DETERMINING THE DOMINANT SOURCE(S) OF FRESHWATER TO A COASTAL ESTUARY: BISCAYNE BAY, FLORIDA

Biscayne Bay, located in southeast Florida, U.S.A., is a federally protected coastal estuary that serves as a nursery for all kinds of marine life. Freshwater from rainfall as well as runoff from the adjacent watershed mixes with sea water from the Atlantic Ocean creating a brackish water environment. Biscayne Bay historically received groundwater discharge from the karst Biscayne aquifer, but due to the construction of canals in South Florida, the bay is receiving different inputs of freshwater. The objective of this project was to identify the dominant freshwater input source in the bay. To address the project’s objective, water chemistry was analyzed to discern the dominant freshwater source to the bay. Water samples were collected from Deering Estate, Florida, adjacent to Biscayne Bay. Water sampling occurred in an inland freshwater spring and on the western shore of Biscayne Bay. The duration of water sampling occurred for 12 weeks (May to August, 2 and a half months), sampling twice a week. Apart from collecting water samples, the salinity, temperature, and specific conductance of these sites were collected using a YSI 2030 during sample collection. Water samples were processed for cations and anions, and stable isotopes of oxygen and hydrogen as geochemical tracers. The salinity of the site located on Biscayne Bay differed from 26.5 to 4.1 ppt, while the salinity of the freshwater spring differed from 24.2 to 0.3 ppt. The lowest salinity values were seen after a major rain event. Chemical analysis suggests that rain is the dominant source of freshwater, followed by canal water then groundwater. Understanding freshwater inputs to this essential coastal estuary will provide an insight on how this may impact the estuary and can be applied to coastal estuaries worldwide.