A Clearing Trend: Tahoe clarity decline flattens out | SierraSun.com

A Clearing Trend: Tahoe clarity decline flattens out

Sun File PhotoU.C. Davis researchers measure Lake Tahoe's clarity by viewing a white disk as it disappears from view beneath the water.

Lake Tahoe was slightly clearer in 2007 than 2006, researchers said Monday, and a new analysis shows the lake’s historic clarity loss may have slowed down.

UC Davis Tahoe Environmental Research Center scientists’ latest numbers reveal a person could see through Lake Tahoe’s waters to an average depth of 70.2 feet in 2007, two and a half feet greater than the 67.7-foot measurement taken during 2006.

More significantly, researchers say, is a new model that shows the roughly foot per year clarity loss in the lake since 1968 has slowed.

“From 1968 to 2000 there was a near-continuous decline in lake clarity,” said Geoffrey Schladow, director of the research center, in a statement from UC Davis and the Tahoe Regional Planning Agency. “There were several years at a time when things seemed to improve, but invariably we returned to the same trend. But since 2001, we have had seven years in which the clarity has consistently been better than the long term trend would have predicted.”

In 1968, the lake was clear to an average depth of 102.4 feet.

Exactly how much the decline in clarity has slowed wasn’t calculated by researchers, but John Reuter, associate director of the research center said clarity decline has slowed “significantly” since 2001.

“There’s no other time in the historical record were we see this sort of reduction in rate of decline,” Reuter said.

Still, Reuter shied away from calling the slow down an “improvement.”

“It’s just not getting worse,” Reuter said.

The results of the latest study don’t include a reason for the slow down in clarity loss and researchers cautioned against extrapolating the data too far into the future.

“It is difficult to use data from a small number of years to draw conclusions about when the trend might change from a slowdown in clarity decline to an improvement in clarity,” according to the press statement.

Nevertheless, researchers are “very guardedly optimistic” about the results, Reuter said.

“We have never seen this before an we hope it’s a trend that will continue,” Reuter said.

Lake Tahoe’s clarity is measured by how far below the surface scientists can see a white, 10-inch plate known as a Secchi disk.

In 2007, the waters of Lake Tahoe were clear to an average depth of 70.2 feet, an improvement from the 67.7 feet reading in 2006, according to a report by researchers with the University of California, Davis.

The report was welcomed by the Tahoe Regional Planning Agency and other agencies charged with protecting the lake, who suggested that the data provide evidence that years of investments in reducing and improving runoff may be paying off.

Federal, state, and local agencies, homeowners, and businesses have spent over half a billion dollars on water quality projects for reducing and improving runoff through Tahoe’s Environmental Improvement Program, which was launched in 1997 by President Clinton.

” Associated Press

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