Hypothesis 1: Water source and residence time influence the relative contribution and quality of OM from marshes, mangroves, and the marine system to FCE estuaries.
Approach - We will assess estuarine OM inputs, mixing, and transport dynamics along salinity transects in each estuary in the wet and dry season (including sampling throughout tidal cycles). In conjunction with the Hydrology and Water Policies Cross-Cutting Theme, we will determine dissolved organic carbon (DOC) quality and exchange dynamics between ground and surface water in Shark River, Taylor River, and Florida Bay. In addition to molecular-level characterizations, stable C isotope determinations of DOC, DIC, and particulate organic carbon will provide C source identification and degradation dynamics.
Hypothesis 2: Variability in water source and residence time control the rates of DOC, POC, and DIC transport in and export from water and soils.
Approach - OM degradation rates will be measured in laboratory photo- and biodegradation incubations of samples from estuarine transects taken during the wet and dry season at high and low tides. DOC reactivity proxies will be used to assess quality and degradation processes throughout the estuaries, calibrated using laboratory simulations. DOM composition will be examined molecularly to determine effects of molecular weight and recalcitrant components (such as black C) on reactivity. We will determine rates of photo-degradation and metabolic CO2 production, and perform in-depth molecular characterizations of all C components in DOM using advanced analytical techniques such as ultra-high resolution mass spectrometry and NMR. We also will continue to document POC (flocculent detrital) dynamics using 13C to track the fate of POC in DOC (in the mesocosm experiments) and rates of DOC generation through photo-dissolution during the wet-dry season cycle in the ecotone. We will compare associated reactivity and composition between photo-derived and biogenic DOC. Watershed influences on OM dynamics will be compared with other LTER sites and in the context of our international research in the Okavango Delta (Botswana), Pantanal (Brazil), and Shark Bay (Australia) using a model developed for the FCE. We will calculate aquatic C export by coupling our measurements of DOC, POC, and DIC concentrations with discharge rates measured at the mouths of TS/Ph and SRS. CO2 efflux to the atmosphere from water, sediments/soils, and vegetation will be determined at estuary sites during the wet and dry season. Measurements of pCO2 (CO2 (aq)) and DIC (dissociation constants determined with continuous pH measurements) will determine soil-water column C flux to reduce error estimates associated with values of hydrologic export of C. Continued measurements of soil, root, and course woody debris CO2 fluxes will disaggregate components of below-canopy CO2 flux, constrain relationships between soil CO2 flux and environmental drivers (i.e., salinity, inundation, temperature), and validate C budget estimates made using alternative methods.