Assessing the importance of seagrass habitat restoration to “blue carbon” sequestration in the shallow coastal zone

Seagrass meadows are highly productive habitats and provide many important ecosystem services to the coastal zone, including carbon and nutrient sequestration.  Organic carbon accumulates in seagrass sediments from both in situ production and sedimentation of water column particles.  We evaluated the impact of seagrass restoration on carbon storage in sediments of shallow coastal ecosystems using the large-scale seagrass restoration (>4000 acres) in the Virginia coastal bays as a model system.  Carbon accumulation rates were determined in meadows 4 and 10 years of age (time since restoration was initiated by seeding) and were compared with nearby unvegetated “bare” sediments.  Sediments of seagrass meadows and bare sites were sampled for organic matter content, percent carbon, and Pb-210 for dating at 1 cm increments to 20 cm depth; in addition, seagrass shoot density, productivity, and above- and below-ground biomass were also determined.  Initial results show that the older 10 year seagrass lagoons have higher levels of organic matter and percent carbon compared to the 4 year meadows and bare sediment. As an initial estimate using Pb-210 dating techniques for sediment accumulation, carbon accumulation was related to seagrass meadow age and shoot density.  This is one of the first studies to address the potential of seagrass habitat restoration in enhance carbon sequestration in the coastal zone.