EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Wadden Sea salt marshes - sinks or sources of methane and nitrous oxide?

Miriam Fuss1, Peter Mueller2, Norman Rueggen1, and Lars Kutzbach1
Miriam Fuss et al.
  • 1Institute of Soil Science, Center for Earth System Research and Sustainability (CEN), University of Hamburg, Hamburg, Germany (
  • 2Institute of Plant Science and Microbiology, University of Hamburg, Hamburg, Germany

Salt marshes are vegetated coastal habitats recognised for their great potential to act as effective soil organic carbon sinks, driven by high rates of photosynthetic CO2 uptake and effective long-term storage of organic matter under reducing soil conditions. However, it is poorly understood when and under which conditions salt marshes can act as sinks or sources of the powerful non-CO2 greenhouse gases CH4 and N2O. A complex interplay of environmental factors characterises the biogeochemistry of these ecosystems. This interplay is in turn controlled by elevation in respect to mean high water level and thereby inundation frequency, forming three vegetation zones, which are on average flooded twice daily with every high tide (pioneer zone), twice per month with every spring tide (low marsh) and sporadically during storm surges (high marsh).

We measured land atmosphere fluxes of CH4, N2O and CO2 at a salt-marsh site in Nordfriesland, Germany, combining a closed chamber approach with in situ measurements of portable infrared gas analysers. From June 2018 to September 2021 we conducted biweekly (Apr-Sept) and monthly (Oct-Mar) campaigns covering the elevational gradient throughout all vegetation zones from pioneer zone to high marsh.

All greenhouse gas fluxes indicated strong dependence on elevation. Ecosystem respiration CO2 fluxes showed highest values in the high marsh. CH4 emissions occurred mainly in the most frequently flooded pioneer zone (up to +0.60 µmol*h-1*m-2), whereas low and high marsh acted as net CH4 sinks (down to -2.0 µmol*h-1*m-2). Contrastingly, N2O mainly showed positive fluxes (up to +1.1 µmol*h-1*m-2) in the high marsh, and the more frequently flooded zones acted as net N2O sinks (down to  0.21 µmol*h-1*m-2). Further analysis of environmental variables like soil temperature, flooding frequency, groundwater level fluctuations and plant community composition will follow to identify drivers of varying greenhouse gas fluxes.

Our findings show that salt marshes are not only effective in assimilating CO2. They also show the ability to take up the strong greenhouse gases CH4 and N2O, emphasizing their important role in mitigating global warming.

How to cite: Fuss, M., Mueller, P., Rueggen, N., and Kutzbach, L.: Wadden Sea salt marshes - sinks or sources of methane and nitrous oxide?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11770,, 2022.