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職名 |
准教授 |
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研究分野・キーワード |
森林水文学 生物地球化学 |
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学内職務経歴 【 表示 ／ 非表示 】
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滋賀県立大学 環境科学部 環境生態学科 准教授 2022年04月 ～ 現在
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滋賀県立大学 環境科学部 環境生態学科 講師 2019年04月 ～ 2022年03月
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滋賀県立大学 環境科学部 環境生態学科 助教 2010年08月 ～ 2019年03月
学外略歴 【 表示 ／ 非表示 】
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独立行政法人農業環境技術研究所 研究員 2007年04月 ～ 2009年03月
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山梨大学医学工学研究部 国際流域環境研究センター 研究員 2009年04月 ～ 2010年07月
論文 【 表示 ／ 非表示 】
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Nitrogen Contamination and Denitrification Occurrence in Shallow Groundwater of Urbanized Area at Kathmandu Valley, Nepal
Nakamura, T., Osaka, K., Chapagain, S. K., Nishida K.
Journal of Geography (Chigaku Zasshi) 2023年03月
共著 共同（副担当）
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Itoh M., Osaka K., Iizuka K., Kosugi Y., Lion M., Shiodera S.
Science of the Total Environment Science of the Total Environment 859 2023年02月
10.1016/j.scitotenv.2022.160319 共著 共同（副担当）
[概要]
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.
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Hydrological control of the chemical characteristics of suspended particulate phosphorus in the Yasu River watershed, Japan: Implications for its source and bioavailability
Osaka, K., Chishiro, S., Matsumoto, Y., Iwata T., Okuda, N.
Hydrological Processes 36 (10) 2022年11月
共著 共同（主担当）
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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
Osaka, K., Yokoyama, R., Ishibashi, T., Goto, N.
Limnology and Oceanography: Methods 20 (1) 1 ～ 14 2022年02月
doi.org/10.1002/lom3.10466 共著 共同（主担当）
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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
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04月
共著 共同（副担当）
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Ide J., Ishida T., Cid-Andres A.P., Osaka K., Iwata T., Hayashi T., Akashi M., Tayasu I., Paytan A., Okuda N.
Limnology Limnology 2020年01月
[概要]
© 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.
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Identification of Phosphorus Sources in a Watershed Using a Phosphate Oxygen Isoscape Approach
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 Environmental Science and Technology 53 (9) 4707 ～ 4716 2019年05月
[概要]
© 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.
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Nitrogen and oxygen isotope enrichment factors of nitrate at different denitrification rates in an agricultural soil.
Osaka, K., Nakajima, Y., Suzuki, K., Eguchi, S., Katou, H.
Soil Science and Plant Nutrition 64 (5) 558 ～ 565 2018年08月
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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,
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04月
共著 共同（副担当）
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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
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04月
共著 共同（副担当）
著書 【 表示 ／ 非表示 】
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「サンタローザ流域における共通の関心(Boundary Object)」in 流域ガバナンス
Ria Lambino, 尾坂兼一, 石田卓也, 上原佳敏, Osbert Privaldos (脇田健一, 谷内茂雄, 奥田昇編)
京都大学学術出版会 2020年12月
単行本（学術書） 分担執筆
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Hydrologic controls on the nitrogen dynamics of forested ecosystems investigated using water and nitrate isotope signatures, In: Earth, Life, and Isotopes
Ohte, N., Tokuchi, N., and Osaka, K., edited by Ohkouch, N, Tayasu, I, Koba, K.
Kyoto University Press 415p 2010年04月
単行本（学術書） 共著
総説・解説記事 【 表示 ／ 非表示 】
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Improvement of analysis for nitrogen and oxygen isotopes of nitrate using denitrifier method: Challenge to reduce methodological blank
Osaka, K., Nakamura, T., Nishida, K., Kazama, F.
University of Yamanashi Annual report 2009,GCOE program 29 ～ 31 2009年04月
共著 共同（主担当）