HR: 0800h
AN: B21A-0853    [Abstracts]
TI: Hydrologic controls on nitrous oxide production and consumption in a forested headwater catchment in central Japan
AU: * Osaka, K
EM: osaka@kais.kyoto-u.ac.jp
AF: Kyoto University, Oiwakechou, Kitashirakawa, Sakyou-ku, Kyoto, 606-8502 Japan
AU: Ohte, N
EM: nobu@bluemoon.kais.kyoto-u.ac.jp
AF: Kyoto University, Oiwakechou, Kitashirakawa, Sakyou-ku, Kyoto, 606-8502 Japan
AU: Koba, K
EM: kkoba@depe.titech.ac.jp
AF: Department of Environmental Science and Technology Interdisciplinary Graduate School of Science and Engineering Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama, 226-8502 Japan
AU: Nakajima, T
EM: nakajima@lbri.go.jp
AF: Lake Biwa Research Institute, 10-1, Uchiidehama, , Ohtu, 520-0806 Japan
AU: Katsuyama, M
EM: katuyama@kais.kyoto-u.ac.jp
AF: Kyoto University, Oiwakechou, Kitashirakawa, Sakyou-ku, Kyoto, 606-8502 Japan
AB: We investigated producing and consuming processes of N$_{2}$O by measuring the N$_{2}$O concentration in the soil gas and of dissolved phase in groundwater in a forested headwater catchment in central Japan. According to the previous study in the same site showing that N$_{2}$O has mainly produced by denitrification in the groundwater, we focused N$_{2}$O dynamics in the groundwater. The concentrations of N$_{2}$O, NO $_{3}$$^{-}$, DOC, DO, and \delta$^{15}$N- N$_{2}$O in the groundwater were measured with monitoring the groundwater revels. Concentrations of dissolved N$_{2}$O in the groundwater ranged from 0.12 to 32.5mgN/l. It is considered that N$_{2}$O produced by denitrification was controlled by DO, NO $_{3}$$^{-}$ and DOC. For the groundwaters taken from the edge part of groundwater body where the highest dissolved N$_{2}$O was observed, negative correlation (r$^{2}$=0.81, p$<$0.005) was found between DO concentration and dissolved N$_{2}$O concentration, while there were no correlations with NO $_{3}$$^{-}$ and DOC concentrations. This indicates that the N$_{2}$O production at the edge part of the groundwater body was regulated only by DO concentration. The edge part of groundwater body could receive both DOC and NO $_{3}$$^{-}$ rich water generated by decomposition of litters in surface soils. This was supplied by saturated through flow from the upstream hillslope, that had relatively short residence time according to the geochemical solute concentration such as Na$^{+}$. \delta$^{15}$N- N$_{2}$O of this point was the smallest (from +1.5 to -19.6 permil, -9.6 permil as the average) and had a negative correlation (r$^{2}$=0.61, p$<$0.05) with N$_{2}$O concentration, confirming that that dissolved N$_{2}$O was produced mainly by denitrification. These observed results suggest that hydrological controls are critical for N$_{2}$O dynamics as a transporting conditions of DOC and NO $_{3}$$^{-}$ from the surface soil to the groundwater body.
DE: 4870 Stable isotopes
DE: 1800 HYDROLOGY
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting