4 Schokland – bottom or top? (Fig. 3: 2)
A second piece of evidence of eelgrass use comes from Schokland, before its incorporation into a large polder in the 1930’s a small island in the Zuiderzee. During archaeological supervision of the reconstruction of a 16th/17th C. water well there, a layer of leaves of dwarf eelgrass was found on the bottom of the well (Brinkkemper 2007). Water wells are frequently found with a layer of plant material or coarse sand in them, probably for filtering. Eelgrass may have been used in this way. It is also possible that the eelgrass was part of a roof over the well. Linnaeus mentions that the 18th-century Dutch made almost indestructible roofs out of eelgrass (Houttuyn 1793, 245). This indestructibility can perhaps be attributed to its fire resistant qualities, as well as to its resistance to decay.[3] This last property can be attributed to the presence of Zosteric acid in the leaves, which inhibits the activity of micro-organisms (but apparently not the fermenting agent mentioned below) (Davies et al. 2007).
Earlier excavations on Schokland had also yielded a layer of eelgrass leaves. This was not documented during the excavation, but the layer seemed to date to the 16th or 17th century AD (Brinkkemper 2007, 83). The excavator interprets them as the remains of a seaweed dike (Van der Heide 1992, 78-79). The same excavator, incidentally, mentions eelgrass that was used as insulation in the walls of the 15th-century monastery of Elburg, a medieval city on the shores of the Zuiderzee, not far away from Schokland. The publication on the restoration, however, does not contain any information about the presence of this species (Jeletich-Visser et al. 2005).