Award: OCE-1237140

The Georgia Coastal Ecosystems Long Term Ecological Research (GCE-LTER) program, based at the University of Georgia Marine Institute on Sapelo Island, was established in 2000 to study long-term change in coastal ecosystems. Estuaries and marshes provide food and refuge for organisms, protect the shoreline, help keep water clean, and store carbon. GCE-LTER researchers track the major drivers that cause long-term change, such as altered freshwater input and sea level rise, and conduct experiments to assess how coastal ecosystems will respond to anticipated changes in climate and human activities. During this funding cycle (GCE-III) we continued a program of research that addresses the five LTER core areas (primary production, populations, organic matter cycling, inorganic nutrients, disturbance) through a combination of long-term observations, field surveys, experimental manipulations and modeling. The GCE-LTER has made major contributions to understanding patterns of primary production, community interactions and ecosystem services along abiotic gradients in intertidal wetlands, as well as the flow of carbon across the coastal landscape and out to the ocean. Key findings include: Estuaries play an outsized role in the global carbon budget: Work at GCE has improved our understanding of the global C budget by demonstrating that estuaries are net sources of CO2 to the atmosphere and coastal ocean and net sinks for oceanic and atmospheric O2. This work challenges the simplistic treatment of estuaries in global C models, and suggests that interactions between river discharge, changes in marsh area, and increasing atmospheric CO2 will alter shelf-ocean C exchange in the future. Ammonia oxidizers transform the nitrogen cycle: Ammonia-oxidizing archaea (AOA) play a key role in the nitrogen cycle by converting ammonium into nitrite, but little is known about their population dynamics and their relation to environmental factors. Research at the GCE found that mid-summer blooms of AOA coincide with a peak in nitrite concentration. Field data from 29 estuaries showed similar summer peaks in nitrite, suggesting that summer blooms of AOA are widespread and play a previously-unrecognized role in driving estuarine nitrogen cycling. Sea level rise alters wetland function. Sea level rise is expected to cause salt marshes to extend upstream at the expense of freshwater wetlands, thereby dramatically altering the intertidal landscape. GCE is conducting a large-scale field experiment to evaluate the ecosystem effects of saltwater intrusion on freshwater wetlands. Experimental salinization reduced primary production, reduces plant species diversity, decreases respiration and leads to loss of marsh elevation. River flow supports marsh production. GCE scientists use a combination of long-term monitoring, remote sensing, and field experiments to study controls on plant composition and productivity in salt marshes. A retrospective analysis found that dominant estuarine plants grow up to 3 times better in years with low salinities, and that salinity is driven most strongly by river discharge. A high frequency of drought in 1998-2012 led to declines in plant biomass over the 28-year period of record for Landsat 8. Mobile predators structure communities: Research at GCE has demonstrated that mobile predators like alligators move between fresh and marine habitats, consume a variety of estuarine prey, and alter the behavior of intermediate predators such as blue crabs. A predator exclusion experiment initiated in 2016 indicates that blue crabs and large fish alter the abundance of marsh invertebrates such as snails and fiddler crabs that in turn mediate plant production and soil biogeochemistry. The GCE-LTER also has strong programs in information management, education and outreach. Nine MS theses and fifteen PhD dissertations were completed by GCE-LTER graduate students, and we routinely involve undergraduates in our research, many of whom have gone on to graduate school. GCE has developed a model for distributed graduate courses taught live on the internet. These courses have a broad reach (>150 graduate students and managers at > 40 institutions) and leverage personnel across the LTER network and beyond to provide a level of expertise in graduate education that no single institution could match. The GCE Schoolyard program provides in-service training in field ecology for K-12 educators, and we have published a children’s book, "And the Tide Comes In," as part of the LTER schoolyard series. The project provides outreach to coastal managers through the Georgia Coastal Research Council, which promotes science-based management of Georgia coastal resources by facilitating information transfer between scientists and managers. The GCE information management program meets the highest LTER IM standards. The GCE Data Catalog (http://gce-lter.marsci.uga.edu/public/app/data_catalog.asp) provides on-line access to data sets. A total of 603 catalog data sets are currently available online, and an additional 793 public data sets are available through the GCE Data Portal, which provides relevant federal data. GCE has also developed and released a number of innovative software products, database systems and web applications, such as the GCE Data Toolbox for MATLAB (https://gce-lter.marsci.uga.edu/public/im/tools/data_toolbox.htm), which has been downloaded by over 4100 registered users for sensor data harvesting and analysis. Last Modified: 12/04/2019 Submitted by: Merryl Alber