137Cs Inventories Research Articles

Relating Intensity of Soil Redistribution to Land Use Changes in Abandoned Pyrenean Fields Using Fallout Caesium‐137

AbstractFallout caesium‐137 has been used to trace soil redistribution in abandoned fields located in the Central Spanish Pyrenees. A total of 28 fields with different lengths, slope angles and time since abandonment were selected on a representative south‐facing slope of the Estarrún valley. The local reference inventory and the magnitude and spatial distribution of 137Cs inventories within these fields were documented and used as a basis for assessing patterns of soil redistribution. The local reference inventory was estimated to be 4,500 Bqm−2. Within the fields, the average 137Cs inventory at the top of the slope was 3,920 Bqm−2, and accumulation of soil at the bottom of the slopes was demonstrated by an average 137Cs inventory of 5,320 Bqm−2. Deviations from the reference inventory were highest for fields with the longest slopes that had been abandoned for less than 30 years. Here, increases in the 137Cs inventory, relative to the reference inventory, in excess of 20% were found at the bottom of the slopes. Considering all the fields and all geomorphic positions within the fields, the greatest 137Cs losses and gains were found in the fields with the longest duration of abandonment, indicating more intense soil redistribution. Irrespective of the timing of abandonment, the ranges of 137Cs inventories in the fields were found to be proportional to the water erosion index. The 137Cs technique demonstrated that patterns of sediment redistribution were closely related to the topographic and physiographic characteristics of the slopes. Copyright © 2017 John Wiley & Sons, Ltd.

Validating a Basic Assumption of Using Cesium‐137 Method to Assess Soil Loss in a Small Agricultural Catchment

AbstractAlthough the fallout radionuclide 137Cs technique has been widely used to provide soil redistribution estimates in recent decades, some researchers have recently challenged the usefulness of this technique. Thus, it is necessary to evaluate the usefulness of the 137Cs technique to study soil redistribution, especially in areas that suffer from severe soil erosion and where the 137Cs inventory distributions vary. This study analyses the abundance of 137Cs deposited in sediment trapped by a check dam over 31 years in a small agriculture catchment in the Loess Plateau, which has experienced some of the most extensive agricultural soil erosion in the world. The 137Cs inventory and soil loss were evaluated, and the results indicated that the sediment deposition rate behind the check dam was approximately 38 cm/year. The specific soil erosion rate of the catchment is estimated to be 178 t ha−1 year−1. A geochemical properties fingerprinting method indicated that the ratio of the inter‐gully erosion from cropland to gully erosion was 0·46:0·54 during the investigated period of 31‐year period. Our results suggest that the 137Cs technique cannot be directly used in the study catchment. Gully erosion is the main type of soil erosion that occurs in the loess catchment, and the amount of gully erosion changes from year to year. Therefore, the abundance of 137Cs cannot be used to estimate soil redistribution where gully erosion is severe. However, after calibration, the inter‐gully soil loss was consistently related to 137Cs abundance, which means that the 137Cs technique can be used at the plot or slope scale on the Loess Plateau. Our results also reveal the particle‐size selectivity of soil detachment and sediment deposition during runoff‐erosion events. The average 137Cs content of the fine group couplets is 63% greater than the 137Cs content of the coarse group. When the studied section spans more than 15 years, the 137Cs inventory is consistent (R2 = 0·95, p < 0·01) with soil loss, which means that the selectivity may be offset over a long period. Our results confirm that the 137Cs method requires careful planning when applied at the catchment scale. Copyright © 2017 John Wiley & Sons, Ltd.

Spatial variation in soil, SOC, and total N redistribution on affected and non-affected slope terraces due to the 8.0 Wenchuan Earthquake in 2008 by using 137Cs technique

