Sand in the salt marsh: Contribution of high-energy conditions to salt-marsh accretion

The environmental dynamics at barrier-island salt marshes are reflected in lateral and vertical textural patterns of the marsh sediment. During normal conditions, fine-grained sediment is deposited, whereas during high-energy conditions also sand accretion can occur. This paper describes the occurrence and importance of sand deposits for the building of salt marshes. The study was carried out in the Wadden Sea on the islands of Schiermonnikoog (NL), Terschelling (NL) and the peninsula of Skallingen (DK). Firstly, we recorded the presence of sand in the sediment representing initial salt-marsh formation. The results indicate that part of the salt marsh developed under conditions that were dynamically enough for sand to be transported. The spatial distribution of these conditions depends on soil elevation and location on the marsh, modified by the presence of artificial sand dikes. Further we recorded the presence and thickness of sand layers within the salt-marsh sediment. Sand layers are found on twenty percent of the marsh area and are partly associated with the local sources of the sand, i.e. marsh creeks, the salt-marsh edge and washovers. In total, sand layers contribute less than ten percent to the volume of marsh deposits on Schiermonnikoog. We dated the layers using the thickness of the deposits and known marsh age. The ages of the layers indicate that for the decadal occurrence of storms capable of depositing sand in the salt marsh, the local hydrodynamics and availability of sand determine whether a site receives sand or not.

► High-energy conditions contribute a modest amount of sand to salt marshes. ► The resulting sand layers are spatially heterogeneous. ► Several sources may contribute simultaneously to sand deposition on a salt marsh. ► Changes in marsh topography through time affect the influence of high-energy events.