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After the Fukushima Daiichi nuclear power plant accident, the terrestrial environment became severely contaminated with radiocesium. Consequently, the river and lake water in the Fukushima area exhibited high radiocesium levels, which declined subsequently. The partition coefficient of 137Cs between the suspended sediment (SS) and dissolved phases, K d , was introduced to better understand the dynamic behavior of 137Cs in different systems. However, the K d values in river water, ranging from 2 × 104 to 7 × 106 L kg−1, showed large spatiotemporal variability. Therefore, the factors controlling the 137Cs partition coefficient in natural water systems should be identified. Herein, we introduce a chemical model to explain the variability in 137Cs K d in natural water systems. The chemical model includes the complexation of Cs+ with mineral and organic binding sites in SS, metal exchange reactions, and the presence of colloidal species. The application of the chemical model to natural water systems revealed that Cs+ is strongly associated with binding sites in SS, and a major chemical interaction between 137Cs and the binding sites in SS is the isotope exchange reaction between stable Cs and 137Cs, rather than metal exchange reactions with other metal ions such as potassium ions. To explain the effect of the SS concentration on K d , the presence of colloidal 137Cs passing through a filter is significant as the dominant dissolved species of 137Cs in river water. These results suggest that a better understanding of stable Cs dissolved in natural water is important for discerning the geochemical and ecological behaviors of 137Cs in natural water. [Display omitted] • Partition coefficients of 137Cs between water and sediment are useful parameter to understand behaviors of 137Cs in environment. • Chemical model was applied to partitioning of 137Cs between natural water and suspended sediment. • Chemical model was based on concepts of isotope exchange equilibrium and mass balance including multi-reaction sites and colloidal forms. • Chemical model could confirm that the K d in fresh waters is inversely related to stable cesium (133Cs) concentrations. • 133Cs concentrations are one of the most important factors to control the K d in natural water systems. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a novel DNA‐encoded library of macrocyclic peptide derivatives are described; the macrocycles are based on three sets of proteinogenic and non‐proteinogenic amino acid building blocks and featuring the use of copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction for ring closure. The library (termed YO‐DEL) which contains 1 254 838 compounds, was encoded with DNA in single‐stranded format and was screened against target proteins of interest using affinity capture procedures and photocrosslinking. YO‐DEL selections yielded specific binders against serum albumins, carbonic anhydrases and NKp46, a marker of activated Natural Killer cells. [ABSTRACT FROM AUTHOR]

Long-term monitoring revealed that radiocesium (137Cs) deposition that fall from the canopy with litterfall was characterized by forest types, seasonal change, and canopy closure (CC). The sum of autumn and spring 137Cs deposition values divided by the sum of summer and winter tended to have higher values in the cedar forest. The angle of view α when the correlation between the CC size and litterfall amount is strongest, was 5° or less in the young cedar forest, but varied in the hardwood–pine mixed forest. This indicates the spatial distribution of 137Cs deposition has heterogeneity and homogeneity in each forest. [ABSTRACT FROM AUTHOR]

Strontium-90 (90Sr) is the major long-lived radionuclide derived from the Chernobyl accident, and is still being detected in the heavily contaminated catchments of the Chernobyl Exclusion Zone. This study examines the long-term decrease in the dissolved-phase 90Sr concentration and the concentration–discharge (90Sr-Q) relationship in stream water since the accident. We show that the slow decline in 90Sr follows a double-exponential function, and that there is a clear relationship between 90Sr and Q. This study is the first to reveal that the log(90Sr)-log(Q) slope has been gradually decreasing since the accident. This trend persists after decay correction. Thus, it is not caused by the physical decay of 90Sr and environmental diffusion, but implies that the concentration formation processes in stream water have been changing over a long period. We propose a hydrochemical model to explain the time-dependency of the 90Sr-Q relationship. This paper presents a mathematical implementation of the new concept and describes the model assumptions. Our model accurately represents both the long-term 90Sr trend in stream water and the time-dependency of the 90Sr-Q relationship. Although this paper considers a small catchment in Chernobyl, the conceptual model is shown to be applicable to other accidental releases of radionuclides. [ABSTRACT FROM AUTHOR]

Abstract We examined spatial variation in vertical 137Cs flux from the litter layer using lysimeters combined with copper-substituted Prussian blue in two forests (deciduous broad-leaved and Japanese cedar (Cryptomeria japonica)), approximately 40 km northwest of the Fukushima Daiichi Nuclear power plant. The study ran from August 2016 to February 2017 in three periods; summer (10 Aug–4 Oct), autumn (5 Oct–30 Nov) and winter (1 Dec–27 Feb). Twenty-five and 15 lysimeters were installed in the deciduous broad-leaved and the Japanese cedar sites within 400 and 300 m2 areas with 3–5 m intervals, respectively. The geometric means of the flux in the deciduous broad-leaved site were 0.51, 0.085 and 0.060 kBq/m2/month in summer, autumn and winter periods, respectively. In the Japanese cedar site, the mean fluxes were 0.45, 0.036 and 0.023 kBq/m2/month. The ratio of 137Cs flux during the survey period to litter 137Cs inventory was 6% and 1% on average in the deciduous broad-leaved and Japanese cedar sites, respectively. The 137Cs flux in the summer period was much larger than those in other periods, resulting from higher precipitation in the summer. Our fine scale observation with 5 m interval showed very large spatial variation in the 137Cs flux and the differences between maximum and minimum range from 8 to 104 times, but were mostly 20–25 times. The spatial variations in the 137Cs flux were affected positively by those in the litter 137Cs inventory and negatively by canopy openness. Highlights • We examined variation in vertical dissolved 137Cs flux through litter. • Ratio of 137Cs flux to litter inventory during the survey was less than 10%. • Spatial variation showed log-normal distribution and had 20–25 times difference. • Spatial variation was determined by litter 137Cs inventory and canopy openness. [ABSTRACT FROM AUTHOR]

Abstract After the Fukushima Dai-ichi Nuclear Power Plant accident on March 2011, several studies showed that the downward migration of 137Cs from litter to mineral soil is more rapid in forests in Fukushima than in forests affected by the Chernobyl accident. Therefore, the downward migration within mineral soil layers is more important for predicting long-term dynamics of 137Cs in forest ecosystems in Fukushima. In the present study, we monitored the detailed vertical distribution of 137Cs in litter and soil layers for 6 y (2011–2017) following the previous study (2011–2012), and found that temporal changes in those distributions were different among mixed forest (MF), mature cedar (MC) and young cedar (YC) forests. The 137Cs concentrations and inventories in the litter layer exponentially decreased with time for all sites, with more than 80–95% of the deposited 137Cs on the forest floor distributed in mineral soil layers by 2017. The percentage of 137Cs inventory in the litter layer to the total 137Cs inventory in litter and mineral soil layers was well fitted by a single exponential equation with decreasing rate of 0.22–0.44 y−1. The slower migration was observed in the YC site, probably because of higher initial interception of 137Cs fallout by dense canopy. As the downward migration from litter to mineral soil progressed, the 137Cs concentration in the first few cm of mineral soil surface gradually increased and became higher than the 137Cs concentration in the litter within 2–3 y of the accident. The 137Cs concentration in mineral soil layers exponentially decreased with depth throughout survey period, and an exponential equation fitted well. The relaxation depth of 137Cs concentration in mineral soil layers estimated by the exponential equation were constantly increasing in the MC and YC sites with 0.08 cm y−1. In contrast, there was no temporal increase in the relaxation depth in the MF site, indicating little migration to subsurface soil layer from not only litter layer but also surface soil layer. Further studies are necessary to identify the forests prone to the downward migration of 137Cs and its factors regarding both forest and soil characteristics. Highlights • 137Cs concentration in soil was fitted by exponential equation at least for 6 y. • Migration from litter to mineral soil was more rapid than in the case of Chernobyl. • 137Cs concentration in surface soil surpassed that of litter within 2–3 y. • Relaxation depth in the two cedar forests has gone down with 0.08 cm y−1. • In contrast, the downward migration in the mixed forest was not clearly observed. [ABSTRACT FROM AUTHOR]

