Impacts of Iron on Eutrophic Nutrients in Two Florida Waterbodies

Work of the late 20th century showed the effects of nitrogen (N) and phosphorus (P) on algal growth and has since influenced environmental management to limit N&P delivery into aquatic systems. The phosphorus inventory of Lake Okeechobee (LO) has exponentially increased due to urbanization, despite nutrient runoff management approaches (e.g., TMDLs) in the Kissimmee-Okeechobee-Everglades system. Likewise, the connected St. Lucie Estuary (SLE) is showing signs of nitrogen limitation as a byproduct of phosphorus loading. Data streams show that sediments are evidently trapping phosphate in the SLE during sediment resuspension. Iron (Fe) is particularly concentrated in LO and SLE and is likely the source of phosphate scavenging. Although, sediment iron concentration evidently varies based on flow and rainfall in the Kissimmee River Drainage Basin. Meanwhile, feammox, a novel microbial process of ferric iron (Fe3+) coupled ammonium oxidation is apparent in LO. Thus, dry season (winter) iron depletion may result in enhanced benthic N-remineralization, contributing to N accumulation in the water column. The project proposes experiments investigating the significance of sediment Fe-P scavenging and Fe-N interactions, regarding yearly N & P fluctuations that contribute to algal bloom formation.