Exchange of Marsh-atmosphere CO2 in a Patchy Terrain Near Sapelo Island

This paper determines the exchange of CO2 in a salt marsh ecosystem dominated by Spartina alterniflora using the eddy-covariance method in a highly heterogeneous landscape near Sapelo Island, GA. The combination of both tidal inundation and different plant canopy heights (Spartina alterniflora) that dominate the study area, when combined with a limited wind direction-dependent fetch challenges the application of the eddy-covariance method. When flooding occurs, short Spartina alterniflora, mostly found away from the river, become completely submerged with rising tide while the tall Spartina alterniflora, mostly found near the river, is often still exposed to the atmosphere. This occurs daily and, as the inundation occurs, a reduction in CO2 exchange is observed as a result of the decrease in photosynthesis activities. Furthermore, the study area is surrounded by a variety of terrain features such as the Duplin river to the West, a forest to the East, and the Atlantic ocean to the South, further adding increased complexity to the interpretation of flux measurements over the salt marsh. Two eddy-covariance systems were set up in July 2013 to capture 10 hz data of fast response CO2 and three-dimensional turbulent velocities. Multiple layers of signal processing and data quality screening were applied to the dataset and 30-min fluxes of CO2 were calculated. Preliminary estimates suggest the salt marsh sequesters approximately 272 g C m-2 yr-1, a value broadly comparable to several tropical ecosystems despite the smaller aboveground biomass and aerial coverage of vegetated coastal ecosystems.