GLOBAL METHANE EMISSIONS FROM RICE PADDIES

Rice paddies are a major source of atmospheric methane (CH4). However, the strength of this source is highly uncertain. To improve estimates of CH4 emission at the regional and global scales requires process-ba sed models, integrating the environmental and biological factors that determine the rate of CH4 emission. In this study, we used such a mode l to calculate the spatial and seasonal variations in CH, emission fro m rice paddies, with the support of an integrated GIS data set definin g distribution of rice paddies, rice calendar, climate, and soil condi tions. The calculated rates of CH4 emission in a rice-growing season v aried greatly, from 5 to 90 g CH4 m(-2), for rice paddies across the g lobe. In most rice paddies daily mean CH4 effluxes were from 50 to 400 mg CH4 m(-2). Annual total emission was estimated to be 53 Tg; two th irds of this was emitted between 10 degrees N and 30 degrees N. Monthl y CH4 emissions ranged from 1.4 Tg in January to 8.7 Tg in August, and more than a half of the emission occurred between June and October. O ur model suggests that, on average, 12% of the simple carbon substrate from decomposition of soil organic matter and rice plants was transfo rmed into CH4, and the emitted CH4 accounted for 6.5% of the rice net primary production. Copyright (C) 1996 Elsevier Science Ltd