Source characterization of dissolved organic matter in a subtropical mangrove-dominated estuary by fluorescence analysis

Measurements of dissolved organic carbon (DOC), UV–visible, fixed wavelength fluorescence, and synchronous fluorescence were performed in an effort to characterize spatial and temporal variability in concentration and source of dissolved organic matter (DOM) in surface waters of the southwest coast of Florida. Concentrations of DOC in the surface water ranged from 318 to 2043 μM and decreased from the upper estuary to the coastal areas, and were not only influenced by source strength but also by the hydrology and geomorphology of the mangrove-dominated southwest Florida estuarine area of Everglades National Park. Mangroves provided a significant input of DOM to the estuarine region. This terrestrially derived DOM underwent conservative mixing in these estuaries, but at salinities ≥30 a clear switch from terrestrial to marine DOM was observed indicating a change in the nature and origin of the dominant DOM. The results show that the dynamics of DOM in these subtropical estuaries are complex and that geomorphologically compartmentalized estuarine subregions can be distinguished based on the optical characteristics of their DOM.