Using the 137Cs technique, we assessed spatial variation in soil erosion and its impact on lateral movements of soil organic carbon (SOC) and total nitrogen (total N) in a terraced series and a complex slope in the Longmenshan Fault zone, China. The complex slope derived from three terraced fields with damaged banks, resulting from the 8.0 Wenchuan Earthquakes in 2008. The terraced series and complex slope are the dominant sloping farmland patterns in this area, which represent for earthquake non-affected and affected sloping farmland, respectively. Soil loss occurred over the upper parts of slopes and deposition occurred towards the downslope boundary of each terrace. Also, soil loss occurred on upper terraces and soil accumulation on lower terraces. Net soil erosion rates for the terraced toposequence were estimated at −3.70±14.38Mgha−1yr−1, indicating the terraced toposequence played an important role in soil conservation. For the complex slope, higher soil erosion rates occurred at the summit and other slope positions with greater slope curvature, and soil accumulation occurred at the toe slope and other slope positions with lower slope curvature (15m, 25m, and 40m). In addition to water erosion, collapses resulting from earthquake and tillage erosion were also important soil erosion processes for the complex slope. Moreover, Net soil erosion rate on the complex slope (4.89±18.03tha−1yr−1) was significantly higher than on the terraced series. SOC and total N inventories showed similar patterns to the 137Cs inventory. Such results confirm that 137Cs can help to trace SOC and total N dynamics on sloping farmland in this area.

Distribution of natural and anthropogenic radionuclides in northwest Mediterranean coastal sediments

The distribution of radionuclides in NW Mediterranean coastal sediments, and the processes controlling their abundance were investigated in three cores taken near the island of Porquerolles and one offshore Monaco. The sediments collected near Porquerolles were strongly anoxic due to diagenetic processes involved in the decomposition of organic matter, whereas they transitioned from oxic to anoxic at a depth of 4 cm beneath the seawater interface at Monaco. Organic carbon (OC) was more abundant in sediments at Porquerolles (by about a factor of 3–5) than at Monaco and elsewhere in the coastal NW Mediterranean. Sediment cores collected NE of Porquerolles also possessed elevated uranium concentrations that correlated with high OC content and strong reducing conditions. The 239,240Pu and 241Am activities in surficial sediments ranged from 1 to 5.7 Bq kg−1 and 0.3 to 1 Bq kg−1, respectively, while the 137Cs activity ranged from 0.3 to 6.2 Bq kg−1. The mean activity ratios of 241Am/239,240Pu and 238Pu/239,240Pu in Porquerolles and Monaco sediments were similar to the global fallout ratios. Sediment inventories of global fallout 239,240Pu (430–800 Bq m−2) and 241Am (150–285 Bq m−2) were by about a factor of 5–10 higher at Porquerolles, whereas the inventory of 137Cs (430–1000 Bq m−2) was substantially lower at the investigated stations than have been reported elsewhere at similar latitudes. Specific local conditions characterised by high OC sediment loads due to the growth and mortality of Posidonia oceanica have been responsible for deposition of large amounts of seagrass tissues at the NE corner of Porquerolles, which have had a profound effect on the distribution of radionuclides in the sediments.

Processes affecting long-term changes in 137Cs concentration in surface sediments off Fukushima

Temporal changes in cesium-137 (137Cs) concentrations in the surface (0–10 cm) layer of seabed sediment were quantified from continuous observation data at 71 stations within a 150-km radius of the Fukushima Daiichi Nuclear Power Plant, and the primary processes affecting temporal changes were identified. From March 2011 to the end of 2015, about 80% of the initially deposited 137Cs in the surface sediment in the coastal region (bottom depth ≤100 m) region has dissipated (radioactive decay is not included). Such a remarkable change in the 137Cs concentration was not observed in the offshore (>100 m) region. This paper focuses on the following three processes that affected the decrease in the 137Cs concentrations, and assesses their relative importance; (1) resuspension and transport of 137Cs-bound sediment, (2) desorption of 137Cs from the sediment, and (3) dilution of 137Cs by vertical mixing of sediment. Consequently, it was estimated that the first two processes together have potentially contributed to reduce the 137Cs inventory in the top 10 cm of the coastal region by at most 35%. Furthermore, by applying a pulse input sediment mixing model to the observed vertical distribution of sedimentary 137Cs, it was also estimated that more than 43% of the 137Cs in the surface sediment was transported to deeper sediment layers by vertical mixing of the sediment. This indicates that the decrease of 137Cs concentrations in coastal sediments was mainly affected by mixing of 137Cs-bound surface sediment with less contaminated sediment in the deeper layers.

