In the case of the lake, that means oxygen-rich surface water that was reliably churned into Tahoe's 1,644-foot depths every four years is now less apt to circulate. Nutrients carted upward and oxygen cycled downward would ebb.
In the worst-case scenario, the study found, the mixing could halt entirely by as early as 2019, a time frame that Schladow said "was very surprising."
If it happens, ecological fallout could come quickly.
"Then it's not a matter of if, it's a matter of when," Reuter said.
Lake trout and other native fish would be forced to huddle in areas that still prove habitable. Phosphorous locked in the lake's bottom sediments would be released, fueling algae blooms on the surface.
That could combine with other factors, such as particles in shoreline runoff, to rob the lake of clarity, turn the air foul and produce bad-tasting drinking water, the scientists said.
Many lakes in California and around the world suffer oxygen depletion, known as anoxia. Lake Tahoe, however, has historically been "above and beyond such things," Schladow said. But without the natural mixing cycle, it becomes "just like any other lake or pond."
The scientists are part of a half-century effort to study the lake, focusing on the causes of Tahoe's declining clarity. UC Davis researchers reported the lake's warming trend in 2004, and Schladow's team built on those findings using a computer model that combined air temperatures, cloudiness and wind speed to determine scenarios for the traditional mixing cycle.
Reuter said the scientists felt most certain about the potential effects on fish and other aquatic life. Less clear is how warming-induced changes will influence Tahoe's cobalt-blue color, he said. If the bottom phosphorous is released, the lake could quickly turn from blue to green.
Lake Tahoe is one of many in the world seeing warming waters, among them Lake Zurich and Lake Biwa in Japan. Researchers from Japan, New Zealand, Chile and the U.S. are attending the conference.
--
eric.bailey@latimes.com
