Methane flux from northern peatlands

Abstract

The concentration of methane (CH4) in the global troposphere is increasing. Ambient air measurements document an approximate rate of increase of 1–2% yr−1 over the past decade1–4. Measurements of CH4 in air bubbles trapped in polar ice indicate that tropospheric concentrations of CH4 several hundred years ago may have been ∼45% of present levels5–7. To understand and assess possible causes of the atmospheric CH4 increase requires improved quantitative knowledge of global sources and sinks of CH4. Previous attempts to estimate sources of atmospheric CH4, based on very few measurements, have suggested that natural and agricultural wetlands are major sources8,9. The major wetland regions of the world are in boreal, low Arctic and tropical ecosystems10. It is these regions, particularly in peatland habitats where major accumulations of organic materials occur under anaerobic conditions, that should be significant sources of global tropospheric CH4. The most extensive peatlands in the world occur in the boreal taiga zone between ∼45° and 65° N latitude. More than 95% of world peat resources occur in the Soviet Union, Canada, the United States, Sweden, Norway, Finland and the United Kingdom10. We report here the first survey of CH4 flux from northern peatlands of the United States. Emission rates ranged from 0.003 to 1.94 g CH4 m−2 day−1, with half of these values between 0.1 and 0.4 g CH4 m−2 day−1. The frequency distribution is log normal (Fig. 1) and the mean emission rate is 0.337 g CH4 m−2 day−1. Such fluxes are higher than most values reported for other ecosystems, suggesting that northern peatlands may be an important source of global tropospheric CH4.