Progressive release of long-stored carbon from tropical peatland disturbances

Koarashi, Jun; Ito, Masayuki*; Atarashi-Andoh, Mariko; Kokubu, Yoko; Matsueda, Makoto; Kusin, K.*; Jaya, A.*; Dohong, S.*; Hirano, Takashi*

Nature Communications (Internet), 17, p.4369_1 - 4369_9, 2026/05

https://doi.org/10.1038/s41467-026-72890-y

Tropical peatlands are globally important, millennia-old carbon sinks, yet unprecedented human-driven degradation is triggering alarming carbon emissions. Comprehensive quantification of carbon dynamics across the disturbance sequence, from peat swamp forests to drained and fire-impacted peatlands, remains a critical knowledge gap. Here we show that over 18 years (1996-2014), drainage and subsequent peat fires released approximately 30-41 kg C m from peatlands in Central Kalimantan, Indonesia, using radiocarbon dating of peat profiles and groundwater dissolved organic carbon. Drainage contributed 5-11 kg C m, primarily from centuries- to millennium-old, previously waterlogged peat. Fires released 23-32 kg C m from peat accumulated over the past 3,000 years, initiating progressive oxidative decomposition of older peat. Extrapolation to Indonesia's disturbed peatlands suggests a release of 0.81-3.70 Gt between 1996 and 2014, with ongoing decomposition releasing an additional 0.03-0.08 Gt C annually, accelerating the impact on the global carbon balance.

Results of environmental impact investigations as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (FY2024)

Kokubu, Yoko; Takeuchi, Ryuji; Nishio, Kazuhisa*; Ikeda, Koki

JAEA-Data/Code 2025-013, 66 Pages, 2026/01

JAEA-Data-Code-2025-013.pdf:5.88MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the environmental monitoring investigation to confirm the environmental impacts associated with the backfilling of shafts and tunnels at the Mizunami Underground Research Laboratory (MIU). This report summarizes the results of the environmental impact investigations conducted as part of the environmental monitoring investigation around the MIU Site in FY2024, which include groundwater level measurement in wells, river flow rate measurement, water analysis of Hazama river, noise and vibration surveys, and soil survey.

Concept for a cesium-free negative ion source based on microwave heating of a low work function granular material

Matsubara, Akihiro*; Kokubu, Yoko; Nishio, Kazuhisa*; Kimura, Kenji*; Kashimura, Keiichiro*; Shimada, Koji; Fujita, Natsuko

Nuclear Instruments and Methods in Physics Research B, 568, p.165863_1 - 165863_5, 2025/11

https://doi.org/10.1016/j.nimb.2025.165863

We propose a concept for a cesium-free negative ion source based on microwave heating of granular low work function materials, which allows for both safety and high efficiency. This negative ion source features a structure where the plasma region and the negative ion generation region are adjacent within a microwave cavity. In the negative ion generation region, granular low work function materials heated by microwaves are placed. The sample gas entering the plasma region is excited, then it enters the negative ion generation region. Subsequently, it comes into contact with the surface of the low work function material, changes into negative ions, and finally, is extracted by an electric field. One advantage of this negative ion source is that, by using low work function materials in granular form, the reactive area is more than ten times larger compared to conventional negative ion sources using low work function materials.

Surface settlement of backfilled shafts and rebackfilling of settled shafts at the Mizunami Underground Research Laboratory

Kokubu, Yoko; Takeuchi, Ryuji; Nishio, Kazuhisa*; Ikeda, Koki

JAEA-Review 2024-066, 67 Pages, 2025/03

JAEA-Review-2024-066.pdf:8.25MB

The Tono Geoscience Center of the Japan Atomic Energy Agency has undertaken backfilling and restoration activities at the Mizunami Underground Research Laboratory (MIU) site since fiscal year 2020. These activities are being conducted in accordance with "The MIU Project from FY2020 Onwards," outlining the procedures for backfilling, restoration, and environmental monitoring at the MIU site. The backfilling activity was completed in January 2022, and thereafter, the observation of the backfilled shafts was commenced. On November 6, 2023, the settlement of the backfilled surface was observed in the Main Shaft and the Ventilation Shaft. By December 5, 2023, the depth of the settlement reached 12.9 m in the Main Shaft and 27.7 m in the Ventilation Shaft. After an evaluation by the MIU safety confirmation committee, which assessed the settlement condition and recommended countermeasures, the affected areas were backfilled for safety reasons. This report summarizes the observed settlement of the backfilled surface, the subsequent rebackfilling efforts, and the condition of the surface settlement areas. The condition of the backfilled sections has been confirmed up to June 2024.

Results of groundwater pressure and hydrochemical monitoring as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (FY2023)

Takeuchi, Ryuji; Kokubu, Yoko; Nishio, Kazuhisa*

JAEA-Data/Code 2024-011, 120 Pages, 2024/12

JAEA-Data-Code-2024-011.pdf:4.68MB
JAEA-Data-Code-2024-011-appendix(CD-ROM).zip:261.39MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the groundwater pressure and hydrochemical monitoring to confirm the restoration process of the surrounding geological environment associated with the backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (MIU). This report summarizes the data of the groundwater pressure and hydrochemical monitoring from boreholes and so forth at and around the MIU conducted in FY2023.

