研究者詳細 - 尾坂　兼一

論文 - 尾坂　兼一

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Phosphate oxygen isotope insights into the coupled distribution of phosphorus, iron, and manganese in lake sediments 査読

Takuya Ishida, Noboru Okuda, Shin-ichi Onodera, Mitsuyo Saito, Yusuke Tomozawa, Xin Liu, Naoshige Goto, Ken'ichi Osaka, Masahiro Maruo, Ichiro Tayasu, Syuhei Ban

Chemical Geology 683 122754 - 122754 2025年6月

Water-temperature equation based on oxygen isotope records of cultured freshwater bivalve Corbicula sandai shells from Lake Biwa, Japan 査読国際誌

Setogawa, M., Domitsu, H., Sakai, S., Osaka, K., Katsuyama, M.

Journal of Paleolimnology 2025年1月

Root exudates in mangrove forests accelerate bicarbonate production in the soil environment 査読国際誌

Kato, N., Osaka, K., Ohtsuka, T., Iimura, Y.

Scientific Reports 14 ( 1 ) 2024年12月

The sources of nitrate exported from a watershed containing mixed forest, paddy fields, and urban areas in Japan: differences between baseflow conditions and rainfall events 査読国際誌

Osaka, K., Takatsu, M., Ishibashi, T., Chihiro, S., Nakamura, T.

Limnology 26 75 - 89 2024年9月

担当区分：筆頭著者,　最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（副担当）

DOI： 10.1007/s10201-024-00762-9

その他リンク： https://link.springer.com/article/10.1007/s10201-024-00762-9/fulltext.html

A simple, safe method for preserving dissolved methane in freshwater samples using benzalkonium chloride 査読国際誌

Osaka, K., Nagata, R., Inoue, M., Ito, M., Hosoi-Tanabe, S., Iwata, H.

Limnology and Oceanography: Methods 22 ( 8 ) 536 - 547 2024年8月

Hydrological and biogeochemical controls of the seasonality of particulate and dissolved nitrogen exports during rainfall events from a forested watershed in monsoon Asia, Japan 査読国際誌

Osaka, K., Kunimatsu, T., Hida, Y., Komai, Y., Katsuyama, M., Ohte, N.

Water Resources Research 59 2023年11月

Nitrogen Contamination and Denitrification Occurrence in Shallow Groundwater of Urbanized Area at Kathmandu Valley, Nepal 査読

Nakamura, T., Osaka, K., Chapagain, S. K., Nishida K.

Journal of Geography (Chigaku Zasshi) 2023年3月

Assessing the changes in river water quality across a land-use change (forest to oil palm plantation) in peninsular Malaysia using the stable isotopes of water and nitrate 査読国際誌

Itoh M., Osaka K., Iizuka K., Kosugi Y., Lion M., Shiodera S.

Science of the Total Environment 859 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Science of the Total Environment 参加形態：共同（副担当）

Land conversion from natural forests to plantations (e.g., oil palm) in Southeast Asia is one of the most intensive land-use changes occurring worldwide. To clarify the effects of oil palm plantations on water quality, we conducted multipoint river and stream water sampling in peninsular Malaysia at the end of the rainy season over a 3-year period (2013–2015). We measured the major dissolved ions and stable isotope ratios of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3− and δ18O-NO3−) in water from the upper streams in mountainous forests to the midstream areas of two major rivers in peninsular Malaysia. The electrical conductivity increased, and the d-excess value (as an index of the degree of evaporation) decreased with increasing distance from the headwaters, suggesting the effect of evaporative enrichment and the addition of pollutants. We separated the sampling points into four groups (G1–G4) through cluster analysis of the water quality data. From the land use/land cover (LULC) classification maps developed from satellite images and local information, we found that G1 and G2 mainly consisted of sampling points in forested areas, while G3 and G4 were located in oil-palm-affected areas. The concentrations of major ions were higher in the oil palm areas, indicating the effects of fertilizer and limestone (i.e., pH adjustment) applications. The dissolved inorganic nitrogen concentration did not differ among the groups, but the dissolved organic carbon, total dissolved nitrogen, and δ15N-NO3− were higher in the oil palm area than in the forested area. Although the nitrogen concentration was low, even in the oil palm area, the significantly higher δ15N-NO3− in the oil palm area indicated substantial denitrification. This implies that denitrification contributed to the lowering of the NO3− concentration in rivers in the oil palm area, in addition to nutrient uptake by oil palm trees.

DOI： 10.1016/j.scitotenv.2022.160319

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85142359418&origin=inward

Hydrological control of the chemical characteristics of suspended particulate phosphorus in the Yasu River watershed, Japan: Implications for its source and bioavailability 査読国際誌

Osaka, K., Chishiro, S., Matsumoto, Y., Iwata T., Okuda, N.

Hydrological Processes 36 ( 10 ) 2022年11月

Effect of dissolved oxygen on nitrogen and phosphorus fluxes from lake sediments and their thresholds based on incubation using a simple and stable dissolved oxygen control method 査読国際誌

Osaka, K., Yokoyama, R., Ishibashi, T., Goto, N.

