Report paints potentially grim impact of global warming on Tahoe

It is possible that despite all the efforts of conservationists to protect the clarity of Lake Tahoe, global warming may have the greatest impact on the transparency of the basin's famed waters.

A scientific report released this spring called "The Warming of Lake Tahoe," alludes to a grim picture of the lake's future if perceived warming trends of its water continue.

The report states the "biogeochemical worst case scenario" for Lake Tahoe would be an unprecedented algae bloom. This phenomenon could be triggered if 1) a warming trend reduces the frequency Tahoe's water mixes from top to bottom, 2) resulting in an anaerobic (without oxygen) layer of nutrients on the bottom of the lake, 3) followed by a deep mixing event that disperses the anaerobic and phosphorus rich bottom toward the surface stimulating the algae bloom.

UC Davis research ecologist Bob Coats helped to research and write the report and emphasized that such a phenomenon is merely long-term speculation based on current data trends. There is no guarantee, Coats said, that such a scenario would ever occur nor is their concurrence as to the time frame required for such a phenomenon to take place.

What is certain is that there is a warming trend of Tahoe's water's similar to warming trends in lakes around the world. The warming trend corresponds with a recent estimate of atmospheric warming around the world. That rate is currently 0.017 degrees Celsius each year.

For Tahoe, an oligotrophic lake - meaning a lake that mixes completely every few years, this warming trend has the potential to alter the oligotrophic structure.

"If the lake is at a lower temperature the mixing is easier, other things being equal," Coats explained. "A warmer lake is a more stable lake - as the lake warms it becomes more resistant to mixing."

Regardless of whether this increased stability leads to the "worst case scenario," the report points out increased stability of the lakes water column impacts other ecological events. It can prolong periods of reduced clarity as sediments aren't dispersed through the volume of the lake, especially after years of heavy runoff.

Increased stability may also affect the population of microscopic plants known as phytoplankton, according to UC Davis researcher Monika Winder. Because the organisms are at the bottom of the food chain, she said, changes in their population can be an advanced warning of throughout the ecosystem.

Increased stability favors blue green algae, a toxic algae that is usually a "very bad indicator for a lake", Winder noted. Right now there are very few blue green algae in Tahoe, but a combination of increased nutrients and stability could create more favorable conditions for their populations.

Neither Winder nor Coats believe Lake Tahoe is doomed.

Because there is a correlation between lake warming and global warming, Coats said, there is the possibility that lake warming trends could level off if global warming trends level off.

According to researchers and conservationists, slowing warming trends is a matter of reducing global warming pollutants into the atmosphere, especially carbon dioxide.

A report released Wednesday by the U.S. Public Interest Research Group points states that Nevada's global warming pollution is rising faster than almost every other state. Between 1960 and 2001 releases of carbon dioxide into the air in Nevada increased by 835 percent.

The Sierra Nevada Alliance, a nonprofit alliance of conservation groups throughout the Sierra Nevada, has made climate change one of their priority programs.

"Climate change is one of the most significant changes our region is going to face in the next 25 years. It impacts everything from species, to watersheds to agriculture to communities," said Joan Clayburgh, executive director of the Alliance.

Clayburgh stressed that there are great opportunities today to make sure doomsday scenarios such as the "greening of lake Tahoe," are avoided.

Restoration efforts undertaken today are especially important, Clayburgh said, "the healthier we can make our ecosystems now the better they will be able to transition into this new climate.

"If you have a really stressed population and then the population is reduced, it has less likelihood, genetically, to make it next time around."