Radioactive atoms will date sediment

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CARNESVILLE, Ga. - The north fork of the Broad River has a lot going for it. It moves well, flowing freely through rural backwaters in north Georgia. And it's cleaned regularly by volunteers who fish out junk and debris.

University of Georgia Crop and Soil graduate research assistant Rajith Mukundan checks equipment used to monitor sediment in the north fork of the Broad River near Carnesville, Ga.  Associated Press
Associated Press
University of Georgia Crop and Soil graduate research assistant Rajith Mukundan checks equipment used to monitor sediment in the north fork of the Broad River near Carnesville, Ga.

But the murky stream is also one of more than 1,000 in the Southeast hindered by high levels of sediment, the fine soil particles that can devastate a river's food supply. Researchers staked along its winding path are testing it using the most unlikely of means - nuclear fallout - in hopes of changing the ways scientists look at river pollution.

The fine dirt particles keep fish from laying eggs on the bottom of the river. The result often saps a waterway of its biodiversity, spawning one or two dominant species instead of a rich variety.

For humans, a sediment-filled river is a financial issue. The muddier the water, the more costly it is to clean it up.

University of Georgia scientist David Radcliffe's experiment will try to prove that destructive farming techniques of the 1800s and early 1900s might be source of modern-day sediment problems.

"If it does turn out that bank erosion is the major source, you've got to change the entire approach," Dr. Radcliffe said. "Suddenly, reducing erosion from the fields isn't going to help."

He will use nuclear fallout to test his theory by gathering sediment samples and measuring how much of the radioactive isotope Cesium-137 remains. If the cesium levels are high, then the sediment was loosed within the past 60 years - when cesium fell because of nuclear bomb tests.

If that's the case, he said environmentalists would need to focus on planting trees on river banks to anchor loose soil and reinforcing rural streams.

Knowing the source of the sediment could help scientists attack what can be a prickly problem.

Dr. Radcliffe and doctoral student Rajith Mukundan will collect more than 1,000 samples over a three-year span to test for cesium and other chemicals. Then with the help of scientists from the National Sedimentation Laboratory in Oxford, Miss., and the Hydrology and Remote Sensing Laboratory in Beltsville, Md., they will analyze the results.


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