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A Narragansett Bay Mesocosm Experiment: Effects of Eelgrass Density on Greenhouse Gas Fluxes
Citation:
Beardwood, A., C. Wigand, S. Ayvazian, D. Cobb, Philip Colarusso, AND N. Schafer. A Narragansett Bay Mesocosm Experiment: Effects of Eelgrass Density on Greenhouse Gas Fluxes. New England Estuarine Research Society (NEERS) Spring Meeting, Freeport, ME, April 18 - 20, 2024.
Impact/Purpose:
Region 1 partners (Phil Colarusso and others) and OWOW are interested in the possible benefits of eelgrass in coastal systems, especially, towards carbon sequestration and climate mitigation. Preliminary data suggest that there are little differences in greenhouse gas (GHG) emissions (sum of carbon dioxide, methane, and nitrous oxide) measured among the different eelgrass densities. During the day and night eelgrass system emissions are dominated by carbon dioxide, followed by nitrous oxide and methane. We suspect that there was not greater carbon dioxide uptake by higher density eelgrass treatments as expected due to respiration from epifauna and epiphytes, which colonized leaf surfaces. These preliminary results in the greenhouse mesocosms suggest that there is a net source of greenhouse gas emissions associated with eelgrass in both the light and dark hours, however, this study did not measure the organic carbon stored in the sediments of the eelgrass. Organic carbon stored in the sediments may offset the sum of the greenhouse gas emissions associated with the eelgrass.
Description:
Seagrass beds provide key benefits, including playing a critical role in climate mitigation. We tested the effects of different eelgrass densities on greenhouse gas (GHG) fluxes at the water-atmosphere interface by creating six treatments (4 reps ea) with different shoot densities (per m2): bare (0), sparse (~60), low (~120), medium (~150), medium-high (~180), and high (~215) in 115-gallon mesocosms with flow-through bay water. Preliminary data suggest that there are little differences in GHG emissions measured among the different eelgrass densities. During the day and night eelgrass system emissions are dominated by CO2 (78–88% CO2e-100y) followed by N2O (11–21%) and CH4 (0.9–1.6 %). We observed N2O uptake in bare treatments, while CO2 and CH4 were emitted. The N2O emissions offset about 13% (CO2e-100y) of the combined CO2 and CH4 emissions in bare sediments. We suspect that there was not greater CO2 uptake by higher density eelgrass treatments as expected due to respiration from epifauna and epiphytes, which colonized leaf surfaces.
