G5: Connecting the N-cycles of a coastal peatland and the Baltic Sea

supervised by Voss, Jurasinski, Rehder


The PhD work should entangle the processes converting nitrogen compounds in the water column, sediments, and peatland to gain a good understanding of the nitrogen cycling on both sides of the beachline. Likewise important is the study of transport processes across the land-sea interface in collaboration with other PhD projects to evaluate the role of submarine ground water discharge and recycled pore waters on the sea side. The nitrogen cycle in the different environmental settings should be clearly understood and quantified to evaluate the eutrophication potential across the beachline.

State of the art

Nitrogen is an essential nutrient for life on land and in the ocean. The use of reactive nitrogen as fertilizer has now reached a quantity much higher than the natural nitrogen fixation and a significant percentage from land reaches the oceans. The Baltic Sea is one example of a highly eutrophied system suffering from anthropogenic nutrient sources, mostly received through river input and atmospheric deposition. What has not yet been studied is the potential connectivity between low lying peatland – a typical landscape in northern Germany and other Baltic Sea states – and the coastal sea. Since fertilizers have been used extensively on land a large potential reservoir in the rewetted peatland “Hütelmoor” may add to the eutrophication. Microbial processes however will likely transform and even remove some of the nitrogen compounds on land and this could reduce the risk of eutrophication. The coastal sea is characterized by highly dynamic currents, coarse and sandy bottom off the “Hütelmoor”and likely able to sequester organic material efficiently. There are reports on the role of ripples for nitrification and denitrification and oxygen consumption from the North Sea, but a non-tidal system may respond differently. Furthermore, microbial nitrogen transformation can produce nitrous oxide, a green- house gas with high warming potential. The formation of nitrous oxide depends on environmental conditions and on concentrations of oxygen and organic matter. Processes on both sides of the land-sea interface are poorly understood and the connection and transport have not yet been studied.

Work program

Quantifying the nitrogen removal and turnover processes on both land and sea side would be a first important step to constrain concentration changes over an annual cycle. Using labelled substrates nitrification and denitrification rates shall be measured. Regulation of the processes and transport should be studied together with other PhD projects. A major focus should be on the generation of nitrous oxide, an efficient green house gas.