersheds that represented (i) a longitudinal mixed agricultural watershed in the south west of England which had a distinct upper and lower zone related to topography and (ii) a distributed mixed agricultural and forested watershed in the mid-hills of Nepal with two distinct sub-watersheds. In the former, geochemical fingerprints were based upon weathering profiles and anthropogenic soil amendments. In the latter compound-specific stable isotope markers based on soil vegetation cover were applied. Mixing model posterior distributions of proportional sediment source contributions differed when sources were pooled across the watersheds (pooled-MixSIAR) compared to those where source terms were stratified by sub-watershed and the outputs deconvoluted (D-MixSIAR). In the first example, the stratified source data and the deconvolutional approach provided greater distinction between pasture and cultivated topsoil source signatures resulting in a different posterior distribution to non-deconvolutional model (conventional approaches over-estimated the contribution of cultivated land to downstream sediment by 2 to 5 times). In the second example, the deconvolutional model elucidated a large input of sediment delivered from a small tributary resulting in differences in the reported contribution of a discrete mixed forest source. Overall D-MixSIAR model posterior distributions had lower (by ca 25–50%) uncertainty and quicker model run times. In both cases, the structured, deconvoluted output cohered more closely with field observations and local knowledge underpinning the need for closer attention to hierarchy in source and mixture terms in river basin source apportionment. Soil erosion and siltation challenge the energy-food-water-environment nexus. This new tool for source apportionment offers wider application across complex environmental systems affected by natural and human-induced change and the lessons learned are relevant to source apportionment applications in other disciplines.

Exploring innovative techniques for identifying geochemical elements as fingerprints of sediment sources in an agricultural catchment of Argentina affected by soil erosion

Identification of hot spots of land degradation is strongly related with the selection of soil tracers for sediment pathways. This research proposes the complementary and integrated application of two analytical techniques to select the most suitable fingerprint tracers for identifying the main sources of sediments in an agricultural catchment located in Central Argentina with erosive loess soils. Diffuse reflectance Fourier transformed in the mid-infrared range (DRIFT-MIR) spectroscopy and energy-dispersive X-ray fluorescence (EDXRF) were used for a suitable fingerprint selection. For using DRIFT-MIR spectroscopy as fingerprinting technique, calibration through quantitative parameters is needed to link and correlate DRIFT-MIR spectra with soil tracers. EDXRF was used in this context for determining the concentrations of geochemical elements in soil samples. The selected tracers were confirmed using two artificial mixtures composed of known proportions of soil collected in different sites with distinctive soil uses. These fingerprint elements were used as parameters to build a predictive model with the whole set of DRIFT-MIR spectra. Fingerprint elements such as phosphorus, iron, calcium, barium, and titanium were identified for obtaining a suitable reconstruction of the source proportions in the artificial mixtures. Mid-infrared spectra produced successful prediction models (R² = 0.91) for Fe content and moderate useful prediction (R² = 0.72) for Ti content. For Ca, P, and Ba, the R² were 0.44, 0.58, and 0.59 respectively.

Adapting the Caesium-137 technique to document soil redistribution rates associated with traditional cultivation practices in Haiti

