Estimating soil erosion losses in Korea with fallout cesium-137

The contents of fallout ¹³⁷Cs in soil profiles were used to estimate erosion losses from steeply sloping croplands in Korea. Seven undisturbed sites with no apparent erosion or deposition, and 15 cropland sites were examined to a depth of 30 cm. The cropland sites had been cultivated for periods ranging from 5 to more than 80 y (median 10 y), and their slopes ranged from 5 to 26% (median 13%). All except one of the cropland sites contained less ¹³⁷Cs than undisturbed sites in the same area. Three cropland sites contained essentially no ¹³⁷Cs, indicating erosion of the entire cultivated layer of soil in from 6 to 10 years. Other cropland sites, particularly those with sandy texture, showed little loss of ¹³⁷Cs over longer periods of cultivation. Cesium-137 measurements may be useful in identifying site characteristics that reduce the vulnerability of sloping soils to erosion damage.     

Calibration of a field-portable gamma detector to obtain in situ measurements of the 137Cs inventories of cultivated soils and floodplain sediments.

Over the past 10 years, a number of studies have exploited the potential for using measurements of fallout 137Cs inventories to document rates and patterns of soil erosion on cultivated land and to estimate rates of overbank sedimentation on river floodplains. Traditional procedures for applying the 137Cs technique involve the collection of soil or sediment cores from a study site and their subsequent transfer to the laboratory for preparation and analysis by gamma spectrometry. Such procedures are time consuming and there may be a considerable delay before the results are available. It is therefore difficult to obtain preliminary results, which could be used to guide the development of an ongoing sampling programme. The use of in situ gamma spectrometry measurements to quantify 137Cs inventories in soils and sediments offers a number of potential advantages over traditional procedures. However, in order to derive a reliable estimate of the 137Cs inventory for a measurement point, it is necessary to take account of the attenuation of 137Cs gamma rays by the soil matrix and information on the depth distribution of 137Cs in the soil or sediment is therefore required. In the present study, empirical relationships between in situ measurements of 137Cs activity and total 137Cs inventories have been established for soils from a cultivated field and for floodplain sediments, based on information on the vertical distribution of 137Cs in the soils and sediments provided by the forward scattering ratio derived from the field measured spectra. These relationships have been used to estimate 137Cs inventories from in situ measurements of 137Cs activity at other locations.     

137Cs tracing dynamics of soil erosion,organic carbon and nitrogen in sloping farmland converted from original grassland in Tibetan plateau

There is a shortage of research concerning the relationships between land-use change, soil erosion, and soil organic carbon (SOC) and nitrogen (N) dynamics in alpine environments such as those found in the Tibetan plateau. In this paper, typical sloping farmlands converted from grassland 50 years ago in eastern Tibet were selected to determine dynamics of soil erosion, SOC, and total N associated with land-use change. Soil samples were collected from sloping farmland and control fields (grassland). The ¹³⁷Cs, SOC, total N contents, and soil particle size fractions were analyzed in these samples. As compared with the control fields, ¹³⁷Cs, SOC, and total N inventories in the sloping farmlands decreased by 30%, 27%, and 33%, respectively. Meanwhile variations in the three parameters were enhanced in the sloping farmlands, with coefficients of variation (CVs) of 38%, 23%, and 20%, respectively, for ³⁷Cs, SOC, and total N. In addition, SOC and total N inventories significantly decreased with increasing soil erosion in the sloping farmland. In a sloping farmland with a steep 24° gradient, the ¹³⁷Cs inventory gradually increased along a downslope transect with its lowest value at 0 Bq m^?2 in the top-slope position (0 m). The soil clay (<0.002 mm) content in such an area increased with decreasing elevation (r=?0.95, p=0.001). Significant correlations between ¹³⁷Cs and clay (r=0.92, p=0.003), SOC (r=0.96, p=0.001), or total N (r=0.95, p=0.001) were also found in the farmland. These results showed that converting alpine grassland to sloping farmland accelerates soil erosion, losses in SOC and N, and increases the soil’s spatial variability. The combined impacts of tillage and water erosion contributed a significant decrease in the soil’s organic carbon and N storages. Particularly in steep sloping farmlands, tillage erosion contributed for severe soil loss, but the soil redistribution pattern was dominated by water erosion, not tillage erosion, due to the lack of boundaries across the field patches. It was also found that ¹³⁷Cs, SOC, and total N moved along the same pathway within these sloping farmlands, resulting in net C and N losses during soil redistribution. The negative influences of land-use conversion from grassland to farmland in sloping areas in the Tibetan plateau should be addressed.     

