Ines Bartl

Research expertise

• Characterization of nitrate, nitrite and DON isotopes in coastal zones of the Baltic Sea
• Determination of nitrification rates in the water column of Baltic coastal zones by ¹⁵N incubations

Title of the dissertation: Nitrogen transformation processes in coastal zones of the Baltic Sea

This PhD-thesis is integrated in the project COCOA, which aims at understanding and quantifying major transformation processes of carbon and nutrients in coastal zones of the Baltic Sea. It will support COCOA by investigating nitrogen transformation processes in river dominated estuaries using stable nitrogen isotopes.

Baltic coastal zones receive high loads of nitrogen from rivers. Especially the southern Baltic Sea suffers from eutrophication. Also the internal cycle of nutrient uptake, particle formation, sedimentation and remineralisation in the bottom water layer has a positive feedback on eutrophication. Nitrification plays a crucial role in the marine N-cycle and in the process of eutrophication in coastal zone. It connects the regeneration of organic matter to ammonium with nitrogen removal processes (anammox, denitrification) and nitrogen retention processes (DNRA, assimilation). Strong correlations between measured nitrification rates and ammonium concentrations in bottom water layers indicate that not only riverine input but also enhanced nitrification can be a source of nitrate to the coastal zone (Hsiao et al., 2014). The central question of my dissertation deals with the role of nitrification in coastal zones. Study sites are the Gulf of Gdansk (Vistula estuary) and the Öre estuary in northern Sweden. We aim to quantify nitrification and ammonium assimilation through 15N-incubations and try to resolve nitrogen processing with the help of isotope abundances of nitrate, nitrite and DON. Furthermore, influencing factors on nitrification and the ongoing processing of nitrate (e.g. denitrification, Dana Hellemann, COCOA-PhD, University Helsinki) will be investigated. In collaboration with Elisabeth Münster Happel from the BLUEPRINT project the relationship between the distribution of nitrifying bacteria and the distribution of nitrification rates will be studied.