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Journal Articles

Dynamics of radiocaesium within forests in Fukushima; Results and analysis of a model inter-comparison

Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.

Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11

 Times Cited Count:0 Percentile:0(Environmental Sciences)

This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.

Journal Articles

Seasonal and snowmelt-driven changes in the water-extractable organic carbon dynamics in a cool-temperate Japanese forest soil, estimated using the bomb-$$^{14}$$C tracer

Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Koarashi, Jun; Kokubu, Yoko; Hirai, Keizo*

Journal of Environmental Radioactivity, 128, p.27 - 32, 2014/02

 Times Cited Count:6 Percentile:23.2(Environmental Sciences)

Although considerable research has been conducted on the importance of recent litter versus older soil organic matter as DOC sources in forest soil, a more thorough evaluation of the temporal patterns of DOC and WEOC is necessary. We investigated the seasonal variation in water-extractable organic carbon in a Japanese cool-temperate beech forest soil by using the carbon isotopic composition ($$^{14}$$C and $$^{13}$$C) of WEOC as a tracer for the carbon sources. Fresh leaf litter DOC significantly contributed to WEOC in May when the snowmelt occurred. In the rainy season, increases in the concentration of WEOC and the proportion of hydrophobic compounds were caused by high microbial activity under wetter conditions. From summer to autumn, the WEOC in the mineral horizons was also dominated by microbial release from the soil organic matter. These results indicate that the origin and dynamics of WEOC are strongly controlled by seasonal changes in the environmental conditions.

Journal Articles

Carbon isotopes of water-extractable organic carbon in a depth profile of forest soil imply a dynamic relationship with soil carbon

Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Koarashi, Jun; Kokubu, Yoko; Hirai, Keizo*

European Journal of Soil Science, 63(4), p.495 - 500, 2012/08

 Times Cited Count:19 Percentile:59.94(Soil Science)

To elucidate the origin and behavior of the water extractable organic carbon (WEOC), we first determined both the $$delta$$$$^{13}$$C and$$Delta$$$$^{14}$$C of fractionated WEOC by DAX-8 resin in a cool-temperate beech forest soil. The enrichment of $$^{13}$$C in WEOC with depth reflected the increasing proportion of the hydrophilic (HPI) fraction to the hydrophobic acid (HPOA) fraction. The changes in $$Delta$$$$^{14}$$C indicated that the major source of WEOC and its fractions was old organic matter in the mineral soil. Our results strengthened previous suggestion that the preferential adsorption of HPOA fraction and the preferential leaching of the indigenous soluble organic carbon in the mineral soils. This dynamic equilibrium between WEOC and the much greater soil organic carbon fraction plays an important role in carbon transport and accumulation throughout the soil profile.

Journal Articles

Seasonal patterns and control factors of CO$$_{2}$$ effluxes from surface litter, soil organic carbon, and root-derived carbon estimated using radiocarbon signatures

Atarashi-Andoh, Mariko; Koarashi, Jun; Ishizuka, Shigehiro*; Hirai, Keizo*

Agricultural and Forest Meteorology, 152, p.149 - 158, 2012/01

 Times Cited Count:31 Percentile:84.71(Agronomy)

Radiocarbon ($$^{14}$$C) signature was used to partition soil respiration in a cool-temperate deciduous forest. Heterotrophic respiration strongly correlated with soil temperature, but the magnitude of the response to soil temperature was different between SOC decomposition and litter decomposition. Autotrophic respiration appeared to correlate strongly with the phenology index rather than soil temperature. The information on the seasonal change about the contribution ratio of each source to the soil respiration is essential to understand the intrinsic temperature sensitivity of each source and the other factors controlling soil respiration.

Journal Articles

Use of carbon isotopes as tracer to estimate carbon dynamics in forest

Atarashi-Andoh, Mariko; Koarashi, Jun; Ishizuka, Shigehiro*; Hirai, Keizo*

JAEA-Conf 2010-001, p.80 - 83, 2010/03

no abstracts in English

Journal Articles

Use of $$^{14}$$C to study soil carbon cycling in beech forest

Atarashi-Andoh, Mariko; Koarashi, Jun; Ishizuka, Shigehiro*; Hirai, Keizo*

KURRI-KR-153, p.8 - 13, 2010/03

Soil organic carbon (SOC) is a complex of materials with different ages. An understanding of soil carbon cycling and thereby predicting its response to climatic change requires knowledge of both the inventory of carbon and the turnover times of SOC. In this study, chemical and density fractionation were examined to separate the organic matter collected from a beech forest into components with different turnover times. Mean residence time (MRT) for each fraction was estimated from its radiocarbon isotope ratio ($$Delta$$$$^{14}$$C) using the $$Delta$$$$^{14}$$C-MRT model. The results show that fractions separated by chemical fractionation with acid-alkali treatment have clearer difference in the isotope ratio than that by density fractionation. This means chemical fractionation is more adequate to estimate MRT composition for the beech forest soil. We also observed differences in the inventory and MRTs of carbon using chemical fractionation for two forests with different vegetation and the mean temperature. The results show that the difference in decomposed carbon flux from these two forests is attributed to the difference in MRT composition in each forest.

