HR: 1340h
AN: B43B-0152    [Abstracts]
TI: Spatial And Temporal Variation Of Methane Fluxes In A Small Humid Temperate Forest Watershed In Japan
AU: * Itoh, M
EM: itoma@kais.kyoto-u.ac.jp
AF: Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-tyo, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Ohte, N
EM: nobu@bluemoon.kais.kyoto-u.ac.jp
AF: Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-tyo, Sakyo-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: Katsuyama, M
AF: Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-tyo, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Hayamizu, K
EM: hayamizu@kais.kyoto-u.ac.jp
AF: Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-tyo, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Kawasaki, M
EM: kawasaki@kais.kyoto-u.ac.jp
AF: Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-tyo, Sakyo-ku, Kyoto, 606-8502 Japan
AB: \qquad It is generally thought that forest soils function as a sink for methane (CH$_{4}$). However, in forests subject to a humid climate, wetlands often occur in riparian zones around streams and ponds. It is possible that CH$_{4}$ emissions in these wetlands exceed the uptake in forest soil. It is still not fully understood whether forest catchments act as net sinks or sources of CH$_{4}$. We routinely monitored CH$_{4}$ fluxes at three different sites in a wetland and three dry hillslopes in a small forested catchment in central Japan. CH$_{4}$ emission was measured using the static chamber technique. At the same time, several environmental factors were measured, too. The study site is covered with mixed stands of secondary broad-leaved deciduous trees and planted coniferous trees. Several wetlands are located along the main stream of the catchment. The area of the entire catchment is 59,900 m$^{2}$ and that of the wetlands is 300 m$^{2}$. CH$_{4}$ was emitted almost throughout the year, with clear seasonality, at the monitored points in the wetland. The CH$_{4}$ emission rates in wetland sites were strongly dependent on soil temperatures, and were highest in summer and lowest in winter. Annual average CH$_{4}$ emissions in the wetland ranged from 13.8 to 92.4 mg CH$_{4}$ m $^{-2}$ d $^{-1}$. Although CH$_{4}$ emissions increased markedly every summer, emissions were constrained by depletion of the water table in the summer of 2002. Most of the forest floor acted as a small sink (annual average fluxes ranged from -0.54 to -0.02 mg CH$_{4}$ m $^{-2}$ d $^{-1}$.), but CH$_{4}$ emissions were occasionally observed in wet parts in summer. Consumption rates in the forest floor did not significantly vary through the year, except for wet areas. \qquad It was found that the water table and soil water content dictated redox conditions and affected CH$_{4}$ production and oxidation in several different parts of the watershed. While the CH$_{4}$ emission rate increased with increased soil temperature, the CH$_{4}$ uptake rate was less affected by fluctuations in soil temperature. Average CH$_{4}$ emission rates from wetland sites were 3 orders of magnitude greater than the uptake rate at the forest floor. Our results suggest that forest watersheds of this type may function as a source of CH$_{4}$, especially when seasonal temperatures are high, in spite of the area of wetland being relatively small compared to the entire watershed area.
DE: 9320 Asia
DE: 4805 Biogeochemical cycles (1615)
DE: 4851 Oxidation/reduction reactions
DE: 4802 Anoxic environments
DE: 1890 Wetlands
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting