Evaluating the impacts of seagrass restoration on ecosystem carbon storage

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Hailey Gilman, Physics, Randolph College, Lynchburg, VA and Sarah Sojka, Environmental Science, Randolph College, Lynchburg, VA

Background/Question/Methods:
Coastal ecosystems capture carbon from the environment, mitigating the climate effects of human carbon emissions. This “blue carbon budget” is significantly impacted by the health of seagrass beds. Restoration of seagrass beds, a key part coastal ecosystems, are seen as a way to enhance carbon storage. However, much of the carbon stored in seagrass beds comes from outside of the beds and there is little information regarding the impact of seagrass restoration on carbon storage in adjacent sediments. This study quantifies the relationship between carbon stored within and local to the restored seagrass beds by evaluating data collected before and after restoration at the Virginia Coast Reserve along the Eastern Shore. Sediment samples were taken at 28 locations in a shallow coastal lagoon before (2003-2004) and after (2020) a seagrass restoration project. The samples were analyzed for percent fine sediment using wet sieving and percent organic matter by loss on ignition. The change in these parameters for each sampling location was calculated and the distance from the nearest restored seagrass bed was determined using ArcMap Pro. The sampling locations ranged from 0 - 5,751 m from the restored seagrass bed.

Results/Conclusions:
Change in percent fine sediment showed no relationship with distance from the seagrass beds, but change in organic content decreased with distance from the seagrass bed (R2=0.21, p=0.02). Based on the relationship between change in organic content and distance from the seagrass bed, a distance of 1,390 m represents the transition point from locations that increase in organic content and locations that decrease in organic content following this seagrass restoration project. This indicates that some of the carbon stored in the seagrass beds may be relocated from other parts of the ecosystem, not a true enhancement of carbon storage. Based on these findings, estimating the carbon storage impact of the seagrass bed without examining impacts on adjacent areas likely misrepresents the actual impact.