Abstract Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the ambient dose rate for forest environments. This study investigated temporal changes in the ambient dose rate in different forest environments of Fukushima Prefecture. We conducted repeated measurements of the ambient dose rate in 2014 and 2016 at the same measurement points as those used by the Ministry of Agriculture, Fishery and Forestry of Japan (MAFF) in 2011. The measurements revealed that the decreasing trend in the ambient dose rate varied among the different forest types and time periods. The ambient dose rate in EGC decreased slower than that induced by the physical decay of radiocesium for the period of 2011–2014. However, such slow declining trend of ambient dose rate was likely followed by quick reduction during the following years (2014–2016 and 2011–2016). On the other hand, in MBL and DBF forests, the ambient dose rate decreased 10–20% faster than that induced solely by physical decay of radiocesium for the observation period 2011–2016. Highlights • Ambient dose rate in Fukushima forests was repeatedly measured. • Ambient dose rates in mixed broad-leaved and deciduous forests were higher than evergreen conifers. • Ambient dose rate in evergreen conifer decreased slower than mixed broad-leaved and deciduous broad-leaved forests for the period of 2011–2014. • Decline of dose in evergreen conifer during the period of 2011–2014 was slower than that induced solely by physical decay of radiocesium. • Decline of dose in mixed and deciduous broad-leaved forest was 10–20% faster than the physical decay of radiocesium. [ABSTRACT FROM AUTHOR]

Transpiration (Et) in forests accounts for a significant fraction of evapotranspiration. However, because Et is influenced by meteorological factors and the physiological response of vegetation, developing an accurate model for predicting Et presents a challenge. In this study, we developed a model to estimate Et specific to cypress plantation forests using satellite remote sensing and sap flow data in Japanese cypress plantations composed of a single forest species. The contribution of Et to meteorological (Et base) and plant physiology (Et leaf) was determined using the decoupling index along with the surface temperature. Using the Forest Inventory (FI), in which the extent of growth of each species, including cypress, was surveyed and Land Remote Sensing Satellite imagery of the FI range was obtained, an index of activity estimation for cypress trees was developed. The sapwood area, which significantly influences Et, was calculated from the tree age obtained from FI or diameter at breast height and incorporated into the model. The developed model exhibited a high correlation of r = 0.74–0.88 with the measured Et. The antecedent precipitation index (API), which represents the wetness of the land surface, can be used to evaluate the confidence level and correction coefficient (if needed) of model estimates. When corrected by API, Et could be estimated with even higher accuracy (r = 0.76–0.89). The model developed in this study considers the physiological responses of vegetation and plant species, and the same approach can be used to develop models to estimate Et for other tree species. Additionally, our model uses reflectance at wavelengths close to visible light and surface temperature and can, therefore, be readily applied to other remote sensing methods, such as unmanned aerial vehicles and airborne methods. The model developed in this study can be used with FI data to estimate Et by tree species to provide detailed and accurate estimates of Et. [ABSTRACT FROM AUTHOR]

Cesium-137 ( 137 Cs) migration in the litter layer consists of various processes, such as input via throughfall, output via litter decomposition, and input from deeper layers via soil organism activity. We conducted litter bag experiments over 2 years (December 2014–November 2016) to quantify the inputs and outputs of 137 Cs in the litter layer in a Japanese cedar plantation ( Cryptomeria japonica ) and a mixed broadleaf forest dominated by Quercus serrata located 40 km northwest of the Fukushima Dai-ichi Nuclear Power Plant. The experiments included four conditions, combining contaminated and non-contaminated litter and deeper layer material, and the inputs and outputs were estimated from the combination of 137 Cs increases and decreases in the litter layer under each condition. The 137 Cs dynamics differed between the two forests. In the C. japonica forest, some 137 Cs input via throughfall remained in the litter layer, and downward 137 Cs flux passed through the litter layer was 0.42 (/year).Upward flux of 137 Cs from the deeper layer was very restricted, < 0.017 (/year). In the broadleaf forest, migration of 137 Cs in throughfall into deeper layers was restricted, downward 137 Cs flux was less than 0.003 (/year).Upward input of 137 Cs from the deeper layer was prominent, 0.037 (/year). 137 Cs output via litter decomposition was observed in both forests. The flux in the C. japonica forest was slower than that in the broadleaf forest, 0.12 and 0.15 (/year), respectively. [ABSTRACT FROM AUTHOR]

Spatial patterns of atmospherically deposited radiocesium on the forest floor and the temporal evolution were measured in two Japanese cedar stands and a secondary mixed broad-leaved forest in the early phase of the Fukushima Daiichi Nuclear Power Plant accident. In situ measurements of the 137 Cs gamma count were made using a portable germanium gamma ray detector. These measurements revealed that the forest floors were contaminated with radionuclides derived from the accident. In the cedar stands, the inter-canopy area had higher 137 Cs count rate relative to the under-canopy area, whereas no clear relationship was found between the radiocesium pattern and canopy cover in the mixed broad-leaved forest. Repeated radiocesium measurements revealed that the spatial pattern of radiocesium activity on the forest floor did not substantially change following additional deposition inputs. Furthermore, the magnitude of canopy cover partially explained spatial variability of the 137 Cs on the forest floor in cedar stands. These results suggest that canopy structure affected the genesis of the horizontal variability of atmospherically deposited radiocesium on the forest floor during the early phase of the Fukushima accident. [ABSTRACT FROM AUTHOR]

Many studies on shallow landslides have focused on seepage mechanisms. However, most of these studies assumed that the hillslope was parallel to the seepage direction and force; they did not consider how the seepage was changed by the topography during failure. To investigate the seepage mechanism, particularly the influence of the topographic change during failure, flume experiments using a 30° sandy slope were performed with artificial rainfall. The factor of safety (FS) equation, which considers the seepage direction and force, and the numerical simulation were also applied to analyze the effect of topographic change on the seepage mechanism. The experiments were divided into two stages: rainfall-induced experiment (RIE) and seepage-induced experiment (SIE) with rainfall. In the RIE with a rainfall intensity of 80 mm/h, seepage erosion occurred followed by undercutting, which resulted from seepage erosion, to upward direction of sandy slope. The analysis of FS in RIE are showing an instability when seepage direction is be a slope parallel with theoretical value, i ( Hydraulic gradient ). In the numerical model, when topographic changes of the surface of the sandy flume were applied, seepage flow concentrated from failure surface of the toe of flume to middle part of flume, which is affected by saturation. In SIE, multiple failures caused by the seepage in the vertically upward direction occurred with a high seepage force, and the failure mass then moved in the downward direction with the seepage flow. FS for SIE showed a high instability than those of RIE when seepage direction with high force already changed from vertically downward seepage flow to increasing slope parallel seepage flow. Applying changed topography (more deep from sandy flume surface) in numerical model is showing concentrated seepage flow at the bottom of failures. This is one of mechanism developing failure mass to downward direction to the toe of flume because soil moisture sensors installed near failures (25 cm-depth) show high value than porosity value, indicating soil mobilization. Therefore, the seepage direction and force play important roles in landslide mechanism, and these factors should be considered in landslide studies. [ABSTRACT FROM AUTHOR]

A wide area of paddy fields was contaminated by radiocesium derived from the Fukushima nuclear accident. Implement of agricultural countermeasures is one of the principle methods to reduce the contamination of rice plants. In this study, the effect of topsoil removal measure and fertilizer application on radiocesium uptake by rice plants was investigated over a four-year period. Some other available countermeasures carried out after the Fukushima nuclear accident were also summarized. The results indicate that the effect of topsoil removal measure on the accumulation of radiocesium in rice plants was effective, but the concentration ratio of radiocesium activity concentration between rice plant and soil increased. This may be correlated with the radiocesium imported from irrigation water and relatively high exchangeable radiocesium proportion of plowing soil in the topsoil removal paddy. We summarized four year's data to further confirm that potassium and nitrogen fertilizers had an opposite effect on the accumulation of radiocesium in rice plants. Increasing potassium and reducing nitrogen fertilizer conditions tended to inhibit the radiocesium uptake by rice plants. Moreover, of all the available countermeasures applied in the paddy fields, the most effective countermeasure was the application of phlogopite. However, further analyses are required to confirm the effectiveness of application of phlogopite considering the limited available information. [ABSTRACT FROM AUTHOR]

