Sustainable seagrass restoration in the Virginia Coastal Bays: assessment of sediment and water qualities

Restoration of eelgrass (Zostera marina) has been successful in the Virginia coastal bays, where >17 km² of eelgrass has been restored since 2001. Water quality (as quantified by total suspended solids, chlorophyll, dissolved nitrogen) is high and sediments are sandy in the coastal bays. In the regions of the coastal bays where restoration efforts have been focused, long-term monitoring of restored sites and modeling of sediment suspension and light attenuation have shown that the maximum depth for Z. marina survival in these bays is1.6 m (mean sea level). Understanding the effects of varying sediment characteristics on depth limits for Z. marina survival is important for extending restoration efforts to other regions of these coastal bays. We quantified sediment characteristics along depth gradients in two bays, one with fine-grained sediment (Gargathy Bay to the north) and the other with coarser sediment, (Magothy Bay to the south), and compared these with bare sites in a centrally located successfully restored bay (Hog Island Bay). Sediment characteristics (percent organic matter, carbon to nitrogen ratio, porosity, grain size) in Gargathy Bay were significantly different from Hog Island Bay. However sediment characteristics in Magothy Bay were not significantly different from Hog Island Bay. Water quality parameters (water column chlorophyll a, total suspended solids, pore-water sulfides) and light attenuation profiles in Gargathy Bay, Magothy Bay, and Hog Island Bay were significantly different with Gargathy Bay and Magothy Bay showing higher concentrations of pore-water sulfides and total suspended solids than Hog Island Bay and with Gargathy Bay showing higher water column chlorophyll a concentrations and Magothy Bay showing lower water column chlorophyll a concentrations than Hog Island Bay.  In future work, we plan to monitor other water quality parameters and do experimental transplanting in order to determine how depth limits may vary with changes in sediment characteristics, specifically organic content.