Climate and site management as driving factors for the atmospheric greenhouse gas exchange of a restored wetland.

The full atmospheric greenhouse gas (GHG) budget of a restored wetland in Western Denmark could be established for the years 2009-2011 from eddy covariance measurements of carbon dioxide (CO₂) and methane (CH₄) fluxes. The water table in the wetland, being restored in 2002, was unregulated, and the vegetation height was limited through occasional grazing by cattle and grass cutting. The annual net CO₂ uptake varied between 195 and 983 gm^-2 and the annual net CH₄ release varied between 11 and 17 gm^-2. In all three years the wetland was a carbon sink and removed between 42 and 259 gCm^-2 from the atmosphere. However, in terms of the annual GHG budget (assuming that 1 g CH₄ is equivalent to 25 g CO₂ with respect to the greenhouse effect) the wetland was a sink in 2009, a source in 2010 and neutral in 2011. Complementary observations of meteorological factors and management activities were used to explain the large inter-annual variations in the full atmospheric GHG budget of the wetland. It is shown that the largest impacts on the annual GHG fluxes, eventually defining their sign, came from site management through changes in grazing duration and animal stocking density and from extreme weather patterns through an unusually long period of snow cover in the second year of observations. Since integrated CO₂ and CH₄ flux data from restored wetlands are still very rare, it is concluded that more long-term flux measurements are needed to predict the role of this land use type in the atmospheric GHG budget more accurately. [ABSTRACT FROM AUTHOR]