Methane Emissions from a Subtropical Grass Marshland, Northern Taiwan

Methane (CH 4 ) is an important greenhouse gas and a significant contributor to global warming. Compared to preindustrial levels, the atmospheric CH 4 concentration has more than doubled. The most dominant non-anthropogenic sources of atmospheric CH 4 have been found to be natural wetlands, but CH 4 fluxes from many wetlands all over the world are largely unexplored. We present the first results of eddy covariance CH 4 flux measurements above a subtropical grass marshland in northern Taiwan. Our results show that this wetland, dominated by Phragmites australis and Brachiaria mutica , is a significant source of CH 4 . During the six-week measuring period in August and September, daily mean emissions of 145 mg CH 4 m −2 were recorded. Clear diurnal variations of the CH 4 fluxes were observed, peaking at 0.187 μmol m −2 s −1 in the early afternoon. Minimal emissions generally occurred between 03:30 and 06:30 h, before sunrise. Significant correlations of the CH 4 flux with the latent heat flux, stomatal conductance, and relative humidity indicated that the diurnal patterns were induced by convective gas flow through the aerenchyma of the plants. Moreover, the magnitude of the CH 4 emissions predominantly responded to water level fluctuations; water levels below the soil surface were associated with significantly lower CH 4 emissions.