Contribution of Ebullition to Methane and Carbon Dioxide Emission from Water between Plant Rows in a Tropical Rice Paddy Field

Although bubble ebullition through water in rice paddy fields dominates direct methane (CH 4 ) emissions from paddy soil to the atmosphere in tropical regions, the temporal changes and regulating factors of this ebullition are poorly understood. Bubbles in a submerged paddy soil also contain high concentrations of carbon dioxide (CO 2 ), implying that CO 2 ebullition may occur in addition to CH 4 ebullition. We investigated the dynamics of CH 4 and CO 2 ebullition in tropical rice paddy fields using an automated closed chamber installed between rice plants. Abrupt increases in CH 4 concentrations occurred by bubble ebullition. The CO 2 concentration in the chamber air suddenly increased at the same time, which indicated that CO 2 ebullition was also occurring. The CH 4 and CO 2 emissions by bubble ebullition were correlated with falling atmospheric pressure and increasing soil surface temperature. The relative contribution of CH 4 and CO 2 ebullitions to the daily total emissions was 95–97% and 13–35%, respectively.