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 6000 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.