Dynamics of Fluorescent Organic Matter Compared between Three Contrasting Estuarine Environments

The purpose of this study was to determine differences in dissolved and particulate organic matter (DOM and POM) quality between three different coastal environments. Tropical, subtropical, and temperate estuaries were studied at sites in the Florida Keys, Corpus Christi, TX and Lower Outer Banks, NC. DOM and base extractable particulate organic matter (BEPOM) absorbance and fluorescence were measured and fluorescence was modeled using parallel factor analysis (PARAFAC), in addition to measuring organic carbon (DOC, BEPOC) concentrations and stable carbon isotope (δ¹³C) values. Bacteria production was measured using ³H-leucine method. Mixing experiments were conducted using seawater samples and freshwater/terrestrial endmembers at each location, while biodegradation was tracked with incubations lasting up to 30 days. Results indicated substantial modification of fluorescence signals as modeled by PARAFAC during mixing cycles within these estuarine systems. We highlight biodegradation process effects on DOM and BEPOM absorbance and fluorescence prior to export to the open ocean, across the salinity gradients of these three different estuarine environments. Our results point to clear differences in the spatial variability of organic matter degradation across biogeochemical “hot spots” such as frontal zones in coastal waters.