Assessment of Landscape-Scale Fluxes of Carbon Dioxide and Methane in Subtropical Coastal Wetlands of South Florida

Abstract

Coastal wetlands play a significant role in the storage of “blue carbon,” indicating their importance in the carbon biogeochemistry in the coastal zone and in global climate change mitigation strategies. We present airborne eddy covariance observations of CO₂ and CH₄ fluxes collected in southern Florida as part of the NASA BlueFlux mission during April 2022, October 2022, February 2023, and April 2023. The flux data generated from this mission consists of over 100 flight hours and more than 6,000 km of horizontal distance over coastal saline and freshwater wetlands. We find that the spatial and temporal heterogeneity in CO₂ and CH₄ exchange is primarily influenced by season, vegetation type, ecosystem productivity, and soil inundation. The largest CO₂ uptake fluxes of more than 20 μmol m⁻² s⁻¹ were observed over mangroves during all deployments and over swamp forests during flights in April. The greatest CH₄ effluxes of more than 250 nmol m⁻² s⁻¹ were measured at the end of the wet season in October 2022 over freshwater marshes and swamp shrublands. Although the combined Everglades National Park and Big Cypress National Preserve region was a net sink for carbon, CH₄ emissions reduced the ecosystem carbon uptake capacity (net CO₂ exchange rates) by 11%–91%. Average total net carbon exchange rates during the flight periods were −4 to −0.2 g CO₂-eq m⁻² d⁻¹. Our results highlight the importance of preserving mangrove forests and point to potential avenues of further research for greenhouse gas mitigation strategies.