Faculty Profiles - OSAKA Kenichi

Papers - OSAKA Kenichi

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

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 2025.6

Water-temperature equation based on oxygen isotope records of cultured freshwater bivalve Corbicula sandai shells from Lake Biwa, Japan Reviewed International journal

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

Journal of Paleolimnology 2025.1

Root exudates in mangrove forests accelerate bicarbonate production in the soil environment Reviewed International journal

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

Scientific Reports 14 ( 1 ) 2024.12

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 Reviewed International journal

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

Limnology 26 75 - 89 2024.9

Authorship：Lead author,　Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Participation form：Joint(The vice charge)

DOI： 10.1007/s10201-024-00762-9

Other Link： 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 Reviewed International journal

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

Limnology and Oceanography: Methods 22 ( 8 ) 536 - 547 2024.8

Hydrological and biogeochemical controls of the seasonality of particulate and dissolved nitrogen exports during rainfall events from a forested watershed in monsoon Asia, Japan Reviewed International journal

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

Water Resources Research 59 2023.11

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

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

Journal of Geography (Chigaku Zasshi) 2023.3

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 Reviewed International journal

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

Science of the Total Environment 859 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Science of the Total Environment Participation form：Joint(The vice charge)

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

Other Link： 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 Reviewed International journal

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

Hydrological Processes 36 ( 10 ) 2022.11

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 Reviewed International journal

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

Limnology and Oceanography: Methods 20 ( 1 ) 1 - 14 2022.2

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 Reviewed

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 2021.4

Factors characterizing phosphate oxygen isotope ratios in river water: an inter-watershed comparison approach Reviewed International journal

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

Limnology 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Limnology Participation form：Joint(The vice charge)

© 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

Other Link： 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 Reviewed International journal

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 2019.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Environmental Science and Technology Participation form：Joint(The vice charge)

© 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

Other Link： 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. Reviewed International journal

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

Soil Science and Plant Nutrition 64 ( 5 ) 558 - 565 2018.8

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, Reviewed

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 2018.4

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 Reviewed

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 2017.4

Influence of bedrock groundwater on streamflow characteristics in a volcanic catchment. Reviewed International journal

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

Hydrological Processes 2016.4

Atmospheric nitrate leached from small forested watersheds during rainfall events: processes and quantitative evaluation Reviewed International journal

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

Journal of Geophysical Research 2016.4

Non-carcinogenic risk assessment of groundwater in South Gobi, Mongolia Reviewed International journal

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

Journal of Water and Health 2016.4

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 Reviewed

久郷達朗、尾坂兼一、川村湧也、永淵修

陸水研究 2 27 - 37 2015.4

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Papers - OSAKA Kenichi