Warming climate fuels lake worries

RENO -- A new study suggests a warming climate could upset Lake Tahoe's food chain and delicate ecosystem.

Researchers from the University of California-Davis Tahoe Environmental Research Center studied diatoms, single-celled plants that form the base of the food chain in Tahoe and other large bodies of water.

Their study finds that warming could alter the way the organisms are distributed in Tahoe's waters and impact other water species.

Among expected changes in the lake associated with warming is a significant reduction in the amount of "mixing" of Tahoe's waters, said Geoffrey Schladow, director of the research center.

Less upwelling of water from Tahoe's depths could make it more difficult for larger algae species to remain suspended at the lake's surface, where there is light for them to grow, Schladow said.

"This allowed the smaller diatoms, which sink more slowly, to proliferate" near the surface, Schladow said.

Diatoms are eaten by tiny animals, zooplankton, which are eaten by tiny fish. Those fish are eaten by larger fish and birds as the process continues up the food chain to larger predators.

Any change in diatom distribution doubtless will have some impact on the overall food chain, said lead researcher Monika Winder.

"It could actually cascade up to the higher levels. It is inconceivable that you could alter the base of the food web and not have other things start changing. What those changes will be, we don't know yet."

Among the possibilities are that some zooplankton species could decline, which could result in a decline of some fish species, researchers said.

Smaller species of algae remaining at Tahoe's surface for longer periods also could reduce the lake's clarity by scattering light, making the water appear greener.

Additional studies are needed to define the impact of warming on Tahoe's diatoms, Winder said.

A warming climate is one of the more threatening problems facing Lake Tahoe and must be considered as scientists and land-use managers work to protect the lake, said John Reuter, a UC Davis researcher involved in the study.

"We have to begin to take the potential effects of long-term climate change into account," Reuter said. "It's just something we cannot avoid."