Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Nagano, Hirohiko*; Kanda, Yuki*; Suzuki, Yuri*; Hiradate, Shuntaro*; Koarashi, Jun; Atarashi-Andoh, Mariko; Guo, Z.*
Discover Soil (Internet), 2, p.27_1 - 27_9, 2025/04
Koarashi, Jun; Takeuchi, Erina; Kokubu, Yoko; Atarashi-Andoh, Mariko
Radiocarbon, 67(2), p.307 - 317, 2025/04
Times Cited Count:0 Percentile:0.00(Geochemistry & Geophysics)Radiocarbon (C) dating of soil samples by accelerator mass spectrometry has been proven useful for studying carbon (C) cycling in terrestrial ecosystems. There are, however, two main difficulties in sample preparation for this application: contamination of samples with modern C and inhibition of graphite formation due to sulfur (S)-containing impurities. Here we evaluated these effects from three different sample preparation methods, by conducting
C measurements of
C-dead sample and S-rich soil samples. The preparation methods were all successful in graphite formation and
C measurement for soil samples with an organic S content
6.9%. The different methods showed different percent Modern Carbon (pMC) values ranging from 0.19% to 0.64% for
C-dead sample. However, the three methods had little influence on the determination of
C age for samples at least younger than 12,000 yr BP. The methods examined in the present study can be used for
C dating with sufficient accuracy in the application to C cycle studies.
Abe, Yukiko; Nakayama, Masataka*; Atarashi-Andoh, Mariko; Tange, Takeshi*; Sawada, Haruo*; Liang, N.*; Koarashi, Jun
Geoderma, 455, p.117221_1 - 117221_11, 2025/03
Times Cited Count:0 Percentile:0.00(Soil Science)Subsoils (typically below a depth of 30 cm) contain more than half of global soil carbon (C) as soil organic C (SOC). However, the extent to which subsoil SOC contributes to the global C cycle and the factors that control it are unclear because quantitative evaluation of carbon dioxide (CO) emission from subsoils through direct observations is limited. This study aimed to quantify CO
emission from subsoils and determine factors that control CO
emission, focusing on the decomposability of soil organic matter (SOM) and the characteristics of the mineral-SOM association in soils. Therefore, a laboratory incubation experiment was conducted using surface soils (0-10 cm and 10-25 cm depth) and subsoils (30-45 cm and 45-60 cm depth) collected from four Japanese forest sites with two different soil types (volcanic ash and non-volcanic ash soils). The CO
emission from the subsoils was found to be responsible for 6%-23% of total CO
emission from the upper 60-cm mineral soil across all sites. Radiocarbon signatures of CO
released from the subsoils indicated the decomposition of decades-old SOM in the subsoils. The correlations between CO
emission rate and soil factors across both soil types suggested that the CO
emission from the subsoils is mainly controlled by the amounts of SOC easily available to soil microbes and microbial biomass C, not by the amounts of reactive minerals. Given the potential active participation of subsoils in terrestrial C cycling, most of the current soil C models that ignore subsoil C cycling are likely to underestimate the response of soil C to future climate change. The quantitative and mechanistic understanding of C cycling through a huge subsoil C pool is critical to accurately evaluating the role of soil C in the global C balance.
Terada, Hiroaki; Tsuzuki, Katsunori; Kadowaki, Masanao; Nagai, Haruyasu
Nihon Genshiryoku Gakkai-Shi ATOMO, 67(2), p.113 - 117, 2025/02
no abstracts in English
Sato, Takuto; Goger, B.*; Nakayama, Hiromasa
SOLA (Scientific Online Letters on the Atmosphere) (Internet), 21, p.17 - 23, 2025/01
Times Cited Count:0 Percentile:0.00(Meteorology & Atmospheric Sciences)In this study, we conducted large-eddy simulations of turbulent flows and plume dispersion over idealized two-dimensional double steep hills. In the simulations, we investigated the distribution patterns of the mean plume concentrations, considering various distances between the hills and emission sources. Our objective was to provide information on the area of influence of local hilly terrains on plume dispersion from the viewpoint of accuracy, i.e., determining if the conventional Gaussian plume model can accurately predict plume concentrations. The result showed that the clockwise circulation was dominant in the area between the windward and leeward hills (valley) when the valley width was less than 10 times the hill height (). This circulation makes the flow close to the stack remain in the valley, resulting in the higher concentrations in the valley than in wider-valley (
10
valley) cases. The effect of the leeward hill on the flow field was negligible when the valley width was greater than 10
. In the area beyond 20
from the crest of the windward hill, estimated plume spreads for all cases were similar, indicating that the area of influence of the hills was approximately 20
.
