Primary production control of methane emission from wetlands

Abstract

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 responsible for the large variations in emission rates found within and across wetland types. Numerous biogeochemical factors are known to affect the activity of methanogenic bacteria3,4 and although there has been some success in relating water level5–7 and temperature8,9 to CH4 emissions within particular systems, these variables are insufficient for predicting emissions across a variety of wetlands2,10. From simultaneous measurements of CO2 and CH4 exchange in wetlands extending from subarctic peatlands to subtropical marshes, we report here a positive correlation between CH4 emission and net ecosystem production and suggest that net ecosystem production is a master variable, integrating many factors which control CH4 emission in vegetated wetlands. We find that about 3 per cent of the daily net ecosystem production is emitted back to the atmosphere as CH4. With projected stimulation of primary production and soil microbial activity in wetlands associated with elevated atmospheric CO2 concentrations11, we envisage the potential for increasing CH4 emissions from inundated wetlands, further enhancing the greenhouse effect.