Coastal Darkening in Florida’s Estuaries

Globally, coastal waters are becoming optically dark and Dissolved Organic Carbon (DOC) rich in a process called coastal darkening, causing a host of environmental problems. This is thought to be caused by terrestrial inputs; however, recent evidence suggests that marine sediments may also contribute both DOC and optically dark waters. Sediment-derived Color Dissolved Organic Matter (CDOM), in part driven by Dissolved Iron (dFe) oxidation at the sediment-water interface, darkens water and cycles carbon in coastal systems. Investigating this phenomenon will take a two-pronged approach: (1) quantifying the sediment and water column DOC, Fe, and CDOM inventory and flux, and (2) conducting laboratory experiments oxidizing Fe(II) in the presence of natural organic matter. This work will primarily focus on the Florida Bay and the Indian River Lagoon, two estuary systems with vastly different biogeochemistry to illuminate the mechanisms behind coastal darkening and determine if sediment carbon cycling’s impact on water column optics is site-specific or universal in Florida coastal systems.