UNDERSTANDING THE NATURE OF METHANE EMISSION FROM RICE ECOSYSTEMS AS BASIS OF MITIGATION STRATEGIES

Methane is considered an important greenhouse gas and rice fields are one of the major atmospheric methane sources. This paper develops samp ling strategies and formulates mitigation options based on diel (day a nd night) and seasonal patterns of methane emissions. The design of sa mpling strategies and identification of abatement strategies were base d on data obtained using automatic closed-chamber systems. Diel patter ns of methane emissions from irrigated rice fields displayed similar p atterns from planting to flowering. Fluxes at 0600, 1200, and 1800 h w ere important components of the total diel flux. Methane fluxes sample d during these times are sufficient to capture most of the diel variat ion observed throughout the growing season. Seasonal patterns of metha ne emissions indicated the intensity of flux measurement that should b e done within the growing season. The characterization of seasonal emi ssion patterns according to ecologies, fertilizer amendments, and wate r management provides a focus for mitigation strategies. Mitigation st rategies, based on seasonal patterns, may be grouped into two approach es: preventive measures and reducing measures. Preventive measures may take into consideration, prior to planting rice, the ecology and fert ilizer management that will give fewer methane emissions. Reducing mea sures become necessary when the option to prevent high emissions is no t possible under a given condition. Other factors may be considered as preventive or reducing measures to mitigate methane emission. These f actors, however, should be evaluated as to how they influence the diel and seasonal patterns of methane emission. Two things can be derived from the evaluation: (i) an improvement of the emission factor for bet ter extrapolation; and (ii) a better understanding of how and when mit igation strategies can best be applied. (C) 1997 Elsevier Science Ltd.