Identifying ecosystems with high carbon uptake is essential to establish protection policies that mitigate the increase of greenhouse gasses due to human activities. Although salt marshes cover small continental areas, they assimilate atmospheric CO2 more efficiently than other terrestrial ecosystems. An atmospheric CO2 flux data set measured with the Eddy Covariance (EC) technique allowed us to calculate the net ecosystem exchange (NEE) in a South American salt marsh. The data gaps usually produced by EC were filled in with parametric models that estimate Ecosystem Respiration (Reco) and Gross Primary Production (GPP). Their performance was tested against the Look-Up Table (LUT) and the REddyProc package developed by the Department for Biogeochemical Integration of the Max Planck Institute, Germany. REddyProc and LUT filled the NEE series with greater accuracy. Instead, Reco and GPP models best accounted for seasonal variability at bi-monthly time steps. Regardless of the gap-filling technique, calculations indicated a net CO2 uptake of 5.09 to 6.39 ton ha−1 from May to December 2018, which is 2 to 3 times higher than Northern Hemisphere salt marshes for the same monthly period. Results suggest that these ecosystems play an important role in CO2 mitigation, revealing the importance of their restoration and conservation.