Suzuki, Yuri*; Hiradate, Shuntaro*; Koarashi, Jun; Atarashi-Andoh, Mariko; Yomogida, Takumi; Kanda, Yuki*; Nagano, Hirohiko*
Soil (Internet), 11(1), p.35 - 49, 2025/01
Times Cited Count:0 Percentile:0.00(Soil Science)Battulga, B.; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Otosaka, Shigeyoshi*; Koarashi, Jun
Environmental Science and Pollution Research, 31, p.60080 - 60092, 2024/10
A ubiquitous distribution of plastic debris has been reported in aquatic and terrestrial environments; however, the interactions between plastics and radionuclides and the radioactivity of environmental plastics remain largely unknown. Here, we characterize biofilms developing on the surface of plastic debris to explore the role of plastic-associated biofilms as an interaction medium between plastics and radiocesium (Cs) in the environment. Biofilm samples were extracted from plastics (1-50 mm in size) collected from two contrasting coastal areas in Japan. The radioactivity of plastics was estimated based on the
Cs activity concentration of the biofilms and compared seasonally with surrounding environmental samples (i.e., sediment and sand).
Cs traces were detected in biofilms with activity concentrations of 21-1300 Bq kg
biofilm (dry weight), corresponding to 0.04-4.5 Bq kg
plastic (dry weight). Our results reveal the interaction between
Cs and plastics and provide evidence that organic and mineral components in biofilms are essential in
Cs retention in environmental plastics.
Battulga, B.; Nakayama, Masataka; Matsuoka, Shunsuke*; Kondo, Toshiaki*; Atarashi-Andoh, Mariko; Koarashi, Jun
Water Research, 264, p.122207_1 - 122207_12, 2024/10
Times Cited Count:8 Percentile:91.02(Engineering, Environmental)Growing attention has been given to microbial attachment and biofilm formation on microplastics (MPs; sizes: 5 mm) in the environment. Here, we explore the microbial communities in the plastisphere to improve our understanding of microbial ecology as well as their impacts on aquatic ecosystems. Using the amplicon sequence of 16S and ITS genes, we identified bacterial and fungal community composition and diversity on MPs, surface waters, bottom sediments, and coastal sands in two contrasting coastal areas of Japan. Significantly different microbial diversity and taxonomic composition were detected depending on sample types and research sites. This research highlights the microbial metabolic functions in MP-associated biofilm, which could be the key to uncovering the true impact of plastic debris on the global ecosystem.
Nakayama, Masataka; Abe, Yukiko; Atarashi-Andoh, Mariko; Tange, Takeshi*; Sawada, Haruo*; Liang, N.*; Koarashi, Jun
Applied Soil Ecology, 201, p.105485_1 - 105485_12, 2024/09
Times Cited Count:3 Percentile:73.33(Soil Science)Nitrogen often limits plant growth in forest ecosystems. Plants, including trees, change vertical root distribution when nutrient competition is strong within surface soil layer and take up nitrogen even from subsurface soil layers in addition to the surface soil. However, there is still limited knowledge about nitrogen cycles within deeper soil layers. In this study, we investigated the vertical profiles (0-60 cm) of the net nitrogen mineralization and nitrification rates at four Japanese forest sites with two different soil types (Andosols and Cambisols). The partial least square path modeling (PLS-PM) was used to determine factors affecting nitrogen-cycling processes. The net nitrogen mineralization and nitrification rates per unit soil weight were considerably higher in surface soil layer than in deeper soil layers in Andosols but not in Cambisols. PLS-PM analysis showed that microbial biomass and soil organic matter quantities were the main factors influencing the net nitrogen mineralization and nitrification rates, indicating that a similar mechanism creating the spatial variations of nitrogen-cycling processes in surface soil layer predominantly regulates the processes in subsoil layers. Moreover, it was estimated that the net nitrogen mineralization rate could be comparable at all soil types and depths when the rate was expressed per unit soil volume. Therefore, our results suggest that subsoil layers are a quantitatively important nitrogen source for plant nutrients in Andosols and Cambisols, supporting high forest productivity.
Battulga, B.; Munkhbat, D.*; Matsueda, Makoto; Atarashi-Andoh, Mariko; Oyuntsetseg, B.*; Koarashi, Jun; Kawahigashi, Masayuki*
Environmental Pollution, 357, p.124427_1 - 124427_10, 2024/09
Times Cited Count:1 Percentile:31.14(Environmental Sciences)The occurrence and characteristics of plastic debris in aquatic and terrestrial environments have been extensively studied. However, there is still limited information on the properties and dynamic behavior of plastic-associated biofilms in the environment. In this study, we collected plastic samples from an inland river system in Mongolia and extracted biofilms from the plastics to uncover the characteristics of the biofilms using analytical, isotopic, and thermogravimetric techniques. Mixtures of organic and mineral particles were detected from extracted biofilms, revealing the plastic as a carrier for exogenous substances including contaminants in the river ecosystem. The present study provides insights into the characteristics and environmental behavior of biofilms which are useful to elucidate the impact of plastic-associated biofilms on organic matter and material cycling in the aquatic ecosystems.
