Award: OCE-1706009

Increased frequency and intensity of storm events such as tropical cyclones or prolonged periods of rain will have a major impact on estuarine and coastal biogeochemical cycling. In this RAPID project, we quantified the short-term (several months) response of carbon and nutrient cycling in the Neuse River Estuary-Pamlico Sound (NRE-PS) ecosystem to floodwaters associated with Hurricane Matthew, which occurred in October 2016. Sampling was conducted weekly in both the NRE-PS (October 2016 to January 2017), the Neuse River (NR) (October to December 2016) and in freshwater wetlands of the Neuse River above head of tides in March and October of 2017. We measured the light-absorbing properties and isotopic composition of river, estuary, and sound water, as well as the amount of dissolved carbon dioxide (CO2) in those waters. The Intellectual Merit of this project was that we found the storm increased the amount of dissolved organic carbon (DOC) in the estuary and the sound by 55% and particulate organic carbon (POC) by 120% for the estuary and about 50% for the sound. The color of the DOC can be seen clearly in satellite imagery. Organic nitrogen (N) loading was similarly increased. While floodwater decreased the inorganic carbon concentrations by roughly 30%, we found the decrease in alkalinity meant that more CO2 was released from floodwaters reaching the NRE-PS after the storm. Chemical measurements of DOC indicated that the increased concentrations originated from wetlands adjacent to the river channel but situated above the head of tides. Our results demonstrate the remarkable changes to coastal ecosystems caused by extreme weather events such as tropical storms and hurricanes. Some of these changes involve stimulating the degradation of organic carbon to CO2 in coastal waters with long water residence times. Our discovery suggests that floodplain wetlands may be "primed" to release DOC which is then degraded to CO2 and released back into the atmosphere. Given that roughly 30% of estuaries are lagoons and have long water residence times, there is potential for this released CO2 to act as an important feedback to the global climate system. Our work has supported a paradigm in the geosciences called the "Pulse-Shunt Concept" which maintains that the majority of carbon and other solutes are released from watersheds during a few episodic, yet extreme events. To date, little work has been done to determine the results of these infrequent but significant pulses of solutes into nutrient-sensitive coastal ecosystems. Our project results suggested that extreme weather events can be key factors in the delivery of carbon and nutrients to coastal waters. This outcome has important implications for the management of coastal water quality with respect to recent trends towards increasing frequency and intensity of extreme weather events. The Broader Impacts of our one-year project were centered on training and support for two graduate students. Each has used project results as part of their thesis. Two public presentations have been given on this project and one student has presented his results at the annual American Geophysical Union Fall Meeting in 2017. Three manuscripts from this project are in preparation. A follow-on proposal to NSF is planned in 2018. Last Modified: 03/03/2018 Submitted by: Christopher Osburn