Magazine article Science News

Seep and Ye Shall Find: Hidden Water Flow

Magazine article Science News

Seep and Ye Shall Find: Hidden Water Flow

Article excerpt

Subterranean rivers flowing slowly through the ground carry freshwater into the ocean in quantities far larger than scientists had suspected, according to recent research conducted off the coast of South Carolina. These invisible seeps season the seas with salts, metals, and pollutants.

During July 1994, groundwater oozed out through sediments on the seafloor along the state's coastline at a rate of 30 billion liters per day. This is a little under half the water entering from the region's rivers, says Willard S. Moore of the University of South Carolina in Columbia.

'What we've done is show that the groundwater input to the coastal ocean is extremely important,' says Moore, who described his results in the April 18 Nature.

'This has tremendous implications for understanding everything from pollution to geochemistry,' comments ecologist George M. Simmons of the Virginia Polytechnic Institute and State University in Blacksburg.

Although hidden from view, water stored in porous, underground rocks constitutes 97 percent of the world's supply of liquid freshwater. Like surface rivers, which flow downhill toward the sea, some of this groundwater migrates downward through subsurface formations that open beneath the ocean.

Scientists have made spot estimates of groundwater entering the sea, but Moore's study is the first to gauge this process on a regional scale.

The South Carolina geochemist happened on a technique for measuring groundwater flow while he was studying naturally occurring radium in a salt marsh. Moore found that the amount of an isotope, 226Ra, in the marsh water exceeded that in ocean water. Because no rivers emptied into the inlet, the radium must have come from groundwater seeping into the marsh, he reasoned.

He then used 226Ra to trace groundwater entering coastal waters and again found excess radium that could not have come from the ocean or rivers. …

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