Late growing season CH4 budget in a rice paddy determined using stable carbon isotope, emission flux and soil storage measurements

The ecosystem-level CH4 budget (production, oxidation, storage and emission) was evaluated with respect to a Japanese rice paddy. The amount of CH4 produced and oxidized was calculated from emission fluxes and oxidized fractions of CH4. The latter were determined from CH4 stable carbon isotope ratios. Average rates of CH4 production and oxidation under flooded conditions were estimated to be 234 and 130 mg CH4 m−2 d−1, respectively. The average ratio of emission to oxidation under flooded conditions was 0.66, but increased significantly to 2.79 during the first 5 days after drainage. CH4 oxidation exceeded CH4 production after 10 days of drainage.