Sources of sediment carbon sequestered in restored seagrass meadows

Seagrass meadows accumulate carbon in sediments as a result of in situ production and sedimentation of particulate organic matter (OM). We quantified the contribution of OM sources to the sediment carbon pool in restored seagrass meadows of different ages (unvegetated and 4 and 10 yr since restoration) in the Virginia coastal bays. Using carbon (C) and nitrogen (N) stable isotopes, we estimated the contribution of seagrass (Zostera marina), benthic diatoms and sestonic particles (BD/S), and macroalgae (MA) to the sediment OM pool influenced by restoration (top 10 cm) with a Bayesian mixing model. Marsh grass was not a likely source based on C: N ratios of the sediment OM. The 4 and 10 yr seagrass meadows had similar OM source contributions to the top 10 cm of sediment, which were distinct from those of unvegetated sites. Seagrass, BD/S, and MA contributed 41, 56, and 3%, respectively, in the 10 yr age treatments and 50, 46, and 4%, respectively, in the 4 yr age treatments. Diagenesis of OM sources had little impact on the source contribution estimates. In combination with carbon accumulation rates at these sites (37 g C m(-2) yr(-1)), these results indicate that 10 yr after seeding, restored seagrass meadows accumulated seagrass carbon at a rate of 14.3 g C m(-2) yr(-1) and non-seagrass carbon (BD/S and MA) at a rate of 22.4 g C m(-2) yr(-1). This study demonstrates how seagrass restoration contributes to the sequestration of 'blue carbon' and quantifies the impact restored seagrass meadow age has on stored sediment carbon.