The Florida Coastal Everglades (FCE) is an oligotrophic wetland characterized by very low quantities of particulate organic matter (POM). POM in this environment occurs as a slow-moving, benthic layer of flocculent material (floc) that has been defined as biogenic, detrital and rich in organic matter. Although it is known that floc is an important component of the food web in the Everglades, still little is known about its biogeochemical dynamics in this environment. Floc has also been thought to be a potentially important source of dissolved organic matter (DOM). In the shallow waters of the FCE, floc is naturally re-suspended through wind and bioturbation, and can therefore be exposed to intense sunlight. Thus, such photo-exposure may result in DOM generation.
To quantify and characterize the DOM generated from floc by photo-irradiation, samples were collected at two sites along the Shark River Slough (SRS), a freshwater site (SRS2) and a mangrove site (SRS6). The floc was incubated in a solar simulator (exposed and dark controls) for different periods of time (up to 7 days). The incubated floc was filtered and the filtrate was characterized using elemental analysis and Excitation Emission Matrix (EEM) Fluorescence coupled with Parallel Factor Analysis (PARAFAC).
Our preliminary results show that the fluorescence intensity of humic-like and protein-like components for samples incubated under dark conditions remained constant, suggesting that microbial degradation and/or leaching might be minor processes for the generation of CDOM from floc. On the other hand, the fluorescence intensity increased substantially for samples exposed to artificial sunlight, indicating that the release of CDOM through photo-induced alterations of floc was significant. Fluorescence Index (FI), a proxy used to differentiate between microbial and terrestrial DOM sources, showed that the CDOM released from floc has terrestrial characteristics comparable to those found in natural water from the FCE.
While these are the first data on the photochemical generation of DOM from floc, more work (i.e., variations on spatial and temporal scales) is needed for a better understanding of photo-chemical effects on floc dynamics. The contribution of the photo-degradation of floc to the overall DOM pool in the FCE needs to be quantified and potential effects of increased water delivery through Everglades restoration on this process need to be assessed.