Assessing the Importance of Seagrass Habitat Restoration to "Blue Carbon" Sequestration in Shallow Coastal Waters

Carbon sequestration is accelerated by the presence of seagrass in coastal habitats as the vegetation promotes the accumulation of carbon-rich sediment. Typically, measurements of carbon sequestration are conducted in mature seagrass meadows. Due to global seagrass decline, seagrass restoration efforts have increased to mitigate the continual loss of seagrass. However, it is unclear to what extent and at what level of maturity restored seagrass meadows effectively accumulate carbon. The objective of this thesis is to quantify the carbon sequestration potential of the restored seagrass habitat at the Virginia Coast Reserve Long Term Ecological Research Site (VCR-LTER). Restoration sites of different ages, 0-, 4-, and 10-years (time since seeding) were used in this study. Seagrass age and density were expected to be the main drivers of carbon accumulation in the restored meadows. Results indicated that carbon accumulation increased with seagrass age and was linked to seagrass density. The oldest restored seagrass meadow sampled (10-years, seeded in 2001) had the largest carbon accumulation rate of 36.7 g C m -2 yr -1 , and is projected to be accumulating carbon within measured ranges of natural seagrasses habitats within 12 years of seeding. Carbon accumulating in seagrass sediment was from both seagrass and nonseagrass sources. The results of a three-source Bayesian mixing model indicated that the restored seagrass meadows were accumulating carbon from seagrass and non-seagrass sources, specifically benthic microalgae, in relatively equal amounts. The 10-year restored seagrass meadow accumulated seagrass carbon at a rate of 15.41 g C m -2 yr -1 and 20.86 g C m -2 yr -1 of non-seagrass materials. iii These findings suggest that with time, restored seagrass habitats can accumulate carbon at the same rate as natural meadows, and from sources other than surrounding seagrass vegetation. In addition, this thesis provides the first measurement of "blue carbon" sequestration for a restored seagrass habitat and identifies the carbon sources that comprise the accumulating carbon pool in a restored meadow. These results support restoration and conservation efforts by providing quantitative evidence of potential atmospheric carbon dioxide emission mitigation and the ecosystem services provided by restored seagrass meadows in the form of carbon sequestration.

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