Journal Articles

Quantitative aspects of heterogeneity in soil organic matter dynamics in a cool-temperate Japanese beech forest; A Radiocarbon-based approach

Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Miura, Satoru*; Saito, Takeshi*; Hirai, Keizo*

Global Change Biology, 15(3), p.631 - 642, 2009/03

 Times Cited Count:35 Percentile:73.07(Biodiversity Conservation)

Although it is well documented the possibility that global warming can lead to an acceleration of microbial decomposition of soil organic carbon (SOC), the magnitude and timing of this effect remains highly uncertain. The main reason is a lack of quantitative aspect of the heterogeneity in SOC biodegradability. To quantify the heterogeneity, we collected the soil and litter samples within a cool-temperate deciduous forest in Japan, separated chemically the samples into SOC fractions, determined their mean residence times (MRTs) based on the radiocarbon ($$^{14}$$C) measurements, and finally represented the soil as a complex of six SOC pools with different range of MRTs. Predicted response of the SOC pools to warming demonstrates that the rate of SOC loss from the fast-cycling SOC pool diminishes quickly because of the substrate availability; in contrast, the warming continues to accelerate SOC loss from slow-cycling pools with MRTs of 20-200 year over the next century.

Journal Articles

Evaluation of carbon cycle in forest by using radiocarbon as a tracer

Atarashi-Andoh, Mariko; Koarashi, Jun; Ishizuka, Shigehiro*; Saito, Takeshi*; Hirai, Keizo*

JAEA-Conf 2008-003, p.75 - 78, 2008/04

C-14 is an effective tracer in investigating the carbon dynamics in the environment. In this study, the measurements of C-14 in soil organic matter (SOM) in a deciduous forest were used to determine the turnover time and CO$$_{2}$$ production rate from SOM. In addition, monthly measurements of carbon isotopic ratios in soil-respired CO$$_{2}$$ and atmospheric CO$$_{2}$$ were conducted to characterize the seasonal variation of the contribution of each CO$$_{2}$$ source, such as SOM decomposition and root respiration.

Journal Articles

Radiocarbon-based estimation of soil carbon turnover in a cool-temperate beech forest

Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Saito, Takeshi*; Hirai, Keizo*; Miura, Satoru*

Proceedings of International Symposium on Application of a Closed Experimental System to Modeling of $$^{14}$$C Transfer in the Environment, p.72 - 76, 2008/00

Recent debate has emphasized that our capacity to predict the response of soil organic carbon (SOC) to climate change depends on a clear understanding of the heterogeneity in SOC biodegradability. We collected soil samples from the Appi forest meteorology research site dominated by Japanese beech, separated the soil samples into three SOC fractions with a chemical method, and determined their radiocarbon isotope ratios using an accelerator mass spectrometry. The radiocarbon signatures allow us to estimate their turnover times (TTs), quantifying the rates of SOC decomposition. According to the estimated TTs, the SOC was distinguished into six SOC pools with distinct TTs of several years to $$>$$ 1000 years. The annual SOC decomposition rate was summed up to 0.47 kgC m$$^{-2}$$ y$$^{-1}$$, about a half of which was from the fastest-cycling pool (litter). Approximately 5% of SOC gave the over-millennium TTs, suggesting that this pool plays a role of a long-term carbon sequestration in the carbon cycle.

JAEA Reports

Analyses of plasma parameter profiles in JT-60U

Shirai, Hiroshi; Shimizu, Katsuhiro; Hayashi, Nobuhiko; Itakura, Hirofumi*; Takase, Keizo*

JAERI-Data/Code 2000-040, 214 Pages, 2001/01

JAERI-Data-Code-2000-040.pdf:7.89MB

no abstracts in English

JAEA Reports

Outline and handling manual of experimental data time slice monitoring software SLICE

Shirai, Hiroshi; Hirayama, Toshio; Shimizu, Katsuhiro; Tani, Keiji; Azumi, Masafumi; Hirai, Kenichiro*; Konno, Satoshi*; Takase, Keizo*

JAERI-M 93-026, 97 Pages, 1993/02

JAERI-M-93-026.pdf:2.77MB

no abstracts in English

Oral presentation

The Use of carbon isotopes to identify the origin of soil-respired CO$$_{2}$$ in beech forest

Atarashi-Andoh, Mariko; Koarashi, Jun; Ishizuka, Shigehiro*; Saito, Takeshi*; Hirai, Keizo*

no journal, , 

Soil organic matter (SOM) is the major reservoir of carbon in terrestrial ecosystems. Thus, to evaluate the CO$$_{2}$$ flux from SOM is an important step toward estimating the effect of environmental change on the terrestrial carbon cycles. In this study, we estimated the contribution of different soil CO$$_{2}$$ sources (SOM, litter and root) to CO$$_{2}$$ flux from the forest floor based on measures of carbon isotopic ratios in SOM, litter, soil-respired CO$$_{2}$$ and atmospheric CO$$_{2}$$ in a cool-temperate deciduous forest.