Limnology and Oceanography: Methods 20 ( 1 ) 1 - 14 2022年2月

元素分析計連結型安定同位体比質量分析計の簡易改造による微量試料炭素窒素安定同位体比測定査読

木庭啓介、木下桂、大西雄二、福島慶太郎、尾坂兼一、松尾奈緒子、舟川一穂、瀬古祐吾、目戸綾乃、平澤理世、小川奈々子、兵藤不二夫、由水千景

RADIOISOTOPE 2021年4月

Factors characterizing phosphate oxygen isotope ratios in river water: an inter-watershed comparison approach 査読国際誌

Ide J., Ishida T., Cid-Andres A.P., Osaka K., Iwata T., Hayashi T., Akashi M., Tayasu I., Paytan A., Okuda N.

Limnology 2020年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Limnology 参加形態：共同（副担当）

© 2020, The Japanese Society of Limnology. We compared the oxygen isotope ratio of dissolved phosphate (δ18OPO4) in two rivers with different land-cover and geological features (Ado River and Yasu River) within Lake Biwa basin, central Japan, to explore what factor primarily characterizes the δ18OPO4. Mean values of δ18OPO4 in river water were 19.0 ± 2.4‰ (n = 7) in Ado River and 13.1 ± 2.3‰ (n = 15) in Yasu River, which were significantly different. Comparisons of δ18OPO4 between river water and potential sources of phosphate revealed that in the Ado River, the δ18OPO4 was similar to that in rocks from the accretionary complex and decreased with increasing sedimentary rock coverage. In the Yasu River, the δ18OPO4 was low in the upper forested areas, but increased with paddy field coverage. These results demonstrate that river δ18OPO4 strongly reflects inputs from geological substances, but is also impacted by land-use activities and varies with anthropogenic land coverage in the watershed. Thus, river δ18OPO4 relates to land or bedrock coverage differentially in each river. Regression analysis showed that residuals of the δ18OPO4 tended to converge to zero with increasing drainage area, suggesting that river δ18OPO4 more explicitly reflects land-cover and geological features on a larger watershed scale.

DOI： 10.1007/s10201-020-00610-6

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85082952035&origin=inward

Identification of Phosphorus Sources in a Watershed Using a Phosphate Oxygen Isoscape Approach 査読国際誌

Ishida T., Uehara Y., Iwata T., Cid-Andres A., Asano S., Ikeya T., Osaka K., Ide J., Privaldos O., Jesus I., Peralta E., Triño E., Ko C., Paytan A., Tayasu I., Okuda N.

Environmental Science and Technology 53 ( 9 ) 4707 - 4716 2019年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Environmental Science and Technology 参加形態：共同（副担当）

© 2019 American Chemical Society. Identifying nonpoint phosphorus (P) sources in a watershed is essential for addressing cultural eutrophication and for proposing best-management solutions. The oxygen isotope ratio of phosphate (δ 18 O PO 4 ) can shed light on P sources and P cycling in ecosystems. This is the first assessment of the δ 18 O PO 4 distribution in a whole catchment, namely, the Yasu River Watershed in Japan. The observed δ 18 O PO 4 values in the river water varied spatially from 10.3‰ to 17.6‰. To identify P sources in the watershed, we used an isoscape approach involving a multiple-linear-regression model based on land use and lithological types. We constructed two isoscape models, one using data only from the whole watershed and the other using data from the small tributaries. The model results explain 69% and 96% of the spatial variation in the river water δ 18 O PO 4 . The lower R 2 value for the whole watershed model is attributed to the relatively large travel time for P in the main stream of the lower catchment that can result in cumulative biological P recycling. Isoscape maps and a correlation analysis reveal the relative importance of P loading from paddy fields and bedrock. This work demonstrates the utility of δ 18 O PO 4 isoscape models for assessing nonpoint P sources in watershed ecosystems.

DOI： 10.1021/acs.est.8b05837

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85064746297&origin=inward

Nitrogen and oxygen isotope enrichment factors of nitrate at different denitrification rates in an agricultural soil. 査読国際誌

Osaka, K., Nakajima, Y., Suzuki, K., Eguchi, S., Katou, H.

Soil Science and Plant Nutrition 64 ( 5 ) 558 - 565 2018年8月

インドネシアスマトラ島ブンクル州における極小規模金採掘・精錬地区の環境媒体中水銀濃度とそのヒト健康リスク評価, 査読

永淵修, 中澤暦, 井上隆信, Elvince R., 川上智規, 尾坂兼一, 金藤浩司

環境科学会誌 31 ( 2 ) 43 - 58 2018年4月

琵琶湖流入河川流域における森林および農地土壌中のリン含有粒子サイズの違い査読

長根美和子、尾坂兼一、阿江教治、大園亨司、保原達

酪農学園大学紀要 41 ( 2 ) 147 - 152 2017年4月

Influence of bedrock groundwater on streamflow characteristics in a volcanic catchment. 査読国際誌

Fujimoto, M., Ohte, N., Kawasaki, M., Osaka, K., Itoh, M., Ohtsuka, I., Itoh, M.

Hydrological Processes 2016年4月

Atmospheric nitrate leached from small forested watersheds during rainfall events: processes and quantitative evaluation 査読国際誌

Osaka, K., Kugo, T., Komaki, N., Nakamura, T., Nishida, K., Nagafuchi, O.

Journal of Geophysical Research 2016年4月

Non-carcinogenic risk assessment of groundwater in South Gobi, Mongolia 査読国際誌

Nakazawa, K., Nagafuchi, N., Okano, K., Osaka, K., Hamabata, E

Journal of Water and Health 2016年4月

ヒノキ人工林集水域における表面流の発生とそれが集水域からの溶存態窒素流出に与える影響査読

久郷達朗、尾坂兼一、川村湧也、永淵修

陸水研究 2 27 - 37 2015年4月

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