Uncertainty assessment method for the Cs-137 fallout inventory and penetration depth

Within the presented study, soil samples were collected in year 2007 at 20 different locations of the Greek terrain, both from the surface and also from depths down to 26 cm. Sampling locations were selected primarily from areas where high levels of 137Cs deposition after the Chernobyl accident had already been identified by the Nuclear Engineering Laboratory of the National Technical University of Athens during and after the year of 1986. At one location of relatively higher deposition, soil core samples were collected following a 60 m by 60 m Cartesian grid with a 20 m node-to-node distance. Single or pair core samples were also collected from the remaining 19 locations. Sample measurements and analysis were used to estimate 137Cs inventory and the corresponding depth migration, twenty years after the deposition on Greek terrain. Based on these data, the uncertainty components of the whole sampling-to-results procedure were investigated. A cause-and-effect assessment process was used to apply the law of error propagation and demonstrate that the dominating significant component of the combined uncertainty is that due to the spatial variability of the contemporary (2007) 137Cs inventory. A secondary, yet also significant component was identified to be the activity measurement process itself. Other less-significant uncertainty parameters were sampling methods, the variation in the soil field density with depth and the preparation of samples for measurement. The sampling grid experiment allowed for the quantitative evaluation of the uncertainty due to spatial variability, also by the assistance of the semivariance analysis. Denser, optimized grid could return more accurate values for this component but with a significantly elevated laboratory cost, in terms of both, human and material resources. Using the hereby collected data and for the case of a single core soil sampling using a well-defined sampling methodology quality assurance, the uncertainty component due to spatial variability was evaluated to about 19% for the 137Cs inventory and up to 34% for the 137Cs penetration depth. Based on the presented results and also on related literature, it is argued that such high uncertainties should be anticipated for single core samplings conducted using similar methodology and employed as 137Cs inventory and penetration depth estimators.

210Pb, 137Cs and 7Be in the sediments of coastal lakes on the polish coast: Implications for sedimentary processes

In this study we combined radioisotopes (210Pb, 137Cs and 7Be) and hydrodynamic modeling to investigate sedimentary processes in three coastal lakes on the Polish Baltic coast. The research aimed at establishing the depth of sediment mixing and its effects on sediment geochemistry as well as showing the relationship between lake water salinity and radionuclide distribution in the sediment cores. We established that the intensity of mixing displayed appreciable variability throughout the lakes and the thickness of sediment mixing layer was between <2 and 22 cm. The mixing was primarily due to wind-induced waves. The vertical mixing was shown to shift sulfidation of the sediments towards deeper layers. We found that the distributions of radioisotopes, 137Cs in particular, in the sediment cores from coastal lakes were strongly affected by the early diagenetic processes, which caused diffusive migration of radionuclides. The inventories of 210Pbex and 137Cs in the lakes were positively related to salinity. The high inventories of both isotopes (3.2–10.9 kBq ·m−2 for 210Pbex and 3.0–6.0 kBq·m−2 for 137Cs) in coastal lakes were explained by enhanced sedimentation within estuarine mixing zone and delivery of “additional” 210Pb and 137Cs to the lakes during saltwater ingressions. The results of this study have implications for the paleolimnology, sedimentology and biogeochemistry of coastal lakes.

Vertical and lateral distribution of fallout 137Cs and soil properties along representative toposequences of central Rif, Morocco

The purpose of this study is to understand and quantify the relationships between current 137Cs inventories and the soil properties and the physiographic characteristics. A total of 36 cores were taken in seven transects with different slopes, lithology and land use. The analysis focused on the 137Cs mass activity as well as inventories and its relationship with soil properties as grain size and organic matter.The mass activity of 137Cs and the inventories varied between 3.6 and 63.7 Bq kg−1 and between 521.7 and 3304.4 Bq m−2, respectively. At uncultivated soils, high concentrations of 137Cs are located in the top 10 cm and decreased exponentially in depth. Cultivated soils record disturbed and heterogeneous 137Cs profiles with values of mass activity and inventories up to 38.7 Bq kg−1 and 2510.8 Bq m−2, respectively.The 137Cs inventories were significantly higher in uncultivated soils (mean: 2086.9 Bq m−2) compared to cultivated soils (mean: 1397.1 Bq m−2). The 137Cs mass activity showed a significant positive correlation with organic matter, silt and clay, but it was negatively correlated with sand and pH respectively. High levels of 137Cs were found at altitudes between 500 m and 640 m a.s.l, and at slopes from 8° to 11°, as well as in dense scrub land and Fersialitic soils. A principal component analysis showed that more than 86.7% of the variance in 137Cs mass activity was explained by the organic matter content and the land use.The results of this study provide insights into the effects of soil properties and physiographic factors on the behaviour of 137Cs in soils of Mediterranean environments of North Africa and strengthen the reliability of this radioisotope as an erosion tracer.