Results of groundwater pressure and hydro-chemical monitoring as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (2022)

Takeuchi, Ryuji; Kokubu, Yoko; Nishio, Kazuhisa*

JAEA-Data/Code 2023-014, 118 Pages, 2024/02

JAEA-Data-Code-2023-014.pdf:4.77MB
JAEA-Data-Code-2023-014-appendix(CD-ROM).zip:249.03MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the groundwater pressure and hydro-chemical monitoring to confirm the restoration process of the surrounding geological environment associated with the backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (MIU). This report summarizes the data of the groundwater pressure and hydro-chemical monitoring from boreholes and forth at and around the MIU conducted in FY2022. In addition, unreported hydro-chemical monitoring data from the boreholes and forth at the MIU conducted in FY2021 were also compiled.

Report of backfilling and restoration works in the Mizunami Underground Research Laboratory

Takeuchi, Ryuji; Mikake, Shinichiro; Ikeda, Koki; Nishio, Kazuhisa*; Kokubu, Yoko; Hanamuro, Takahiro

JAEA-Review 2023-007, 114 Pages, 2023/07

JAEA-Review-2023-007.pdf:12.02MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center has been conducting the Mizunami Underground Research Laboratory (MIU) Project to enhance the reliability of geological disposal technologies through investigations of the deep geological environment in the crystalline rock (granite) at Mizunami City, Gifu Prefecture, central Japan since fiscal year 1996. Backfilling and restoration works in the MIU site have been being conducted based on "the MIU Project from FY2020 onwards" which is defined the way forward of backfilling and restoration works and environmental monitoring investigations in the MIU site, since fiscal year 2020. This report summarizes the outline, process, and achievements of the construction and the safety patrol of the backfilling and restoration works in the MIU site performed from May 16, 2020 to January 16, 2022.

Be analysis of the rock samples from the northeastern shore of Lake Pumoyum Co in south Tibetan Plateau

Nara, Fumiko*; Watanabe, Takahiro; Kokubu, Yoko; Zhu, L.*

Nuclear Instruments and Methods in Physics Research B, 539, p.28 - 32, 2023/06

https://doi.org/10.1016/j.nimb.2023.03.007

Lake Pumoyum Co is located on the south Tibetan Plateau. The lake terraces are developed on the eastern lake shore, and it supposed that the large lake level changes would have happened in Pumoyum Co. The in-situ terrestrial cosmogenic adionuclides can be used to estimate the earth surface processes, such as the erosion rate and exposure age dating of rocks. Here we report the results of Be values of the rock samples from the lake terraces around Pumoyum Co. The concentrations of Be were measured by the JAEA-AMS-TONO-5MV in the Tono Geoscience Center, Japan Atomic Energy Agency. The Be concentrations ranged from 3.78 to 10.810 (atoms/g), but the Be values showed the decreasing trend following to the distance from the lake shore. This result indicates that Be values of the rocks at the shore of Pumoyum Co could be influenced from the erosion rate or tectonic process rather than the exposure date resulting from the lake level changes.

Present status of the JAEA-AMS-TONO (2021)

Matsubara, Akihiro*; Fujita, Natsuko; Miyake, Masayasu; Ishii, Masahiro*; Watanabe, Takahiro; Kokubu, Yoko; Nishio, Tomohiro*; Ogawa, Yumi; Jinno, Satoshi; Kimura, Kenji; et al.

JAEA-Conf 2022-002, p.55 - 62, 2023/03

https://doi.org/10.11484/jaea-conf-2022-002

We report the present status of the JAEA-AMS-TONO. Particularly, the destructions of varistors used in the beamline equipment will be presented. The cause of the destruction as well as implementation of the safety measures are mentioned.

Separation of quartz for measurement of beryllium-10 and aluminium-26; Application of cell handler

Kokubu, Yoko; Utsumi, Yoshinori*; Ito, Saburo*; Shimada, Koji

Dai-23-Kai AMS Shimpojiumu Hokokushu, p.60 - 63, 2022/12

In the case of estimating erosion rates of ground surfaces from measurement of beryllium-10 and aluminum-26, quartz contained in rocks and sediments is used as a measurement sample. In this paper, we present an example of separating quartz using a cell handler, which is a cell separation system, without chemical treatment using hydrofluoric acid. By optimizing the way to apply light to the mineral sample with the cell handler and the exposure time of the camera of the cell handler, quartz and other minerals, such as feldspar, were able to be distinguished from other minerals, such as feldspar in image recognition. An experimental measurement using rock samples was then performed under these conditions. As a result, only quartz was successfully separated through a fully automatized process by that distinguishes and picks quartz using the image recognition software and picking system built into the cell handler.