Oral presentation

Radiocarbon-based estimation of soil carbon turnover and its potential response to global warming

Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Saito, Takeshi*; Hirai, Keizo*; Miura, Satoru*

no journal, , 

no abstracts in English

Oral presentation

Dissolved organic carbon dynamics in a cool temperate forest soil; Clues from $$^{13}$$C and $$^{14}$$C signatures

Nakanishi, Takahiro; Koarashi, Jun; Atarashi-Andoh, Mariko; Hirai, Keizo*

no journal, , 

Dissolved organic carbon (DOC) is an important constituent in forest soils, because it affects soil formation and transport of heavy metals, is a source of C for microbes, and contributes to soil organic carbon (SOC) accumulation. In this study, we measured $$delta$$$$^{13}$$C and $$Delta$$$$^{14}$$C in water extractable organic carbon (WEOC) to investigate the dynamics of DOC at Appi, a cool temperate deciduous forest in Japan. The $$delta$$$$^{13}$$C values of WEOC were slightly higher than those of SOC. Such enrichment in $$^{13}$$C indicated that WEOC production, which was coupled with the microbial activity, mainly used a $$^{13}$$C-enriched SOC fraction (including sugars, amino acids, etc.) of the total SOC. Indeed, hydrophilic fractions were enriched in $$^{13}$$C compared to the total WEOC. Hydrophilic fractions are considered more biologically available for decomposition. The result of $$Delta$$$$^{14}$$C indicated that WEOC consists mainly of $$^{13}$$C-enriched, labile, hydrophilic organic materials with faster turnover times (several decades).

Oral presentation

Identifying sizes and turnover times of rapidly-cycling soil organic carbon pools by thin-layered soil incubations and $$^{14}$$C measurements

Moriya, Koichi*; Koarashi, Jun; Atarashi-Andoh, Mariko; Moriizumi, Jun*; Yamazawa, Hiromi*; Hirai, Keizo*

no journal, , 

Soil organic carbon (SOC) decomposition is an important component of the global carbon cycle, because SOC is the largest carbon reservoir in terrestrial ecosystems and a small change in the CO$$_{2}$$ flux from SOC may lead to a large change in atmospheric CO$$_{2}$$ concentration. For the accurate estimation of SOC decomposition, it is important to identify sizes and turnover times of SOC pools. We tried to estimate three SOC pools (active, slow and resistant) with different mean residence times (MRTs) by a combination of soil incubation and $$^{14}$$C analysis. The active SOC held $$sim$$1% of the total SOC with MRTs of 1-3 weeks. The slow SOC accounted for 20-50% of the total with MRTs of 1 to 17 years. The active and slow SOC contributed greatly to the total CO$$_{2}$$ production, and the primary source shifted from the active to the slow one. Our result shows the importance of quantifying the dynamics of rapidly-cycling SOC pools to accurately predicting the response of soils to climate change.

Oral presentation

Seasonal and spatial variations in carbon isotopic ratios in CO$$_{2}$$ respired from a beech forest floor

Atarashi-Andoh, Mariko; Koarashi, Jun; Moriya, Koichi; Nakanishi, Takahiro; Ishizuka, Shigehiro*; Hirai, Keizo*

no journal, , 

no abstracts in English

Oral presentation

Estimation of the depth profiles of soil organic carbon degradability by using radiocarbon

Moriya, Koichi; Koarashi, Jun; Atarashi-Andoh, Mariko; Moriizumi, Jun*; Yamazawa, Hiromi*; Hirai, Keizo*

no journal, , 

no abstracts in English

Oral presentation

Absorption and translocation of radioactive cesium in Cypress planted trees

Hirai, Keizo*; Komatsu, Masafumi*; Akama, Akio*; Noguchi, Ryotaro*; Nagakura, Junko*; Ohashi, Shinta*; Saito, Tetsu*; Kawasaki, Tatsuro*; Yazaki, Kenichi*; Ikeda, Shigeto*; et al.

no journal, , 

no abstracts in English

18 (Records 1-18 displayed on this page)
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