Tracing freshwater-saltwater exchange and biochemical cycling using continuous radon and chemical measurements on a barrier island (Spiekeroog, Northern Germany)

Clarissa Glaser1, Benjamin Gilfedder1
1 Department of hydrology, University of Bayreuth

P 3.1 in Water and the environment: From biosphere to geosphere

The Wadden Sea of Northern Germany is one of the largest regions shaped by tidal processes in the world. The large tidal range has a significant influence on hydrological processes such as water fluxes and nutrient cycles. The aim of this study was to show that 222-radon can be used as natural tracer for the investigation of the exchange of freshwater and saltwater in a tidal flat. Furthermore tidal cycling of nutrients such as Dissolved Organic Carbon (DOC), Fe, P and NO3 was observed. The interaction of freshwater and saltwater was studied on the barrier island Spiekeroog which is located in the North Sea on the coast of Northern Germany. Continuous radon measurements has mostly be done in the laboratory or over only short periods. Here we measure radon directly in situ in the water with a mobile radon-in-air monitor (RAD7) coupled with a special hydrophobic membrane with a high permeability with regard to radon diffusion. The aims were to find a correlation between the tidal range and the amount of radon due to the influence of radon enriched fresh groundwater during low tide. The exchange of nutrients depends on whether the nutrient arose from the freshwater lens, sea water or chemical interactions in the sediments during tidal cycling. High concentrations of nutrients during low tide are a hint for the influence of the freshwater for the concentrations.



Keywords: Spiekeroog Island, Tidal flats, Freshwater-saltwater interaction, Radon, In situ Determination, Nutrient cycles
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