Exchange of CO2 between a Southeastern Salt Marsh and the Atmosphere

Coastal salt marshes are among the most productive ecosystems on Earth and play an important role in the global carbon cycle. The present study quantifies the net ecosystem exchange in a salt marsh dominated by large heterogeneous patches of Spartina alterniflora near Sapelo Island, GA, USA. Continuous high-frequency eddy-flux measurements were made between 2013 and 2016. The method provides both the temporally continuous and a spatial integration of the carbon exchange between the salt marsh and the atmosphere. Over the course of this multi-year study, the salt marsh ecosystem was found to be a net sink of carbon.  In 2015, annual net ecosystem exchange (-138.72 g C m²) was 55% smaller than in 2014 (-309.36 g C m^-2). This can be attributed to the high temperatures and the occurrence of Proxigean Spring tides combined with persistent onshore winds arising from the indirect effect of Hurricane Joaquin. The ecosystem acted as carbon source with cumulative net ecosystem exchange value of 0.02 g m^-2 day^-1 during the event. In addition, both the photosynthetically active radiation and the air temperature are the main environmental drivers in the marsh. Higher air temperatures and incoming photosynthetic active radiation level limit photosynthetic activity. Further work suggests the collection of a longer record to capture the impact of climatic and other environmental variations on the strength of the carbon sink. Also, the inclusion of the lateral component of the carbon fluxes as part of the seasonal and annual budgets would also considerably augment our understanding of the functioning of the salt marsh along the southeastern coast on the US.