Hurricane winds have large effects on forests, but may have smaller effects on the vegetation of coastal marshes because grasses and forbs are flexible and in any case may be protected from winds by storm surge. However, hurricanes may affect coastal wetlands in other ways, such as by driving saline water upstream into areas that usually are low-salinity habitats, or by moving sediments. Hurricanes Matthew and Irma passed near the Georgia coast in October 2016 and September 2017, providing a unique opportunity to evaluate the effects of a hurricane in a coastal area that historically has rarely experienced hurricane disturbance. To evaluate the effects of these hurricanes on coastal systems, we examined data from the Georgia Coastal Ecosystems Long-Term Ecological Research program, which started in 2000. We examined fast-responding variables (e.g., water column salinity) using data from continuously-recording instruments, and slow-responding variables (e.g., plant biomass) using data from monthly, quarterly or annual sampling.
Results/Conclusions
Both hurricanes increased wind speeds, precipitation and sea level on the Georgia Coast for ~2 days. Heavy precipitation increased the barrier island water table. Rising sea levels pushed ocean water upstream in the Altamaha River estuary, leading to 1-2 day spikes of salinity in brackish and tidal fresh habitats. This was followed by ~2 weeks of heavy river discharge, leading to depressed salinities at some sites, and exporting large amounts of terrigenous dissolved organic material into the estuary. Salt marsh plants and invertebrates appeared relatively unaffected by the hurricane, but tidal fresh marsh plants and tidal fresh forest trees at the downstream ends of their distributions showed premature leaf senescence or death indicative of salt stress. The hurricanes appeared to increase deposition of sediment onto the marsh surface at some sites. Thus, although effects of the hurricanes on the studied salt marshes were mild or positive (increased accretion), the hurricanes appeared to harm low-salinity vegetation types at the downstream ends of their distributions.