Particulate organic matter in rivers of Fukushima: An unexpected carrier phase for radiocesiums.

The role of particulate organic matter in radiocesium transfers from soils to rivers was investigated in areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident. Suspended and deposited sediments, filtered water, macro organic debris and dead leaves were sampled along the six most contaminated coastal river catchments of the Fukushima prefecture in the early autumns 2013 and 2014. Radiocesium concentrations of river samples and total organic carbon concentrations in suspended and deposited sediments were measured. Radiocesium concentrations of suspended and deposited sediments were significantly correlated to 137Cs inventories in soils and total organic carbon. The distributions of radiocesium between the organic and mineral phases of both types of sediment were assessed by using a modelling approach. The results suggest that, during the early autumn season, the organic fraction was the main phase that carried the radiocesiums in deposited sediments and in suspended sediments for suspended loads <25mg·L-1. For higher suspended loads like those occurring during typhoon periods, the mineral fraction was the main carrier phase. Thus, high apparent distribution coefficient values noted by various authors in Fukushima could be attributed to the high radiocesium contents of particulate organic matter. Since it is well known that organic compounds generally do not significantly adsorb radiocesium onto specific sites, several hypotheses are suggested: 1) Radiocesiums may have been absorbed into organic components at the early stage of atmospheric radioactive deposits and/or later due to biomass recycling and 2) Those elements would be partly carried by glassy hot particles together with organic matter transported by rivers in Fukushima. Both hypotheses would lead to conserve the amount of radiocesiums associated with particles during their transfers from the contaminated areas to the marine environment. Finally, such organically bound radiocesium would lead to significant deliveries of bioavailable radiocesium for living organisms at Fukushima.

Variability of 137Cs inventory at a reference site in west-central Iran

137Cs technique has been widely used for the evaluation rates and patterns of soil erosion and deposition. This technique requires an accurate estimate of the values of 137Cs inventory at the reference site. This study was conducted to evaluate the variability of the inventory of 137Cs regarding to the sampling program including sample size, distance and sampling method at a reference site located in vicinity of Fereydan district in Isfahan province, west-central Iran. Two 3 × 8 grids were established comprising large grid (35 m length and 8 m width), and small grid (24 m length and 6 m width). At each grid intersection two soil samples were collected from 0 to 15 cm and 15–30 cm depths, totally 96 soil samples from 48 sampling points. Coefficients of variation for 137Cs inventory in the soil samples was relatively low (CV = 15%), and the sampling distance and methods used did not significantly affect the 137Cs inventories across the studied reference site. To obtain a satisfactory estimate of the mean 137Cs activity in the reference sites, particularly those located in the semiarid regions, it is recommended to collect at least four samples along in a grid pattern 3 m apart.

137Cs tracing dynamics of soil erosion, organic carbon, and total nitrogen in terraced fields and forestland in the Middle Mountains of Nepal