Fallout beryllium-7 as a tracer in soil erosion investigations.

Recent developments in the use of the environmental radionuclides 137Cs and 210Pb for documenting medium-term soil erosion rates must be seen as an important advance. However, measurements of these radionuclides provide estimates of medium-term (i.e. ca. 45 or 100 years) soil redistribution rates and there is a need to explore the potential for using complementary radionuclides, to estimate erosion rates associated with individual events or short periods. Beryllium-7 (7Be, t0.5 = 53 days) has the potential to fulfil these requirements. This contribution presents some preliminary results from an investigation undertaken in a field near Crediton, UK, which successfully demonstrates the potential for using 7Be as a tracer in soil erosion investigations.     

Estimation of soil erosion from caesium-137 measurements in a small,cultivated catchment in Australia

Measurements are reported of the distribution of ¹³⁷Cs within a 6.6 ha drainage basin on cultivated black earth soils located near Merriwa in New South Wales (N.S.W.). The results were used to estimate net loss as well as accumulation of soil. The losses of ¹³⁷Cs from the catchment slopes were assessed relative to an estimated input of ¹³⁷Cs of 100 mBq cm⁻².A regression equation was developed which relates the net loss of soil by erosion of black earth soils (kg ha⁻¹ y⁻¹) as a function of the measured loss of ¹³⁷Cs activity in the soil expressed as a percentage of the normal input value.Each input datum of ¹³⁷Cs activity into the regression equation was obtained under similar conditions. Rates of soil losses, estimated at 19 sites, ranged between 420 and 2970 kg ha⁻¹ y⁻¹ with an average of 1530 kg ha⁻¹ y⁻¹. The results confirmed the usefulness of the ¹³⁷Cs technique for estimating loss of soil by erosion.     

Determination of the vertical distribution of radioelements (K, U, Th, Cs) in soils from portable HP-Ge spectrometer measurements: a tool for soil erosion studies.

Soil erosion studies, based on the 137Cs technique, require a lot of time-consuming cores to determine soil loss or gain. We show that portable HP-Ge spectrometer can be used to determine the content and the distribution in the soil of natural and artificial radionuclides. Simulations of gamma-rays transport throughout the soil profile used a Monte Carlo code. The methodology requires a unique undisturbed coring site to build the models, calibrate the spectrometer readings and derive soil denudation or accumulation thickness.     

Using Cesium-137 technique to study the characteristics of different aspect of soil erosion in the Wind-water Erosion Crisscross Region on Loess Plateau of China.

The most serious soil erosion on Loess Plateau exists in the Wind-water Erosion Crisscross Region. In the past 20 years, the types and intensity of soil erosion and its temporal and spatial distribution were studied, but studies on the difference of soil erosion between slope aspects and slope positions in this area have no report. However, it is very important to analyze and evaluate quantitatively the characteristics of different aspects and positions of soil loss for the prevention and treatment of soil erosion in this area. The spatial pattern of net soil loss on 4 downslope transects in four aspects (east, west, south and north) on a typical Mao (round loess mound) in Liudaogou catchment in Wind-water Erosion Crisscross Region was measured in 2000 using the resident cesium-137 deficit technique. The purposes of this investigation were undertaken to determine whether or not 137Cs measurement would give a useful indication of the extent of soil loss and their characteristics from cultivated hillsides in different slope aspect and slope position in the study area. The results showed that the difference of soil erosion in different aspect was significant and the erosion rate was in this order: north > east > south > west. Compared with other areas, the difference of erosion rate between north hillside and south hillside was on the contrary, and the possible explanations could be the effect of wind erosion. Also, the percentage of wind erosion was estimated to be at least larger than 18% of total soil loss by comparing the difference of erosion amount in south hillside and north hillside. The erosion rates on different slope positions in all aspects were also different, the highest net soil loss occurred in the lower slope position, and the upper and middle slope positions were slight. The general trend of net soil loss on sloping surface was to increase in fluctuation with increasing downslope distance.     

