Data presented here were collected between June 2015 to April 2017 within the BEFmate project (Biodiversity - Ecosystem Functioning across marine and terrestrial ecosystems; https://www.icbm.de/verbundprojekte/befmate/ ) of the Universities of Oldenburg and Göttingen and the Nationalparkverwaltung Niedersächsisches Wattenmeer. Experimental islands and saltmarsh control plots were created in the back barrier tidal flat and in the saltmarsh zone of Spiekeroog island. Data were measured with local installed pressure logger within the experimental islands as well as in the saltmarsh control plots at different elevation levels. Logger were mounted within filter pipes to measure groundwater level. Pressure logger used here are Hobo U20L Water Level Loggers (S/N 10685287, 10685288, 10685289, 10685290, 10685291, 10685292) (Onset Computer Corporation, Bourne, MA/USA) as well as a DEFI-D Miniature Pressure Recorder (S/N OA5K008). The Pressure loggers were pre-calibrated by the manufacturer. Recorded data were internal logged till readout afield with the Hobo Underwater Shuttle (U-DTW-1) and following with the HOBOware Pro (V3.7.4) software or rather with the DEFI Series software (V1.02). Processing was done using MATLAB (R2012b). For depth calculations pressure data were manually corrected by atmospheric pressure. The position was derived from a portable DGPS-system. Data were visually checked and outliers removed. Date and Time is given in UTC.