The full greenhouse gas balance of an abandoned peat meadow

Abstract. Globally, peat lands are considered to be a sink of CO₂, but a source when drained. Additionally, wet peat lands are thought to emit considerable amounts of CH₄ and N₂O. Hitherto, reliable and integrated estimates of emissions and emission factors for this type of land cover have been lacking and the effects of wetland restoration on methane emissions have been poorly quantified. In this paper we estimate the full greenhouse gas (GHG) balance of a restored natural peat land by determining the fluxes of CO₂, CH₄ and N₂O through atmosphere and water, while accounting for the different Global Warming Potentials (GWP's).

The site is an abandoned agricultural peat meadow, which has been converted into a wetland nature reserve ten years ago, after which the water level was raised. GHG fluxes were measured continuously with an eddy covariance system (CO₂) and flux chamber measurements (CH₄ and N₂O). Meteorological and hydrological measurements were collected as well. With growing seasons of respectively 192, 168 and 129 days, the annual net ecosystem exchange of CO₂ (NEE) was −446+±83 g C m⁻² yr⁻¹ for 2004, −311±58 g C m⁻² yr⁻¹ for 2005 and −232±57 g m⁻² yr⁻¹ for 2006. Ecosystem respiration (R_eco) was estimated as 869±668 g C m⁻² yr⁻¹ for 2004, 866±666 g C m⁻² yr⁻¹ for 2005 and 924±711 g C m⁻² yr⁻¹ for 2006. CH₄ emissions from the saturated land and water surfaces were high compared to the relatively dry land. Annual weighted CH₄ emissions were 31.27±20.40 g C m⁻² yr⁻¹ for 2005 and 32.27±21.08 g C m⁻² yr⁻¹ for 2006. N₂O fluxes were too low to be of significance. The water balance of the area was dominated by precipitation and evapotranspiration and therefore fluxes of carbon and CH₄ through seepage, infiltration and drainage were relatively small (17.25 g C m⁻² yr⁻¹). The carbon-balance consisted for the largest part of CO₂ uptake, CO₂ respiration and CH₄ emission from water saturated land and water. CO₂ emission has decreased significantly as result of the raised water table, while CH₄ fluxes have increased. In GWP's the area was a small net GHG sink given as CO₂-equiv. of −86 g m⁻² yr⁻¹ (over a 100-year period).