Large-scale deforestation, intensive land use and unfavourable rainfall conditions are responsible for significant continuous degradation of the Haitian uplands. To develop soil conservation strategies, simple and cost-effective methods are needed to assess rates of soil loss from farmland in Haiti. The fallout radionuclide caesium-137 (¹³⁷Cs) provides one such means of documenting medium-term soil redistribution rates. In this contribution, the authors report the first use in Haiti of ¹³⁷Cs measurements to document soil redistribution rates and the associated pattern of erosion/sedimentation rates along typical hillslopes within a traditional upland Haitian farming area. The local ¹³⁷Cs reference inventory, measured at an adjacent undisturbed flat area, was 670 Bq m^-2 (SD = 100 Bq m^-2, CV = 15%, n = 7). Within the study area, where cultivation commenced in 1992 after deforestation, three representative downslope transects were sampled. These were characterized by ¹³⁷Cs inventories ranging from 190 to 2200 Bq m^-2. Although, the study area was cultivated by the local farmers, the ¹³⁷Cs depth distributions obtained from the area differed markedly from those expected from a cultivated area. They showed little evidence of tillage mixing within the upper part of the soil or, more particularly, of the near-uniform activities normally associated with the plough layer or cultivation horizon. They were very similar to that found at the reference site and were characterized by high ¹³⁷Cs activities at the surface and much lower activities at greater depths. This situation is thought to reflect the traditional manual tillage practices which cause limited disturbance and mixing of the upper part of the soil. It precluded the use of the conversion models normally used to estimate soil redistribution rates from ¹³⁷Cs measurements on cultivated soils and the Diffusion and Migration conversion model frequently used for uncultivated soils was modified for application to the cultivated soils of the study area, in order to take account of the unusual local conditions. The model was also modified to take account of the fact that cultivation in the study area commenced in 1992, rather than predating the period of weapons test fallout which extended from the mid 1950s to the 1970s. Erosion rates on the upper parts of the hillside involved in the study were found to be relatively high and ca. -23 t ha^-1 y^-1 with low spatial variability. In the lower, flatter areas at the bottom of the slope, deposition occurred. Deposition rates were characterized by high spatial variability, ranging from 6.0 to 71 t ha^-1 y^-1. Soil redistribution rates of this magnitude are a cause for concern and there is an urgent need to implement soil conservation measures to ensure the longer-term sustainability of the local agricultural practices.

Excess Lead-210 and Plutonium-239+240: Two suitable radiogenic soil erosion tracers for mountain grassland sites

The expected growing population and challenges associated with globalisation will increase local food and feed demands and enhance the pressure on local and regional upland soil resources. In light of these potential future developments it is necessary to define sustainable land use and tolerable soil loss rates with methods applicable and adapted to mountainous areas. Fallout-radionuclides (FRNs) are proven techniques to increase our knowledge about the status and resilience of agro-ecosystems. However, the use of the Caesium-137 (¹³⁷Cs) method is complicated in the European Alps due to its heterogeneous input and the timing of the Chernobyl fallout, which occurred during a few single rain events on partly snow covered ground. Other radioisotopic techniques have been proposed to overcome these limitations. The objective of this study is to evaluate the suitability of excess Lead-210 (²¹⁰Pb_ex) and Plutonium-239+240 (^239+240Pu) as soil erosion tracers for three different grassland management types at the steep slopes (slope angles between 35 and 38°) located in the Central Swiss Alps. All three FRNs identified pastures as having the highest mean (± standard deviation) net soil loss of -6.7 ± 1.1, -9.8 ± 6.8 and -7.0 ± 5.2 Mg ha^-1 yr^-1 for ¹³⁷Cs, ²¹⁰Pb_ex and ^239+240Pu, respectively. A mean soil loss of -5.7 ± 1.5, -5.2 ± 1.5 and-5.6 ± 2.1 was assessed for hayfields and the lowest rates were established for pastures with dwarf-shrubs (-5.2 ± 2.5, -4.5 ± 2.5 and -3.3 ± 2.4 Mg ha^-1 yr^-1 for ¹³⁷Cs, ²¹⁰Pb_ex and ^239+240Pu, respectively). These rates, evaluated at sites with an elevated soil erosion risk exceed the respective soil production rates. Among the three FRN methods used, ^239+240Pu appears as the most promising tracer in terms of measurement uncertainty and reduced small scale variability (CV of 13%). Despite a higher level of uncertainty, ²¹⁰Pb_ex produced comparable results, with a wide range of erosion rates sensitive to changes in grassland management. ²¹⁰Pb_ex can then be as well considered as a suitable soil tracer to investigate alpine agroecosystems.

