COI Funded Project: Using Electrical Resistivity to Map Fresh Water Discharge: a Survey Near Wrightsville Beach, North Carolina

Robert Evans,

Project Duration: 6/1/00-12/31/01

Final Report

The discharge of terrestrially derived fresh water onto the continental shelf is a growing area of research, and has been seen to provide an important flux of nutrients onto the seafloor. Yet, there are few geophysical techniques that are sensitive to the presence of fresh pore water in sediments on the continental shelf, and consequently, constraints on the volumes and distributions of subbottom fresh water remain weak.

The salinity dependence of seawater conductivity suggests that this might provide a means of identifying zones of freshwater. We have been funded by ONR to run a cruise using electromagnetic techniques to identify zones of freshwater discharge off Wrightsville Beach, North Carolina. We request supplemental funds from the Rinehart Coastal Research Center to allow us to make a set of resistivity measurements inshore of Wrightsville Beach and, by so doing, provide a link between the onshore hydrologic systems and offshore fresh water discharge. These measurements will, through necessity, be made with different equipment to the offshore profiles. As a test of our proposed techniques, we will also make a series of measurements in Waquoit Bay, an area of local interest, that also features fresh subbottom pore water.