@phdthesis{Gutekunst2024, author = {Gutekunst, Cordula}, title = {Microorganisms as drivers of methane emissions in rewetted coastal peatlands}, institution = {Institut f{\"u}r Botanik und Landschafts{\"o}kologie \& Botanischer Garten}, pages = {217}, year = {2024}, abstract = {Peatland rewetting is a recognized nature-based solution to reduce CO2 emissions and has the potential to create carbon sinks. The necessity to reduce greenhouse gases (GHG) from both natural and from anthropogenic sources is one of the most urgent challenges of our time. Rewetting artificially drained peatlands with freshwater can induce initially high methane (CH4) emissions. Using sulfate-containing brackish water to rewet coastal peatlands may prevent these CH4 peaks. This is due to substrate usage by thermodynamically more favorable microbial metabolic processes, such as sulfate reduction, instead of methanogenesis. Together with colleagues, I investigated two peatlands with different histories of rewetting and management, located on the Baltic Sea coast in north-east Germany: A coastal fen that was rewetted with freshwater and another rewetted with brackish water. In the freshwater rewetted fen, which experienced a drought shortly before a storm surge inundated the area with brackish water, a reduction of its previously high CH4 emissions was observed. While abundances of methanogenic archaea decreased during the drought, we did not see a further reduction after the brackish water inflow. Although a large part of the CH4 emission reduction is certainly a legacy effect of the drought, the increasing abundances of sulfate-reducing bacteria (SRB) following the inflow may have caused competition with methanogens for substrate. In addition or alternatively, SRB might be involved in the anaerobic oxidation of CH4. However, we did not observe increases in CH4 oxidation or in abundances of anaerobic methanotrophs in the peat soil. This suggests that methanotrophy may have taken place in the water column above the investigated peat soil. In contrast, the brackish water rewetted fen showed relatively low CH4 emissions immediately after rewetting compared to freshwater rewetted fens. Relative to the fen's drained state, abundances of SRB and methanogens increased after rewetting, but substrate competition and CH4 oxidation most likely limited excess CH4 emissions. However, the high CO2 emissions did not decrease as expected despite rewetting, while ecosystem respiration and thus peat decomposition was significantly reduced. We observed a severe die-back of both grassland plants and near-ditch fen vegetation following the intense inundation with brackish water. The reason for the persistent CO2 emissions after rewetting could be ecosystem respiration, which was fueled by large amounts of available labile substrate, irrespectively of peat decay. Additionally, high CO2 emissions could not be prevented due to the lack of CO2 uptake by photosynthesis. This thesis contributes to the discussion on coastal peatland rewetting and provides new ideas about the interplay between a fen's microbiology and biogeochemistry among different spatial compartments. When aiming for GHG emission reduction after rewetting this thesis highlights that not only the water type might be important to consider, but also the frequency of brackish water input as well as the flooding intensity. In order to define and evaluate rewetting approaches for future projects, comparing rewetted peatlands according to their GHG emission development is necessary. Further, long-term monitoring and multidisciplinary research are needed to provide insight on the influence of brackish water on coastal fens beyond the first year after rewetting.}, subject = {Methan , Moor}, language = {en} }