The Middle Mountains is one of the regions of Nepal most vulnerable to water erosion, where fragile geology, steep topography, anomalous climatic conditions, and intensive human activity have resulted in serious soil erosion and enhanced land degradation. Based on the Cs-137 tracing method, spatial variations in soil erosion, organic carbon, and total nitrogen (TN) in terraced fields lacking field banks and forestland were determined. Soil samples were collected at approximately 5 m and 20 m intervals along terraced field series and forestland transects respectively. Mean 137Cs inventories of the four soil cores from the reference site was estimated at 574.33 +/- 126.22 Bq m(-2) (1 Bq (i.e., one Becquerel) is equal to 1 disintegration per second (1 dps)). For each terrace, the Cs-137 inventory generally increased from upper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, Cs-137 data showed that abrupt changes in soil erosion rates could occur between the lower part of the upper terrace and the upper part of the immediate terrace within a small distance. This result indicated that tillage erosion is also a dominant erosion type in the sloping farmland of this area. At the same time, we observed a fluctuant decrease in soil erosion rates for the whole terraced toposequence as well as a net deposition at the toe terrace. Although steep terraces (lacking banks and hedgerows) to some extent could act to limit soil sediment accumulation in catchments, soil erosion in the terraced field was determined to be serious. For forestland, with the exception of serious soil erosion that had taken place at the top of slopes due to concentrated flows from a country road situated above the forestland site, spatial variation in soil erosion was similar to the "standard" water erosion model. Soil organic carbon (SOC) and TN inventories showed similar spatial patterns to the Cs-137 inventory for both toposequences investigated. However, due to the different dominant erosion processes between the two, we found similar patterns between the < 0.002 mm soil particle size fraction (clay sized) and Cs-137 inventories in terraced fields, while different patterns could be found between Cs-137 inventories and the < 0.002 mm soil particle size fraction in the forestland site. Such results confirm that Cs-137 can successfully trace soil erosion, SOC and soil nitrogen dynamics in steep terraced fields and forestland in the Middle Mountains of Nepal.

Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source

AbstractCultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the caesium‐137 (137Cs) inventories of lake and floodplain cores as well as the 137Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment.Low 137Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. Caesium‐137 activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks.Pre‐1963 sediment yields were approximately 11.2 t km−2 yr−1 and post‐1963 was approximately 11.9 t km−2 yr−1. The lack of increased sediment yield post‐1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km−2 yr−1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material.The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of 137Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilization of 137Cs from sedimentary deposits. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Effects of plant diversity on soil erosion for different vegetation patterns

Vegetation effectively prevents soil erosion. However the relationship between plant diversity and soil erosion remains ambiguous under various environmental conditions. To explore the role that plant diversity plays in soil erosion, this study was conducted in the Three-River-Source region, located in the hinterlands of the Qinghai–Tibet Plateau, China. After examining 99 plots within the study area, and analyzing the soil 137Cs inventory within the plots, we found that with a greater number of plants distributed within an aggregation pattern, there was greater interception of the soil particles by the vegetation patch. This phenomenon results in a more developed vegetation patch that can support greater vegetation coverage and higher plant diversity than it previously could. Although a positive correlation exists between plant diversity and vegetation coverage, the relationship between the extent of soil erosion and plant diversity is modulated by the vegetation pattern. When plants are distributed in a relatively homogeneous pattern, vegetation coverage decreases with increasing plant diversity, which leads to increased soil erosion. When plants are distributed between a homogenous and a heterogeneous pattern, no relationship is found between plant diversity and soil erosion. With a heterogeneous plant distribution, vegetation coverage increases with plant diversity, and soil erosion is inhibited under such conditions.

Estimation of the inventory of the radioactive wastes in Fukushima Daiichi NPS with a radionuclide transport model in the contaminated water

ABSTRACTQuantification of the radioactive waste inventory remaining inside the reactors at Fukushima Daiichi NPS is necessary to effectively plan their recovery, treatment, and disposal. Analysis of radionuclide concentrations and secondary wastes in the contaminated water treatment system can provide a means to estimate the radioactive waste inventory, which is not possible by more direct methods due to problems of accessibility and high levels of radiation. A predictive model has therefore been developed to estimate the radioactive waste inventory from the radionuclide concentrations and throughputs in the contaminated water. Model fitting has enabled the estimation of the key parameters, such as the initial radionuclide concentration C0, the continuous release rate F, and inventory of source of continuous release IS0. An estimated one-third of the total 137Cs inventory has already made its way into the water treatment system as secondary wastes, whereas half still remains inside the damaged reactors as of 13 March 2014.