We have demonstrated design, synthesis, and biological evaluation of apratoxin A mimetics. In the first generation, the moCys moiety was replaced with seven simple amino acids as their 3D structures can be similar to that of apratoxin A. Apratoxins M1-M7 were synthesized using solid-phase peptide synthesis and solution-phase macrolactamization. Apratoxin M7, which contains a piperidinecarboxylic acid moiety, exhibited potent cytotoxicity against HCT-116 cells. In the second generation, substitution of each amino acid residue in the tripeptide Tyr(Me)-MeAla-MeIle moiety in apratoxin M7 led to the development of the highly potent apratoxin M16 possessing biphenylalanine (Bph) instead of Tyr(Me), which exhibited an IC50 value of 1.1 nM against HCT-116 cells. Moreover, compared to apratoxin A, apratoxin M16 exhibited a similarly high level of growth inhibitory activity against various cancer cell lines. The results indicate that apratoxin M16 could be a potential candidate as an anticancer agent. [ABSTRACT FROM AUTHOR]

Radiocesium ( 137 Cs) migration from headwaters in forested areas provides important information, as the output from forest streams subsequently enters various land-use areas and downstream rivers. Thus, it is important to determine the composition of 137 Cs fluxes (dissolved fraction, suspended sediment, or coarse organic matter) that migrate through a headwater stream. In this study, the 137 Cs discharge by suspended sediment and coarse organic matter from a forest headwater catchment was monitored. The 137 Cs concentrations in suspended sediment and coarse organic matter, such as leaves and branches, and the amounts of suspended sediment and coarse organic matter were measured at stream sites in three headwater catchments in Yamakiya District, located ∼35 km northwest of Fukushima Dai-ichi Nuclear Power Plant (FDNPP) from August 2012 to September 2013, following the earthquake and tsunami disaster. Suspended sediment and coarse organic matter were sampled at intervals of approximately 1–2 months. The 137 Cs concentrations of suspended sediment and coarse organic matter were 2.4–49 kBq/kg and 0.85–14 kBq/kg, respectively. The 137 Cs concentrations of the suspended sediment were closely correlated with the average deposition density of the catchment. The annual proportions of contribution of 137 Cs discharge by suspended sediment, coarse organic matter, and dissolved fraction were 96–99%, 0.0092–0.069%, and 0.73–3.7%, respectively. The total annual 137 Cs discharge from the catchment was 0.02–0.3% of the deposition. [ABSTRACT FROM AUTHOR]

In this study, we investigated the transfer of canopy-intercepted radiocesium to the forest floor following the Fukushima Dai-ichi Nuclear Power Plant accident. The 137 Cs content of throughfall, stemflow, and litterfall were monitored in two coniferous stands (plantations of Japanese cedar) and a deciduous mixed broad-leaved forest stand (oak with red pine) from July 2011 to December 2012. The forest floor of cedar stands had received higher levels of additional 137 Cs deposition compared with the mixed broad-leaved stand during the sampling period. The cumulative 137 Cs deposition during the study period was 119 kBq m −2 for the mature cedar stand, 105 kBq m −2 for the young cedar stand, and 41.5 kBq m −2 for the broad-leaved stand. The deposition of 137 Cs to the forest floor occurred mainly in throughfall during the first rainy season, from July to September 2011 (<200 d after the initial fallout); thereafter, the transfer of 137 Cs from the canopy to forest floor occurred mainly through litterfall. A double exponential field-loss model, which was used to simulate the removal of 137 Cs from canopies, was the best fit for the temporal changes in the canopy 137 Cs inventory. [ABSTRACT FROM AUTHOR]

Shallow landslides are affected by various conditions, including soil depth and subsurface flow via an increase in the pore water pressure. In this study, we evaluate the effect of soil depth and subsurface flow on shallow landslide prediction using the shallow landslide stability (SHALSTAB) model. Three detailed soil depth data—the average soil depth, weathered soil depth, and bedrock soil depth—were collected using a knocking pole test at a small hillslope site composed of granite in the Republic of Korea. The SHALSTAB model was applied to a ground surface topographic digital elevation model (DEM) using the three soil depths and upslope contributing area (SCA) assuming subsurface flow calculated from four DEMs: a ground surface topography (GSTO) DEM, weathered soil topography (WSTO) DEM, bedrock topography (BSTO) DEM, and low-level bedrock topography (EBSTO) DEM. The model performance was measured using a receiver operating characteristic (ROC) analysis. While evaluating the effect of the soil depth with SCA using GSTO DEM, it was found that the bedrock soil depth had higher prediction accuracy compared to that of the average soil depth or weathered soil depth. To evaluate the saturated subsurface flow between the soil and bedrock, SCAs calculated using WSTO and BSTO DEMs were applied. From these simulations, we found that SCA from BSTO DEM and the bedrock soil depth affect the shallow landslide prediction; however, these prediction effects are not significantly increased by large differences in the elevation (between the lowest and highest elevation values). Therefore, we considered the influence of the bedrock depression and SCA from EBSTO DEM. In applying SCA from EBSTO, the prediction accuracy was significantly increased compared to the other predictions. Our results demonstrate that the influence of the bedrock topography on the prediction of shallow landslides may be particularly significant at the scale of a hillslope. [ABSTRACT FROM AUTHOR]

The depth distribution of pre-Fukushima and Fukushima-derived 137 Cs in undisturbed coniferous forest soil was investigated at four sampling dates from nine months to 18 months after the Fukushima nuclear power plant accident. The migration rate and short-term temporal variability among the sampling profiles were evaluated. Taking the time elapsed since the peak deposition of pre-Fukushima 137 Cs and the median depth of the peaks, its downward displacement rates ranged from 0.15 to 0.67 mm yr −1 with a mean of 0.46 ± 0.25 mm yr −1 . On the other hand, in each examined profile considerable amount of the Fukushima-derived 137 Cs was found in the organic layer (51%–92%). At this moment, the effect of time-distance on the downward distribution of Fukushima-derived 137 Cs seems invisible as its large portion is still found in layers where organic matter is maximal. This indicates that organic matter seems the primary and preferential sorbent of radiocesium that could be associated with the physical blockage of the exchanging sites by organic-rich dusts that act as a buffer against downward propagation of radiocesium, implying radiocesium to be remained in the root zone for considerable time period. As a result, this soil section can be a potential source of radiation dose largely due to high radiocesium concentration coupled with its low density. Generally, such kind of information will be useful to establish a dynamic safety-focused decision support system to ease and assist management actions. [ABSTRACT FROM AUTHOR]

Thinning results in more open-stand canopies and then immediately modifies the environmental factors that influence forest floor evaporation ( E f ). Thus, the changes in E f induced by thinning would play an important role in the forest water cycle, whereas few studies have reported this topic. This study analyzes the effect of strip thinning on E f , its spatial variation and identifies the factors influencing it in a Japanese cypress ( Chamaecyparis obtusa Endl.) plantation in Tochigi Prefecture, Japan. Strip thinning, which removed 50% of the stems, was conducted in a headwater basin during the period of October 11–November 5, 2011. The E f was monitored by weighing lysimeters before and after thinning. The daily E f was strongly correlated with the daily solar radiation ( R 2 = 0.62) followed by vapor pressure deficit ( R 2 = 0.41) below the canopy, whereas the soil water content had a poor effect on it in post-thinning. After thinning, the daily E f among the measuring points had no significant difference, indicating that the daily E f had a small spatial variation. This responded to the small spatial variability in the daily solar radiation under the canopy. Additionally, on an annual scale, thinning resulted in the daily mean E f increasing from 0.34 ± 0.23 to 0.68 ± 0.47 mm d −1 . The total E f increased by 97.6% from 124.0 to 245.0 mm. These findings indicate that E f composes a significant part of the forest water budget after thinning and emphasize the importance of E f measurements for management practices. This study also provides useful information for modeling the changes in hydrological processes at the forest floor and for evaluating the E f response to different management practices. [ABSTRACT FROM AUTHOR]

