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 (CO
2) and nitrous oxide (N
2O) sources but methane (CH
4) sinks, restored (i.e. rewetted) peatlands rather incorporate CO
2, tend to be N
2O neutral and release CH
4. 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. CH 4 and N 2O fluxes were recorded bi-weekly, and net ecosystem exchange (NEE) measurements were carried out every 3–4 weeks. Annual sums of CH 4 and N 2O fluxes were estimated by linear interpolation while NEE was modelled.
Regarding GWP, the intensive grassland site emitted 564 ± 255 g CO 2–C equivalents m −2 yr −1 and 850 ± 238 g CO 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 g CO 2–C equivalents m −2 yr −1 and 94 ± 200 g CO 2–C equivalents m −2 yr −1, while it added up to 45 ± 117 g CO 2–C equivalents m −2 yr −1 and −101 ± 93 g CO 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 g CO 2–C equivalents m −2 yr −1, 14 ± 162 g CO 2–C equivalents m −2 yr −1 and 31 ± 75 g CO 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.