The reduction of partitioned wind and water erosion by conservation agriculture

Soil loss due to wind and water erosion degrades the soil on-site and results in environmental problems due to deposition in off-site areas downstream and downwind of the source field. Wind and water erosion may both occur to varying extents particularly in semi-arid environments. Soil conservation strategies require information about the processes of soil redistribution to mitigate its impact. However, very few studies have partitioned soil erosion between contributions of wind and water. We quantified wind and water erosion on six graded terraces under a uniform crop rotation since 1949 and two tillage management practices begun in 1981. Detailed runoff and sediment yield data have been recorded on all the terraces since 1984. We used a stratified random sampling design to collect soil which were then bulked to form six composites for each terrace. From an adjacent undisturbed native prairie, soil cores were collected and composited similarly to provide a reference. The cores were composited by 15cm layers in the terraces and, in the reference area, the upper 15cm layer was subdivided into 5cm layers and all were measured for 137Cs activity which was converted to 137Cs inventory. We then employed an established computer model that equates loss of 137Cs inventory with soil loss and direct measurement of water-borne sediment loss to estimate 30year mean wind erosion losses on the terraces by tillage type. We found that no-till management reduced total soil loss by one-third compared with stubble mulch tillage, reduced water-borne sediment loss by about the same amount, and that for both tillage systems, wind erosion was responsible for about 75% of the total soil loss.

A multi-radionuclide approach to evaluate the suitability of 239 + 240Pu 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 239Pu and 240Pu as a method to assess soil erosion magnitude by comparison to more established fallout radionuclides such as 137Cs and 210Pbex. 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−1yr−1). Pu isotopes further allowed determining the origin of the fallout. Both 240Pu/239Pu atomic ratios and 239+240Pu/137Cs activity ratios were close to the global fallout ratio. However, the depth profile of the 239+240Pu/137Cs activity ratios in undisturbed sites showed lower ratios in the top soil increments, which might be due to higher migration rates of 239+240Pu. The activity ratios further indicated preferential transport of 137Cs from eroded sites (higher ratio compared to the global fallout) to the depositional sites (smaller ratio). As such the 239+240Pu/137Cs activity ratio offered a new approach to parameterize a particle size correction factor that can be applied when both 137Cs and 239+240Pu have the same fallout source. Implementing this particle size correction factor in the conversion of 137Cs inventories resulted in comparable estimates of soil loss for 137Cs and 239+240Pu. The comparison among the different fallout radionuclides highlights the suitability of 239+240Pu through less preferential transport compared to 137Cs and the possibility to gain information regarding the origin of the fallout. In conclusion, 239+240Pu 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 137Cs, there is a clear need for a wider agro-environmental testing.

Estimates of late Holocene soil production and erosion in the Snowy Mountains, Australia

Soil production in actively uplifting or high precipitation alpine landscapes is potentially rapid. However, these same landscapes are also susceptible to erosion and can be sensitive to changes in climate and anthropogenic activity which can upset the balance between soil production and erosion. The Snowy Mountains, southeastern Australia, are a tectonically stable, low relief, moderate precipitation mountain environment. The alpine area is extensively blanketed by soil that has been subjected to more intensive episodes of erosion during past periods of anthropogenic disturbance and under cold climate conditions of the late Quaternary. In this study, rates of soil development and hillslope erosion were investigated using radiocarbon dating, fallout radionuclides and sediment cores collected from lakes and reservoirs. Estimated Holocene soil development rates were 20–220t/km2/y. Erosion rates determined from the radionuclides 137Cs and 210Pb were equivocal, due to the inherent spatial variability of radionuclide inventories relative to apparent erosion rates. Estimated average erosion rates over the past 100years, determined from 210Pbex inventories, were 60t/km2/y (95% CI: 10, 90). Inventories of 137Cs observed at the same site implied that more recent erosion rates (over the past 60years) was below the detection limits of the sampling method applied here (i.e.<70t/km2/y). The upper estimate of 90t/km2/y is comparable to the mean erosion rate estimated using the radionuclide method for uncultivated sites in Australia and is significantly lower than that measured at sites were vegetation cover was disturbed by livestock grazing prior to its exclusion from the alpine area in the 1940s CE. Low erosion and high soil production rates relative to the lowland soils are likely related to extensive vegetation cover, which, in this context, protects soils against erosion and contributes to the formation of organic alpine soils, that rapidly accumulate organic matter by comparison to other soil types.