Estimating the erosion and deposition rates in a small watershed by the 137Cs tracing method

Understanding the erosion and deposition rates in a small watershed is important for designing soil and water conservation measures. The objective of this study is to estimate the net soil loss and gain at points with various land use types and landform positions in a small watershed in the Sichuan Hilly Basin of China by the ¹³⁷Cs tracing technique. Among various land use types, the order of erosion rate was bare rock > sloping cultivated land > forest land. The paddy field and Caotu (a kind of cultivated land located at the foot of hills) were depositional areas. The erosion rate under different landform was in this order: hillside > saddle > hilltop. The footslope and the valley were depositional areas. The ¹³⁷Cs technique was shown to provide an effective means of documenting the spatial distribution of soil erosion and deposition within the small watershed.     

Sampling in freshwater environments: Suspended particle traps and variability in the final data.

This paper reports one practical method to estimate the measurement uncertainty including sampling, derived by the approach implemented by Ramsey for soil investigations. The methodology has been applied to estimate the measurements uncertainty (sampling and analyses) of (137)Cs activity concentration (Bqkg(-1)) and total carbon content (%) in suspended particle sampling in a freshwater ecosystem. Uncertainty estimates for between locations, sampling and analysis components have been evaluated. For the considered measurands, the relative expanded measurement uncertainties are 12.3% for (137)Cs and 4.5% for total carbon. For (137)Cs, the measurement (sampling+analysis) variance gives the major contribution to the total variance, while for total carbon the spatial variance is the dominant contributor to the total variance. The limitations and advantages of this basic method are discussed.     

Retrospection of recent 30-year changes in the process of soil wind erosion in the Luanhe River Source Area of North China using Cesium-137

The Luanhe River Source Area belongs to typical semi-arid, agro-pastoral ecotone of North China. It is very important for the prevention and treatment of soil erosion in North China to analyze and evaluate quantitatively the recent 30-year changes in the process of soil wind erosion in this area. Based on long field observations, soil samples from different depths in a representative wind-deposited soil profile in the Luanhe River Source Area were collected. Then the ¹³⁷Cs activity of soil samples from different depths in the soil profile was determined using a GEM series HPGe (high-purity germanium) coaxial detector system (ADCAM-100), and their soil properties, such as the soil particle fraction and so on, were analyzed. According to the detected ¹³⁷Cs activity of different depths, a continuous time sequence of the wind-deposited soil profile in the study area was established. Furthermore, through assumption on a soil relative wind erosion intensity index (SWEI), recent 30-year changes in the process of soil wind erosion in the Luanhe River Source Area were retrospected . The analysis results revealed that weaker soil wind erosion occurred in the study area from the 1970s to the early 1980s and from the late 1980s to the mid to late 1990s. Conversely, intense periods of soil wind erosion occurred in the mid-1980s and from the late 1990s to 2002.     

Results of an IAEA inter-comparison exercise to assess 137Cs and total 210Pb analytical performance in soil

Fallout radionuclides (FRNs) such as ²¹⁰Pb and ¹³⁷Cs have been widely used to assess soil erosion and sedimentation processes. It is of major importance to obtain accurate analytical results of FRNs by gamma analysis before any data treatment through conversion model and to allow subsequent comparison of erosion and sedimentation rates from different case studies.Therefore, IAEA organized an inter-comparison exercise to assess the validity and reliability of the analytical results of ¹³⁷Cs and total ²¹⁰Pb using γ-spectrometry in the various laboratories participating in the IAEA Co-ordinated Research Project on “Assess the effectiveness of soil conservation measures for sustainable watershed management using fallout radionuclides”.Reference materials were distributed to 14 participating laboratories and, using a rating system, their analytical results were compared to the reference values assigned.In the case of ¹³⁷Cs, the analytical results were satisfactory with 66% of the laboratories producing acceptable results. Only the sample with low ¹³⁷Cs activity (2.6±0.2 Bq kg⁻¹) gave less accurate results with more than 25% not acceptable results. The total ²¹⁰Pb analysis indicated a clear need for corrective actions in the analysis process as only 36% of the laboratories involved in the proficiency test was able to access total ²¹⁰Pb with occurrence (bias ⩽10%). This inter-laboratory test underlines that further inter-comparison exercises should be organized by IAEA or regional laboratories to ensure the quality of the analytical data produced in Member States. As a result of the above-mentioned proficiency test, some recommendations have been provided to improve accurate gamma measurement of both ¹³⁷Cs and total ²¹⁰Pb.     

