Carbon isotopic composition of methane in Florida Everglades soils and fractionation during its transport to the troposphere

The δ 13 C stable carbon isotopic composition of methane collected in bubbles from the submerged soils of specific environments within the Everglades wetland in southern Florida, United States, varied from −70‰ to −63‰ across the system while organic carbon in the soils and dominant plants varied from −28‰ to −25‰. A methane isotopic budget based upon the soil bubble isotope data and published methane flux measurements predicted a flux of isotopic composition −65‰, a value 5‐10‰ more depleted in 13 C than the isotopic composition of methane emanating to the atmosphere. Emergent aquatic plants, which are known to be active methane transporters between soil and atmosphere in this ecosystem, were found to transport methane of δ 13 C content up to 12‰ different from the δ 13 C content of the soil methane bubble reservoir. Methane 14 C content at one site was determined to be 108.6% modern (Δ 14 C = 83 ± 10‰).