Towards developing IPCC methane ‘emission factors’ for peatlands (organic soils)

(1) Huge reductions of carbon dioxide (CO2) and nitrous oxide (N2O) effluxes can be attained by rewetting drained peatlands, but this will increase methane (CH4) effluxes.(2) The scientific data base for methane effluxes from peatlands is much larger than that for CO2 or N2O. Once anoxic conditions are provided, the availability of fresh plant material is the major factor in methane production. Old (recalcitrant) peat plays only a subordinate role in gas efflux.(3) The annual mean water level is a surprisingly good indicator for methane effluxes, but at high water levels the cover of aerenchymous shunts (gas conductive plant tissue) becomes a better proxy. Ideally, both water level and cover of aerenchymous shunts should be assessed to arrive at robust estimates of methane effluxes.(4) The available data provide sufficient guidance for arriving at moderately accurate (Tier 1) estimates consistent with IPCC methodologies. For more accurate estimation (higher tier approaches), vegetation provides a promising basis for development of more detailed efflux factors. Vegetation is a good proxy for mean water levels and can provide - with extra attention to aerenchymous shunts - a robust proxy for accurate and spatially explicit estimates of methane effluxes over large areas.