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“While we expected that the lake would mix less in the future,
learning that we may be only a decade or two from the complete
shutdown of deep mixing was very surprising.”
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Warming Could Radically Change Lake Tahoe in 10 Years

March 24, 2008

A new UC Davis study predicts that climate change will irreversibly
alter water circulation in Lake Tahoe, radically changing the
conditions for plants and fish in the lake — and it could happen in
10 years.

One likely result would be a warmer lake overall, with fewer
cold-water native fish, and more invasive species, such as
large-mouth bass, bluegill and carp.

Still unclear is how the changes would affect the lake’s phenomenal
clarity and cobalt-blue color, which have helped to make the Tahoe
Basin an international vacation destination.

The new findings were announced March 18 at a Tahoe scientific
conference by three lake experts from the Tahoe Environmental
Research Center at UC Davis — Director Geoffrey Schladow, Associate
Director John Reuter and postdoctoral researcher Goloka Sahoo.

“What we expect is that deep mixing of Lake Tahoe’s water layers will
become less frequent, even non-existent, depleting the bottom waters
of oxygen. This will result in major, permanent disruption to the
entire lake food web,” Schladow said.

“This is not unheard of,” he continued. “Anoxia (oxygen depletion)
occurs annually in most lakes and reservoirs in California in the
summer. But Tahoe has always been special. It’s been above and beyond
such things.

“A permanently stratified Lake Tahoe becomes just like any other lake
or pond. It is no longer this unique, effervescent jewel, the finest
example of nature’s grandeur.”

Schladow said research is ongoing to determine if lowered global
greenhouse-gas emissions would significantly slow the lake’s decline,
or even prevent it.

UC Davis researchers are in their 50th year of teasing apart the
intertwining threads of biology, chemistry and physics that determine
what Lake Tahoe looks like and what organisms live in it.

One of their chief objectives has been to understand the
clarity-clouding effects of pollution from population growth and
development, so that policymakers can devise solutions. Then, in
December 2004, they reported that the lake was showing a new
influence: Its water was warming up, probably because of global
climate change.

The new study combined 40 years of weather data in the basin with
mathematical models of global climate to create likely scenarios of
future climate conditions at Lake Tahoe. Using those scenarios, the
team employed a lake physics model to see how various combinations of
probable air temperatures, cloudiness and wind speed would affect the
mixing of water layers in the lake.

Currently, Lake Tahoe water mixes, on average, every four years. The
deepest mixing typically occurs in late February. This winter — a
particularly cold and snowy one — Lake Tahoe experienced mixing
throughout its entire 1,644-foot depth.

This mixing has profound ecological and water-quality impacts. Deep
mixing moves nutrients from the lake bottom to the water surface,
where they promote the growth of algae. And it takes oxygen from the
surface and distributes it throughout the lake, which supports
aquatic life.

The new study showed that, if global greenhouse-gas emissions
continue at current levels, mixing could become less frequent and
less deep — even stop altogether as soon as 2019.

Schladow said that was quite a shock. “While we expected that the
lake would mix less in the future, learning that we may be only a
decade or two from the complete shutdown of deep mixing was very
surprising.

“If mixing shuts down, then no new oxygen gets to the bottom of the
lake, and creatures that need it, such as lake trout, will have a
large part of their range excluded,” Schladow said.

Equally worrying, he said, is the likelihood that when the oxygen is
gone, phosphorus that is currently locked up in the lake-floor
sediments will get released. This phosphorus will eventually reach
the lake’s surface, where it will fuel algal growth. Algae blooms can
cause many problems, including reduced lake clarity, unpleasant odors
and bad-tasting drinking water.

The climatic changes that are expected to affect Lake Tahoe are also
impacting lakes around the world. These widespread concerns have been
the topic of a science workshop at the Tahoe Environmental Research
Center that runs through March 25. Researchers from Japan, New
Zealand, Chile and the United States will discuss strategies to pool
and analyze data from many of the lakes in the Pacific Rim region.
Their goal is to learn more about the security of drinking-water
supplies and the ecological sustainability of these lake systems.

About the Tahoe Environmental Research Center at UC Davis

The Tahoe Environmental Research Center conducts and supports
multidisciplinary research, education and public outreach on lake
systems and their contributing watersheds and airsheds. Lake systems
encompass the physical, biogeochemical and human environments, and
the interactions between them. The center is committed to providing
objective scientific input to support the restoration and long-term
sustainability of the Lake Tahoe Basin. It is a program of the John
Muir Institute of the Environment at UC Davis.

Additional information:
UC Davis news release, Dec. 20, 2004: UC Davis Study Shows Lake Tahoe
Is Warming Up
UC Davis news release, Aug. 15, 2007: UC Davis Issues New Tahoe
Status Report; Shows Warming Trend

Media contact(s):
* Geoff Schladow, Tahoe Environmental Research Center, (775)
881-7563, gschladow@ucdavis.edu (On March 22-25, reach him by cell
phone: (530) 902-2272.)
* John Reuter, Tahoe Environmental Research Center, (530) 304-1473,
jereuter@ucdavis.edu
* Sylvia Wright, UC Davis News Service, (530) 752-7704, swright@ucdavis.edu

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