Using Dissolved Organic Matter (DOM) Optical Properties and Stable Isotopes to Quantify Mangrove Contributions to the DOM Pool in the Shark and Harney Rivers, Florida Everglades, USA

The Shark and Harney Rivers drain water from the freshwater marshes in the Everglades through fringe mangrove forests to the Florida Shelf.  Dissolved organic matter (DOM) concentration and optical properties including fluorescence and UV-Vis spectroscopy were analyzed along transects from the freshwater Tarpon Bay to saline Florida Shelf during both the wet and dry seasons and during two tidal cycles in the Shark River during the dry season.  Eight fluorescent components have been identified for the Everglades from previous studies using excitation emission fluorescence spectroscopy and Parallel factor analysis (EEM-PARAFAC).  DOC in the Shark River estuary showed general non-conservative behavior, with additional carbon inputs throughout the mangrove ecotone. These mangrove inputs were characterized by EEM-PARAFAC and stable carbon isotope analyses and quantitatively differentiated from the freshwater Everglades derived DOC.  The PARAFAC results showed that mangroves added significant terrestrial humic-like DOC to these coastal streams, which was confirmed by stable carbon analyses of the DOC and DIC. One fluorescent component derived from freshwater soil oxidation, did behave conservatively and can be used as a freshwater derived conservative DOC tracer.  The protein-like components behaved differently depending on the season and the river and were either conservative (wet season) or consumed at higher salinity (high P; dry season).  Principle component analysis (PCA) was used to help understand the major factors controlling PARAFC component relative abundance and supported the finding that the terrestrial humic-like components have a source in the mangroves as well as upstream from the freshwater marsh.  The tidal study results suggest that DOM is pumped from the mangroves into the river as high tide recedes. South Florida fringe mangrove streams were found to contribute significant carbon loads from both freshwater marsh and mangrove swamp environments to the Florida Shelf.