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 decade^1–4. 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 levels^5–7. 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 sources^8,9. 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.