HIGH-TECH WATER DIVINING COULD HELP SCIENTISTS BETTER UNDERSTAND COASTAL BAY ECOLOGY
08 February 2006 - University of Texas at Austin

A marine chemist at the University of Texas Marine Science Institute has found hidden pockets of saltwater seeping into Nueces Bay, Texas from beneath its floor.

Like a water diviner for the 21st century, Dr. John Breier used an electrical resistivity device that penetrated sediments along the bay floor with an electrical current. The data gathered from the device showed Breier where saltwater was seeping up into the bay.

“We found two areas in the bay where there is a submarine supply of water that’s high in salinity and low in dissolved oxygen,” says Breier, a former graduate student in the lab of UTMSI professor Dr. Hedy Edmonds.

Knowing the locations of the submarine water inputs will help coastal ecologists better understand how changes in the bay’s fresh- and saltwater mix can lead to problems like harmful algal blooms. Bays are highly productive and commercially important ecosystems that can be affected by changes in nutrients and water chemistry.

Prior to Breier’s study, the location and contributions of important submarine water inputs into Nueces Bay were unknown.

To find the submarine water inputs, Breier towed the electrical resistivity instrument behind a boat on a 10-mile track around the bay. The instrument emitted a continuous electrical current.

Much like sound waves are used by seismologists to survey the earth, the electrical current penetrated the sediments and returned data on the salinity of water seeping up from below the bay floor. Breier measured sediments as deep as 20 feet below the floor of the bay.

He and his colleagues also measured the salinity, water temperature, oxygen levels and radium concentrations (a naturally occurring isotope enriched in groundwater and oil field brine) in surface water around the bay.

When Breier combined all of the data, he found two large areas in the bay where the water was high in salinity, low in dissolved oxygen, high in radium and elevated in temperature. These characteristics are indicative of submarine saltwater discharging into the bay.

“The saltwater could be coming from natural groundwater discharge or from leaky petroleum wells and pipelines,” says Breier.

Breier and his UTMSI colleagues are pursuing further studies to determine if the submarine water inputs are from natural discharge or from oilfield brine leaking through old wellheads or pipelines in the bay.

Oilfield brine is salty water found naturally with oil. It shares many of the chemical characteristics of brackish groundwater but is more concentrated in tracers such as radium. Small discharges of these brines could have the same effect as a large flow of groundwater.

Regardless of the source of the submarine water discharge, Breier says that knowing the location of the submarine inputs into the bay will help scientists better understand changes that could lead to problems in the bay ecosystem.

“To us what’s most important about this work is our ability to find these discharges, like submarine groundwater discharge, which aren’t apparent to the naked eye and doing so with enough spatial detail that we can begin to address their ecological impacts,” says Breier.

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