Lake Tahoe clarity

[Crowdog]

UCD scientists to help in study of Lake Tahoe
A new research tool may identify what's causing the lake to lose clarity.
By Chris Bowman -- Bee Staff Writer
Published 2:15 a.m. PDT Saturday, June 15, 2002
TAHOE CITY -- University of California, Davis, scientists have developed a computer model to better identify the causes of Lake Tahoe's declining water clarity and find ways to halt the degradation or even reverse it.

Researchers will use the new tool to help the U.S. Environmental Protection Agency set limits on sediment and algae-inducing nitrogen and phosphorous entering the lake from urban runoff and air pollution.

The water-clarity model is part of a $6 million multiagency research and data-collection effort between now and 2007 to develop land management plans at Lake Tahoe that are more firmly grounded in science. Eight university and government scientists outlined the project Friday at a news briefing at the Tahoe City Marina.

"This is the most exciting and comprehensive scientific effort ever at Lake Tahoe," said John Reuter, a leader of the UC Davis Tahoe Research Group who developed the model with Geoff Schladow, a civil and environmental engineering professor at UC Davis.

Deemed a "national treasure" by Congress, Lake Tahoe is one of world's clearest and deepest alpine lakes. Its clarity, however, has declined in the past 35 years with the buildup of ski resorts, casino-hotels and vacation homes in the 500-square-mile Tahoe basin.

Charles Goldman of UC Davis, the first scientist to foresee Tahoe's troubles, has recorded the clarity diminishing at an average rate of 18 inches a year. Today, a white plate lowered into the lake is visible only to about 74 feet.

The bistate Tahoe Regional Planning Agency has set a clarity goal of about 100 feet, the depth Goldman measured when he began his monitoring 35 years ago.

"This is going to take years -- decades actually," said Dave Roberts, a scientist with California's Lahontan Regional Water Quality Control Board.

Though Tahoe is one of the most studied lakes in the world, land-use regulators imposed many building restrictions to control runoff without knowing what pollution reduction, if any, resulted.

"The research never really told anybody how much reduction has been achieved or how much is needed," Reuter said.

The UCD model, which has been in the works since 1997, will allow scientists to predict outcomes based on extensive lake monitoring.

"The lake is a deck of cards, and each card, each layer, has its own characteristics," Schladow said. "Each day, the lake goes through cycles."

Each layer has different nutrients, sizes of particles, depth, temperatures and exposures to sunlight, he said. The model accounts for the changes every two hours.

One of the most pressing questions scientists hope to answer is the effect of air pollution on the lake.

Scientists have established that the atmosphere seeds the lake with fine particles of dust and soot and oxides of nitrogen, mostly from vehicle exhaust. But many questions need to be answered before regulators would considering restrictions on cars and fireplace smoke, said Harold Singer, executive officer of the Lahontan board: How are these pollutants responsible for the clouding the lake? To what extent are they generated within the basin or blown in from the Sacramento Valley?

"When we make the final decision, we want to be able to base it on the best available data," Singer said.

The chief cause of the loss of water clarity is the growth of algae, according to the Tahoe researchers. The free-floating, tiny green cells absorb light, reducing water clarity.

Unnaturally high volumes of sediment washed into the lake overfertilize the water with nutrients that feed algae, accelerating the population.

The nutrients are nitrogen, primarily from air pollution, and phosphorous from fertilizers and soil.

http://www.sacbee.com/content/news/story/3216076p-4255588c.html

Copyright © The Sacramento Bee
-----------------------------------------------------------------------------

[Crowdog]

Unclear if Tahoe clarity on mend
2001 improvement could be anomaly
Glen Martin, Chronicle Environment Writer
Monday, June 17, 2002
©2002 San Francisco Chronicle.

URL: http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2002/06/17/BA154624.DTL


It has been a good year for Lake Tahoe -- the best, which is to say the clearest, in five years. Trouble is, no one can tell if that's a result of assiduous environmental measures or a simple fluke of nature.

This alpine lake's fable clarity has been declining for more than two decades. In 1997, following 10 years of analysis, government officials authorized expenditures of $900 million to turn things around, invoking rigorous strictures on construction, water discharges and sediment run-off.

In 2001, the Secchi disc -- a small white disc that is used to gauge visibility -- didn't disappear from sight until it reached approximately 23 meters, deeper than the 20 meters recorded in 2000.

That's good news, depending on who you talk to.

"I like to think we're turning it around," said Gabby Barrett, a manager for the Tahoe Regional Planning Agency, during a workshop at the Tahoe City Marina. "But it could be due to the drought."

