Nuclear fallout is an unlikely ally in hunt for pollution source

<p>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.</p><p>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.</p><p>As most gutsy experiments go, University of Georgia scientist David Radcliffe's takes aim at a central environmental premise.</p><p>For years, scientists have assumed that sediment filling rivers comes from soil eroding from farms, construction sites and dirt roads. But his team wonders whether the sediment pollution may be a legacy of history instead of today's abuses.</p><p>He intends to prove that destructive farming techniques during cotton's heyday in the late 1800s and early 1900s may be source of modern-day sediment problems. And proving the point could change the tactics used to crack down on this sort of "non-point" pollution.</p><p>"If it does turn out that bank erosion is the major source, you've got to change the entire approach," said Radcliffe. "Suddenly, reducing erosion from the fields isn't going to help."</p><p>To test his theory, Radcliffe has turned to one of man's most horrific inventions: Nuclear fallout.</p><p>Nuclear bomb tests after World War II dispersed the radioactive isotope Cesium-137 into the atmosphere, and it settled in the top few inches of soil. Radcliffe and Ph.D. student Rajith Mukundan will use the isotope as a timestamp of sorts to determine the sediment's age.</p><p>If the cesium levels are high, then the sediment was loosed within the last 50 years, and likely comes from the more traditional sources of erosion, such as nearby fields and construction sites. However, if the level is low, then it means the sediment is older, and may have been kicked up generations ago when every inch of ground was farmed for cotton.</p><p>If that's the case, then he said environmentalists would have to consider a new approach to reducing the sediment, one which may focus on planting trees on river banks to anchor loose soil and a plan to reinforce rural streams at critical points.</p><p>Knowing the source of the sediment could help scientists attack what can be a prickly problem.</p><p>The fine dirt particles rob fish of the cobbly bottom and clean rocks that provide hard surfaces for eggs to adhere, as well as the tiny crevices where eggs can be hidden from predators. The result often saps a river of its biodiversity, spawning one or two dominant species instead of the rich variety naturally found in many waterways.</p><p>For humans, a sediment-filled river is a financial issue. The muddier the water, the more costly it is to clean it up.</p><p>Radcliffe and Mukundan have their work cut out for them.</p><p>They must 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.</p><p>The process will take the foresight of a forecaster. Because the brunt of sediment is carried in by storms, the researchers will need to predict when large storms roll in to set up their equipment.</p><p>"The perfect situation for us is a tropical storm system," said Radcliffe with a shrug.</p><p>"If we're right, then it's a whole new ballgame," he said. "If not, then we'll be confident our current system works. A bad experiment is one you can't prove right or wrong."</p><p>___</p><p>On the Net:</p><p>HASH(0x2deed10)</p>

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