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

Abstract

A field campaign was undertaken over a rice paddy in Central Taiwan to investigate the flux of CH 4 through the flux-gradient method. During the campaign period, the average observed concentrations of CH 4 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 CH 4 was lower during day time when compared to night time. However, the flux of CH 4 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 CH 4, six meteorological variables were studied. It was observed that soil heat flux has a linear positive correlation with the flux of CH 4. During the study period, the maturity stage of rice paddy, the rice paddy ecosystem was behaving as sources of CH 4 and CO 2. Over a 100-year time frame, the global warming potential (GWP) fluxes of CH 4 and CO 2 observed at this study site were 0.16 and 0.71 μmol CO 2 equivalents m −2 s −1, respectively . The total GWP flux (CH 4 and CO 2) was 0.86 μmol CO 2 equivalents m −2 s −1 in which CH 4 and CO 2 contribute 18% and 82%, respectively.