Nakanishi, Takahiro; Sakuma, Kazuyuki; Oyama, Takuya; Hagiwara, Hiroki; Suzuki, Takashi
Environmental Pollution, 355, p.124213_1 - 124213_7, 2024/08
Times Cited Count:4 Percentile:67.42(Environmental Sciences)This study investigated the transport behavior of I by riverbank surveys conducted from 2013 to 2015 in a watershed where the
I/
Cs activity ratio is low in the mountainous area and high in the plain as of 2011. Until 2015, the
I/
Cs activity ratio of the levee crown in the studied watershed was similar to that of the surrounding area in 2011. However, the
I/
Cs ratios of the surface riverbank sediments were all low, indicating that radionuclides transported from the mountainous area were deposited on the riverbank in the plain. The vertical distribution of the
I/
Cs ratio in the riverbank sediments indicated that some
I and
Cs deposited during the accident remained in the lower layers, but most were eroded immediately after the accident. Based on the
I/
Cs ratios of sediments deposited on the riverbank, which remained constant until 2015 after the accident, the amount of
I discharged to the ocean was determined from the previously evaluated
Cs discharge. It was calculated that 1.8
10
Bq and 1.2
10
Bq of
I were discharged with sediment from the studied watershed and the contaminated river watersheds (Abukuma River and Fukushima coastal rivers, including the study river), respectively. The results of this study indicate that the continuous
I discharge from the river contribute little to their amount in the seafloor sediments along the Fukushima coast.
Nagai, Haruyasu; Nakayama, Hiromasa; Satoh, Daiki; Tanimori, Toru*
Dai-52-Kai Kashika Joho Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2024/07
A novel monitoring method for the quantitative visualization of 3D distribution of a radioactive plume accidentally released from a nuclear facility is proposed, and the feasibility of its analysis method is demonstrated by preliminary test using hypothetical data. The proposed method is the combination of gamma-ray imaging spectroscopy with the electron tracking Compton camera (ETCC) and real-time high-resolution atmospheric dispersion simulation based on 3D wind observation with Doppler lidar. ETCC can acquire the angle distribution images of direct gamma-ray from a specific radionuclide in a target radioactive plume. The 3D distribution of radioactive plume is inversely reconstructed from direct gamma-ray images by several ETCCs located around the target by harmonizing with the air concentration distribution pattern of the plume predicted by real-time atmospheric dispersion simulation. Analysis methods were developed and tested by using hypothetical data generated by numerical simulations of atmospheric dispersion and radiation transport.
Periez, R.*; Bezhenar, R.*; Maderych, V.*; Brovchenko, I.*; Liptak, L.*; Kobayashi, Takuya; Min, B.-I.*; Suh, K. S.*; Little, A.*; Iosjpe, M.*; et al.
IAEA-TECDOC-2060, 55 Pages, 2024/07
This publication describes the work undertaken by Working Group 7, Assessment of Fate and Transport of Radionuclides Released in the Marine Environment of the IAEA's Modelling and Data for Radiological Impact Assessments (MODARIA II) programme (2016-2019). In MODARIA II, the degree of complexity of the models used was increased in order to effectively consider additional processes, specifically uptake by biota, and the spatiotemporal scales of the simulations were also expanded.
Iimoto, Takeshi*; Shimada, Kazumasa; Hashimoto, Makoto; Nagai, Haruyasu; Hohara, Shinya*; Murakami, Kenta*
Nihon Genshiryoku Gakkai-Shi ATOMO, 66(7), p.356 - 360, 2024/07
no abstracts in English
Nakayama, Hiromasa; Kono, Takaaki*
Proceedings of 22nd International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes (HARMO22), 4 Pages, 2024/06
In safety and consequence assessment of nuclear facilities at short distances up to several kilo-meters from an emission source under normal operation or accident conditions, it is important to accurately and quickly predict air concentrations. We developed a real-time calculation method by coupling the three-dimensional (3D) wind observation with Doppler lidar and pre-calculated LES-database. In this study, we first analyze one-year meteorological data at a nuclear facility site and then classify the turbulence intensity for improving a real-time atmospheric dispersion simulation model.
