HR: 1340h
AN: B13B-1195    [Abstracts]
TI: Simultaneous Flux Measurements of CO₂, its Stable Isotope Ratios and Trace Gases Based on Eddy Accumulation Technique for Flux Partitioning
AU: * Takahashi, Y
EM: yoshiyu@nies.go.jp
AF: Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, 305-8506, Japan
AU: Hirata, R
EM: hirata.ryuichi@nies.go.jp
AF: Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, 305-8506, Japan
AB: For the purpose of determining the CO₂ uptake by terrestrial ecosystem, eddy covariance method (EC) is commonly used in the tower-flux measurements. The flux measured by this method is called enet ecosystem exchange (NEE)f. NEE has the meaning of difference between two component fluxes, photosynthetic uptake and respiratory release of CO₂. Magnitude of both the component fluxes is far larger than NEE. Both the component fluxes have difference in response function against changes in environmental factors, such as temperature and water. Therefore it is important to evaluate the characteristics of variations in the comporent fluxes individually in the future prediction of CO₂ uptake by terrestrial ecosystem. Separation of NEE into the componet fluxes is usually done by using an approximate temperature expression of respiratory flux. This approximate expression is based on the assumption that the NEE observed at nighttime equals to the respiratory flux. The photosynthetic uptake of CO₂ is defined as difference between the observed NEE and grespirationh approximated as a temperature-function. Because of its technical simplicity, this approach has provided useful information about climatology of the gross CO₂ fluxes. However, the temperature expression of respiratory flux has several limitations in its application. We are now developing a flux-partitioning method using chemical tracers (e.g. stable isotopes of CO₂ and carbonyl sulfide) as additional constraints. The flux partitioning using stable isotopes of CO₂ is based on the imbalance of net flux of the CO₂ isotopes between grespirationh and gphotosynthesish. On the other hand, because of this similarity in the control factors for uptake ratio, the net flux of carbonyl sulfide (COS) is regarded as a possible constraint for the functioning of variations in photosynthetic CO₂ uptake by terrestrial ecosystem. Field observation of fluxes of those chemical tracers by EC method is difficult due to stringent requirements for on-site measurement. Therefore, as a first step, we are planning to measure those fluxes based on an eddy accumulation technique coupled with flask sampling and high precision lab analysis. We report current progress of the development.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0452 Instruments and techniques
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting