Coastal research in the foreland of the Kaiser-Wilhelm-Koog

28 August 2024, by RTG2530

Photo: UHH/RTG2530/Hauten

Just a few metres above sea level and surrounded by mighty dykes, the Kaiser-Wilhelm-Koog lies in Dithmarschen, Schleswig-Holstein. This coastal area on the North Sea near the mouth of the Elbe River is renowned for its marshlands, which are formed by sea and river water deposits. Over centuries, these lands have been extensively diked and are now mainly used for agriculture. Researchers from the Research Training Group 2530 are investigating the dynamics of this ecosystem in the area in front of the dykes, known as the foreland.

In the foreland of the Kaiser-Wilhelm-Koog, salt marshes with net-like drainage channels still develop today due to tidal flooding. These salt marshes create a diverse ecosystem that provides habitats for numerous animal and plant species. Researchers from the Research Training Group 2530 have set up four research stations here, where sensors continuously measure environmental parameters such as soil moisture, soil temperature, salinity, and the so-called redox potential. A high redox potential indicates that more oxidative processes are taking place in the environment, such as the decomposition of organic material with the consequent release of carbon dioxide. A low redox potential indicates that more reductive processes are taking place in the environment, such as the decomposition of organic material in the absence of oxygen, i.e. anaerobic decomposition, and the possible formation of methane.

The stations have been specifically placed in different vegetation zones to collect data that is important for analysing the environmental conditions and their impact on the ecosystem. The stations near the water are flooded twice a day by the tides, while those in the upper marsh are flooded only during storm surges and are partly agricultural due to sheep grazing. 

PhD students Elena Hauten, Fay Lexmond, and Sina Remmers are also conducting research in this area. They are investigating where the carbon in this ecosystem comes from and how it is distributed in the salt marshes of the foreland. Carbon in the form of CO₂ is absorbed from the air by land plants and algae, converted into biomass, and passed on to the food chain. Creatures such as ground beetles absorb carbon through their food – some of which is bound by algae in the Wadden Sea – and transport and distribute it on land, releasing CO₂ again, among other things. Sina Remmers is investigating the extent to which carbon is distributed in this way, considering the environments to which the animals are best adapted and the food they prefer.

Elena Hauten's research focuses on the distribution of carbon in coastal waters and tidal creeks by fish species such as smelt, flounder, and ruffe. Using a method called 'stable isotope analysis,' she can determine where the carbon absorbed by the fish comes from and identify their preferred habitats. To understand how the fish influence the carbon cycle throughout the year, she has caught and analysed fish at different times of the year.

While Elena Hauten and Sina Remmers' research focuses primarily on the lateral, i.e., horizontal, transport and distribution of carbon, Fay Lexmond is investigating the exchange fluxes of certain greenhouse gases between soil, vegetation, and the atmosphere at various locations in the salt marshes of the Kaiser-Wilhelm-Koog. To do this, she uses a transparent plastic hood equipped with sensors to measure the exchange fluxes of carbon dioxide (CO₂), methane (CH₄), or nitrous oxide (N₂O) in the air in real-time. These gases are mainly produced by microorganisms that decompose organic material, such as plant residues. Certain environmental conditions, such as the frequency of site flooding or the development of vegetation, affect the greenhouse gas fluxes.