Spatial variation in the 137Cs inventory in soils in a mixed deciduous forest in Fukushima, Japan

The spatial variation of the radiocesium inventory in forest soil was studied c.a. 44 km northwest of the Fukushima Daiichi Nuclear Power Plant, Japan. This study focuses on the effects of canopy interception and downward transfer from the forest canopy to the forest floor via stemflow and throughfall. We established a study plot (400 m2) in the canopy layer of a secondary mixed deciduous forest dominated by Japanese oak (Quercus crispula) and Japanese fir (Abies firma), in August and November 2014. Soil was sampled from 0 to 5 cm depth and 137Cs was measured under the canopy using a 2-m grid and also at the tree trunk bases. We divided the study plot into the five different types of subplot according to the canopy projection areas and the tree species for the analysis. The geometric mean and coefficient of variation of the 137Cs inventory were 202 kBq m−2 and 0.11 (0.52 in the arithmetic coefficient of variation), respectively. Within the forest, the variation in the 137Cs inventory under trees was larger than in crown gap areas. The large spatial variation may be attributed to canopy interception of the initial deposition and downward transfer of radiocesium via stemflow and throughfall.

Long-term retention of 137Cs in three forest soil types with different soil properties

Current 137Cs activity concentrations were studied at three localities in individual soil horizons of Stagnosol, Arenic Podzol and Haplic Cambisol soil units in soil blocks with dimensions of 20 × 20 × 40 cm situated below pine canopies (n = 3) and spruce canopies (n = 3), and below small canopy gaps, at least 15 × 15 m in area (n = 3 + 3), which have probably endured since 1986. The main zone of 137Cs accumulation in all the localities was found to be in the organic horizons (H and F). No significant transport and accumulation of 137Cs into illuvial soil horizons (Bm, Bs or Bhs, Bv and Bv/IIC) was found. The estimated current total 137Cs activity concentrations in the soil blocks 40 cm in depth were only slightly higher below the coniferous canopy than they were below nearby canopy gaps. The inventory of 137Cs in the soils was found to be in accordance with the estimated 137Cs inputs from the Chernobyl fallout and from global fallout. The low amounts of 137Cs found accumulated in the aboveground biomass (mosses, grasses, needles) did not substantially bias the studied radiocaesium balance in the soils. The vertical migration rate of 137Cs in soils (cm/year) had a tendency to be higher below canopies than below canopy gaps and below pine canopies than below spruce canopies. We expected the current 137Cs activity concentrations in the individual soil horizons to be related to the studied soil parameters: pH (H2O), pH (CaCl2), content of organic matter and mineral portion and portion of humic and fulvic acid contents (Q4/6). However, this was not confirmed. Similarly, we observed a weak tendency toward higher 137Cs activity in soils below the canopy than in soils below canopy gaps. The available gaps used in our study may have been too small, and they may have been affected by an accumulation of litter and humus containing 137Cs from the surrounding plots situated below neighbouring canopies.

Impact of the Fukushima accident on tritium, radiocarbon and radiocesium levels in seawater of the western North Pacific Ocean: A comparison with pre-Fukushima situation

Tritium, radiocarbon and radiocesium concentrations in water column samples in coastal waters offshore Fukushima and in the western North Pacific Ocean collected in 2011–2012 during the Ka'imikai-o-Kanaloa (KoK) cruise are compared with other published results. The highest levels in surface seawater were observed for 134Cs and 137Cs in seawater samples collected offshore Fukushima (up to 1.1 Bq L−1), which represent an increase by about three orders of magnitude when compared with the pre-Fukushima concentration. Tritium levels were much lower (up to 0.15 Bq L−1), representing an increase by about a factor of 6. The impact on the radiocarbon distribution was measurable, but the observed levels were only by about 9% above the global fallout background. The 137Cs (and similarly 134Cs) inventory in the water column of the investigated western North Pacific region was (2.7 ± 0.4) PBq, while for 3H it was only (0.3 ± 0.2) PBq. Direct releases of highly contaminated water from the damaged Fukushima NPP, as well as dry and wet depositions of these radionuclides over the western North Pacific considerably changed their distribution patterns in seawater. Presently we can distinguish Fukushima labeled waters from global fallout background thanks to short-lived 134Cs. However, in the long-term perspective when 134Cs will decay, new distribution patterns of 3H, 14C and 137Cs in the Pacific Ocean should be established for future oceanographic and climate change studies in the Pacific Ocean.