Data presented here were collected between October 2014 to November 2018 within the BEFmate project (Biodiversity - Ecosystem Functioning across marine and terrestrial ecosystems, https://uol.de/icbm/verbundprojekte/abgeschlossene-projekte/befmate/) of the Universities of Oldenburg and Göttingen 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 pH, water content and loss on ignition were taken bi-/monthly in surface sediments (0-3 cm depth). Samples were measured in the laboratory within two month after sampling.

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.