Tidal influences on carbon assimilation by a salt marsh

Salt marshes are among the most productive ecosystems on Earth, and play an important role in the global carbon cycle. Net carbon dioxide (CO 2 ) ecosystem exchanges in coastal salt marshes remain poorly investigated. In Spartina alterniflora dominated North American Atlantic coast marshes, the lack of a clear understanding of how Spartina alterniflora responds to flooding limits our current ability to understand and predict salt marsh response to sea-level rise. Here we investigate the processes influencing ecosystem-level carbon exchanges between a S. alterniflora dominated salt marsh on the eastern shore of Virginia and the atmosphere. We examined the impacts of tidal inundation on the marsh–atmosphere carbon exchanges through a combination of eddy covariance measurements and in situ photosynthetic measurements. Maximum daytime carbon fluxes were observed during the middle of the growing season (July and August) and amounted to −10 μmol CO 2 m −2 s −1 , and the marsh assimilated 130 gC m −2 during the 2007 growing season. Our study is the first to quantify the effects of tidal inundation on marsh plants, which caused anywhere from 3% to 91% reductions in atmospheric carbon fluxes, with a mean reduction of 46 ± 26%, when compared to non-flooded conditions.