INCLINE VILLAGE, Nev. – As environmental engineer Geoffrey Schladow launched this week into his startling new findings about the potentially dire consequences of global warming at Lake Tahoe, a member of the audience gasped.
"That was the correct response," said Schladow, who directs the UC Davis Tahoe Environmental Research Center.
The news about one of California's recreational jewels was grim. According to a study by Schladow and other Davis researchers, a warming trend already under way could shut down the deep churning of oxygen and nutrients that supports life in the lake – in just 11 years.
That, in turn, could trigger a wave of ecological disruptions from a "dead zone" at the bottom to unprecedented algae blooms near the surface, changing the clear, predominantly cobalt blue lake to murky green.
Schladow characterized such a change as "a really scary thing."
Just as the melting permafrost in the Arctic has proved a living laboratory for studying climate change, scientists are examining large, deep-water lakes – in part because water temperatures at lower depths reflect long-term climatic changes more accurately than temperatures at the surface.
What they are finding troubles them. Lake Zurich in Europe is warming. So, too, are Lake Tanganyika in Africa and Lake Biwa in Japan, where the deep mixing of nutrients and oxygen already has been impaired.
"Lakes around the world … are showing extreme stress, particularly in their ability to mix," said Charles Goldman, an internationally recognized lake scientist at UC Davis.
Goldman and other scientists are gathering today at Tahoe for a workshop on lakes and climate change. Among those attending is Michio Kumagai, a Japanese researcher and eyewitness to the problems at Lake Biwa, a drinking water source for 14 million people.
"Last year, we had a warm winter and a hot summer – so Lake Biwa did not mix well," Kumagai said. "That led to the deaths of many ducks from a toxin in the algae. Also, many fish were killed because of low oxygen near the bottom. Last year was terrible."
Tahoe could one day resemble Lake Biwa if the changes Schladow outlined at the fourth Biennial Tahoe Basin Science Conference occur. Such a transformation could complicate – perhaps even unravel – decades of costly and controversial efforts to restore Tahoe's clarity.
Water treatment costs could increase, due to algae blooms. And the fabled mackinaw, a trout introduced to Lake Tahoe in the 19th century and which thrives in deep cold water, would likely suffer, while more recent warm-water arrivals such as largemouth bass and Eurasian watermilfoil – an aquatic plant – would thrive.
"This would be a real change of state for the lake," said Robert Coats, a UC Davis research ecologist in the conference audience Tuesday. "It would be the kind of thing people call a tipping point."
The "worst-case scenario," Coats added, would be the release of large volumes of phosphorus, a nutrient that spurs algae growth, now locked in sediment on the lake bottom. "In a very short time, the lake would go from blue to green," he said.
Schladow's new research grew out of a 2006 study by him, Coats, Goldman and others that was published in the journal Climate Change. It found Lake Tahoe's water temperature had increased an average 0.027 degrees Fahrenheit a year between 1969 and 2002 – nearly one degree overall.
While that change may seem small, Schladow said it is significant: A warmer lake is more stable and more resistant to mixing.
One reason for the change, he said, is a trend toward warmer nights at the lake over the past century. Since 1911, the average annual nighttime low has risen more than four degrees and now is close to the freezing point of 32 degrees.
A glittering sheet of mica in the morning sun, a summer getaway for generations of Californians, a blue gem encircled by snowcapped mountains – Lake Tahoe is all of that and more. But its beauty belies a maze of threats unknown to many.
Call The Bee's Tom Knudson, (530) 582-5336.