Hillslope hydrology studies have shown that bedrock surface topography maybe the most important factor affecting subsurface flow, and that soil thickness and soil properties related to topography are important factors in shallow landslide prediction. In this study, the physically based H-slider (hillslope-scale shallow landslide-induced debris flow risk evaluation) model was used to evaluate the effects of topography and soil parameterisation reflecting soil depth on shallow landslide prediction accuracy. Two digital elevation models (DEMs; i.e. ground surface and bedrock surface) and three soil thicknesses (average soil thickness, soil thickness to weathered rock and soil thickness to bedrock) and physical soil parameters (cohesion and internal friction angle) at a small hillslope site in Jinbu, Kangwon Prefecture, eastern part of the Korean Peninsula, were considered. Each prediction result simulated with the H-slider model was evaluated by receiver operating characteristic (ROC) analysis for modelling accuracy. The results of the ROC analysis for shallow landslide prediction using the ground surface DEM (GSTO) and the bedrock surface DEM (BSTO) indicated that the prediction accuracy was higher using the GSTO compared to the BSTO. Moreover, the prediction accuracy based on soil parameterisation reflecting soil thickness was highest in all cases. These results imply that the effect of soil parameters on shallow landslide prediction could be larger than the effects of topography and soil thickness. Therefore, we suggest that using soil properties representing the effect of soil thickness can improve the accuracy of shallow landslide prediction, which should contribute to more accurately predicting shallow landsides. [ABSTRACT FROM AUTHOR]

The Fukushima Daiishi nuclear power plant (FDNPP) accident led to a massive radionuclide deposition mainly onto Japanese forest canopies. In our previous study, an improved double exponential (IDE) equation including rainfall intensity was proposed to estimate the 137 Cs hydrological transport from evergreen canopies to the ground. This equation used two types of parameters, kinetic ( k 1 and k 2 ) and leachable stock ( A 1 and A 2 ). Those parameters have been estimated by adjusting them in the IDE equation in order to accurately describe the measured cumulative leached 137 Cs from canopies ( k 1 = 4.2E-04–5.0E-04 d −1 , k 2 = 1.2E-02–1.7E-02 d −1 , A 1 = 62–99 kBq/m 2 , A 2 = 25–61 kBq/m 2 ). In this study, we linked the total leachable stock ( A leachable , a parameter of the IDE equation corresponding to A 1 + A 2 ) to a physiological criteria (the canopy closure CC, which can be measured with a simple camera equipped with a fish-eye objective). Furthermore, the kinetic parameters measured for Japanese cedar ( k 1 = 5.0E-04 d −1 , k 2 = 1.2E-02 d −1 , and r 12 = 0.22 ( r 12 = A 1 / A 2 ) could also be used for two other coniferous species: Japanese cypress and spruce. This suggests that these parameters could be constants for coniferous forests. [ABSTRACT FROM AUTHOR]

This study investigated the spatial distribution of radiocesium deposited by the Fukushima Daiichi Nuclear Power Plant accident in a densely planted Japanese cedar stand. Systematic grid sampling was conducted to determine 137Cs inventories in the layers of deposited organic material and mineral soil at two different spatial scales (hillslope [60 m2] and small [1 m2]). The results showed that 137Cs inventories along the hillslope were heterogeneously distributed, with coefficients of variation for the deposited organic material and mineral soil layers of 46.4% and 48.9%, respectively. The 137Cs inventory in each layer tended to show a lognormal distribution. The correlation between the 137Cs inventories in deposited organic material and mineral soil in the same sampling grid was weak. The controlling mechanisms of the 137Cs inventories in the litter and mineral soil layers differed due to differences in the underlying key processes, such as canopy-forest floor transfer due to hydrological and biological processes. No significant correlation was found between the distance from the nearest tree trunk and the 137Cs inventory in the deposited organic layer at each sampling point. In contrast, the 137Cs inventory in the soil tended to increase as the distance from the nearest tree trunk increased at both the hillslope and small scales. It was found that the initial spatial patterns of 137Cs in the soil layer due to atmospheric deposition were preserved in the cedar stand. Finally, we tested the effects of soil sampling density on the reliability of mean soil 137Cs inventory estimations in the cedar stand. The results indicated that a soil sampling area greater than 0.06 m2 at the hillslope scale and 0.008 m2 at the small scale enabled the mean 137Cs inventory to be estimated with an uncertainty of less than 20% in the cedar stand. [Display omitted] • A grid sampling experiment revealed 137Cs distribution on forest floor. • Hillslope and small scale 137Cs spatial patterns were determined. • The peripheral area of the canopy accumulated more 137Cs. • The initial 137Cs input pattern was preserved in forest soil. • The optimized sampling guideline for forest 137Cs was presented. [ABSTRACT FROM AUTHOR]

Forest is an important part of the environmental system, which has a significant impact on soil hydrological characteristics and forest landscapes, because these processes are influenced by forest management and understory vegetation. Quantitative understory vegetation biomass (UVB) measurement and estimation are vital processes in forest ecology and environmental management. However, these estimations are difficult to make on a large scale especially dense planted forest. Here, we applied catchment-scale Structure from Motion and a manually operated ultralow-flying drone under the canopy of a dense planted (2000 stems/ha) Japanese cedar/cypress plantation forest to reconstruct the understory. An understory drone survey was performed over a 1.1-ha sub-catchment to generate a canopy height model based on dense point cloud data. A biomass survey of three 16-m2 harvesting plots was conducted to compute understory vegetation volume data based on point clouds. Combined with harvested biomass data in the field, quantitative models were developed between the understory vegetation volume and biomass. Subsequently, the models were used to map spatial understory vegetation biomass distribution in the sub-catchments. Aerial photos taken by the ultralow-flying drones under the canopy yielded a high-resolution catchment-scale understory with point cloud density >10/cm2. Strong cubic model coefficients of determination (R 2 = 0.75) predicted the understory vegetation biomass based on the canopy height model. The mean understory vegetation biomass was 0.82 kg/m2 and dominated by low ferns. In the present study, we successfully reconstructed the multilayered forest structure and generated understory vegetation biomass distribution models. This results also will be essential to evaluate the erosion and evapotranspiration in dense plantation forests and future environmental management. [Display omitted] • Achieved first understory biomass survey by drone under high-density forest canopy. • Applied high-density cloud point dataset in calculating understory vegetation volume. • Developed a model for predicting understory vegetation biomass. • Provided a new insight for understory biomass estimation and forest management. [ABSTRACT FROM AUTHOR]

Summary We examined the effect of strip thinning on rainfall interception ( E i ) in a 32-year-old Japanese cypress plantation in central Japan. Strip thinning was conducted in the catchment in October 2011; that removed 50% of the stems. The gross precipitation ( P g ), throughfall ( TF ) and stemflow ( SF ) were monitored in a 12-m × 13-m plot before and after thinning. E i was calculated as the difference between P g and the sum of TF and SF . The interception processes were illustrated using the revised Gash model with quantifying interception parameters. The results showed that the Gash model successfully predicted E i on a rainy-season basis in both pre- and post-thinning periods. Thinning altered the interception components whereas the largest part during and after rainfall accounted for similar proportion in both periods. Additionally, after thinning, the annual TF rate was increased from 61.4% to 73.0%, whereas the annual SF rate was decreased from 9.8% to 6.1%, and the annual E i rate was decreased from 28.7% to 20.8%. The summarized findings of previous studies indicate that the degree of decline in the E i caused by thinning is related to P g and the thinning ratio. These results provide useful information for understanding the changes in interception processes induced by thinning, and for acquiring a more accurate forecast of the effects of forest management practices on water resources in the watershed. The response in rainfall partitioning to strip thinning can also help us to acquire an integrated understanding of the changes in canopy water balance under different forest practices. [ABSTRACT FROM AUTHOR]

Radiocaesium wash-off associated with soil erosion in different land use was monitored using USLE plots in Kawamata, Fukushima Prefecture, Japan after the Fukushima Dai-ichi Nuclear Power Plant accident. Parameters and factors relating to soil erosion and 137 Cs concentration in the eroded soil were evaluated based on the field monitoring and presented. The erosion of fine soil, which is defined as the fraction of soil overflowed along with discharged water from a sediment-trap tank, constituted a large proportion of the discharged radiocaesium. This indicated that the quantitative monitoring of fine soil erosion is greatly important for the accurate evaluation of radiocaesium wash-off. An exponential relationship was found between vegetation cover and the amount of eroded soil. Moreover, the radiocaesium concentrations in the discharged soil were greatly affected by the land use. These results indicate that radiocaesium wash-off related to vegetation cover and land use is crucially important in modelling radiocaesium migration. [ABSTRACT FROM AUTHOR]

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident resulted in extensive radioactive contamination of the environment via deposited radionuclides such as radiocesium and 131 I. Evaluating the extent and level of environmental contamination is critical to protecting citizens in affected areas and to planning decontamination efforts. However, a standardized soil sampling protocol is needed in such emergencies to facilitate the collection of large, tractable samples for measuring gamma-emitting radionuclides. In this study, we developed an emergency soil sampling protocol based on preliminary sampling from the FDNPP accident-affected area. We also present the results of a preliminary experiment aimed to evaluate the influence of various procedures (e.g., mixing, number of samples) on measured radioactivity. Results show that sample mixing strongly affects measured radioactivity in soil samples. Furthermore, for homogenization, shaking the plastic sample container at least 150 times or disaggregating soil by hand-rolling in a disposable plastic bag is required. Finally, we determined that five soil samples within a 3 m × 3-m area are the minimum number required for reducing measurement uncertainty in the emergency soil sampling protocol proposed here. [ABSTRACT FROM AUTHOR]

This study deals with the description of the vertical distribution of radiocaesium ( 137 Cs and 134 Cs) in a representative coniferous forest soil, investigated 10 months after the Fukushima radioactive fallout. During soil sampling, the forest floor components (understory plants, litter (Ol-) and fermented layers (Of)) were collected and treated separately. The results indicate that radiocesium is concentrated in the forest floor, and high radiocesium transfer factor observed in the undergrowth plants (3.3). This made the forest floor an active exchanging interphase for radiocesium. The raw organic layer (Ol + Of) holds 52% (5.3 kBq m −2 ) of the Fukushima-derived and 25% (0.7 kBq m −2 ) of the pre-Fukushima 137 Cs at the time of the soil sampling. Including the pre-Fukushima 137 Cs, 99% of the total soil inventory was in the upper 10 cm, in which the organic matter (OM) content was greater than 10%, suggesting the subsequent distribution most likely depends on the OM turnover. However, the small fraction of the Fukushima-derived 137 Cs at a depth of 16 cm is most likely due to the infiltration of radiocesium-circumscribed rainwater during the fallout before that selective adsorption prevails and reduces the migration of soluble 137 Cs. The values of the depth distribution parameters revealed that the distribution of the Fukushima-derived 137 Cs was somewhat rapid. [ABSTRACT FROM AUTHOR]

To investigate the effects of vegetation canopy on surface runoff, four runoff plots (2 m × 1 m in size) were established under different types of forest canopies (S1: sawtooth oak and Japanese larch; S2: Chinese cork oak; S3: shrub; and S4: Korean pine) on a mountain slope in central Korea. Rainfall, throughfall, and surface runoff were measured from July 2007 to October 2009. During the observation period, there was no storm event with a rainfall intensity that exceeded the average value for infiltration rates at the runoff plots. Each plot showed differences in surface runoff generation (S1 > S2 ≒ S3 > S4). The plots with broad-leaf litter layers had higher maximum water storage capacities than the plot with a needle-leaf litter layer. These results imply that the water storage capacity and the leaf shape of the litter layer affected surface runoff generation. Moreover, under dry conditions (<20 mm of API 7 ), the rainfall threshold for all plots, except S4, required for surface runoff generation decreased and surface runoff from all plots increased slightly compared with relatively wet conditions (>20 mm of API 7 ). Storm runoff coefficients at all plots decreased drastically as the value of API 7 increased. This suggests that the lowering of the rainfall threshold for surface runoff generation and the resulting increase in surface runoff might be related to the development of hydrophobic conditions on the soil surface caused by dry conditions. Therefore, in addition to leaf shape and water storage capacity of the litter layer, the soil water condition also can be an important factor in plot-scale evaluations of surface runoff generation from a slope well covered with litter layer. [ABSTRACT FROM AUTHOR]

The deposition of Fukushima-derived radiocesium via falling litter in a coniferous forest 180 km downwind immediately following the nuclear power plant accident was investigated. The litterfall contribution to the transfer of radiocesium from the forest canopy to the forest floor was determined, and this pathway was compared with hydrological pathways. The results demonstrated that during the observation period, a total of approximately 5.5 kBq m − 2 of Fukushima-derived radiocesium was deposited on the forest floor through throughfall (53%), stemflow (2.3%) and litterfall (45%) routes. The data revealed that the contributions of hydrological pathways became less important as time passed. However, the litterfall route, which transferred approximately 31% (2.5 ± 0.6 kBq m − 2 ) of the local fallout within the observation period, continued depositing radiocesium onto the forest floor. [ABSTRACT FROM AUTHOR]

This study aimed to quantify the flux of radiocesium in the Abukuma Basin (5,172 km2), the largest river system affected by fallout from the Fukushima Daiichi Nuclear Power Plant (FDNPP) event. In the period from 10 August 2011 to 11 May 2012 an estimated 84 to 92% of the total radiocesium transported in the basin's fluvial system was carried in particulate form. During this monitoring period Typhoon Roke (September 2011) was observed to induce a significant and temporally punctuated redistribution of radiocesium. The storm-mobilised radiocesium was an estimated 6.18 Terabecquerels corresponding to 61.4% of the total load delivered to the coastal zone during the observation period. The total flux of radiocesium into the Pacific Ocean estimated at the outlet station (basin area 5,172 km2) was 5.34 TBq for 137Cs, and 4.74 TBq for 134Cs, corresponding to 1.13% of the total estimated radiocesium fallout over the basin catchment (890 TBq). This was equivalent to the estimated amount of direct leakage from FDNPP to the ocean during June 2011 to September 2012 of 17 TBq and the Level 3 Scale Leakage on 21August 2013 (24 TBq). [ABSTRACT FROM AUTHOR]

Abstract: In this study, the hydrogeological response of a hillslope affected by gravitational deformation was analyzed based on the data obtained for two observation boreholes: a 10-m borehole representing a relatively superficial section of the hillslope dominated by soil and old landslide deposits and a 40-m borehole representing the bedrock aquifer. For this analysis, the precipitation events in the area, groundwater levels of the two boreholes, electrical conductivity and isotopic concentration (oxygen and hydrogen) of the groundwater in the boreholes and rainfall samples were measured. Derived from the rainfall data, the antecedent precipitation index (API) with a 6-h half-life offers a good correlation with the peaks in the groundwater levels in the bedrock aquifer. The characteristics of the groundwater response suggest the existence of a single structure in the bedrock that controls the response of the hillslope. The structure serves as a conduit, which rapidly drives the rainfall water (recharge) into the bedrock. Evidently, this process is unrelated to the superficial section represented by the observations in the 10-m borehole. The structure is associated with an area of high hydraulic conductivity in the bedrock caused by the gravitational deformation in the hillslope. The strong control of this structure in the hillslope's hydrogeological response makes it responsible for the hillslope's stability during high-precipitation events. This information is highly relevant to areas featuring the generation of several deep-seated landslides under heavy-rain conditions. [Copyright &y& Elsevier]

Highlights: [•] We presented a field experiment examining throughfall in Japanese cypress plantation. [•] We combined a conventional field monitoring of throughfall and isotopic technique. [•] The data suggested that wind condition can influence the throughfall patterns. [•] The isotopic technique can serve as a tool for understanding interception processes. [ABSTRACT FROM AUTHOR]

Abstract: The relationships of erosion-induced displaced soil organic carbon (SOC) to discharged 210Pbex and 137Cs in a hillslope forested area were investigated using runoff plots in three different forest types. A significant correlation was found between the displaced SOC and the radionuclides in each examined forest type. Compared with 137Cs, however, the discharge of 210Pbex is more closely correlated with the displaced SOC and shows a far lower RMSE value by approximately a factor of two. This finding suggests that 210Pbex and SOC are more likely than 37Cs and SOC to move together in the course of soil erosion processes. Moreover, because 137Cs was introduced in the 1960s by thermonuclear bomb tests and is being depleted, its availability in the environment could be limited in the foreseeable future. 210Pbex, in contrast, is continuously replenished from its ubiquitous natural source (222Rn) in a manner similar to the replenishment of SOC from sources consisting of organic material (e.g., litter). In the light of this basic understanding, our findings provide practical evidence of the potential of 210Pbex application for assessing and documenting the water-induced distribution of SOC on forested hillslopes. [Copyright &y& Elsevier]

Abstract: Soil, vegetation and other ecological compartments are expected to be highly contaminated by the deposited radionuclides after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident triggered by a magnitude 9.0 earthquake and the resulting tsunami on 11 March 2011. However, there is no field measurement data on the depth distributions of radiocaesium and 131I concentrations in soil profile. In this study, the depth distribution of the deposited radionuclides in the cultivated soil profile was investigated in one of the most contaminated area after FDNPP accident. The result of this study demonstrated that greater than 86% of total radiocaesium and 79% of total 131I were absorbed in the upper 2.0 cm in the soil profile. The relaxation mass depth (h 0) derived from the depth distribution of radiocaesium and 131I in the soil profile at the study site were 9.1 kg m−2 and 10.4 kg m−2, respectively. The h 0 of 137Cs in the studied soil profile was greater than those for the cultivated soils nearby the Chernobyl NPP. The positive relationship was found between clay content of topsoil and the h 0 of 137Cs. However, further analysis is required to clarify the effect of clay content on the initial penetration depth of deposited 137Cs in soil profile. [Copyright &y& Elsevier]

Abstract: To evaluate the spatial variability of throughfall amount, raindrops, and erosivity under a single canopy during calm meteorological conditions, indoor experiments were conducted using a 9.8-m-tall transplanted Japanese cypress (Chamaecyparis obtusa) and a large-scale rainfall simulator. Drop size distribution, drop velocity, and kinetic energy of throughfall varied spatially under a single canopy as did throughfall amount and rain rate. Compared with throughfall rain rate, the variability was similar in drop size distribution, lower in drop velocity, and higher in kinetic energy. The results suggest that the spatial distribution of throughfall amount was dominated by the canopy shape and position of branches inside the canopy, and thus the spatial distribution was correlated with the radial distance from the trunk. Throughfall amount and rate were lower at the midway point between the trunk and the canopy edge. Throughfall drop size indices (drop size distribution, drop velocity, and unit kinetic energy) varied spatially while did not differ significantly. On the other hand, time-specific throughfall kinetic energy was correlated with the radial distance from the trunk. The dependence the throughfall kinetic energy on the radial distance from the trunk was dominated by the spatial distribution of throughfall amount. The trend in the spatial distribution of throughfall revealed in this study will aid in modelling canopy water processes and in predicting soil erosion on the bare forest floor. [Copyright &y& Elsevier]

Abstract: Forest fires on granitic soils often increase overland flow and erosion. Runoff generation was monitored on a small hillslope plot on Mt. Vision near Point Reyes Peninsula, California, after it had been burned by a wildfire on October 3, 1995. After the fire, the ground surface was covered with up to 2 cm of ash, which overlaid a 5–20 cm thick hydrophobic (water repellent) soil layer. We used nine recording tensiometers to monitor soil-water potentials during infiltration and runoff. Surface-runoff rates were determined by diverting the flow into a collection tank. The subsurface flow through the upper 6 cm of soil was collected and measured in a second tank. The surface runoff was diverted to a tank in order to record its rate. The initial intense rainfall infiltrated into the base of the ash-bed; here, the hydrophobicity limited deeper penetration and led to both subsurface and shallow saturation overland flow. The preferential flow paths through the ash layer contributed to deeper water penetration. As the ash was eroded and consolidated with successive rainstorms, the preferential flow paths clogged, the infiltration capacity reduced, thus preventing the storage of shallow permeable soil; therefore, the runoff generation changed to Hortonian overland flow. Correspondingly, the runoff ratio increased from approximately 0.2 during the early storms to 0.8 during intense rain bursts. These results suggest that runoff mechanisms evolve simultaneously with the eroding soil surface. [Copyright &y& Elsevier]

Summary: In Mongolia, overgrazing and mismanagement are considered to be the causes of soil erosion and land degradation. However, the field data available on soil erosion and land degradation processes are limited. Two experimental watersheds were selected within the Kherlen river basin in Mongolia to assess the state and cause of soil erosion; this was done by monitoring the water–sediment discharge in two small catchments with different vegetation covers. The two sites—Kherlenbayan-Ulaan (KBU; 6.9ha) and Baganuur (BGN; 7.6ha)—have relative heights of 100m and 150m, respectively. In addition, one of the two hillslope plots (50m×25m) established in each area was surrounded by a fence. The overland flow was monitored by Parshall flumes; rainfall, raindrop impact, and soil water suction were also recorded. The amount of sediment yields from the BGN and KBU catchments during the observation period were 0.37t/ha/years and 0.02t/ha/years, respectively. The surface runoff percentage and amount of sediment discharge show a good correlation with the raindrop impact energy; however, the peak rainfall shows a poor correlation. These data suggest that raindrop impact plays an important role in water and sediment discharge. The long-term erosion rate estimated by the 137Cs inventory is lower in the BGN catchment than the KBU one, suggesting that the high sediment yield in the former might be due to the susceptibility to erosion by recent overgrazing. [Copyright &y& Elsevier]

Summary: In order to examine the runoff generation processes in an extremely steep terrain underlain by relatively unweathered granite and shale, four small (0.78–7.1ha) watersheds were monitored – two in shale and two in granite. The two shale watersheds exhibited distinctly different runoff responses to identical storm events, whereas the two granite watersheds exhibited similar responses in which the maximum runoff peak coincided with the rainfall peak. The majority of storm water runoff events in the shale watersheds and more than half of those in the granite watersheds was “old water”. Based on soil water percolated into the bedrock in the shale watersheds even during storm events, whereas subsurface storm flow parallel to the slope was observed in the granite watersheds. These data and observation suggest that the subsurface storm flow was dominant even in these extremely steep mountains. Furthermore, subsurface stormflow through the soil mantle was dominant in the granite watersheds, whereas bedrock flow was dominant in the shale watersheds. [Copyright &y& Elsevier]

The deposited 137Cs is one of the long-lived radionuclides, that was released following the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, has been hydrologically transported as particulates in the terrestrial environment of the Fukushima region. The impact of freeze-thaw processes and subsequent runoff affecting the 137Cs flux and concentration in sediment discharge were revealed in bare land erosion plot following the FDNPP accident by detailed monitoring and laser scanner measurement on the soil surface. We found that surface topographic changes due to the frost-heaving during the winter-spring period, and rill formation during the summer. We also found the evident seasonal changes in 137Cs concentration; high during the early spring and gradually decreased thereafter, then surface runoff from the plot frequently occurred during spring and autumn when rainfall was high and reached a maximum in summer. From these results, the higher 137Cs concentration in spring was caused by a mixture of unstable surface sediment following freeze-thaw processes and then transported in the early spring, but erosion amount is not significant because of the less rainfall event. The sediment with a lower 137Cs concentration, which was supplied from the rill erosion and its expansion, was wash-offed during the summer, contributing most of the flux from erosion in bare land in Fukushima region. In case, heavy rainfall occurs in the early spring, caution is required because high concentrations of cesium may flow down into the river. Unlabelled Image • 137Cs dynamics and sediment discharge in Fukushima were studied. • Freeze–thaw processes and rill formation make 137Cs wash-off seasonal. • Erosion processes must be considered to improve understanding of 137Cs dynamics. [ABSTRACT FROM AUTHOR]

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, immediate soil and vegetation sampling were conducted according to the action plan of nuclear emergency monitoring; however, analysing the monitoring dataset was difficult because the sampling protocols were not standardised. In this study, the sampling protocols applied just after the FDNPP accident were reviewed, and the monitoring data were analysed. The detailed protocols and results can provide a sound basis for guidelines of soil and vegetation sampling for nuclear emergency monitoring. The activity concentrations of 137Cs and 131I in weed samples measured immediately after the FDNPP accident were related to the air dose rate at 1 m. Consequently, vegetation sampling is recommended when the additional dose rate (above background) is higher than 0.1 μSv/h. To enhance the efficiency of a protective response in the case of a nuclear accident, predetermined sampling points for soil and vegetation sampling should be considered in the preparedness plan for nuclear emergencies. Furthermore, sampling and analytical measurement capacities (time, people, cost) during the early phase after nuclear emergencies need to be considered in the preparedness and action plan, and sampling and measurement exercises are highly recommended. • The sampling protocols applied just after the FDNPP accident have been reviewed and the protocols for emergency the soil and vegetation sampling were proposed. • As a result of Fukushima's outcome, vegetation sampling will be recommended when the additional dose rate (above background) is higher than 0.1 μSv/h. • Predetermined sampling points for soil and vegetation sampling and measurement exercises are highly recommended. [ABSTRACT FROM AUTHOR]

Cesium is an element that belongs to the same group as K, and is known to show similar behaviour to that of K in plants. In this study, we conducted a serial leaching test for 120 h to compare the leaching characteristics of dissolved 137Cs and K in forest litter, obtained from Japanese cedar and deciduous broadleaf forests located 40 km from the site of the 2011 Fukushima Dai-ichi nuclear power plant accident. The litter was collected in 2018 and was divided into three groups according to the decomposition level. The cumulative leachable fraction of 137Cs at 120 h ranged from 0.3% to 3.3%, suggesting that most of the 137Cs in the litter was hardly leachable in water. The leachable fraction of 137Cs generally decreased with the decomposition level of the litter, implying that the easily leachable 137Cs eluted into the water during the first stage of decomposition. Meanwhile, the cumulative leachable fraction of K at 120 h was approximately 10 times greater than that of 137Cs and ranged from 22.7% to 54.8%. The leaching speeds of 137Cs and K decreased suddenly with elapsed time regardless of the tree species, decomposition degree, or element. Our findings contribute to the long-term understanding of the 137Cs cycle in forest ecosystems. • We conducted serial leaching tests on 137Cs and K from forest litter. • Leaching speed of 137Cs and K decreased as leaching proceeded. • Leachable fraction of 137Cs decreased with increasing decomposition degree. • Leachable fraction of 137Cs was less than one-tenth of the leachable fraction of K. [ABSTRACT FROM AUTHOR]

Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the ambient dose rate for forest environments. This study investigated temporal changes in the ambient dose rate in different forest environments of Fukushima Prefecture. We conducted repeated measurements of the ambient dose rate in 2014 and 2016 at the same measurement points as those used by the Ministry of Agriculture, Fishery and Forestry of Japan (MAFF) in 2011. The measurements revealed that the decreasing trend in the ambient dose rate varied among the different forest types and time periods. The ambient dose rate in EGC decreased slower than that induced by the physical decay of radiocesium for the period of 2011–2014. However, such slow declining trend of ambient dose rate was likely followed by quick reduction during the following years (2014–2016 and 2011–2016). On the other hand, in MBL and DBF forests, the ambient dose rate decreased 10–20% faster than that induced solely by physical decay of radiocesium for the observation period 2011–2016. • Ambient dose rate in Fukushima forests was repeatedly measured. • Ambient dose rates in mixed broad-leaved and deciduous forests were higher than evergreen conifers. • Ambient dose rate in evergreen conifer decreased slower than mixed broad-leaved and deciduous broad-leaved forests for the period of 2011–2014. • Decline of dose in evergreen conifer during the period of 2011–2014 was slower than that induced solely by physical decay of radiocesium. • Decline of dose in mixed broad-leaved and deciduous broad-leaved forest was 10–20% faster than the physical decay of radiocesium. [ABSTRACT FROM AUTHOR]

Since headwater catchments are the source areas of 137Cs for downstream river systems, 137Cs discharge from headwater areas needs to be evaluated. Dissolved form (Dissolved), coarse organic matter (Org), and suspended sediments (SS) were sampled and 137Cs concentrations were measured from June 2011 to November 2016 in four headwater catchments in Yamakiya District, located 35 km northwest of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP). The data up to September 2013 (2.5 y after the accident) have been already published (Iwagami et al., 2017a, b). The data up to November 2016 (5.7 y after the accident) are newly reported in the present paper together with data at a new sampling site. The whole data from June 2011 to November 2016 is discussed. The normalized 137Cs concentrations (137Cs concentrations normalized by the average deposition density of each catchment) in Dissolved, Org, and SS were in the order of 10−6 m2/L, 10−2 m2/kg, and 10−1 m2/kg, respectively, before 2013 and declined to around 10−8 m2/L, 10−4 m2/kg, and 10−2 m2/kg, respectively, in 2016. As a result of the decontamination program, the discharge of SS increased, whereas 137Cs concentrations in SS declined significantly and the total flux of 137Cs decreased. Although the clear effect of land use on decline trend in normalized 137Cs concentrations in Dissolved was not found, more data are necessary for elucidating the relation between them. • 137Cs concentrations were monitored at headwater catchments after FDNPP accident. • Normalized 137Cs concentrations declined 1-2 order during 2011–2016. • 137Cs concentrations in suspended sediment declined after the decontamination work. • Total flux of 137Cs decreased after the decontamination work. [ABSTRACT FROM AUTHOR]

After the Fukushima Dai-ichi Nuclear Power Plant accident on March 2011, several studies showed that the downward migration of 137Cs from litter to mineral soil is more rapid in forests in Fukushima than in forests affected by the Chernobyl accident. Therefore, the downward migration within mineral soil layers is more important for predicting long-term dynamics of 137Cs in forest ecosystems in Fukushima. In the present study, we monitored the detailed vertical distribution of 137Cs in litter and soil layers for 6 y (2011–2017) following the previous study (2011–2012), and found that temporal changes in those distributions were different among mixed forest (MF), mature cedar (MC) and young cedar (YC) forests. The 137Cs concentrations and inventories in the litter layer exponentially decreased with time for all sites, with more than 80–95% of the deposited 137Cs on the forest floor distributed in mineral soil layers by 2017. The percentage of 137Cs inventory in the litter layer to the total 137Cs inventory in litter and mineral soil layers was well fitted by a single exponential equation with decreasing rate of 0.22–0.44 y−1. The slower migration was observed in the YC site, probably because of higher initial interception of 137Cs fallout by dense canopy. As the downward migration from litter to mineral soil progressed, the 137Cs concentration in the first few cm of mineral soil surface gradually increased and became higher than the 137Cs concentration in the litter within 2–3 y of the accident. The 137Cs concentration in mineral soil layers exponentially decreased with depth throughout survey period, and an exponential equation fitted well. The relaxation depth of 137Cs concentration in mineral soil layers estimated by the exponential equation were constantly increasing in the MC and YC sites with 0.08 cm y−1. In contrast, there was no temporal increase in the relaxation depth in the MF site, indicating little migration to subsurface soil layer from not only litter layer but also surface soil layer. Further studies are necessary to identify the forests prone to the downward migration of 137Cs and its factors regarding both forest and soil characteristics. • 137Cs concentration in soil was fitted by exponential equation at least for 6 y. • Migration from litter to mineral soil was more rapid than in the case of Chernobyl. • 137Cs concentration in surface soil surpassed that of litter within 2–3 y. • Relaxation depth in the two cedar forests has gone down with 0.08 cm y−1. • In contrast, the downward migration in the mixed forest was not clearly observed. [ABSTRACT FROM AUTHOR]

