Applicability of steel slag as a substrate in eelgrass (Zostera marina L.) beds restoration in coastal Japan

We evaluated mixed materials made from dephosphorization slag, a byproduct of the steelmaking process, as a basal material and dredged material (DM) as a silt-clay source in constructing beds to grow eelgrass (Zostera marina L.). Silica sand was used as a reference basal material. The slag increased in pH to about 9.0 in interstitial water, but adding DM to slag mitigated the increase. The addition of DM to slag and sand enhanced the growth of eelgrass, primarily because of the increased NH4-N and PO4-P supply. No difference was found in growth between slag- and sand-based sediments having the same proportion of DM even though slag-based sediments exhibited substantially higher pH and lower PO4-P concentrations than sand-based sediments. No significant differences were found between the macrobenthic community structures in the two sediment types. Dephosphorization slag mixed with DM was considered useful as a construction material for eelgrass beds.