Climate Change Could Mean Cloudy Future for Lake Tahoe
New threats to lake's clarity are emerging just as restoration funding is drying up
Lauren Sommer
KQED
10/11/2011
Over the last 15 years, more than a billion dollars has been spent to protect Lake Tahoe’s clear waters from runoff and erosion. Now, new threats to lake’s clarity are emerging, just as restoration funding is drying up.
Researchers from UC Davis are hot on the trail of one of those threats. On a recent late summer morning, Katie Webb and a team from UC Davis’s Tahoe Environmental Research Center went looking for it on a boat near South Lake Tahoe.
“So what we’re looking for is a metal clam corral,” Webb says, pulling on her scuba gear. The “clam corral” is a wire basket that holds clams living on the lake bottom. Webb swims down to it and attaches a rope, so the team can pull it on board.
The clams inside are Asian clams, an invasive species. They were not a welcome visitor when they were discovered in Lake Tahoe in 2002. Webb and her team are monitoring these corralled clams to see how fast the population is growing.
“So you can see this individual is number 11,” she says, pointing to a tiny number super-glued on its shell. They use the numbers to track individuals over time. “We can see how much they’ve grown since we checked them in February and it should be a lot. They grow a lot in the summertime,” Webb says.
“What they do is somewhat disturbing,” says Geoff Schladow, director of the Tahoe Environmental Research Center. Asian clams filter massive amounts of lake water and that’s where the problem starts.
“Of everything they filter, they consume about 10 percent of it and 90 percent they excrete. So their excretions are like these huge nutrient bombs,” Schladow says.
With thousands of clams per square meter in some parts of the lake, their “nutrient bombs” help create algae blooms.
“So you have this bright green, stringy algae, sort of clinging to the bottom, a few tens of yards from the beach. People would be astounded to see this cause it looks like any place but Tahoe,” he says.
In the face of this invasion, a team from UC Davis has been experimenting with rubber mats that suffocate Asian clams on the lake bottom. So far, the treatment looks promising.
Tahoe Basin Building Boom
Keeping the lake blue – and not green – has been a rallying cry for both environmental groups and Tahoe’s tourism industry. Forty years ago, scientists could see 100 feet into the lake. Today, the clarity has decreased significantly to 64 feet.
“We’re essentially like a bowl and what happens on the land affects the water,” says Julie Regan of the Tahoe Regional Planning Agency. The agency oversees development on both the California and Nevada sides.
“What happened on the land in the 50s, 60s and 70s is that we had a lot of development – rampant overdevelopment,” she says. Tahoe hosted 1960 Winter Olympics at Squaw Valley. Casinos went up. Building was booming. And soon, the region had a runoff problem.
“It’s driveways. It’s houses. What you cover on the land then interferes with the soils ability to filter runoff. That’s what’s causing clarity loss,” says Regan.
Over the past 15 years, local agencies have tried to stop this decline with $1.5 billion of federal, state and local money. They’ve preserved open space and built projects to control erosion and filter runoff.
“In 2008 we got the news from the scientific community that we had stopped the slide and decline of lake clarity. That was great news,” says Regan.
