Anchorage and resistance to uprooting forces of eelgrass (Zostera marina L.) shoots planted in slag substrates

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Different types of slag (air-cooled, granulated and carbonated granulated slag) were employed as basal media of eelgrass, Zostera marina L. We investigated how factors such as slag type, particle size and sedimentation of fine particles affected anchorage of eelgrass to the substrates. It was found that eelgrass planted in slag substrates could endure current velocity of 10 to 50 cm s-1. Thus, slag substrates can adequately support and anchor the eelgrass plants even during severe current flow (50 cm s-1). Root establishment and anchorage were also examined by looking at the resistance of the plants to uprooting forces. Results showed that shoots in slag substrates with the finest particle size (<1.18 mm) gave the highest resistance to uprooting among the particle sizes tested (<1.18, 1.18-2.36 and 2.36-4.75mm). Among the slag substrates, shoots in granulated slag pots gave the highest resistance to uprooting. Addition of dredged sediment (DS) or settling of fine particles improved the root establishment, anchorage of eelgrass and root-rhizome extension. However, it was suggested that addition of DS or settling of fine particles to slag may be beneficial to root establishment up to a certain extent only and too much of it might be harmful to eelgrass plants.