Correlation of erosion measurements and soil caesium-137 content

This paper reports a calibration between measured soil loss from small plots and measured soil ¹³⁷Cs content (expressed as a percentage loss relative to the ¹³⁷Cs content of a local stable reference soil). The regression represents a simple and rapid tool for the estimation of net soil loss from sites which have a uniform and continuous history of land-use.     

Cs contamination of Techa river flood plain in Brodokalmak settlement

137Cs contamination of the Techa river flood plain inside the Brodokalmak settlement has been mapped. The collimated scintillated detector technique was used for 137Cs deposit measurements. The 137Cs contamination is very heterogeneous. A comparison of this technique with the traditional sample method was performed at selected locations. The sampling data are in good agreement with in-situ data. Soil surface activity of 90Sr was determined from the samples. It was shown that 137Cs contamination correlates with 90Sr contamination within the flood plain of the settlement.     

Assessment of the transfer of Cs in three types of vegetables consumed in Hong Kong

A dynamic food chain model has been built for the modeling of the transfer of ¹³⁷Cs in three types of vegetables consumed in Hong Kong, namely, white flowering cabbage (Brassica chinensis), head lettuce (Lactuca sativa) and celery (Apium graveolens). Some parameters have been estimated from the experimental data obtained in this work. The experimental data include the transfer factors of ¹³⁷Cs from soil to the different vegetable species which are determined through high resolution gamma spectrometry, maximum crop biomasses for the vegetable species, the dry-to-fresh ratios for the vegetable species, the bulk density of soil layers and the average concentration of ¹³⁷Cs in air. The derived parameters include the deposition rate and the root uptake rate, information for tillage, the logistic growth model and radionuclide concentrations in vegetables. The dynamic food chain model is solved by the Birchall–James algorithm to give the ¹³⁷Cs concentration in subsurface soil, from the 0.1–25 cm soil layer, and the ¹³⁷Cs concentration in harvested and unwashed vegetables. As validation of the model and parameters, the concentrations obtained experimentally and from the model are compared and are found to be in good agreement.     

Applicability study of using in-situ gamma-ray spectrometry technique for 137Cs and 210Pbex inventories measurement in grassland environments

In-situ measurement of fallout radionuclides ¹³⁷Cs and ²¹⁰Pb_ex has the potential to assess soil erosion and sedimentation rapidly. In this study, inventories of ¹³⁷Cs and ²¹⁰Pb_ex in the soil of Inner Mongolia grassland were measured using an In-situ Object Counting System (ISOCS). The results from the field study indicate that in-situ gamma-ray spectrometry has the following advantages over traditional laboratory measurements: no extra time is required for sample collection, no reference inventories are required, more economic, prompt availability of the results, the ability to average radionuclide inventory over a large area, and high precision.     

137Cs contamination of Techa river flood plain in Brodokalmak settlement

¹³⁷Cs contamination of the Techa river flood plain inside the Brodokalmak settlement has been mapped. The collimated scintillated detector technique was used for ¹³⁷Cs deposit measurements. The ¹³⁷Cs contamination is very heterogeneous. A comparison of this technique with the traditional sample method was performed at selected locations. The sampling data are in good agreement with in-situ data. Soil surface activity of ⁹⁰Sr was determined from the samples. It was shown that ¹³⁷Cs contamination correlates with ⁹⁰Sr contamination within the flood plain of the settlement.     

