Paper in Press
JOURNAL OF GEOPHYSICAL RESEARCH, doi:10.1029/2011JG001696
Carbon isotopic composition, methanogenic pathway and fraction of CH4 oxidized in rice field flooded all year round
- Floodwater CH4 was heavier in δ13C value than porewater CH4
- Emitted CH4 was heavier in the fallow season than in the rice season
- Low acetoclastic methanogenesis and high CH4 oxidation was observed
Values of δ13C were investigated of CH4 trapped in the soil porewater and floodwater of and emitted from a rice field under continuous flooding throughout the fallow and following rice seasons, and CH4 produced via different pathways and fraction of CH4 oxidized was calculated by using the isotopic data. Porewater CH4 was relatively 13C-depleted, with δ13C values about -65‰ over the season except between July and August (around -55‰). Also, hydrogenotrophic methanogenesis was very important (around 50%) for the most of the season, while acetoclastic methanogenesis dominated (about 70%) only between July and August. Floodwater CH4 was heavier in δ13C value (from -50 to -34‰) than porewater CH4 (from -68 to -54‰) over the season, demonstrating that it is highly influenced by methanotrophy. The δ13C value of emitted CH4 was negatively correlated with flux in temporal variation (P < 0.05), and it was more positive in the fallow season (between -56 and -44‰) than in the rice season (between -68 and -48‰). This indicates that plant-mediated CH4 transport is probably a more important pathway, and causes less CH4 oxidation during the rice season than during the fallow season, which is further confirmed by the fraction of CH4 oxidized being generally greater in the fallow season (60-90%) than in the rice season (10-80%). These findings suggest a low contribution of acetoclastic methanogenesis and a high fraction of CH4 being oxidized in the field, especially in the fallow season.
Received 22 February 2011; accepted 19 August 2011.
Citation: (2011), Carbon isotopic composition, methanogenic pathway and fraction of CH4 oxidized in rice field flooded all year round, J. Geophys. Res., doi:10.1029/2011JG001696, in press.