Barrett explained that dry periods -- such as the kind Tahoe has experienced during the last two years -- meant less water running off into the lake. Virtually all the water that drains into Tahoe is saturated with sediment and nutrients that stimulate algae. Sediment and algae translate to reduced clarity.

Still, it's an encouraging development, and one that government staffers, university scientists and environmentalists are eager to encourage. So on Saturday, they rolled out the newest phase of the long-term plan to clean up Tahoe: The Total Maximum Daily Load formula, or more succinctly, TMDL.

A functional TMDL will allow researchers to precisely identify the amount and variety of crud that can go into the lake while still maintaining clarity goals.

It's a process that will allow researchers to fine-tune the clean-up process, to put the money where it will do the most good.

"Up until now we've had a kind of scatter-gun generic approach to reducing the pollution load," said Harold Singer, the executive director for the state's Lahontan Regional Water Quality Control Board, the lead agency in setting pollution reduction standards for the Tahoe Basin.

"The TMDL we're developing will be much more refined," said Singer. "It will answer the question of 'How effective have we been?' and indicate where we should concentrate our energies and our dollars."

So far, said Singer, every property owner in the basin has had to take meticulous pains to reduce sedimentation and nutrient run off. Whether it's a new driveway or a new freeway, any proposed project is required to jump through a series of daunting regulatory hoops.

That may change when the final TMDL is adopted by Tahoe's regulating agencies as policy, a move expected by 2007.

"You could see significant tightening in some areas, and loosening in others," said Singer. "For example, our data may show we could get a lot more bang for our buck by coming down hard on road activity in a particularly problematic watershed rather than enforcing rather broad rules for all the roads in the basin."

When all the data are in, the TMDL may reach out and touch people well beyond the Tahoe Basin.

"We know that some of the nitrogen deposition for the lake could be coming from vehicle exhaust (as far away as the Central Valley and the Bay Area)," said Jeremy Sokulsky, an associate engineer for the Lahontan water quality board.

"If our data show cars account for only 5 percent of the nitrogen, it's no big deal," said Sokulsky. "But if it's 50 percent, it may be the basis for proposing new vehicle emission standards (for the state)."

But just because some rules may change, said Singer, that doesn't mean the lake will receive less protection.

"Our goal, as always, is to achieve visibility of 29.6 meters," he said. "That was the visibility we had in the 1970s, and while it's admittedly an aesthetic rather than a health standard, it's widely held as desirable. It's what people think Tahoe should look like."

Environmentalists are generally sanguine that the TMDL is no shell game.

"Actually TMDL's are required by the federal Clean Water Act for (clean-up projects of Tahoe's magnitude)," said Jon-Paul Harries, a program director for the League To Save Lake Tahoe, an environmental watchdog group.

"There'll be slackening in some areas and tightening in others, but the fact remains that this is all pollutant-driven," said Harries. "The goal remains the same -- reduce sediment and nutrients. We're naturally going to track how this all develops, but we're basically positive at this point."

On Saturday, scientists unveiled a nifty tool that will aid them in hammering out an effective TMDL: a new Tahoe clarity computer model developed by the Tahoe Research Group at UC Davis.

The model allows scientists to log inputs -- sunlight, rainfall, creek levels, groundwater seepage -- and predict the clarity of the lake in two hour increments over the course of any given day.

"How well does it do?" asked Geoff Schladow, professor of civil and environmental engineering at Davis. "Very well."

Schladow backed up his contention with printouts of phytoplankton densities and Secchi disc readings from a particular day in 1999. The predicted values for the plankton and disc readings mimicked the measured values to an uncanny degree.

"This will be very useful in predicting future clarity responses to nutrient reduction plans," Schladow said.

But no matter how well the computer models work, no matter how accurate the final TMDL is, no matter how much money is devoted to Tahoe, it's clear, so to speak, that expectations should be moderate.

The current Secchi disc readings are heartening, scientists say. But they may be mere statistical hiccups, not evidence of a solid turnaround.

"The nutrient loads change all the time, and the lake itself is constantly changing," said Schladow. "It's a dynamic system."

In the final analysis, cleaning up Tahoe is a marathon, not a sprint, say researchers.

"Basically, it's going to take years, if not decades, to halt the degradation and improve clarity," said Dave Roberts, an environmental scientist with Lahontan water quality board.

E-mail Glen Martin at glenmartin@sfchronicle.com.

©2002 San Francisco Chronicle.

http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2002/06/17/BA154624.DTL