Measuring Greenhouse Gases Emissions In a Rice Paddy Field Using Micrometeorological Techniques.

Global climate change is an important issue for human beings. A major contributor for the global climate change may be increasing greenhouse gases. Carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) are considered as major greenhouse gases in agricultural land. In particular, a rice paddy field is a major anthropogenic source for CH₄ and N₂O. Recently, micrometeorological techniques for measuring trace gas flux have progressed. Gas fluxes obtained with micrometeorological techniques represent spatially integrated fluxes in a macro-scale; therefore, the techniques provide sufficient site special representations. In addition, a measuring system doesn’t disturb environmental conditions during measurement. Eddy-correlation technique (EC) is a popular and reliable micrometeorological technique. The EC requires a sensor whose response time must be sufficiently small to detect fluctuation of a gas concentration on the order of 10Hz to measure gas flux. Relaxed eddy accumulation technique (REA), on the other hand, measure gas flux without requiring a fast response sensor to analyze gas concentration. Slow response sensors reduce a cost for measurement. If gas fluxes measured with a REA system are in reasonable agreement with an EC system in rice paddy fields, a REA system will be an alternative technique to evaluate gas emissions in rice paddy fields without spending high cost instruments. The objective of this study is to evaluate EC and REA for measuring CH₄ and N₂O fluxes in rice paddy fields using EC and REA. Field experiments will be conducted in a rice paddy field, Japan. Gas fluxes (CH₄, N₂O) will be continuously measured using EC and REA. Gas concentrations (CH₄, N₂O) will be analyzed by a Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS, Aerodyne Research Inc., USA) in the EC system and a photoacoustic field gas-monitor (model 1412, Innova Air Tech Instruments, Denmark) in the REA system. Results will be discussed.