Modelling Deposition and Erosion rates with RadioNuclides (MODERN) - Part 2: A comparison of different models to convert 239+240Pu inventories into soil redistribution rates at unploughed sites

Sheet erosion is one of the major threats to alpine soils. To quantify its role and impact in the degradation processes of alpine grasslands, the application of Fallout Radionuclides (FRN) showed very promising results. The specific characteristics of plutonium 239 + 240 (^239+240Pu), such as the homogeneous fallout distribution, the long half-life and the cost and time effective measurements make this tracer application for investigating soil degradation in Alpine grasslands more suitable than any other FRN (e.g. ¹³⁷Cs). However, the conversion of ^239+240Pu inventories into soil erosion rates remains a challenge. Currently available conversion models have been developed mainly for ¹³⁷Cs with later adaptation to other FRN (e.g. Excess ²¹⁰Pb, and ⁷Be), each model being defined for specific land use (ploughed and/or unploughed) and processes (erosion or deposition). As such, they may fail in describing correctly the distribution of Pu isotopes in the soil. A new conversion model, MODERN, with an adaptable algorithm to estimate erosion and deposition rates from any FRN inventory changes was recently proposed (Arata et al., 2016). In this complementary contribution, the authors compare the application of MODERN to other available conversion models. The results show a good agreement between soil redistribution rates obtained from MODERN and from the models currently used by the FRN scientific community (i.e. the Inventory Method).

A multi-radionuclide approach to evaluate the suitability of (239+240)Pu as soil erosion tracer

Fallout radionuclides have been used successfully worldwide as tracers for soil erosion, but relatively few studies exploit the full potential of plutonium (Pu) isotopes. Hence, this study aims to explore the suitability of the plutonium isotopes (239)Pu and (240)Pu as a method to assess soil erosion magnitude by comparison to more established fallout radionuclides such as (137)Cs and (210)Pbex. As test area an erosion affected headwater catchment of the Lake Soyang (South Korea) was selected. All three fallout radionuclides confirmed high erosion rates for agricultural sites (>25tha(-1)yr(-1)). Pu isotopes further allowed determining the origin of the fallout. Both (240)Pu/(239)Pu atomic ratios and (239+240)Pu/(137)Cs activity ratios were close to the global fallout ratio. However, the depth profile of the (239+240)Pu/(137)Cs activity ratios in undisturbed sites showed lower ratios in the top soil increments, which might be due to higher migration rates of (239+240)Pu. The activity ratios further indicated preferential transport of (137)Cs from eroded sites (higher ratio compared to the global fallout) to the depositional sites (smaller ratio). As such the (239+240)Pu/(137)Cs activity ratio offered a new approach to parameterize a particle size correction factor that can be applied when both (137)Cs and (239+240)Pu have the same fallout source. Implementing this particle size correction factor in the conversion of (137)Cs inventories resulted in comparable estimates of soil loss for (137)Cs and (239+240)Pu. The comparison among the different fallout radionuclides highlights the suitability of (239+240)Pu through less preferential transport compared to (137)Cs and the possibility to gain information regarding the origin of the fallout. In conclusion, (239+240)Pu is a promising soil erosion tracer, however, since the behaviour i.e. vertical migration in the soil and lateral transport during water erosion was shown to differ from that of (137)Cs, there is a clear need for a wider agro-environmental testing.

Modelling Deposition and Erosion rates with RadioNuclides (MODERN) - Part 1: A new conversion model to derive soil redistribution rates from inventories of fallout radionuclides

The measurement of fallout radionuclides (FRN) has become one of the most commonly used tools to quantify sediment erosion or depositional processes. The conversion of FRN inventories into soil erosion and deposition rates is done with a variety of models, which suitability is dependent on the selected FRN, soil cultivation (ploughed or unploughed) and movement (erosion or deposition). The authors propose a new conversion model, which can be easily and comprehensively used for different FRN, land uses and soil redistribution processes. The new model MODERN (Modelling Deposition and Erosion rates with RadioNuclides) considers the precise depth distribution of any FRN at the reference site, and allows adapting it for any specific site conditions. MODERN adaptability and performance in converting different FRN inventories is discussed for a theoretical case as well as for two already published case studies i.e. a ¹³⁷Cs study in an alpine and unploughed area in the Aosta valley (Italy) and a ²¹⁰Pb_ex study on a ploughed area located in the Transylvanian Plain (Romania). The tests highlight a highly significant correspondence (i.e. correlation factor of 0.91) between the results of MODERN and the published results of other models currently used by the FRN scientific community (i.e. the Profile Distribution Model and the Mass Balance Model). The development and the cost free accessibility of MODERN (see modern.umweltgeo.unibas.ch) will ensure the promotion of wider application of FRNs for tracing soil erosion and sedimentation.

Temporal variability of beryllium-7 fallout in southwest UK

Cosmogenic beryllium-7 has been widely employed as a sediment tracing tool and continued development of its use as a soil erosion tracer requires knowledge of fallout temporal dynamics. Data regarding beryllium-7 fallout in the UK are scarce and here the authors provide a record of beryllium-7 fallout in southwest England spanning a two-year period. A monthly fallout record was developed for Plymouth, UK using regular rainfall sampling to determine beryllium-7 rainfall activity concentration (Bq L(-1)) and deposition flux (Bq m(-2)). Data showed a general tendency for higher activity during the spring/summer months and lower activity in the autumn/winter months. Comparison with data for other UK sites (Chilton and Aberporth) for the same period found significant differences in (7)Be activity in rainwater and lower variability in Plymouth than Chilton and Aberporth. Total deposition was largely controlled by rainfall in Plymouth although regression coefficients suggested greater importance of other atmospheric controls at the Chilton and Aberporth sites. Use of a deposition proportion to rainfall proportion ratio identified periods when deposition was influenced by varying (7)Be activity in rainfall. Broad ranges in ratios were found for Chilton and Aberporth and this has implications for sediment tracer studies requiring estimates of (7)Be deposition flux across months or seasons.

Assessment of soil redistribution rates by (137)Cs and (210)Pbex in a typical Malagasy agricultural field

Soil degradation processes affect more than one-third of the Malagasy territory and are considered as the major environmental threat impacting the natural resources of the island. This innovative study reports about a pioneer test and use of radio-isotopic techniques (i.e. Cs-137 and Pb-210ex) under Madagascar agroclimatic condition to evaluate soil erosion magnitude. This preliminary investigation has been conducted in a small agricultural field situated in the eastern central highland of Madagascar, 40 km East from Antananarivo. Both anthropogenic Cs-137 and geogenic Pb-210 soil tracers provided similar results highlighting soil erosion rates reaching locally 18 t ha(-1) yr(-1,) a level almost two times higher than the sustainable soil loss rate under Madagascar agroclimatic condition. The sediment delivery ratio established with both radiotracers was above 80% indicating that most of the mobilized sediment exits the field. Assessing soil erosion rate through fallout radionuclides in Madagascar is a first step towards an efficient land and water resource management policy to optimise the effectiveness of future agricultural soil conservation practices.

Use of a (137)Cs re-sampling technique to investigate temporal changes in soil erosion and sediment mobilisation for a small forested catchment in southern Italy

Soil erosion and both its on-site and off-site impacts are increasingly seen as a serious environmental problem across the world. The need for an improved evidence base on soil loss and soil redistribution rates has directed attention to the use of fallout radionuclides, and particularly (137)Cs, for documenting soil redistribution rates. This approach possesses important advantages over more traditional means of documenting soil erosion and soil redistribution. However, one key limitation of the approach is the time-averaged or lumped nature of the estimated erosion rates. In nearly all cases, these will relate to the period extending from the main period of bomb fallout to the time of sampling. Increasing concern for the impact of global change, particularly that related to changing land use and climate change, has frequently directed attention to the need to document changes in soil redistribution rates within this period. Re-sampling techniques, which should be distinguished from repeat-sampling techniques, have the potential to meet this requirement. As an example, the use of a re-sampling technique to derive estimates of the mean annual net soil loss from a small (1.38 ha) forested catchment in southern Italy is reported. The catchment was originally sampled in 1998 and samples were collected from points very close to the original sampling points again in 2013. This made it possible to compare the estimate of mean annual erosion for the period 1954-1998 with that for the period 1999-2013. The availability of measurements of sediment yield from the catchment for parts of the overall period made it possible to compare the results provided by the (137)Cs re-sampling study with the estimates of sediment yield for the same periods. In order to compare the estimates of soil loss and sediment yield for the two different periods, it was necessary to establish the uncertainty associated with the individual estimates. In the absence of a generally accepted procedure for such calculations, key factors influencing the uncertainty of the estimates were identified and a procedure developed. The results of the study demonstrated that there had been no significant change in mean annual soil loss in recent years and this was consistent with the information provided by the estimates of sediment yield from the catchment for the same periods. The study demonstrates the potential for using a re-sampling technique to document recent changes in soil redistribution rates.

Uncertainty related to input parameters of (137)Cs soil redistribution model for undisturbed fields

This study presents an alternative method to empirically establish the effective diffusion coefficient and the convective velocity of (137)Cs in undisturbed soils. This approach offers the possibility to improve the parameterisation and the accuracy of the (137)Cs Diffusion and Migration Model (DMM) used to assess soil erosion magnitudes. The impact of the different input parameters of this radiometric model on the derived-soil redistribution rates has been determined for a Romanian pastureland located in the northwest extremity of the Transylvanian Plain. By fitting the convection-diffusion equation to the available experimental data, the diffusion coefficient and convection velocity of (137)Cs in soil could be determined; 72% of the (137)Cs soil content could be attributed to the (137)Cs fallout originating from Chernobyl. The medium-term net erosion rate obtained with the calculated input parameters reached -6.6 t ha(-1) yr(-1). The model highlights great sensitivity to parameter estimations and the calculated erosion rates for undisturbed landscapes can be highly impacted if the input parameters are not accurately determined from the experimental data set. Upper and lower bounds should be established based on the determined uncertainty budget for the reliable estimates of the derived redistribution rates.

Suitability of 239+240Pu and 137Cs as tracers for soil erosion assessment in mountain grasslands

Anthropogenic radionuclides have been distributed globally due to nuclear weapons testing, nuclear accidents, nuclear weapons fabrication, and nuclear fuel reprocessing. While the negative consequences of this radioactive contamination are self-evident, the ubiquitous fallout radionuclides (FRNs) distribution form the basis for the use as tracers in ecological studies, namely for soil erosion assessment. Soil erosion is a major threat to mountain ecosystems worldwide. We compare the suitability of the anthropogenic FRNs, 137Cs and 239+240Pu as soil erosion tracers in two alpine valleys of Switzerland (Urseren Valley, Canton Uri, Central Swiss Alps and Val Piora, Ticino, Southern Alps). We sampled reference and potentially erosive sites in transects along both valleys. 137Cs measurements of soil samples were performed with a Li-drifted Germanium detector and 239+240Pu with ICP-MS. Our data indicates a heterogeneous deposition of the 137Cs, since most of the fallout origins from the Chernobyl April/May 1986 accident, when large parts of the European Alps were still snow-covered. In contrast, 239+240Pu fallout originated mainly from 1950s to 1960s atmospheric nuclear weapons tests, resulting in a more homogenous distribution and thus seems to be a more suitable tracer in mountainous grasslands. Soil erosion assessment using 239+240Pu as a tracer pointed to a huge dynamic and high heterogeneity of erosive processes (between sedimentation of 1.9 and 7 t ha(-1) yr(-1) and erosion of 0.2-16.4 t ha(-1) yr(-1) in the Urseren Valley and sedimentation of 0.4-20.3 t ha(-1) yr(-1) and erosion of 0.1-16.4 t ha(-1) yr(-1) at Val Piora). Our study represents a novel and successful application of 239+240Pu as a tracer of soil erosion in a mountain environment.

