Groundwater Characterization in Marine Areas of Biscayne National Park

This project was designed to identify whether or not groundwater was migrating through coastal aquifers and discharging into Biscayne Bay and nearby reef tracts. The approach had two objectives.

The first objective was to use geochemical tracers such as isotopes of radon and radium and cations/anions (e.g., calcium, magnesium) to identify water masses. Other water quality parameters are necessary in understanding potential sources of contamination to the ecosystem. Air and surface water sources are relatively easy to investigate but groundwater beneath a marine system is much more difficult to access. This project quantified water quality parameters such as nutrients (nitrogen and phosphorus species), trace elements (e.g., zinc, copper, arsenic), wastewater compounds (e.g., 17beta-estradiols, coprostanol, caffeine, surfactants), pesticides (e.g., Lindane, Endosulfan, DDT), as well as field parameters (pH, dissolved oxygen, salinity, temperature). These parameters were used to characterize the groundwater beneath Biscayne Bay.

The second objective to further our understanding of the subsurface flow regime beneath Biscayne Bay and within Biscayne National Park. Groundwater flow is driven by changes in water level (potentiometric surface gradient) in the adjacent Biscayne Aquifer. Potentiometric surfaces for groundwater have been investigated extensively for onshore regions of south Florida and to some extent for the coastline, but no information exists farther offshore. To complicate natural flow gradients, tidal pumping is known to create flow patterns in marine groundwaters. Although tidal pumping has been investigated using seepage meters, it is most accurately quantified by using observation wells. Determining the pressure gradients produced between groundwater and surface water by the action of tidal pumping can potentially provide data on vertical and horizontal groundwater movement.