Untersuchung der Fraktionierung von Stickstoffisotopen in marinen Sedimenten, abhängig von unterschiedlichen Sedimentcharakteristika

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Reactive nitrogen is entrained to the ocean at large scales, leading to eutrophication of coastal oceans. As this enhances primary production, it also affects global carbon cycling. In the light of these increased inputs and an ongoing revision of the marine nitrogen budget, the outlined research project shall provide tools for a better estimation of nitrogen sinks in the ocean. Specifically, we aim to measure stable nitrogen isotope fractionation during sedimentary denitrification and anammox (anaerobic ammonia oxidation), which we expect to be more variable than previously assumed. The focus is set on the influence of bioirrigation and the influence of varying sediment redox conditions on the isotope fractionation of both nitrogen removal processes. During sediment incubations, the porewater shall be analysed for concentrations and isotopic composition of different nitrogen species that are sequestered or produced by the respective micro-organisms. Because of the high natural variability regarding redox state, anthropogenic nitrogen or carbon loads and oxygen saturation in bottom waters, the Baltic/North Sea transition provides an excellent study area for the variances in isotope effects. This can later be used as a basis for modelling approaches to improve the estimation of nitrogen removal by shelf sediments.