Award: OCE-1803159

Storm surge is often considered the greatest threat to life and property associated with a hurricane. Hurricane Irma, which passed over the US on Sept. 11, 2017, caused the highest storm surge ever recorded on the central Georgia coast and resulted in salt water moving much further upstream than usual. The NSF-sponsored Georgia Coastal Ecosystems Long Term Ecological Research Project (GCE-LTER) has long-term experiments and monitoring programs that provided "before" data and a context for understanding the effects of this event. In the year following the hurricane, we 1) augmented sampling of the GCE-LTER wetland monitoring sites distributed along the salinity gradient in the Altamaha River estuary; 2) took advantage of an ongoing GCE-LTER field experiment to determine whether prior saline disturbance affected responses to the hurricane storm surge; and 3) collected aerial imagery that to look at landscape level shifts in habitat distribution compared to pre-storm maps. We found that the storm surge resulted in large physical changes to the system: 1) upstream salinity intrusion in the Altamaha River estuary flooded intertidal areas that are normally exposed to brackish and fresh water (including the tidal fresh forest), with a concurrent increase in inundation; 2) the surge resulted in a large increase in sediment deposition in the marshes, as measured by sediment elevation tables; 3) there was an increase in sediment slumping into tidal creeks at long-term monitoring sites; and 4) there were large increases in the amount of wrack in the study area (dead marsh grass and other material that washes up onshore), as documented by aerial photographs. We also found evidence for changes in the chemical and biological properties of the ecosystem, including increases in the amount of dissolved organic material in estuary water, an increase in the amount of sugars that are readily broken down by microbes, and decreases in the amount of salt marsh plants and invertebrates (snails, fiddler crabs), particularly in areas close to the water's edge. Most of these had recovered a year after the storm passed, suggesting that they were resilient to the event. Other characteristics that we evaluated did not show a hurricane response: we did not see differences in the concentrations of nutrients in the water contained in the soil, nor large shifts in the distribution of marsh plants and trees associated with the event, nor was there evidence that methane emission or the growth of plants changed in our field experiment. This could be because the effect of the storm was short-lived (e.g. we may have missed flushing of nitrogen out of the tidal fresh areas upon exposure to salt water), or that some of these attributes were highly resistant to the event. We are following up on this project in several ways. First, we are writing up the analyses of our marsh monitoring data, the habitat classification maps, and the characterization of dissolved organic matter for publication in scientific journals. Second, we have incorporated both the tidal tree survey and the transitional plots into the long-term monitoring being conducted by the GCE-LTER project, and are continuing to track the incidence of wrack. This will allow us to evaluate changes over longer time-scales and also provide a baseline for future events. Finally, we are continuing to investigate the effects of perturbations and disturbance responses in the GCE domain, with several experiments planned to evaluate the effects of standardized disturbance treatments. This research involved 2 PhD students, 1 post-doctoral assistant, and 8 undergraduates, and was also part of a teacher training workshop. Data from the project are available in the GCE Data Catalog (http://gce-lter.marsci.uga.edu/public/app/data_catalog.asp) and through BCO-DMO. Last Modified: 02/10/2020 Submitted by: Merryl Alber