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Fieldwork

USGS and Florida State University Scientists Collaborate on Submarine-Ground-Water-Discharge Study in the Northern Gulf of Mexico


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Submarine-ground-water-discharge site
Above: Submarine-ground-
water-discharge site at FSU Marine Lab; the small boat was used as a platform for thermal-seepage-meter dataloggers, as well as for an instrument making time-series measurements of 222Rn. Also visible are well casings from a series of shallow wells that extend offshore along a shore-perpendicular transect. [larger version]


Time-series resistivity cable.
Above: Time-series resistivity cable, showing electrode spacing (one sand bag per electrode) across the freshwater/saltwater interface. [larger version]

Two electromagnetic-seepage-meter control panels
Above: Two electromagnetic-seepage-meter control panels on the beach close to the FSU Marine Lab. [larger version]

During the week of January 30, 2006, scientists from the U.S. Geological Survey (USGS) joined scientists from Florida State University (FSU) to begin an investigation of the links between submarine ground-water discharge and climatic (seasonal) change. Submarine ground-water discharge—the flow of ground water directly into seawater—can strongly influence coastal ecosystems, with the potential for harmful effects if the ground water contains high levels of contaminants or excess nutrients.

For the recent study, part of a multiyear project funded by the National Science Foundation, USGS scientist Peter Swarzenski and his SGD team members Chris Reich (USGS) and Jason Greenwood (ETI Professionals, Inc.) traveled from their office in St. Petersburg, Fla., to the FSU Marine Laboratory at Turkey Bayou on Florida's northwest coast (south of Tallahassee). There they worked with FSU professor of oceanography Bill Burnett and his team of students (Natasha Dimova, Benjamin Mwashote, Rick Peterson, and Isaac Santos) at a study site near the lab. USGS participation in the study was twofold:

  1. To conduct a series of intercalibration experiments using two new types of autonomous seepage meters—devices that can measure direct ground-water discharge at a particular point. The USGS seepage meters are equipped with electromagnetic flow meters (for more information on these seepage meters, see "An autonomous, electromagnetic seepage meter to study coastal groundwater/surface-water exchange"), whereas the FSU seepage meters use thermal flow meters. Intercalibrating the two types of instruments will allow us to compare high-resolution data collected with each type of meter.

  2. To study the subtle response of the freshwater/saltwater interface to water-level changes over several tidal cycles, using a new, high-resolution (56 electrodes with 2-m spacing) resistivity array that collects data at regular intervals (time-series data). Such an approach can produce very high resolution snapshots of the dynamic mixing processes that occur within the freshwater/saltwater interface.

On February 2, Peter Swarzenski was invited to present the recent results of submarine-ground-water-discharge studies at a seminar hosted by the FSU Department of Oceanography.

Preliminary results suggest that during this dry-season, 5-day experiment, fluctuations in the submarine-ground-water-discharge rate as measured by one electromagnetic seepage meter appeared to respond almost predictably to water-level changes, with discharge increasing during times of low water levels (low tides).

In the coming months, additional analyses, including time-series measurements of 222Rn, 223Ra, 224Ra, 226Ra, 228Ra, and possibly thoron (a radioactive isotope of radon, 220Rn, with a half-life of just 55 seconds!), will complement the resistivity and seepage-meter work. These isotopes are much more abundant in ground water than in surface water and therefore serve as effective tracers of ground-water discharge. An advantage of geochemical tracers over seepage meters is that they provide a regional-scale estimate of submarine ground-water discharge, rather than the extremely local coverage provided by seepage meters.
The scientists plan to deploy instruments at the site again during the wet season (July-September) to gather data for comparison with those they collected during the recent dry-season experiment.

For more information about submarine ground-water discharge, see "Submarine Ground-Water Discharge and Its Influence on Coastal Processes and Ecosystems," in Sound Waves, June 2004; "Submarine Groundwater Discharge: An Unseen Yet Potentially Important Coastal Phenomenon"; and "Submarine Ground-Water Discharge".


Related Sound Waves Stories
Submarine Ground-Water Discharge and Its Influence on Coastal Processes and Ecosystems
June 2004
Integrated Science Team Deploys New Tools to Study Submarine Ground Water in North Carolina
June 2004
Studying Submarine Ground Water in Rhode Island Under Arctic Conditions
March 2004
Studying Underwater Water in the Land of Misty—Chincoteague Bay, Maryland
October 2003
Progress in Delineating Submarine Ground-Water Discharge in Delmarva Coastal Bays
June 2002

Related Web Sites
Submarine Ground-Water Discharge
U.S. Geological Survey (USGS)
An autonomous, electromagnetic seepage meter to study coastal groundwater/surface-water exchange
U.S. Geological Survey (USGS)
FSU Marine Laboratory
Florida State University, Tallahassee, Florida
FSU Department of Oceanography
Florida State University, Tallahassee, Florida
Submarine Groundwater Discharge: An Unseen Yet Potentially Important Coastal Phenomenon
University of Florida, Institute of Food and Agricultural Sciences

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in this issue: Fieldwork
cover story:
Monitoring Eruption of Augustine Volcano

Submarine Groundwater Discharge Study

USGS Assists in Search for Airplane Wreckage

Research Methane Hydrate off Southern California Coast

Outreach Open House at FISC St. Petersburg

Falmouth Science Teachers visit USGS Woods Hole

Sea-Floor-Mapping Systems Described on New Web Pages

Awards Wetland Ecologist Named Fulbright Senior Specialist

Multiple Award Winner in USGS Photography Contest

Staff USGS Scientist on Nanjing University Committee

Publications March 2006 Publications List


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Updated April 15, 2014 @ 01:53 PM (JSS)