Quantifying bubbling emission (ebullition) of methane from a rice paddy using high-time-resolution concentration data obtained during a closed-chamber measurement

作者：Masako Kajiura, Takeshi Tokida · 发表于：Journal of Agricultural Meteorology · 年份：2021 · DOI：10.2480/agrmet.d-21-00022 · 被引用次数：29 · 研究领域：Atmospheric and Environmental Gas Dynamics、Groundwater flow and contamination studies、Hydrocarbon exploration and reservoir analysis

Methane (CH4) produced in rice-paddy soil is transported to the atmosphere either via the rice plants or by bubbling events (ebullition); however, little is known about the frequency and intensity of bubbling CH4 emissions and the factors that affect them. We developed a method to quantify ebullition using high-time-resolution (~1 Hz) CH4 concentration data obtained by closed-chamber measurements. Field measurements were conducted in a Japanese rice paddy at different rice growth stages: panicle formation (PF), booting (BT), and heading (HD). A dataset of 132 chamber measurements was used to develop and evaluate the method. A scripting file written in R programing language was used to automatically determine CH4 emissions via the two pathways. Plant-mediated CH4 emission intensity was constant during chamber deployment and was reflected as a steady linear increase in chamber [CH4] with time or as a constant baseline in a flux time series. We found that the plant-mediated emission could be determined as the peak with the lowest flux intensity in the flux frequency distribution even if bubbling events occurred during the chamber deployment. The field measurement results in combination with established data processing protocols showed that at PF, ebullition contributed only 4% of the total emission, whereas it accounted for 32% and 60% of the total emission at BT and HD, respectively. In contrast, the plant-mediated flux variation among growth stages was smaller. Both ebullition...