Clarity of Lake Tahoe declines in 2010
By SANDRA CHEREBAssociated Press
Published: Friday, Aug. 12, 2011 - 1:43 pm
CARSON CITY, Nev. -- The clarity of Lake Tahoe declined last year to its second lowest level since record keeping on the "jewel of the Sierra" began in the 1960s, researchers said Friday.
In the annual "state of the lake" report, scientists with the University of California, Davis Tahoe Environmental Research Center said Tahoe's waters last year were clear to an average depth of 64.4 feet, down from 68.1 feet in 2009.
"Taken alone, that decline in clarity is unusual but it is within the range of normal fluctuations," said Geoffrey Schladow, director of the UC Davis research center in Incline Village.
"However, an analysis of other key variables makes us think that the transparency of the lake's water may be now influenced by a new set of factors," he said.
Tahoe's clarity is measured by how far below the surface scientists can see a white, 10-inch plate known.
In 1968, the lake was clear to an average depth of 102.4 feet.
Over the last 43 years, more than half of those years saw measurement swings - both positive and negative - as great or greater than this year's decline.
Friday's report comes in advance of the 15th annual Tahoe Summit, to be held next Tuesday at Homewood Mountain Resort on the west side of the lake. The summit has been held every since 1997, when President Clinton launched the inaugural event that brought international attention to the environmental threats plaguing the "jewel of the Sierra."
In that year, the lake's clarity reached its lowest reading of 64.1 feet.
The report suggests climate change may have created conditions that favor a single-cell algae, which can cloud clarity.
"This year in particular, these single-cell algae were concentrated very close to the surface, strongly scattering light and thereby impacting lake clarity," said John Reuter, associate director of the research center.
The report also showed that while winter water clarity has been improving over the last decade, likely because of strides in reducing urban storm water runoff, summer clarity continues to deteriorate. The culprit there could be excess nutrients that spur algae growth.
Satellite images showed that clarity on the eastern shore of Lake Tahoe in Nevada is "significantly lower" than on the western shore in California. That finding could heighten the urgency for discussions between Nevada and California to settle their differences over how environmental issues in the shared Tahoe Basin should be managed.
Nevada lawmakers this year passed a bill that calls for Nevada's possible withdrawal from the bi-state compact that governs development and environmental issues unless a new regional plan more than 20 years overdue is adopted.
The report said the new findings underscore the need for the two states to cooperate.
"The causes of these spatial differences are currently being studied, but it appears to be closely linked to the patterns of water movements around the lake," the report said. "What happens in the waters of Lake Tahoe is a direct reflection of activities in both states.
"If a concrete example of why Lake Tahoe needs to be managed by the two states is needed, than this is one," it said.
"Taken alone, that decline in clarity is unusual but it is within the range of normal fluctuations," said Geoffrey Schladow, director of the UC Davis research center in Incline Village.
"However, an analysis of other key variables makes us think that the transparency of the lake's water may be now influenced by a new set of factors," he said.
Tahoe's clarity is measured by how far below the surface scientists can see a white, 10-inch plate known.
In 1968, the lake was clear to an average depth of 102.4 feet.
Over the last 43 years, more than half of those years saw measurement swings - both positive and negative - as great or greater than this year's decline.
Friday's report comes in advance of the 15th annual Tahoe Summit, to be held next Tuesday at Homewood Mountain Resort on the west side of the lake. The summit has been held every since 1997, when President Clinton launched the inaugural event that brought international attention to the environmental threats plaguing the "jewel of the Sierra."
In that year, the lake's clarity reached its lowest reading of 64.1 feet.
The report suggests climate change may have created conditions that favor a single-cell algae, which can cloud clarity.
"This year in particular, these single-cell algae were concentrated very close to the surface, strongly scattering light and thereby impacting lake clarity," said John Reuter, associate director of the research center.
The report also showed that while winter water clarity has been improving over the last decade, likely because of strides in reducing urban storm water runoff, summer clarity continues to deteriorate. The culprit there could be excess nutrients that spur algae growth.
Satellite images showed that clarity on the eastern shore of Lake Tahoe in Nevada is "significantly lower" than on the western shore in California. That finding could heighten the urgency for discussions between Nevada and California to settle their differences over how environmental issues in the shared Tahoe Basin should be managed.
Nevada lawmakers this year passed a bill that calls for Nevada's possible withdrawal from the bi-state compact that governs development and environmental issues unless a new regional plan more than 20 years overdue is adopted.
The report said the new findings underscore the need for the two states to cooperate.
"The causes of these spatial differences are currently being studied, but it appears to be closely linked to the patterns of water movements around the lake," the report said. "What happens in the waters of Lake Tahoe is a direct reflection of activities in both states.
"If a concrete example of why Lake Tahoe needs to be managed by the two states is needed, than this is one," it said.
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