Impact of summer drought on greenhouse gas fluxes and nitrogen availability in a restored bog ecosystem with differing plant communities

Natural peatlands are important carbon sinks and potential sources of methane (CH4). In contrast drained peatlands turn from a carbon sink to a carbon source and can emit nitrous oxide (N2O). Therefore restoration of peatlands implies climate change mitigation. In addition, climate change is expected to have a significant impact on the peatland carbon store and changes in precipitation amount and frequency are potentially damaging for peatlands. Thus, the carbon dioxide (CO2) and greenhouse gas balance (GHG) balance of three different plant communities at a restored bog site was investigated and the impact of summer drought was estimated by a manipulative field experiment using rainout shelters. As study site, the Himmelmoor in the metropolitan region of Hamburg was chosen which is one of the largest ombrotrophic bogs in Schleswig-Holstein and is still used for peat mining. At the peat mining area and in the restored boundary fluxes of CO2, CH4 and N2O were monitored with closed chambers, for a one year period, with and without drought treatment. This study thus presents the first annual estimates of the CO2 and the GHG balance for parts of the Himmelmoor. In addition, nitrogen availability and meteorological and hydrological measurements were collected as well. All three vegetation communities established in the restored study site, as well as the industrial peat mining area turned out to be sources of CO2 ranging between 0.60 ± 1.43 t CO2 ha-1 year-1 (Sphagnum dominated vegetation) and 3.09 ± 3.86 t CO2 ha-1 year-1 (vegetation dominated by heath plants) in the restored area. The industrial peat mining area had with 7.30 ± 0.67 t CO2 ha-1 year-1 the greatest CO2 emissions which were approximately 15 times higher, when the C content of the extracted peat was included in the calculation (114.02 ± 6.70 t CO2 ha-1 year-1). While accounting for the different global worming potentials (GWP) of the three greenhouse gases, the annual GHG emissions at the restored area ranged between 19 and 40 t CO2-eq ha-1 year-1 and were dominated by huge emissions of CH4 (15 to 37 t CO2-eq ha-1 year-1) while N2O emissions did not play a significant role. These CH4 emissions are the highest emissions so far reported for bog ecosystems in temperate Europe. The highest annual emission rates were found at the site that was dominated by dense stands of purple moor grass (Molinia caerulea). As the restored area was subject to large fluctuations in water table it can be expected that