Effect of litter removal five years after the Fukushima accident on Cs uptake by Japanese cedar.

Removal of litter-associated Cs from the forest floor (litter removal) can reduce the Cs uptake by plants; however, the proposed effective period for litter removal was 1-2 years after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. This is because the Cs in forest soil migrates rapidly from the litter to surface mineral soil layers in Japanese forests, and thus the effectiveness of litter removal will quickly become limited. However, it is unknown whether this approach can be applied to forests whose vertical migration of Cs in the forest soil is relatively slow.

A pilot study of radiocesium activity concentration in the stemflow of deciduous broad-leaved trees: Its relationship with leaves and outer bark as of 2022-2023.

The radiocesium (Cs) activity concentration in stemflow, which is an element of the Cs cycle in the forest, is determined by the supply of Cs from the outer bark and leaves. Long-term monitoring data of deciduous broad-leaved trees since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident have shown the Cs activity concentration in the outer bark decreasing exponentially, while that in the leaves has remained nearly constant. Therefore, it is expected that the contribution of the outer bark to Cs in stemflow eventually becomes smaller than that of leaves over time.

Factors influencing the difference in dissolved ion inputs to the forest floor between deciduous and coniferous stands: comparison under high and low atmospheric deposition conditions.

It is necessary to clear the relationship between physical and vegetation factors on the processes governing dissolved ion inputs to the forest floor to estimate correctly the values of atmospheric input to the forest. This study identified the factors influencing the differences in dissolved ion inputs to the forest floor between coniferous evergreen and broad-leaved deciduous species by analyzing the phenological variations of dry deposition and canopy exchange calculated by the canopy budget model under a high-deposition site near the city of Tokyo and a low-deposition site 84 km further away. At low-deposition site, vegetation factors such as capture efficiency did not explain the differences in Na or Cl dry deposition.

Ten-year trends in vertical distribution of radiocesium in Fukushima forest soils, Japan.

To elucidate interannual changes in the vertical distribution of Cs in forest ecosystems contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident, we investigated Cs inventories in forest soils (both organic and mineral soil horizons) at 10 sampling plots with different Cs deposition levels and dominant species for up to 10 years after the accident. We examined the temporal variation of the Cs inventories by depth with exponential regression models (assuming that the transition and partitioning of Cs are still active) and exponential offset regression models (assuming a shift to a stable Cs distribution, defined as the "quasi-equilibrium steady-state" in the Chernobyl accident). In the organic horizon, the Cs inventories were exponentially decreasing, and it might take more time to converge in the quasi-equilibrium steady-state at most plots.

Dynamics of radiocaesium within forests in Fukushima-results and analysis of a model inter-comparison.

Forests cover approximately 70% of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident in 2011. Following this severe contamination event, radiocaesium (Cs) is anticipated to circulate within these forest ecosystems for several decades. Since the accident, a number of models have been constructed to evaluate the past and future dynamics of Cs in these forests.

A dataset of Cs activity concentration and inventory in forests contaminated by the Fukushima accident.

The majority of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident is covered with forests. We developed a dataset for radiocaesium (Cs) in trees, soil, and mushrooms measured at numerous forest sites. The Cs activity concentration and inventory data reported in scientific journal papers written in English and Japanese, governmental reports, and governmental monitoring data on the web were collated.

Calculations for ambient dose equivalent rates in nine forests in eastern Japan from Cs and Cs radioactivity measurements.

Understanding the relationship between the distribution of radioactive Cs and Cs in forests and ambient dose equivalent rates (H˙(10)) in the air is important for researching forests in eastern Japan affected by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. This study used a large number of measurements from forest samples, including Cs and Cs radioactivity concentrations, densities and moisture contents, to perform Monte Carlo radiation transport simulations for H˙(10) between 2011 and 2017. Calculated H˙(10) at 0.

Estimation of the rate of Cs root uptake into stemwood of Japanese cedar using an isotopic approach.

Japanese cedar (Cryptomeria japonica) is the main timber species in Japan. The prediction of the temporal changes in the Cs concentration in the stemwood of Japanese cedar after the Fukushima nuclear accident is essential for optimizing forest management in contaminated areas. However, it is difficult to estimate the respective contributions of root and foliar uptake to Cs accumulation in stemwood from simple field measurements, especially in trees that contain the residue of initially-deposited Cs.

Vertical distributions of radiocesium in Japanese forest soils following the Fukushima Daiichi Nuclear Power Plant accident: A meta-analysis.

This study investigated the temporal change in vertical distributions of radiocesium inventories in Japanese forest soils during the early phase (from 2011 to 2017) following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, using three simple parameters. We calculated the fraction in the organic layer (F), the migration center (X) and the relaxation depth (α) using 99 soil inventory data sets. F decreased significantly from 2011 to 2017 (logistic analysis, p < 0.

Temporal changes in the spatial patterns of air dose rate from 2012 to 2016 at forest floors in Fukushima, Japan.

This study investigates temporal changes in the distribution of air dose rates at forest floors from 2012 to 2016 by measuring air dose rates at a height of 10 cm. The study was conducted at four different topography forest sites in Fukushima Prefecture, Japan. At each forest site, the air dose rate was found to have decreased by 7%-22% over time from 2012 to 2016 owing to the movement of radiocesium from organic layers to mineral soil layers in the forest site.

New predictions of Cs dynamics in forests after the Fukushima nuclear accident.

Most of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident is covered by forest. In this paper, we updated model predictions of temporal changes in the Cs dynamics using the latest observation data and newly provided maps of the predicted Cs activity concentration for wood, which is the most commercially important part of the tree body. Overall, the previous prediction and latest observation data were in very good agreement.

Effects of radiocesium fixation potentials on Cs retention in volcanic soil profiles of Fukushima forests.

Radiocesium is well-known to be stabilized by clay minerals in soils, while volcanic soils could typically be poor in micaceous clays that fix Cs effectively. We investigated Cs fixation potentials [radiocesium interception potential (RIP)] and depth distribution of Cs stocks in volcanic soils to analyze effects of clay content and mineralogy on soil retention and migration of Cs after the Fukushima nuclear accident. Clay minerals of the volcanic soils were dominated by hydroxy-interlayered vermiculite (HIV) and short-range-order minerals, irrespective of bedrocks.

Calibration of forest Cs cycling model "FoRothCs" via approximate Bayesian computation based on 6-year observations from plantation forests in Fukushima.

Predicting the environmental fate of Cs in forest ecosystems along with the concentrations of Cs in tree parts are important for the managements of radioactively contaminated forests. In this study, we calibrate the Forest RothC and Cs model (FoRothCs), a forest ecosystem Cs dynamics model, using observational data obtained over six years from four forest sites with different levels of Cs contamination from Fukushima Prefecture. To this end, we applied an approximate Bayesian computation (ABC) technique based on the observed Cs concentrations (Bq kg) of five compartments (leaf, branch, stem, litter, and soil) in a Japanese cedar plantation.

Temporal changes in the radiocesium distribution in forests over the five years after the Fukushima Daiichi Nuclear Power Plant accident.

To elucidate the temporal changes in the radiocesium distribution in forests contaminated by the Fukushima Daiichi Nuclear Power Plant accident, we monitored the Cs concentration and inventory within forests from 2011 to 2015 across nine plots containing variable tree species and different contamination levels. The Cs concentrations in needles and branches decreased exponentially at all coniferous plots, with effective ecological half-lives of 0.45-1.

Stemflow-induced spatial heterogeneity of radiocesium concentrations and stocks in the soil of a broadleaved deciduous forest.

The transport of radiocesium from the canopy and quantification of the spatial distribution of radiocesium in the soil of konara oak forests are important to better understand the variability of Cs stocks in the soil between proximal and distal stem areas as well as fine-scale variations around the tree trunk. Moreover, a better understanding of fine-scale spatial variabilities of Cs concentrations and stocks will provide insights for optimizing soil sampling strategies to provide a more robust estimation of contamination at the stand scale. This study aims to elucidate the transport of Cs by stemflow in a radioactively contaminated konara oak forest in Tsukuba, Japan by describing and quantifying the fine-scale spatial distribution of Cs in the soil and preferential flowpaths of stemflow on the tree stem by a dye tracing experiment.

Nitrate isotopic composition reveals nitrogen deposition and transformation dynamics along the canopy-soil continuum of a suburban forest in Japan.

Rationale: Heavy nitrogen (N) deposition often causes high nitrate (NO3(-)) accumulation in soils in temperate forested ecosystems. To clarify the sources and production pathways of this NO3(-), we investigated NO3(-) isotope signatures in deposition processes along the canopy-soil continuum of a suburban forest in Japan.

Methods: The stable isotopes of N and oxygen (O) were used to trace the source and transformation dynamics of nitrate (NO3(-)) in two forest stands: a plantation of Cryptomeria japonica (coniferous tree; CJ) and a natural secondary forest of Quercus acutissima (broadleaf, deciduous tree; QA).