HR: 08:30h
AN: B41G-03 INVITED    [Abstracts]
TI: Isotopomeric Signature of Nitrous Oxide Discharged from Lake Biwa in Japan and a Polluted River in Mongolia
AU: * Makabe, A
EM: makabe.a.aa@m.titech.ac.jp
AF: Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan
AU: Koba, K
EM: keikoba@cc.tuat.ac.jp
AF: Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, 183-8509, Japan
AU: Toyoda, S
EM: toyoda.s.aa@m.titech.ac.jp
AF: Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan
AU: Yoshida, N
EM: yoshida.n.aa@m.titech.ac.jp
AF: Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan
AB: Nitrous oxide (N₂O) is one of the greenhouse gases and considered to be substantially emitted from aquatic ecosystems eutrophicated by anthropogenic nitrogen. N₂O is produced by nitrification (hydroxylamine oxidation) and denitrification (nitrite reduction) which also consumes N₂O. Recent studies have demonstrated that isotopomeric signatures of N₂O (δ¹⁵N, δ¹⁸O and site preference; SP) are useful to gain insight into production and consumption processes of N₂O. Sutka et al. (2004, 2006) clearly revealed that SP can be used to identify production process of N₂O, and Ostrom et al. (2007) expanded the usefulness of SP for tracing consumption process. Isotope ratios of substrates such as ammonia, nitrate, dissolved oxygen, and water could give much information to support interpretations from SP data. In this study, firstly, multiple stable isotope measurements have been conducted in Lake Biwa, a monomictic lake in Japan whose oxygen concentration is moderate. Stable isotope ratios of ammonium and nitrate in both lake water and sediment suggested several possible processes for N₂O production, such as nitrification in water column and sediment, and denitrification in sediment. However, a lack of significant correlations in δ¹⁵N and δ¹⁸O of N₂O with substrates, and δ¹⁵N and SP for sedimental N₂O source estimated from Keeling plot suggested that N₂O accumulated in Lake Biwa would be produced by nitrification in the sediment and diffuse into water column. Secondly, diurnal variation of N₂O has been investigated in a river of Mongolia where a large amount of ammonium was directly flowed from sewage plant. Stable isotope ratios of ammonium, nitrate, and nitrite indicated that nitrification would occur in daytime and denitrification would occur in night time. Site Preference of N₂O were always close to that produced by nitrite reduction though dissolved oxygen concentration increased in daytime. Thus, SP is particularly useful tool to diagnose processes of N₂O emission.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0458 Limnology (1845, 4239, 4942)
DE: 0469 Nitrogen cycling
DE: 1803 Anthropogenic effects (4802, 4902)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting