Research on nitrogen transformations in estuaries has identified a novel group of microbes that are likely involved in converting ammonia to nitrate (nitrification). Hollibaugh et al. (2014) documented a consistent summer peak in these ammonia-oxidizing archaea, which correlates to a peak in dissolved inorganic nitrogen, suggesting a temporary uncoupling in the nitrogen cycle. Hollibaugh has a current NSF grant to follow up on the geochemical consequences of these observations.
Dissolved Organic Carbon
Bacterioplankton control the flux of dissolved organic carbon (DOC) into the coastal microbial food web and influence the release of inorganic carbon to the atmospheric and offshore reservoirs. Yet there are thousands of compounds making up the DOC pool and hundreds of heterotrophic bacterial taxa participating in DOC processing. Recent work resulting from M. A. Moran’s research at Sapelo suggests that sulfonates represent a major class of sulfur-containing DOC compounds whose role in the marine carbon cycle has not previously been recognized (Durham et al. 2014, 2015).
How similar are plant communities as they get further and further apart? Guo et al. (2015) examined characteristics of plant community composition at a series of salt marsh sites being studied in Georgia in comparison to sites located on the Gulf Coast in Texas from three perspectives. They found that there was strong variation in community composition within individual salt marsh sites across elevation; in contrast, community similarity decayed with distance four to five orders of magnitude more slowly across sites within each region. These results indicate that local gradients are relatively more important than regional processes in structuring coastal salt marsh communities.
In a series of studies of the American Alligator, Nifong (Nifong et al. 2012, Nifong and Silliman 2013) demonstrated that gut contents of alligators included numerous salt marsh species, including blue crabs. They also found that alligators in marine/estuarine habitats were significantly larger than those captured in freshwater (Nifong et al. 2015). These studies show that large predators such as alligators move between ecosystems and can strongly affect ecological communities.
Increases in salinity can alter wetlands, decreasing carbon storage and inorganic nitrogen removal and increasing the generation of toxic sulfides. Herbert et al. (2016) identified various mechanisms that can result in salinization in coastal wetlands (saltwater intrusion, storm surges, changes in freshwater flow, physical changes in the coastline) and found that they represent a growing threat, especially given the fact that almost all of these mechanisms may be intensified by global climate change. The GCE LTER is studying all of these mechanisms.