PRIMARY PRODUCTION CONTROL OF METHANE EMISSION FROM WETLANDS

WETLANDS, both natural and agricultural, contribute an estimated 40 to 50% of the total methane emitted to the atmosphere each year. Recent efforts in atmospheric modelling1 and attempts to constrain CH4 source strengths2 have indicated the need to delineate the processes respons ible for the large variations in emission rates found within and acros s wetland types. Numerous biogeochemical factors are known to affect t he activity of methanogenic bacteria3,4 and although there has been so me success in relating water level5-7 and temperature8,9 to CH4 emissi ons within particular systems, these variables are insufficient for pr edicting emissions across a variety of wetlands2,10. From simultaneous measurements of CO2 and CH4 exchange in wetlands extending from subar ctic peatlands to subtropical marshes, we report here a positive corre lation between CH4 emission and net ecosystem production and suggest t hat net ecosystem production is a master variable, integrating many fa ctors which control CH4 emission in vegetated wetlands. We find that a bout 3 per cent of the daily net ecosystem production is emitted back to the atmosphere as CH4. With projected stimulation of primary produc tion and soil microbial activity in wetlands associated with elevated atmospheric CO2 concentrations11, we envisage the potential for increa sing CH4 emissions from inundated wetlands, further enhancing the gree nhouse effect.