Fig 1.
Map over the Gullmar Fjord area with sampling sites and mapped seagrass areas.
The map has been generated in ArcGIS pro, version 2.5.0 (ESRI, 2020). The base map was provided by the EEA geospatial data catalogue and available from: https://sdi.eea.europa.eu/catalogue/srv/eng/catalog.search#/metadata/db4cfdd3-0687-4460-a2c7-fd10ca29c214.
Fig 2.
Concentration profiles of 210Pb for the sediment cores.
The blue fields represent the supported 210Pb levels and the green fields show the sections for which sedimentation rates could be calculated.
Table 1.
Summary of sediment and mass accumulation rates (SAR and MAR, respectively) and Corg content.
For Kristineberg 1 and 2 and Getevik, SAR and MAR could not be established for the entire excess 210Pb depth section (see Fig 2) due to sediment mixing and the values were therefore extrapolated towards the sediment surface. Bold values show the average sedimentation rates and were used for calculating the CARs in the cores. All values are presented as mean ± SD and SAR is corrected for core compression.
Fig 3.
Carbon accumulation rate (CAR) for the different sites.
Literature CAR values for Z. marina in other regions [22–24,42–44] are shown as dashed lines and shaded box (the width of the box covers the range of values for the referenced studies). The estimated mean value for Posidonia oceanica, which is considered the most efficient seagrass species for carbon sediment sequestration, is included as a reference for the seagrasses’ potential as carbon sinks.
Fig 4.
Corg stocks (kg C m-2) shown as (A) cumulative accumulation of the sediment depths, (B) standardized stocks down to 50 cm sediment depth and (C) the total accumulation for the entire sediment core depths.
Fig 5.
The proportion of seagrass, macroalgae and terrestrial organic matter contributing to the sedimentary Corg pool for the sediment depth of 0–50 cm, except for Västra Korsvik, for which the seagrass sediment depth was 0–11 cm.
Table 2.
Seagrass sediment depth, sediment compression, and mean (± SD) of Corg content and stable isotopic signatures for 0–50 cm depth layer.