New research at Lake Tahoe focuses on growth of algae

RENO -- Scientists at Lake Tahoe have launched a new study to try to better understand what causes clarity-robbing algae growth on some shores around the azure lake in the Sierra Nevada.

The Desert Research Institute and Tahoe Environmental Research Center are leading the research that will examine a variety of sources of nutrients that cause the growth, from air pollution and erosion spurred by development to over-fertilized lawns.

Rising water temperatures also contribute to algae growth, as do Asian clams, an invasive species that serves as food for algae when they die.

Algae growth has remained fairly consistent during the past decade but ebbs and flows on an annual basis, said Scott Hackley, a researcher who has overseen similar studies for the University of California, Davis' Tahoe Environmental Research Center in Incline Village.

"It's something we're monitoring. We are trying to understand where it is growing the heaviest and why," he told the Reno Gazette-Journal last week. "To the extent you can, you want to control the nutrients."

In the past 20 years, Lake Tahoe's clarity has shown an eight-foot improvement. That means a white measuring disc can be seen as deep as 78 feet below the surface, compared with 70 feet in 1990.

Efforts to protect the lake are aimed at extending the clarity to 100 feet. It was more than 102 feet the first year scientists formally measured it in 1968.

Studies have placed increased emphasis on nitrogen from fertilizers, which can accelerate algae growth. Hackley said he does not believe "it's a major contributor."

"It's a combination of inputs," he said, adding that urban development in general spurs algae growth

Recent examinations of data collected by Hackley from 2004 to 2006 showed periphyton algae levels near communities were three to six times higher than levels found in 1982 to 1985.

Skip Jarvis is among the area residents who said there's significantly more algae near some beaches, including Hidden Beach near Sand Harbor State Park south of his home in Incline Village.

"The rocks are a lot slipperier than last year," Jarvis said.

The Tahoe Regional Planning Agency should more strictly regulate landscapers and gardeners around the lake, Jarvis said. Landscapers caught over-fertilizing or using the wrong fertilizers should be fined, and repeat offenders should lose their business licenses, he said.

"That would take care of a high degree of it," Jarvis said.

Jeff Cowen, TRPA community liaison, said an ordinance requires landowners with more than an acre of turf to submit fertilizer management plans to the agency, and those plans are monitored. There's no requirement for smaller parcels.

Doug Martin, Nevada Tahoe Conservation District manager, said many residents follow the fertilizer guidelines and keep runoff largely on their property.