The Janssand is a sand flat located in the back-barrier area of Spiekeroog Island, and is characterized by mesotidal conditions. Janssand is covered by 1-2 m of water during high tide and becomes exposed for approx. 4-6 h during low tide. Due to this long exposure as well as the good accessibility by boat, Janssand became a model research area within the DFG research unit BioGeoChemistry of tidal flats. Permanent in-situ samplers were installed allowing pore water sampling down to 5 m depth. Janssand is still a study area e.g., for advanced lab classes, and serves as campaign based research site, even though the DFG research group has officially ended in 2009.