Comparative assessment of erosion and deposition rates on cultivated land in the Transylvanian Plain of Romania using ¹³⁷Cs and ²¹⁰Pbex

Soil erosion and sedimentation are natural landscape forming processes. However, they can be accelerated by human activities and therefore increase negative impacts on agricultural production as well as disturbing watershed management. Romania currently faces major environmental challenges and pressure on soil and water resources due to unsustainable farming practices and inappropriate tillage practices. The present work represents the first attempt to test the combined use of radionuclide approaches (i.e. (137)Cs and (210)Pb(ex)) to quantify soil erosion changes in cultivated Transylvanian fields (Romania) at different temporal scales. Fourteen soil cores were collected along two transects in a cultivated field and two reference sites were selected to establish the mean reference inventories for both (137)Cs and (210)Pb(ex). A value of 5460 ± 880 Bq m(-2) (n = 10; CV = 16%) was determined for the (137)Cs mean reference inventory for both sites, given as areal activity ± standard deviation, at 2σ confidence interval. As regarding (210)Pb(ex) reference inventory, its value (9640 Bq m(-2)) is only given by the areal activity of one soil core from the second site. The high erosion rates obtained with the (210)Pb(ex) approach are an effect of the up and down ploughing practices which took place at the time of the local agricultural cooperative starting in the late 1950s. The middle-term redistribution rates provided by the (137)Cs technique highlighted preponderant deposition processes in the field investigated, reflecting the changes in the cultivation system with ploughing across the slope at the beginning of 1990s.

Assessment of soil erosion and deposition rates in a Moroccan agricultural field using fallout 137Cs and 210Pbex

In Morocco land degradation - mainly caused by soil erosion - is one of the most serious agroenvironmental threats encountered. However, only limited data are available on the actual magnitude of soil erosion. The study site investigated was an agricultural field located in Marchouch (6°42' W, 33° 47' N) at 68 km south east from Rabat. This work demonstrates the potential of the combined use of (137)Cs, (210)Pb(ex) as radioisotopic soil tracers to estimate mid and long term erosion and deposition rates under Mediterranean agricultural areas. The net soil erosion rates obtained were comparable, 14.3 t ha(-1) yr(-1) and 12.1 ha(-1) yr(-1) for (137)Cs and (210)Pb(ex) respectively, resulting in a similar sediment delivery ratio of about 92%. Soil redistribution patterns of the study field were established using a simple spatialisation approach. The resulting maps generated by the use of both radionuclides were similar, indicating that the soil erosion processes has not changed significantly over the last 100 years. Over the previous 10 year period, the additional results provided by the test of the prediction model RUSLE 2 provided results of the same order of magnitude. Based on the (137)Cs dataset established, the contribution of the tillage erosion impact has been evaluated with the Mass Balance Model 3 and compared to the result obtained with the Mass Balance Model 2. The findings highlighted that water erosion is the leading process in this Moroccan cultivated field, tillage erosion under the experimental condition being the main translocation process within the site without a significant and major impact on the net erosion.

Fallout radionuclide-based techniques for assessing the impact of soil conservation measures on erosion control and soil quality: an overview of the main lessons learnt under an FAO/IAEA Coordinated Research Project

This paper summarizes key findings and identifies the main lessons learnt from a 5-year (2002-2008) coordinated research project (CRP) on "Assessing the effectiveness of soil conservation measures for sustainable watershed management and crop production using fallout radionuclides" (D1.50.08), organized and funded by the International Atomic Energy Agency through the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. The project brought together nineteen participants, from Australia, Austria, Brazil, Canada, Chile, China, Japan, Morocco, Pakistan, Poland, Romania, Russian Federation, Turkey, United Kingdom, United States of America and Vietnam, involved in the use of nuclear techniques and, more particularly, fallout radionuclides (FRN) to assess the relative impacts of different soil conservation measures on soil erosion and land productivity. The overall objective of the CRP was to develop improved land use and management strategies for sustainable watershed management through effective soil erosion control practices, by the use of ¹³⁷Cs (half-life of 30.2 years), ²¹⁰Pb(ex) (half-life of 22.3 years) and ⁷Be (half-life of 53.4 days) for measuring soil erosion over several spatial and temporal scales. The environmental conditions under which the different research teams applied the tools based on the use of fallout radionuclides varied considerably--a variety of climates, soils, topographies and land uses. Nevertheless, the achievements of the CRP, as reflected in this overview paper, demonstrate that fallout radionuclide-based techniques are powerful tools to assess soil erosion/deposition at several spatial and temporal scales in a wide range of environments, and offer potential to monitor soil quality. The success of the CRP has stimulated an interest in many IAEA Member States in the use of these methodologies to identify factors and practices that can enhance sustainable agriculture and minimize land degradation.

