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SECOS - TP 6 (2.4): SECOS: Küstenmeerforschung: Die Leistung der Sedimente in deutschen Küstenmeeren; WP 2.4 Gas exchange at the sediment-water interface

The release of gases from the sediments is strongly prone to changes in relation to changes in external forcings (i.e. eutrophication and climate change), and is a sedimentary function which has not been put in the context of sediment classification and habitat in a systematic way so far. Nitrous oxide fluxes from marine sediments have been shown to depend strongly on the availability of other N-intermediates. N2O-production can partly be seen as a side-reaction during denitrification, with the factors controlling the production of N2O to total N-loss not well clarified. The flux of methane is strongly dependent on both sediment type and redox state of the overlying water column, the latter highly variable for Baltic Sea sediments. The net N-loss of sediments is independent of the individual N2-generating process, and provides an integrated measure of nitrogen removal. Using benthic chambers, fluxes of N2, N2O and CH4 will be determined for key sediment types based on modern analytical strategies. For some gases, stable isotopic signatures will be determined. Together with the detailed assessment of the hydrographic forcings (2.1) diagenetic reactions (2.3) and the key microbial drivers of the transformation processes (2.5), this aims for a mechanistic understanding of the loss of the CH4 and N2O from the sediments as a first step towards implementation in the model framework. Perturbation experiments will be additionally used to assess the feedback of gas fluxes on external parameters. All measurement will be interpreted in the GIS-based framework of the entire data set available for the individual key sites.