TRPA hears dire forecast for Tahoe | SierraSun.com

TRPA hears dire forecast for Tahoe

Adam Jensen
Sun News Service

SOUTH LAKE TAHOE ” Their training is primarily in law, development, real estate, engineering and business, but members of the Tahoe Regional Planning Agency’s Governing Board got a lesson in limnology Wednesday.

This particular presentation in limnology – the study of freshwater rivers and lakes – focused on the effects that climate change could have on Lake Tahoe in as few as 10 years.

A spring runoff that occurs two weeks earlier than historically and the movement of species to higher elevations are two of the examples of the already visible effects of warming, Geoffrey Schladow, director of the Tahoe Environmental Research Center, said Wednesday.

But the eventual collapse of deep-water mixing in Lake Tahoe because of a warmer, more stable lake was the major focus of Schladow’s presentation, which included information from a recently completed University of California, Davis, study, the results of which were released last month.

Typically, Lake Tahoe mixes throughout its depth on average once every four years, according to a statement from the university.

Without this mixing, which supplies oxygen to Lake Tahoe’s depths, the bottom of the lake could become uninhabitable to many of the species that reside there, including recreational fish species, Schladow said.

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An oxygen-depleted lake also could cause the phosphorus to be released from lake-floor sediments, fueling algae blooms, Schladow said.

The effects warming would have on Lake Tahoe’s clarity are unknown, but after Schladow’s presentation, TRPA Executive Director John Singlaub encouraged board members to keep Schladow’s statements regarding phosphorus in mind during the board’s decision-making discussions.

Nitrogen and phosphorus once were thought to be the primary cause of Lake Tahoe’s clarity loss, but the Lahontan Regional Water Quality Control Board’s Total Maximum Daily Load now has identified fine sediment as the major factor in the decline.

Although the exact timeline of when deep-water mixing in the lake could be anywhere from 10 to 30 years, “it will, in all likelihood, happen,” Schladow said.

And it likely will take a global effort to change it.

“Locally, there is not a lot we can do,” Schladow said. “We can do our little part and advocate more be done.”

With California’s passage of AB 32, the TRPA is required with the rest of California’s agencies to reduce greenhouse-gas emissions to 1990 levels by 2020.

Greenhouse-gas reduction strategies are expected to be included in the update to the Lake Tahoe Basin’s Regional Plan, now to be presented to the board for adoption in June 2009.