Increasing measurement throughput of methane emission from rice paddies with a modified closed-chamber method

Manually operated closed-chamber methods have been used extensively to measure CH 4 emissions from rice paddies, but the long chamber deployment time ( e.g ., 30 min ) , together with the labor required for gas sampling and subsequent analysis by gas chromatography severely limit their usefulness for multiple, high-throughput measurements. The objective of this study was to develop a modified closed-chamber method suitable for high-throughput measurements. The design of the modified system is based on a conventional method, but uses a portable spectroscopic gas analyzer and a newly developed dehumidification system. Results of a series of test operations showed that the use of a portable gas analyzer substantially reduced the time needed for each chamber deployment to as little as 4–5 min. A simple dehumidification system employing a selective water vapor-permeable tube was introduced to effectively dehumidify the sample gas so that the risk of water condensation was removed without attenuating the CH 4 concentration signal. The chamber must be equipped with a fan to ensure that the chamber air is well mixed and to attain representative CH 4 concentration values. The new method is suitable for high-throughput CH 4 emission measurements and can also be used for studying bubbling CH 4 emissions.