Ascertaining the initial amount of accidently released radiocesium is fundamental for determining the extent of radioactive contamination following nuclear accidents, and is of key importance to environmental transfer models. A series of the airborne monitoring surveys of radioactivity have conducted by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), and provide basic information on radioactive contamination following the accident. However, there are no clear guidelines regarding the selection of airborne monitoring survey results for estimating the initial fallout input in studies of the environmental transfer of radiocesium. This study reconstructed a fallout map of Fukushima accident-derived radiocesium based on a comparison of the radiocesium deposition densities (D l) derived from the third and fifth airborne monitoring surveys. The D l derived from the fifth airborne monitoring survey were adjusted for variation in the measured radioactivity associated with the influence of radioactive decay, natural weathering processes, variation in the calibration procedure, and other, undefined mechanisms. The calibrated deposition density of the fifth airborne monitoring survey for each land use type (A ′ 5th* l) were used to establish the initial fallout map in the East Japan area. Furthermore, the airborne monitoring surveys which were independently conducted in each prefecture area were used to complement the lack of data in the South Kanto region and the mountainous area in the North Kanto region due to snow cover during the measurement period of the fifth airborne monitoring survey. The reconstructed initial fallout map of the Fukushima accident derived 137Cs was opened to the public via the database of the Center for Research in Isotopes of Environmental Dynamics, University of Tsukuba, Japan (www.ied.tsukuba.ac.jp/∼fukushimafallout/). Finally, the total atmospheric deposition of Fukushima Dai-ichi Nuclear Power Plant accident-derived radiocesium onto each prefecture and land uses was estimated based on the reconstructed map in this study. • Initial 137Cs fallout map was established based on airborne monitoring surveys. • Reduction of the measured inventories between the third and fifth airborne surveys varied between different landuses. • Forest area accumulated 72% of total 137Cs deposition on land. • Total 137Cs deposition on land area of Japan was calculated as 2.5 PBq. [ABSTRACT FROM AUTHOR]

Understanding solid 137Cs wash-off in sediment sources is important for predicting radiological risks in zones contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident. Yoshimura et al. (2015) studied solid 137Cs wash-off using soil erosion plots representing different land uses in Fukushima. However, temporal trends of 137Cs activity concentration in sediments remained unclear owing to the short duration of their observations. This study is a follow-up to that of Yoshimura et al. (2015) and provides additional observations that test the dependency of temporal variations in 137Cs activity concentration in sediment and solid wash-off processes of 137Cs on land use types. Eight soil erosion plots were observed, and data from 2011 to 2014 were analyzed. A normalized 137Cs solid entrainment coefficient, defined as Sc (m2 kg−1), was calculated by dividing 137Cs activity concentration in sediment by initial 137Cs deposition. A particle size-corrected Sc , defined as Sc correct (m2 kg−1), was also calculated based on granulometry. Sediment quantity-weighted mean values of Sc and Sc correct , ranged from 0.0072 to 0.084 m2 kg−1 and 0.0052–0.078 m2 kg−1, respectively. Annual wash-off rates of solid 137Cs were 0.0029–12% year−1. There was no significant decreasing trend in Sc or Sc correct on most of the plots due to its huge variability. However, on an uncultivated farmland after the removal of surface vegetation, marked surface erosion including formation of rill network was found, and Sc correct significantly decreased as the cumulative sediment discharge increased. Our follow-up observations suggest that temporal changes in 137Cs activity concentration in sediment at the sediment source should be controlled by soil erosion processes and their intensity. • Solid 137Cs wash-off were observed using eight erosion plots during 2011–2014. • There was no significant decreasing trend in 137Cs concentration in most of the plots. • The 137Cs concentration in sediment significantly decreased on bare soil. • The 137Cs concentration in sediment decreased only due to significant soil erosion. [ABSTRACT FROM AUTHOR]

The study investigated temporal changes in the 137Cs concentrations in vegetal and hydrological samples collected from various forests in Yamakiya District, Kawamata Town of Fukushima prefecture over six years following the Fukushima Dai-ichi nuclear power plant accident. Cesium-137 was detected in all forest environmental samples. However, the concentration in most samples decreased exponentially with time. The 137Cs concentrations in throughfall samples exhibited a double-exponential decreasing trend with time. Temporal changes in the 137Cs concentration in vegetal samples and stemflow were approximated by using a single-exponential equation. A comparison of the decline coefficient for the latter observation period (>2 y since the accident) revealed that the declining trend of 137Cs concentrations varied between foliage and the outer barks of the Japanese cedar and Japanese konara oak trees. The 137Cs concentration in cedar needles decreased exponentially while that in konara oak leaves was constant over the last six years. Conversely, the declining trend of 137Cs concentration in the outer bark of konara oak exceeded that of cedar. The results suggested that self-decontamination processes and internal recycling of 137Cs varied among tree species and different tree parts. The results indicated that the leaching of 137Cs in the throughfall in Japanese cedar was dependent on the 137Cs concentration in needles. However, a comparison of 137Cs concentrations in vegetal and hydrological samples from each sampling year showed that the leaching rate decreased with time. Conversely, the 137Cs concentrations in the stemflow were independent of the concentrations in the outer bark. The declining trend of 137Cs concentrations in litterfall (λ : 0.31–0.33 y−1) was similar to that of the mean of new/old needles (λ : 0.26–0.33 y−1) for cedar stands. With respect to the hydrological components, the 137Cs concentration in the stemflow (λ : 0.32–0.33 y−1) decreased at a slightly slower rate than that in the throughfall (λ : 0.36–0.54 y−1) for the cedar forest. The decline coefficients of 137Cs concentration in the aforementioned types of hydrological components slightly exceeded that for the vegetal samples. The results suggest that monitoring of 137Cs concentrations in hydrological components and vegetal samples can aid in further understanding the leaching mechanisms of 137Cs from trees to rainwater. • The decline trend of 137Cs concentrations in hydrological and vegetal samples over 6 y was determined for Japanese forests. • Vegetal samples exhibited a single-exponential declining trend over 6 y. • The decline in the 137Cs concentration in the throughfall was approximated via a double-exponential model. • The decline in the 137Cs concentration in the stemflow was slightly slower than that in the throughfall for a cedar forest. • The leaching rate of 137Cs from foliage to throughfall decreased with respect to time. [ABSTRACT FROM AUTHOR]

After the Fukushima Daiichi Nuclear Power Station (F1NPS) accident, 137Cs activity concentrations have not yet decreased to pre-accident levels because of direct release from the site and fluvial discharges of 137Cs deposited on land. It is necessary to consider dispersion processes in the coastal area to understand the impact of multiple river discharges and direct release. To achieve this goal, we carried out oceanic dispersion simulations that considered direct release and fluvial discharges and compared the results with the annual averages of observed data. We assumed that particulate 137Cs discharged from rivers to the ocean quickly resuspended and re-leached after coagulation and precipitation, and that all of the 137Cs was dispersed. The reproducibility of results was improved by considering fluvial discharges of particulate 137Cs at all sites between 2013 and 2016, except near the F1NPS. In other words, particulate 137Cs discharged from rivers was found to influence the results of ocean surface activity concentrations within a relatively short period of time. The impact of direct release was dominant for the observed 137Cs activity concentrations adjacent to the F1NPS, which was used to estimate direct releases. [ABSTRACT FROM AUTHOR]