Elemental Composition, Stable Carbon Isotope Ratios and Spectrophotometric Properties of Humic Substances Occurring in a Salt Marsh Estuary
Humic and fulvic acids were isolated from living and dead S. alterniflora plants and the marsh muds of a Georgia salt marsh estuary. Elemental compositions of these compounds are similar to published data for humic and fulvic acid isolated from marine, terrestrial and freshwater aquatic environments, although atomic ratios of the elements appear unique to some extent. Stable carbon isotope data show a trend toward heavier ratios of - 12%:-15%:-18%, for whole plants, humic and fulvic acids from whole plants, and humic and fulvic acids from marsh muds, respectively, indicating a potential fractionation of stable carbon isotopes in salt marsh carbon sources or additional sources for salt marsh sediment humic and fulvic acids.
Spectral analyses of the isolates show maxima in the usual UV and visible light wavelengths, but spectral and elemental data for the methanol extracts of these compounds indicate that fluorescence is due to a tightly associated, minor component of the humic mixtures. Tannic acid and lignosulfonic acid-like compounds do not appear to be components of the humic matter isolated from salt marsh estuaries.