Project: RAPID: Waiting to Exhale: Quantifying Tropical Storm-Induced Increased Flux of Coastal Wetland Carbon into the Atmosphere?

NSF Award Abstract:
In the summer and fall of 2020, the coastal bays of Louisiana have experienced impacts from a number of tropical storms/hurricanes in close procession. Tropical storm Marco, Hurricanes Laura, Sally and Beta made their closest approaches to Barataria Bay from 81 km for Marco, up to 379 km for Beta. Storm erosion can lead to carbon from coastal soils being released to the atmosphere as carbon dioxide (CO2). Scientists rarely have the opportunity to assess the impact of tropical storms on the conversion of wetland soil carbon to CO2 release to the atmosphere, because they don’t have detailed measurements from before the storms to compare with post-storm data. This project has an opportunity to benefit from an existing NSF grant with four years of extensive measurements. RAPID-response funding will support intensive sampling of Barataria Bay in the immediate aftermath of the 2020 storms, and up to a year afterwards.

Despite no direct strikes to the coastal basin, marsh edge erosion rates were up to 60 times higher than the 4-year long-term average. This is already an important finding since most measurements focus on coastlines with direct strikes but clearly, substantial wetland erosion occurs from tropical storms imparting wind fields driving wave energy at substantial distances. Consequently, a particularly active tropical storm season has led to significant carbon-rich wetland soil being dumped into the shallow, aerobic waters of the Barataria Bay in a relatively short period of time. The primary questions to be addressed by this project are whether and how accelerated erosion from the 2020 storm season will lead to a significant increase in CO2 outgassing from the bay to the atmosphere, and for how long the effects will persist. The team of investigators will continue to measure marsh edge erosion over the next year correlated to twice a month water sampling of bay surface waters for determination of dissolved inorganic and organic carbon, and dissolved CO2. Sampling will be conducted along transects running from close proximity to the wetland erosion stations out in the open bay. Air-sea CO2 flux will be estimated using a model and correlated to the wetland erosion rates. The team will compare the storm event-induced “bay respiration” rate with that of next year. This RAPID project will yield several important outcomes: 1) Determination of the increase and temporal impact of wetland carbon loss to the atmosphere from a number of significant storms, similar to what is expected for the future under a changing climate; 2) Understanding if the organic C breakdown to CO2 will increase coastal acidification within the coastal bay.