Effects of land use intensity on the full greenhouse gas balance in an Atlantic peat bog

Wetlands can either be net sinks or net sources of greenhouse gases (GHGs), depending on the mean annual water level and other factors like average annual temperature, vegetation development, and land use. Whereas drained and agriculturally used peatlands tend to be carbon dioxide (CO2) and nitrous oxide (N2O) sources but methane (CH4) sinks, restored (i.e. rewetted) peatlands rather incorporate CO2, tend to be N2O neutral and release CH4. One of the aims of peatland restoration is to decrease their global warming potential (GWP) by reducing GHG emissions. We estimated the greenhouse gas exchange of a peat bog restoration sequence over a period of 2 yr (1 July 2007-30 June 2009) in an Atlantic raised bog in northwest Germany. We set up three study sites representing different land use intensities: intensive grassland (deeply drained, mineral fertilizer, cattle manure and 4-5 cuts per year); extensive grassland (rewetted, no fertilizer or manure, up to 1 cutting per year); near-natural peat bog (almost no anthropogenic influence). Daily and annual greenhouse gas exchange was estimated based on closed-chamber measurements. CH4 and N2O fluxes were recorded bi-weekly, and net ecosystem exchange (NEE) measurements were carried out every 34 weeks. Annual sums of CH4 and N2O fluxes were estimated by linear interpolation while NEE was modelled. Regarding GWP, the intensive grassland site emitted 564 +/- 255 gCO(2)-C equivalents m(-2) yr(-1) and 850 +/- 238 gCO(2)-C equivalents m(-2) yr(-1) in the first (2007/2008) and the second (2008/2009) measuring year, respectively. The GWP of the extensive grassland amounted to -129 +/- 231 gCO(2)-C equivalents m(-2) yr(-1) and 94 +/- 200 gCO(2)-C equivalents m(-2) yr(-1), while it added up to 45 +/- 117 gCO(2)-C equivalents m(-2) yr(-1) and -101 +/- 93 gCO(2)-C equivalents m(-2) yr(-1) in 2007/08 and 2008/09 for the near-natural site. In contrast, in calendar year 2008 GWP aggregated to 441 +/- 201 gCO(2)-C equivalents m(-2) yr(-1), 14 +/- 162 gCO(2)-C equivalents m(-2) yr(-1) and 31 +/- 75 gCO(2)-C equivalents m(-2) yr(-1) for the intensive grassland, extensive grassland, and near-natural site, respectively. Despite inter-annual variability, rewetting contributes considerably to mitigating GHG emission from formerly drained peatlands. Extensively used grassland on moderately drained peat approaches the carbon sequestration potential of near-natural sites, although it may oscillate between being a small sink and being a small source depending on inter-annual climatic variability.