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

Abstract

Manually operated closed-chamber methods have been used extensively to measure CH4 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 CH4 concentration signal. The chamber must be equipped with a fan to ensure that the chamber air is well mixed and to attain representative CH4 concentration values. The new method is suitable for high-throughput CH4 emission measurements and can also be used for studying bubbling CH4 emissions.