The water occupying estuarine systems such as Biscayne Bay is a balance of
saltwater influx from the open ocean and freshwater inputs from
precipitation, surface water runoff, and submarine groundwater discharge.
While the estuary receives fresh water flow from the mainland, it also
affects the coastal wetlands and the aquifer through saltwater intrusion.
The flow dynamics of these coastal systems are often poorly understood and
difficult to differentiate and quantify. This proposal will use naturally
occurring geochemical constituents as tracers to separate and quantify the
sources of freshwater, i.e. rainfall, canal flow, and groundwater discharge
to Biscayne Bay and geophysical techniques to image the salt water intrusion
into the adjacent aquifer. Discrete samples of precipitation, canal water,
terrestrial groundwater, marine groundwater, and bay surface water will be
collected monthly for two years, and analyzed for the stable isotopes of
hydrogen and oxygen, as well
as for major cations and anions. Both the stable isotopes and ion values
will be placed in a mixing model to discern the dominant sources of
freshwater into the Bay in both time and space. Helium (4He) will be used as
a third independent geochemical technique to measure the total groundwater
discharge (fresh and saline) into the bay. 4He samples will be collected
twice in one year, once in the wet season and once in the dry season in
surface bay water, canal water and both fresh and brackish groundwater.
Additionally an electromagnetic survey will be conducted along the coast of
Biscayne Bay to image the underlying saltwater mixing zone. A simple and
quick detection of the three-dimensional saltwater/freshwater intrusion
interface has been problematic without the use of extensive sounding surveys
or multiple well sampling. This study will develop a rapid electromagnetic
technique for 2D and 3D saltwater front imaging in shallow near- shore
systems. This technique will not only refine my conceptual model, but can
potentially be applied to coastal systems worldwide.