Vegetated coastal ecosystems have been increasingly recognized for their capacity to sequester organic carbon in their soils and sediments under the term blue carbon. The vegetation of these habitats shows specific adaptations to severe abiotic soil conditions, particularly, waterlogging and salinity, and supports therefore ecosystem functioning and services. Wadden Sea salt marshes in Schleswig-Holstein (Germany) have been utilized for high density sheep grazing over centuries. At the beginning of the 1990s, in many parts of salt marshes livestock densities were reduced and the maintenance of the anthropogenic drainage system was ceased. In 2012, 17 years after the change of land utilization, the contents, densities, and accumulation rates of surface soil carbon were investigated at 50 sampling positions with different elevations along eight transects in Wadden Sea mainland salt marshes at Hamburger Hallig, Schleswig-Holstein, Germany, under different livestock grazing regimes (ungrazed, moderately grazed, intensively grazed). Surface soil was collected in 150 permanent plots (2 m * 2 m) at 50 sampling positions, covering a salt marsh area of 1050 ha. The carbon contents, pH, and bulk density were determined from dried soil. The elevations of the 150 permanent plots were measured and annual vertical accretion rates were calculated from 17 years sedimentation monitoring. This study was supported by the BASSIA project (Biodiversity, management, and ecosystem functions of salt marshes in the Wadden Sea National Park of Schleswig-Holstein), funded by the Bauer-Hollmann Foundation and Universität Hamburg.

The vegetation data, originally included in the raw data published in the Global Index of Vegetation Databases (http://www.givd.info/ID/EU-DE-033) by Stock (2012), has been transformed into percentage values through the normalization of Londo scale values (0.1, 0.2, 0.4, 1, 2, ..., 10) using plot cover (representing the percentage of plot area covered by vegetation); Species names nomenclature according to Wisskirchen et al. (1998), Standard List of Ferns and Flowering Plants of Germany, Eugen Ulmer Gmbh.