Establishment of control site baseline data for erosion studies using radionuclides: a case study in East Slovenia

The aim of the present study was to establish a reference site and its soil characteristics for use of fallout radionuclides in erosion studies in Slovenia. Prior to this study, no reference site and baseline data existed for Slovenia for this purpose. In the agricultural area of Goricko in East Slovenia, an undisturbed forest situated in Salamenci (46 degrees 44'N, 16 degrees 7'E), was selected to establish the inventory value of fallout 137Cs and to establish a baseline level of multi-elemental fingerprint (major, minor, trace elements including heavy metals) and naturally occurring radionuclides in soils. A total of 20 soil profiles were collected at four 10 cm depth increments for evaluation of baseline level of 137Cs inventory. An exponential distribution for 137Cs was found and the baseline level inventory was established at 7300 +/- 2500 Bq m-2 with a coefficient of variation of 34%. Of this mean present-day inventory, approximately 45% is due to the Chernobyl contribution. The physical degradation of soils through erosion is linked with biochemical degradation. This study introduces an approach to establishment of the naturally occurring radionuclide and elemental fingerprints baseline levels at a reference site which can provide comparative data to those from neighbouring agricultural fields for assessment of soil redistribution magnitude using fallout radionuclides. In addition, this information will be used to determine the impact of soil erosion processes and agricultural practices on soil quality and redistribution within agricultural landscapes in Slovenia.

Comparative advantages and limitations of the fallout radionuclides (137)Cs, (210)Pb(ex) and (7)Be for assessing soil erosion and sedimentation

The fallout radionuclides (FRNs) (137)Cs, (210)Pb(ex) and (7)Be are increasingly being used as a means of obtaining quantitative information on soil erosion and sediment redistribution rates within agricultural landscapes, over a range of different timescales, and they are frequently seen to represent a valuable complement to conventional measurement techniques. The recent development of the (7)Be method has greatly extended the timescale over which FRNs can be used, by permitting assessment of short-term soil erosion linked to individual events and changing soil management practices. This paper aims to review the advantages and limitations of each of the three FRNs and to identify key knowledge gaps linked to their use. In addition, guidelines for selecting the most appropriate FRN and associated approach, in order to deal with a range of spatial and temporal scales and to investigate specific sets of agro-environmental problems, are provided. Key requirements for future work, related to the application of FRNs in soil erosion investigations, are also identified. These include the upscaling of the approach to the catchment scale and a shift from use of the approach as a research tool to a decision support tool.

Assessment of spatial distribution of fallout radionuclides through geostatistics concept

After introducing geostatistics concept and its utility in environmental science and especially in Fallout Radionuclide (FRN) spatialisation, a case study for cesium-137 ((137)Cs) redistribution at the field scale using geostatistics is presented. On a Canadian agricultural field, geostatistics coupled with a Geographic Information System (GIS) was used to test three different techniques of interpolation [Ordinary Kriging (OK), Inverse Distance Weighting power one (IDW1) and two (IDW2)] to create a (137)Cs map and to establish a radioisotope budget. Following the optimization of variographic parameters, an experimental semivariogram was developed to determine the spatial dependence of (137)Cs. It was adjusted to a spherical isotropic model with a range of 30 m and a very small nugget effect. This (137)Cs semivariogram showed a good autocorrelation (R(2)=0.91) and was well structured ('nugget-to-sill' ratio of 4%). It also revealed that the sampling strategy was adequate to reveal the spatial correlation of (137)Cs. The spatial redistribution of (137)Cs was estimated by Ordinary Kriging and IDW to produce contour maps. A radioisotope budget was established for the 2.16 ha agricultural field under investigation. It was estimated that around 2 x 10(7)Bq of (137)Cs were missing (around 30% of the total initial fallout) and were exported by physical processes (runoff and erosion processes) from the area under investigation. The cross-validation analysis showed that in the case of spatially structured data, OK is a better interpolation method than IDW1 or IDW2 for the assessment of potential radioactive contamination and/or pollution.