Determination of methane and carbon dioxide fluxes during the rice maturity period in Taiwan by combining profile and eddy covariance measurements

A field campaign was undertaken over a rice paddy in Central Taiwan to investigate the flux of CH4 through the flux-gradient method. During the campaign period, the average observed concentrations of CH4 during the campaign period at the lower height (22.2 m above ground level, agl) and upper height (27.5 m agl) were around 2.04 ppm and 2.01 ppm, respectively. It was noticed that the profile concentration of CH4 was lower during day time when compared to night time. However, the flux of CH4 was observed to be higher during the day time than during night hours. In order to understand the relationship between the influences of meteorological variables on the flux of CH4, six meteorological variables were studied. It was observed that soil heat flux has a linear positive correlation with the flux of CH4. During the study period, the maturity stage of rice paddy, the rice paddy ecosystem was behaving as sources of CH4 and CO2. Over a 100-year time frame, the global warming potential (GWP) fluxes of CH4 and CO2 observed at this study site were 0.16 and 0.71 μmol CO2 equivalents m−2 s−1, respectively. The total GWP flux (CH4 and CO2) was 0.86 μmol CO2 equivalents m−2 s−1 in which CH4 and CO2 contribute 18% and 82%, respectively.