Project: 2018 Hurricane Season: Influence on organic carbon input and biodegradation in marsh-dominated estuaries

NSF Award Abstract:
This project will examine changes in dissolved organic matter (DOM) composition and microbial decay processes in a marsh-dominated estuary that occur in response to the passage of hurricanes and tropical storms. The investigators will focus on the estuary around Sapelo Island off Georgia, which is the site of the Georgia Coastal Ecosystem Long Term Ecological Research (GCE-LTER) program. After decades escaping major storms, the estuary was hit by Hurricane Matthew in October 2016 and by Hurricane Irma in September 2017, and it is likely to be influenced by heavy rainfall from the passage of Hurricane Michael around October 11-12th, 2018. Although pulses in river discharge can deliver fresh, easily consumed organic matter to the estuary, the effects of DOM delivery during hurricanes on microbial processes are not well constrained. This is important because microbial processing of DOM can influence air-sea fluxes of carbon dioxide and other biogeochemical processes. This project will promote education by supporting a graduate student. Findings from this research will be disseminated in the Schoolyard Program that is organized every summer by the NSF-funded Georgia Coastal Ecosystem LTER. The program immerses science and math K-12 teachers from across the State of Georgia in hands-on research activities and discussions on coastal processes. All data generated as part of this project will be made publicly available.

A detailed year-long investigation of DOM composition based on optical measurements and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) data in 2015-2016 captured the effects of Hurricane Matthew, which resulted in a significant input of dissolved organic carbon (DOC) and change in DOM composition in the estuary. Sampling in 2017 captured a similar effect shortly after the passage of Hurricane Irma. DOC consumption by microbes was found to be strongly tied to DOM composition. The investigators propose to collect additional samples in the estuary in mid-October 2018, when Hurricane Michael is expected to impact the region because of heavy rainfall inland. They will also quantify biologically labile DOM via microbial dark incubations. They will compare DOM composition and lability between background samples not influenced by hurricanes and samples from the 3 hurricanes that will have been captured by the combined studies. While the two earlier hurricanes caused large storm surges in the estuary, Hurricane Michael is expected to cause heavy rainfall but smaller storm surge. The occurrence of three major hurricanes in three consecutive years is highly unusual for this estuary, and together with the fortuitous fact that two detailed programs to investigate DOM dynamics were in place, provides an excellent opportunity to quantify the impact of hurricanes on organic carbon delivery and processing in a marsh-dominated estuary.

Additional resources:
Georgia Coastal Ecosystems Long-Term Ecological Research site BCO-DMO Project page: https://www.bco-dmo.org/project/550511

Datasets available from the GCE-LTER page:

• "DOM composition changes in Altamaha River and Sapelo Sound estuaries measured by FT-ICR mass spectrometry from September 2015 to September 2016" http://gce-lter.marsci.uga.edu/data/ORG-GCET-1904
• "DOM composition in Altamaha River and Sapelo Sound estuaries measured by FT-ICR mass spectrometry in 2017 (April, July, October) and 2018 (January and October)" http://gce-lter.marsci.uga.edu/data/ORG-GCED-2208