FROM SOURCE TO SINK: LINKING DISSOLVED ORGANIC AND INORGANIC NUTRIENT SOURCES FROM THE EVERGLADES TO BIOLOGICAL PROCESSES IN FLORIDA BAY

The ecological success of the Florida Everglades restoration relies on our ability to understand and predict how regional changes in the nature and distribution of dissolved organic and inorganic nutrients will govern the downstream ecological and geochemical dynamics of planktonic and benthic communities. Re-establishing surface-water flow through the Everglades will lead to changes in the amount, sources, and ratios of nutrient (C, N and P) delivery to Florida Bay, particularly dissolved organic nutrients. We have developed a multi-proxy approach to predicting downstream restoration impacts which combines stable isotopic signatures with inorganic and organic C, N and P nutrient pool measurements, ecological process measurements and nutrient bioassay experiments within Florida Bay and the Everglades. This approach allows us to link upstream, regionally distinct C and N nutrient sources (Shark River, Taylor Slough, Canal 111) in the Everglades with downstream biological processing of these nutrients within Florida Bay and to predict future ecological impacts.

Our results indicate that regional variability in the ratio of organic and inorganic nutrients, particularly nitrogen, strongly influences the selection for different phytoplankton communities in Florida Bay. Blooms of cyanobacteria, diatoms and heterotrophic bacteria occur in different regions of the bay in response to different ratios of dissolved nutrients, with cyanobacteria and diatoms responding to organic and inorganic N respectively while bacteria respond to phosphorus. Large differences in the N isotopic composition of both pelagic and benthic microalgae within Florida Bay correspond to the regional changes in the uptake and elemental stoichiometry of dissolved nutrients as well as phytoplankton community composition within the Bay. An east-west gradient in the N isotopic composition of 12‰ in algae, sea grass and sediments within Florida Bay co-varies directly with a 10‰ regional gradient in Everglade biological materials and an 18‰ gradient in Everglade DOM. These results show that our multi-proxy approach can accurately trace changing input of nutrient sources and provides a framework to predict downstream response in the structure and function of both planktonic and benthic habitats resulting from Everglades restoration.