[Water_news] 3. DWR'S CALIFORNIA WATER NEWS: WATERSHEDS - 9/3/08

Department of Water Resources

California Water News

A daily compilation of significant news articles and comment

 

September 3, 2008

 

3. Watersheds –

 

 

Asian clams another possible threat to Lake Tahoe

Reno Gazette-Journal- 9/3/08

By Jeff Delong  

                                

With concern mounting that Lake Tahoe could be overrun by invasive mussels, some scientists are considering the possibility that another foreign visitor now living in the lake already be causing problems.

 

The number of Asian clams, first discovered on Tahoe's bottom in 2001, is "far more extensive" than previously thought, scientists said.

 

Clam beds have been found along a swath of Tahoe's southeast shore from South Lake Tahoe northward to the Zephyr Cove area.

 

Researchers are exploring whether the clams might be associated with a bloom of algae in the area this summer.

 

Others are concerned that the clams could boost calcium levels in isolated areas of the lake, potentially allowing destructive quagga or zebra mussels to become established.

 

"It might be this existing invader is modifying the bottom environment," said Sudeep Chandra, an environmental science researcher at the University of Nevada, Reno. "One invader can facilitate another."

 

Officials at Lake Tahoe are increasingly concerned that quagga or zebra mussels, already thriving in parts of California and Southern Nevada, could become established in the landmark alpine lake. The quickly reproducing mollusks could profoundly alter the lake's ecosystem, clog water intakes and litter now-pristine beaches with sharp and stinking shells.

 

The threat was magnified in late August, when quagga mussels were discovered on the stern of a cabin cruiser about to be launched at South Lake Tahoe. The mussels apparently attached to the vessel while it was in Lake Mead earlier this summer.

 

"I think it's a pretty serious issue," said Mara Bresnick, chairwoman of the Tahoe Regional Planning Agency's governing board. "It could wreak havoc."

 

Unknown is whether the lake's waters contain sufficient calcium levels for the mollusks to grow their shells.

 

Chandra recently finished the first phase of a risk assessment into the potential mussel invasion of Tahoe. The work involved taking water samples from 83 locations along Tahoe's shoreline and measuring the water for calcium.

 

The next stage of research will involve laboratory tests to determine if mussels can survive in water taken from Tahoe.

Preliminary results of the assessment's first phase, Chandra said, are somewhat encouraging.

 

"There is some variability but overall, calcium levels seem relatively low," Chandra said.

 

But in the few locations where calcium levels were higher also are in some of the same areas where Asian clams are found, Chandra said.

 

 That raises the possibility that as the clams grow and die, they leach out calcium into the water. That could pose a danger because quagga or zebra mussels, if introduced in those areas, might find sufficient calcium to gain a toe-hold in the lake.

 

"It creates a little hot bed zone," Chandra said. "Elevated calcium levels could be favorable to the quagga."

 

Scientists from the University of California-Davis Tahoe Environmental Research Center are studying whether there might be a connection between Asian clams and the bloom of algae in the waters of Marla Bay just south of Zephyr Cove. Tests have not found a link, UC Davis researcher Brant Allen said.

 

"Visually, the clams and the algae are utilizing the same area of the lake," Allen said.#

http://www.rgj.com/apps/pbcs.dll/article?AID=/20080903/NEWS04/809030422/1321/NEWS