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To quantify the spatial variation and spatial structure of nitrous oxide (N2O) and nitric oxide (NO) emission from forest soils, we measured N2O and NO emission rates from surface soil cores taken at 1 m intervals on a cross-line transect (65 m × 20 m) on a slope of Japanese cedar ( Cryptomeria japonica) forest in a temperate region of central Japan and analyzed the spatial dependency of N oxide gas emissions using geostatistics. We divided N2O emission into N2O from denitrification and N2O from nitrification using the acetylene inhibition method. According to the geostatistical analysis, N2O emission rates on the slope had large spatial variation and weak spatial dependency. This weak spatial dependency was caused by the inordinately high N2O emissions on the slope, which were derived mainly from denitrification. In contrast, NO emission rate on the slope had large spatial variation, but strong spatial dependency and a distinct spatial distribution related to slope position, that is, high in the middle of the slope and low in the shoulder and the foot of the slope. The CN ratio and water-filled pore space were the dominant factors controlling NO emission rate on a slope. Our results suggest that spatial information about topographic factors helps to improve the estimation of both N2O emission and NO emission from forest soils. [ABSTRACT FROM AUTHOR]

To determine the relationship between nitrous oxide (N2O) and nitric oxide (NO) emission rates and soil properties in forest soils, N2O and NO emission rates in soils were measured in incubation experiments under standardized temperature and water conditions (water content at a water-holding capacity of 60%) using soils packed into a cylindrical core, and variations in the soil properties were also determined. The N2O emission rates from nitrification and from denitrification were determined separately using a nitrification inhibitor (10 Pa acetylene). Soil samples were taken from 25 forest stands in a central temperate area of Japan. The N2O and NO emission rates were highly variable, even under the standardized temperature and water-holding capacity (60%) conditions. According to a partial least squared regression model analysis, the C:N ratio and pH strongly affected the N2O emission rate, whereas , water-soluble Al and the C:N ratio strongly affected the NO emission rate. The C:N ratio negatively affected the emission rate of both N oxide gases, suggesting that N mineralization is an important factor in the rates of N oxide gas emission. The acetylene inhibition experiment showed that N2O emission from denitrification was positively affected by pH, water-filled pore space and filling density, and negatively affected by the C:N ratio, total carbon and total nitrogen. [ABSTRACT FROM AUTHOR]

The benefits of the artificial fixation of reactive nitrogen (Nr, nitrogen [N] compounds other than dinitrogen), in the form of N fertilizers and materials are huge, while at the same time posing substantial threats to human and ecosystem health by the release of Nr to the environment. To achieve sustainable N use, Nr loss to the environment must be reduced. An N-budget approach at the national level would allow us to fully grasp the whole picture of Nr loss to the environment through the quantification of important N flows in the country. In this study, the N budgets in Japan were estimated from 2000 to 2015 using available statistics, datasets, and literature. The net N inflow to Japanese human sectors in 2010 was 6180 Gg N yr−1 in total. With 420 Gg N yr−1 accumulating in human settlements, 5760 Gg N yr−1 was released from the human sector, of which 1960 Gg N yr−1 was lost to the environment as Nr (64% to air and 36% to waters), and the remainder assumed as dinitrogen. Nr loss decreased in both atmospheric emissions and loss to terrestrial water over time. The distinct reduction in the atmospheric emissions of nitrogen oxides from transportation, at −4.3% yr−1, was attributed to both emission controls and a decrease in energy consumption. Reductions in runoff and leaching from land as well as the discharge of treated water were found, at −1.0% yr−1 for both. The aging of Japan's population coincided with the reductions in the per capita supply and consumption of food and energy. Future challenges for Japan lie in further reducing N waste and adapting its N flows in international trade to adopt more sustainable options considering the reduced demand due to the aging population. [Display omitted] • Nitrogen budgets in Japan from 2000 to 2015 were estimated for all sectors. • Reactive nitrogen loss to the environment in 2010 was 1960 Gg N yr−1. • Another 3800 Gg N yr−1 was rendered useless by conversion to dinitrogen. • Reactive nitrogen loss to air and water decreased from 2000 to 2015. • There is room for further reductions in nitrogen waste in Japan. [ABSTRACT FROM AUTHOR]

After the Fukushima Daiichi Nuclear Power Plant accident, there has been an increasing concern regarding the contamination of wild mushrooms with radiocesium (134Cs and 137Cs) in eastern Japan. In this study, we analyzed the radioactivity monitoring data of 3189 wild edible mushrooms of 107 species collected by the 265 local municipalities in eastern Japan to investigate the radiocesium levels in wild mushrooms. Results of the analysis showed that radiocesium concentrations in mushrooms were normalized with radioactivity deposition data from aircraft monitoring, and then we evaluated the effects of species, sampled location, sampling year and regional deviation between 134Cs and 137Cs activity of specimens using a hierarchical Bayesian approach considering spatial autocorrelation (an intrinsic CAR model). Normalized activity concentration by species ranged from 1.1 × 10 − 4 to 2.3 × 10 − 2 (m2 kg−1, fresh weight). As reported in previous studies, the mycorrhizal species tended to have higher radiocesium concentrations. Some saprophytic species (e.g. Pholiota lubrica) also had high concentrations. For the mushroom species that were also evaluated in the post-Chernobyl studies, we found that the same species had similar trends of absorption capacities. Our results indicate the extensive analysis of public monitoring data is helpful to understand the situation of mushroom contamination and evaluate the internal dose by ingestion of wild mushrooms according to species and areas. Image 1 • Radioactivity data of 3189 wild edible mushrooms of 107 species were analyzed. • A hierarchical Bayesian analysis considering spatial autocorrelation worked well. • Mycorrhizal and some saprophytic species tended to have higher radioactivity. • Species-wise radioactivities were positively correlated with those in Chernobyl. We provided reliable species characteristics of radiocesium in wild mushrooms which could be utilized for current and future contamination issues. [ABSTRACT FROM AUTHOR]

Reducing synthetic nitrogen fertilizer (SNF) use is critical for mitigating environmental nitrogen (N) pollution caused by excessive reactive nitrogen and lowering the cost of chemical N fertilizer inputs in agricultural management. In response, Japan has set a national target to reduce chemical fertilizer inputs, with a goal of 30% reduction in SNF use. To assess the feasibility of this target, we collected ca. 1700 records from domestic SNF reduction experiments and conducted a meta-analysis to examine the effects of SNF reduction on crop yield. Using a linear plateau response model of yield to SNF application in the experiments, we assumed that the conventional SNF rates used in control plots were sufficient to reach maximum yield. Our meta-analysis indicates that a 30% SNF reduction in SNF is achievable without significant yield loss on average. This reduction can be facilitated through the use of functional fertilizers and replacement of SNF with organic materials. Additionally, we evaluated changes in nitrogen waste from domestic cropland under the new national target using simple scenarios. Our results show that a 30% SNF reduction, without substituting by organic materials, would only decrease N waste by 8.8%. However, our meta-analysis finds that greater reductions in nitrogen input are possible, indicating potential for further optimization of N management, including the use of organic amendments., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kazuya Nishina reports financial support was provided by The Environment Research and Technology Development Fund. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The nuclear power plant accident in Fukushima had led to pollution of forest ecosystems with 137 Cs in 2011. In this study, we simulated the spatiotemporal distribution of 137 Cs concentrations of litter layer in the contaminated forest ecosystems in two decades from 2011, which is one of the key environmental components of 137 Cs migration in the environment due to the high bioavailability of 137 Cs in the litter. Our simulations showed that 137 Cs deposition is the most important factor in the degree of contamination of the litter layer but vegetation type (evergreen coniferous/deciduous broadleaf) and mean annual temperature are also important for changes over time. Deciduous broadleaf trees had higher initial concentrations in the litter layer due to the direct initial deposition on the forest floor. However, the concentrations remained higher than those in evergreen conifers after 10 years due to redistribution of 137 Cs by vegetation. Moreover, areas with lower average annual temperatures and lower litter decomposition activity retained higher 137 Cs concentrations in the litter layer. The results of the spatiotemporal distribution estimation of the radioecological model suggest that, in addition to 137 Cs deposition, elevation and vegetation distribution should also be considered in the long-term management of contaminated watersheds, which can be informative in identifying hotspots of 137 Cs contamination on a long-term scale., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kazuya Nishina reports financial support was provided by JSPS KAKENHI., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Forests cover approximately 70% of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident in 2011. Following this severe contamination event, radiocaesium ( 137 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 137 Cs in these forests. To explore the performance and uncertainties of these models we conducted a model inter-comparison exercise using Fukushima data. The main scenario addressed an evergreen needleleaf forest (cedar/cypress), which is the most common and commercially important forest type in Japan. We also tested the models with two forest management scenarios (decontamination by removal of soil surface litter and forest regeneration) and, furthermore, a deciduous broadleaf forest (konara oak) scenario as a preliminary modelling study of this type of forest. After appropriate calibration, the models reproduced the observed data reliably and the ranges of calculated trajectories were narrow in the early phase after the fallout. Successful model performances in the early phase were probably attributable to the availability of comprehensive data characterizing radiocaesium partitioning in the early phase. However, the envelope of the calculated model end points enlarged in long-term simulations over 50 years after the fallout. It is essential to continue repetitive verification/validation processes using decadal data for various forest types to improve the models and to update the forecasting capacity of the models., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The majority of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident is covered with forests. We developed a dataset for radiocaesium ( 137 Cs) in trees, soil, and mushrooms measured at numerous forest sites. The 137 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. The ancillary information describing the forest stands were also collated, and further environmental information (e.g. climate) was derived from the other databases using longitude and latitude coordinates of the sampling locations. The database contains 8593, 4105, and 3189 entries of activity concentration data for trees, soil, and mushrooms, and 471 and 3521 entries of inventory data for trees and soil, respectively, which were collected from 2011 to 2017, and covers the entire Fukushima prefecture. The data can be used to document and understand the spatio-temporal dynamics of radiocaesium in the affected region and to aid the development and validation of models of radiocaesium dynamics in contaminated forests.

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 137 Cs dynamics using the latest observation data and newly provided maps of the predicted 137 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. However, further validation revealed that the migration from the soil surface organic layer to the mineral soil was overestimated for evergreen needleleaf forests. The new prediction of the 137 Cs inventory showed that although the 137 Cs distribution within forests differed among forest types in the first 5 years, the difference diminished in the later phase. Besides, the prediction of the wood 137 Cs activity concentrations reproduced the different trends of the 137 Cs activity concentrations for cedar, oak, and pine trees. Our simulation suggests that the changes of the wood 137 Cs activity concentration over time will slow down after 5-10 years. Although the model uncertainty should be considered and monitoring and model updating must continue, the study provides helpful information on the 137 Cs dynamics within forest ecosystems and the changes in wood contamination.