Distribution of the radionuclide 137Cs in the soils of a wet mountainous forest in Taiwan

The behavior of ¹³⁷Cs was studied in the Yuanyang lake ecosystem, a wet mountainous forest in subtropical Taiwan. Soils investigated are either partially podzolic soils or nearly pure peats with a high organic matter concentration in the surface layer. Concentration of ¹³⁷Cs was highest in the organic surface layers, particularly in the Oe horizon or in the underlying A horizon. The downwards migration to the mineral horizons is limited, in spite of the high rainfall. Topography is a critical factor for the distribution of ¹³⁷Cs. It is shown that the concentration of ¹³⁷Cs is highest at the foot of the slope and lower near the summit and near the lakeshore. The variation of the concentration along the landscape has been attributed to erosion–deposition in combination with surface run-off of the undisturbed forest. The amount of ¹³⁷Cs in the site studied is significantly higher than at any other place in Taiwan. The accumulation of ¹³⁷Cs is attributed to the high rainfall, which brought large amounts of ¹³⁷Cs with the precipitation in the early 1960s. A very remarkable feature of the ecosystem is that ¹³⁷Cs is not leached to the subsoils, but is stored in the biomass. Due to permanent recycling it remains available, without being leached downward.     

Recent peat accumulation rates in minerotrophic peatlands of the Bay James region, Eastern Canada, inferred by (210)Pb and (137)Cs radiometric techniques.

(210)Pb and (137)Cs dating techniques are used to characterise recent peat accumulation rates of two minerotrophic peatlands located in the La Grande Rivière hydrological watershed, in the James Bay region (Canada). Several cores were collected during the summer 2005 in different parts of the two selected peatlands. These minerotrophic patterned peatlands are presently affected by erosion processes, expressed by progressive mechanical destruction of their pools borders. This erosion process is related to a water table rise induced by a regional increase of humidity since the last century. The main objective of the present paper is to (1) evaluate if (210)Pb and (137)Cs dating techniques can be applied to build accurate chronologies in these environments and (2) detect changes in the peat accumulation rates in regard to this amplification of humidity. In both sites, unsupported (210)Pb shows an exponential decreasing according to the depth. Chronologies inferred from (210)Pb allow to reconstruct peat accumulation rates since ca. 1855 AD. The (137)Cs data displayed evident mobility and diffusion, preventing the establishment of any sustained chronology based on these measurements. In the two sites, peat accumulation rates inferred from (210)Pb chronologies fluctuate between 0.005 and 0.038gcm(-2)yr(-1). As a result, the rise of the water table during the last decade has not yet affected peat accumulation rates.     

Application of the Monte Carlo code DETEFF to efficiency calibrations for in situ gamma-ray spectrometry

We studied the applicability of the Monte Carlo code DETEFF for the efficiency calibration of detectors for in situ gamma-ray spectrometry determinations of ground deposition activity levels. For this purpose, the code DETEFF was applied to a study case, and the calculated (137)Cs activity deposition levels at four sites were compared with published values obtained both by soil sampling and by in situ measurements. The (137)Cs ground deposition levels obtained with DETEFF were found to be equivalent to the results of the study case within the uncertainties involved. The code DETEFF could thus be used for the efficiency calibration of in situ gamma-ray spectrometry for the determination of ground deposition activity using the uniform slab model. It has the advantage of requiring far less simulation time than general Monte Carlo codes adapted for efficiency computation, which is essential for in situ gamma-ray spectrometry where the measurement configuration yields low detection efficiency.     

Determination of radioactivity levels and hazards of soil and sediment samples in Firtina Valley (Rize, Turkey).

The natural radioactivity levels in soil and sediment samples of Firtina Valley have been determined. To our knowledge, there seems to be no information about radioactivity level in the Firtina Valley soils and sediments so far. For this reason, soil and sediment samples were collected along the Firtina Valley and analysis on the collected samples were carried out to determine 238U, 232Th, 40K and 137Cs radioisotopes using high purity germanium detector. The activity concentrations obtained for 226Ra, 214Pb, 214Bi, 228Ac, 208Tl, 40K and 137Cs are given in the unit of Bq/kg. The results have been compared with other radioactivity measurements in different country's soils and sediments. The radium equivalent activity (Raeq), the absorbed dose rate (D), the external hazard index (Hex), the annual gonadal dose equivalent (AGDE) and the annual effective dose equivalent (AEDE) were also calculated and compared with the international recommended values.