Five years of transition – atmospheric C-exchange dynamics of a coastal fen after rewetting

Gerald Jurasinski1, Franziska Koebsch2, Marian Koch1, Stefan Koch1, Juliane Hahn1, Stephan Glatzel3
1 Landscape Ecology, University of Rostock
2 GFZ German Research Centre for Geosciences, Potsdam, Germany
3 University of Vienna, Geoecology, Vienna, Austria

O 12.1 in Restoration and rehabilitation of ecosystems

17.07.2014, 11:00-11:20, H19

Question: In which direction and how fast changes the atmospheric C-exchange of a coastal fen after hydrological conditions switched from moderately rewetted to flooded? The rewetting of drained peatlands is widely regarded as an adequate measure for the mitigation of greenhouse emissions. Therefore, especially in NE Germany, many peatlands are being rewetted. Our knowledge about greenhouse gas exchange associated with rewetting is mainly based on short-term experiments or space-for-time substitutions. These approaches do not consider the transient character of ecosystem acclimatization to flooding by rewetting. Here, we present more than 5 years of data on GHG (CO2 and CH4) exchange in a coastal fen after rewetting by flooding.

Methods: On the “Rodewiese” a coastal fen within the NSG “Hütelmoor und Heiligensee” in the Northeast of Rostock, NE Germany, we have established a long term research observatory addressing the atmospheric C-exchange. The site is part of to the TERENO Northeast network. Since summer 2009 we determine CH4 fluxes with closed chambers distributed widely across the study site and CO2-exchange with eddy covariance. Further, we record data on vegetation, hydrology, biogeochemistry, and microbiology.

Results: Gross photosynthesis as well as ecosystem respiration of the growing season both strongly decreased after  flooding. However, because both decreased with the same magnitude, net carbon dioxide exchange (NEE) was almost constant at around 12 t*ha-1*a-1. The latter holds for the following years as well. Furthermore, flooding increased methane release rates to extremely high levels of up to 4.3 t*ha-1*a-1 for sedge stands and 2.7 t*ha-1*a-1 on average, which amounts to 67.5 t*ha-1*a-1 in CO2 equivalents. Thereafter, the averaged annual methane emissions decreased asymptotically and where at an average of 0.4 t*ha-1*a-1 (10 t*ha-1*a-1 in CO2 equivalents) in 2013.  Factoring in the NEE of the growing season suggests that the system may be slightly above neutral with respect to the greenhouse warming potential of its atmospheric C-exchange 5 years after flooding. Analyses of peat and water biochemistry showed that the system had been destabilized in the first year following flooding and repeated vegetation analysis combined with remote sensing reveal strong and directed change in vegetation patterns.

Conclusions: Our data suggest that, when focusing on greenhouse gas mitigation, flooding should be avoided if possible. However, the successional development in vegetation, peat and water chemistry and atmospheric C-exchange we see in the 5 years after flooding hint at an adaptation of ecosystem functioning to the flooded conditions associated with reaching desirable annual rates of C-exchange and vegetation development during an acceptable time frame.

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Letzte Änderung 19.06.2014