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

The atmospheric greenhouse gas (GHG) budget of a restored wetland in western Denmark was established for the years 2009-2011 from eddy covariance measurements of carbon dioxide (CO2) and methane (CH4) fluxes. The water table in the wetland, which was restored in 2002, was un- regulated, and the vegetation height was limited through oc- casional grazing by cattle and grass cutting. The annual net CO2 uptake varied between 195 and 983 g m 2 and the an- nual net CH4 release varied between 11 and 17 g m 2 . In all three years the wetland was a carbon sink and removed be- tween 42 and 259 g C m 2 from the atmosphere. However, in terms of the full annual GHG budget (assuming that 1 g CH4 is equivalent to 25 g CO2 with respect to the greenhouse ef- fect over a time horizon of 100 years) the wetland was a sink in 2009, a source in 2010 and neutral in 2011. Complemen- tary observations of meteorological factors and management activities were used to explain the large inter-annual varia- tions in the full atmospheric GHG budget of the wetland. The largest impact on the annual GHG fluxes, eventually defining their sign, came from site management through changes in grazing duration and animal stocking density. These changes accounted for half of the observed variability in the CO2 fluxes and about two thirds of the variability in CH 4 fluxes. An unusually long period of snow cover in 2010 had the sec- ond largest effect on the annual CO2 flux, whose interannual variability was larger than that of the CH4 flux. Since inte- grated CO2 and CH4 flux data from restored wetlands are still very rare, it is concluded that more long-term flux measure- ments are needed to quantify the effects of ecosystem dis- turbance, in terms of management activities and exceptional weather patterns, on the atmospheric GHG budget more ac- curately.