Climate Drivers of Spartina alterniflora Saltmarsh Production in Georgia, USA
Tidal wetlands are threatened by global changes related not only to sea level rise but also to altered weather patterns. To predict consequences of these changes on coastal communities, it is necessary to understand how temporally varying abiotic conditions drive wetland production. In 2000–2011, we conducted annual surveys of Spartina alterniflora biomass in tidal marshes at nine sites in and around the Altamaha river estuary on the coast of Georgia, USA. End of the year live biomass was assessed in the creekbank and midmarsh zones to estimate annual net primary production (ANPP). River discharge was the most important driver of S. alterniflora ANPP, especially in creekbank vegetation. Increased river discharge reduces water column salinity, and this was most likely the proximate driver of increased production. In the midmarsh zone, the patterns were less distinct, although river discharge was again the best predictor, but maximum temperature had similar predictive ability. In contrast to results from terrestrial grasslands, we found no consistent evidence for a sharply delimited critical period for any climate driver in the tidal marsh, which indicates that plant growth was responsive to abiotic drivers at any time during the growing season. Results were broadly consistent across multiple sites within a geographic region. Our results differ from previous analyses of production in S. alterniflora marshes, which either identified oceanic drivers of S. alterniflora production or were unable to identify any drivers, likely because the low-latitude sites we studied were hotter and more affected by river discharge than those in previous studies.
Keywordssmooth cordgrass tidal marsh estuary ANPP river discharge sea level
We thank NSF (OCE06-20959) for funding. Hongyu Guo, Alana Lynes, Amy Kunza, Chuan-Kai Ho, Huy Vu, Jacob Shalack, Daniel Saucedo, Ken Helm, Jane Buck, and many others helped with this project. We thank Christine Angelini, Adrian Burd, Matt Kirwan, Jim Morris, Joan Sheldon, Marylin C. Ball, and two anonymous reviewers for comments on the manuscript, Joseph Craine for assistance with the critical climate period analysis, and Adam Sapp for the Altamaha River estuary figure. This is Contribution Number 1035 of the University of Georgia Marine Institute. This work is a contribution of the Georgia Coastal Ecosystems Long-Term Ecological Research program.
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