Data presented here were collected between January 2019 to October 2019 within the research unit DynaCom (Spatial community ecology in highly dynamic landscapes: From island biogeography to metaecosystems, https://uol.de/dynacom/) of the Universities of Oldenburg, Göttingen, and Münster, the iDiv Leipzig and the Nationalpark Niedersächsisches Wattenmeer. Experimental islands and saltmarsh enclosed plots were created in the back barrier tidal flat and in the saltmarsh zone of the island of Spiekeroog.Sediment samples for the determination of pore-water salinity in soil were taken bi-/monthly in surface sediments (0-3 cm depth). Samples were measured in the laboratory within two month after sampling according to DIN ISO 11265:1997-06.Post-processing of measured data was done using MATLAB (R2018a). Quality control was performed by quality check algorithms:QC = 4 (bad data) - do not use this data-point.QC = 3 (questionable data) - likely bad data-point.QC = 2 (probably good data) - likely good data-point.QC = 1 (good data) - certainly good data-point.QC = 0 (unknown data) - no data point available.Further data sets will be added regularly.

Pore-water salinity measurements in surface sediments