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Keep Tahoe Blue book is lengthy

KINGS BEACH – While state, federal and regional officials have rallied around the idea that raising $900 million should keep the brilliantly blue waters of Lake Tahoe from turning green, people should be aware that all incoming money and restoration efforts help. And, while getting Tahoe’s environment back to what it was 150 years ago may be impossible, the goal of reversing Tahoe’s declining clarity is achievable.

This was a message delivered Wednesday by Dennis Murphy, science leader for the just-released Lake Tahoe Watershed Assessment, at an event to unveil the 1,200 page, $1.4 million scientific report.

“With a commitment of federal and state funds and the best available science applied in resource management, we should be able to make some headway in reversing the declining clarity situation at Lake Tahoe,” said Murphy, a researcher at the University of Nevada, Reno.



“Some people have suggested it’s an all or nothing. ‘If we don’t get $900 million, why care about it.’ Any commitment of substantial funds is likely to help the situation.

“I think the primary value of the Lake Tahoe Watershed Assessment is that it’s going to allow the whole community to focus their restoration activities and take better proactive action to maximize the return on federal and state investments.”




Efforts to create the study started two years ago as a result of the 1997 Lake Tahoe Presidential Forum when concerns about Tahoe’s declining clarity came to a head, uniting environmentalists, businesses, scientists and government leaders to address the problem.

For more than 30 years, Tahoe’s clarity has diminished by more than a foot a year. Algae, the primary cause for the increased murkiness, continues to grow about 5 percent a year.

The algae growth has been spurred primarily by loading of nitrogen and phosphorous, which come from numerous sources: atmospheric deposition from car exhaust and smoke in the air; shore erosion and untreated, sediment-filled water runoff; and more.

A Secchi disk – a white dinner plate-shaped device used to measure Tahoe’s clarity – was visible at depths of more than 100 feet in the 1960s. That number is in the 60s now, and the disk would be visible only as deep as 40 feet by the year 2030 if the decline goes unchecked.

What the watershed assessment was supposed to do was compile almost all of the Tahoe research that has been completed so far into one document. Much of the information in the watershed assessment is not new; it summarizes what has already been done in areas such as Tahoe’s history, air quality, water quality, biology and socioeconomics.

“The goal of the program in the first place was to create an information base to better inform decision making at Lake Tahoe,” Murphy said.

Around the time of the president’s visit, the Tahoe Regional Planning Agency established its Environmental Improvement Program,which outlined the $900 million needed for environmental restoration at Tahoe. TRPA now is planning an EIP review, and officials said Wednesday that the watershed assessment would be used to prioritize efforts.

“I’m really, really pleased with the process,” said Chris Knopp of the Forest Service and one of the leaders in developing the report. “I think this exceeds our expectations. It doesn’t just create a compilation of existing science; there’s significant new information in every chapter.”

Some of the findings in the report include:

n Nutrient budget

Nitrogen and phosphorous contribute to algae growth, which is a major reason for Tahoe’s increasing murkiness. Historically, algae growth at Tahoe has been controlled by nitrogen input, but phosphorous has now become a more significant controlling factor. This means algae grows more rapidly when phosphorous enters the lake rather than nitrogen.

In the watershed assessment, researchers have created a nutrient budget, an estimation of the sources of nitrogen or phosphorous.

“Of the total nitrogen influx into the lake in a given year, approximately 55 percent can be attributed to atmospheric deposition, 10 percent to direct surface runoff from land immediately adjacent to the lake, 20 percent to stream loading and 15 percent to groundwater discharge,” the report states. “Of the total phosphorous load, approximately 27 percent comes from atmospheric deposition, 34 percent from direct surface runoff, 29 percent from stream loading and 9 percent from groundwater discharge.

“While specific sources of nutrients within each category have yet to be identified, understanding the contribution from any single category can help focus future management efforts,” the report states.

n Wildfire threat

In many basin forests, the report states, a wildfire that escapes early suppression could burn out of control and kill nearly half of the trees.

Officials at Tahoe have long been concerned about that possibility. The report, however, dispels that fear.

“Even under the most extreme conditions, prevailing wind patterns and local topography will contain fires to no more than one or two subwatersheds,” the report states.

n Air quality

Low-intensity wildfires that burned through Tahoe Basin forests hundreds of years ago likely made the basin’s air much more smoky than it is today, but it wouldn’t have had much impact on the lake’s clarity. That likely would not be the case if a large wild blaze happened.

“Ground-based, low-intensity prehistoric forest fires didn’t release a lot of nitrates into the air, which is one of the factors that cause the lake to become green, whereas today, nitrate emissions are part of high-intensity crown fires,” said Tom Cahill, a U.C. Davis scientist and author of the air-quality chapter of the assessment. “Additionally, modern wildfires have huge updraft plumes that can carry wood ash and phosphorous into the lake.”

n BMP effectiveness

BMPs, or Best Management Practices, could include lining ditches with rock, using natural vegetation or installing traps to catch sediment particles, with the idea that these actions will remove nutrients from runoff before water runs into Tahoe.

TRPA requires all new projects to implement BMPs, or Best Management Practices, and all property owners in the basin will eventually have to retrofit their properties with them.

The watershed assessment calls for more research on BMP effectiveness.

“Current levels of funding for research and monitoring in the areas of Best Management Practices effectiveness, source identification and control, and treatment of runoff in the Tahoe Basin is inadequate to meet the demands,” the report says.

The need for further study in the area is a suggestion with which TRPA agrees.

Said Carl Hasty, EIP coordinator for TRPA: “It’s something we know works; we don’t know how well it works.”


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