Abstract
Abstract. In Central Europe, most bogs have a history of drainage and many of them are currently being restored. Success of restoration as well as greenhouse gas exchange of these bogs is influenced by environmental stress factors as drought and atmospheric nitrogen deposition. We determined the methane and nitrous oxide exchange of sites in the strongly decomposed center and less decomposed edge of the Pietzmoor bog in NW Germany in 2004. Also, we examined the methane and nitrous oxide exchange of mesocosms from the center and edge before, during, and following a drainage experiment as well as carbon dioxide release from disturbed unfertilized and nitrogen fertilized surface peat. In the field, methane fluxes ranged from 0 to 3.8 mg m−2 h−1 and were highest from hollows. Field nitrous oxide fluxes ranged from 0 to 574 μg m−2 h−1 and were elevated at the edge. A large Eriophorum vaginatum tussock showed decreasing nitrous oxide release as the season progressed. Drainage of mesocosms decreased methane release to 0, even during rewetting. There was a tendency for a decrease of nitrous oxide release during drainage and for an increase in nitrous oxide release during rewetting. Nitrogen fertilization did not increase decomposition of surface peat. Our examinations suggest a competition between vascular vegetation and denitrifiers for excess nitrogen. We also provide evidence that the von Post humification index can be used to explain nitrous oxide release from bogs, if the role of vascular vegetation is also considered. An assessment of the greenhouse gas release from nitrogen saturated restoring bogs needs to take into account elevated release from fresh Sphagnum peat as well as from sedges growing on decomposed peat. Given the high atmospheric nitrogen deposition, restoration will not be able to achieve an oligotrophic ecosystem in the short term.
Highlights
Due to the high amount of carbon stored in the peatlands of the world and the sensitivity of biogeochemical processes in these ecosystems to climate change, research on matter cycling in peatlands has received considerable interest
Especially sedges are known for high CH4 release (Joabsson et al, 1999; Strack et al 2006) and Eriophorum vaginatum tussocks are CH4 emission hotspots as they provide substrate for methanogenesis and provide a pathway for CH4 release (Tuittila et al, 2000; Marinier et al, 2004)
Water table did not control CH4 release and the highest CH4 release (7.8 mg m−2 h−1) took place on 08/04/04 with the water table at 24.5 cm below the surface (Fig. 7). This is in contrast to the well established relationship between CH4 release and water table (Moore and Knowles, 1989, Moore and Dalva, 1993) and the idea of water table acting as an “on-off-switch” for CH4 emissions
Summary
Due to the high amount of carbon stored in the peatlands of the world and the sensitivity of biogeochemical processes in these ecosystems to climate change, research on matter cycling in peatlands has received considerable interest. Despite large areas of (often degraded) peat bodies in temperate regions, research on peat bogs is mostly from natural boreal sites and focuses on the role of the water table (Roulet et al, 1992; Nykanen et al, 1998; Blodau, 2002). In temperate Germany, widespread drainage of bogs resulted in a serious decline of peatland area. In NW Germany (Lower Saxony) merely 5% of formerly 2348 km bog area remain undisturbed or in a close to natural state (Schmatzler, 1990). The most important environmental constraints on the successful restoration of these bogs are i) a low water table, a result of previous drainage and climate change, ii) atmospheric N deposition, and iii) strong decomposition of degraded peat
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