Ikenoue, Tsubasa; Nakanishi, Takahiro; Shimadera, Hikari*; Kawamura, Hideyuki; Kondo, Akira*
E3S Web of Conferences (Internet), 530, p.02005_1 - 02005_10, 2024/05
The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) caused a radioactive contamination in seabed sediment. The Cs supply from rivers could be an important process for the long-term behavior of
Cs in seabed sediment. In this study, a ten-year simulation of the
Cs behavior in seabed sediment was conducted using an oceanic dispersion model combined with a prediction model of
Cs behavior in land and river. In the waters north of FDNPP, the simulation results suggested that the
Cs supply from rivers had a great impact on the concentrations in coastal sediment due to the initial low concentrations in seabed sediment and the large supply of
Cs from rivers. In the waters near FDNPP and south of FDNPP, the simulation results suggested that the impact of the
Cs supply on the temporal variation of
Cs concentration in coastal sediment was relatively small due to the large initial adsorption from seawater. Overall, these results indicated that
Cs supply from rivers had an impact on the spatiotemporal distribution of
Cs concentrations in seabed sediment on a decadal time scale and the impact was especially great in the waters north of FDNPP.
Nakayama, Hiromasa; Takemi, Tetsuya*
Atmospheric Science Letters, 25(4), p.e1204_1 - e1204_9, 2024/04
Times Cited Count:1 Percentile:14.77(Geochemistry & Geophysics)We proposed a dynamically controlled recycling method. The magnitude of turbulent fluctuations is dynamically controlled to match with the target turbulence statistics using a turbulence enhancement coefficient based on the ratio of the target to the computed values. When compared to the recommended data of Engineering Science Data Unit (ESDU) 85020, the turbulence characteristics were quantitatively generated well. Furthermore, the spanwise and vertical plume spreads were also reproduced well. It is concluded that the dynamically controlled recycling method successfully simulates plume dispersion in a neutral turbulent boundary layer.
Togawa, Orihiko; Okuno, Hiroshi
JAEA-Review 2023-043, 94 Pages, 2024/03
In order to translate nuclear disaster prevention documents written in Japanese into English, the Basic Act on Disaster Management, the Act on Special Measures Concerning Nuclear Emergency Preparedness, and the Convention on Nuclear Safety were surveyed for corresponding terms in Japanese and English. The survey results were integrated and unified English translations were selected. As a result, a Japanese-English correspondence table of technical terms in the field of nuclear disaster prevention was prepared and proposed.
Togawa, Orihiko; Hokama, Tomonori; Hiraoka, Hirokazu; Saito, Shota
JAEA-Research 2023-011, 78 Pages, 2024/03
When radionuclides are released into the atmospheric environment at a nuclear emergency, protective measures such as evacuation and temporal relocation are carried out using motor vehicles such as private cars and buses to reduce radiation exposure to residents. To confirm conditions of contamination for the evacuated/relocated residents and the used motor vehicles, contamination inspection is conducted in the middle of the route from border areas of Nuclear Emergency Planning Zone to evacuation shelters. In the present inspection in Japan, a value of OIL4 = 40,000 cpm is used as decontamination criteria. For the details and derivation methods of the value, however, no official documents are found which give systematically detailed descriptions and explanation. It is also recognized that even few experts on nuclear emergencies can explain these subjects in detail as a whole. In order to explain scientifically and technically the OIL4 value of decontamination criteria used in contamination inspection in Japan, this report aims at investigating and estimating the deviation methods of OIL4, and examining and considering these results. To achieve the objectives, we show the bases for decontamination criteria, and investigate and estimate the derivation methods for limits of a surface contamination density corresponding to the generic criteria for each exposure pathway. Moreover, we give the OIL4 value some consideration and suggestions from a viewpoint of positioning and feature of OIL4 in Japan, and cautionary points at revising the value.
Nakanishi, Chika*; Ota, Masakazu; Hirouchi, Jun; Takahara, Shogo
JAEA-Research 2023-012, 29 Pages, 2024/02
The OSCAAR program is a probabilistic risk assessment program for reactor accidents developed by Japan Atomic Energy Agency. To improve the model included in the OSCAAR program, which is about long-term exposure caused by the resuspension of radioactive materials deposited on soil surfaces, we calculated resuspension factors for Cs-137. The one- dimensional atmosphere-SOiL-VEGetation model, SOLVEG-R was utilized to compute resuspension factor. The wind velocity was kept constant in this study since it significantly affects particle resuspension behavior. Our calculations indicate that wind velocities below 6 m s resulted in little variation in the annual mean resuspension factor at a height of 1 m. However, as wind velocities increased above 6 m s
, the resuspension factor significantly increased. The resuspension factors ranged from 10
to 10
m
for wind velocities ranging from 1 m s
to 7 m s
.