DISCERNING FRESHWATER INPUTS TO A COASTAL ESTUARY: BISCAYNE BAY, FLORIDA

Groundwater discharge to coastlines contributes to freshwater and constituents to coastal estuaries. Coastal estuaries are nurseries for an array of marine life as freshwater from the mainland mixes with saltwater, creating a brackish water environment. Biscayne Bay is a vital estuary that receives runoff from canals and groundwater discharge from the adjacent karst Biscayne aquifer. The goal of this project was to identify fresh groundwater discharge to Biscayne Bay, situated in Miami, Florida, U.S.A. The project’s goal was addressed by using water chemistry to discern the sources of fresh water in the bay. Water samples were collected from an inland freshwater spring and from Biscayne Bay adjacent to Deering Estate, Miami, Florida. The duration of water sampling took about 11 weeks (about 2 and a half months), 2-6 times a week. Salinity, temperature, and specific conductance were recorded during sample collection. Water samples were analyzed for major cations (including strontium) and anions and stable isotopes of oxygen and hydrogen to trace fresh groundwater inputs to the Bay. Data on bay water levels, rainfall, and nearby canal operations were obtained to discern how fresh groundwater discharge varied with climate or water management. The salinity of the freshwater spring varied from 24.2 to 0.3 ppt, while the salinity of the bay varied from 26.5 to 4.1 ppt. The lowest salinity values were seen following a major rain event. The results of this study will provide an understanding of groundwater inputs to an essential and protected estuary in Florida but can also be applied to coastal estuaries worldwide.