Pollution low in 1999 likely won’t continue | TahoeDailyTribune.com
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Pollution low in 1999 likely won’t continue

The engines are cleaner, but there will be more of them.

The dramatic success of the Tahoe Regional Planning Agency’s watercraft ban last year likely won’t be replicated quite so well this year, scientists predict.

The presence of gasoline compounds in Lake Tahoe’s waters in 2000 will surely be down when compared to 1997 and 1998, when levels of gasoline pollutants like benzene, toluene and MTBE were significant. However, the incredible decreases in 1999 probably won’t be achieved again; pollutants were reduced by as much as 90 percent in places last year.



The reason 1999’s results will be unachievable again is because it was the first year of the ban, and there was a limited number of newly compliant watercraft available. Not only did the cleaner engines keep gasoline out of the water, the fact that there were fewer boats and personal watercraft on the lake helped cut down pollution, too.

This year there will be more watercraft available that are powered by direct-fuel-injected two-stroke engines, which are allowed.



“It’s probably not going to be substantial, but we expect an increase in gasoline in the lake compared to last year,” said Glenn Miller, director of the University of Nevada, Reno’s team of Tahoe researchers.

Joined by researchers from the University of California, Davis; U.S. Geological Survey; and Desert Research Institute, UNR scientists will continue monitoring the lake this summer to ensure that the ban was a success.

TRPA’s crackdown on carbureted two-stroke motors started June 1, 1999. During the two years before that when TRPA indicated plans for the ban, the agency held multiple hearings, was sued, resolved the lawsuit out of court and had a team of scientists involved in extensive research to reinforce the regulation.

The targeted engines power many small boats and almost all Jet Skis and other personal watercraft. The motors, researchers said, cause much more pollution than other boat engines, releasing as much as 25 percent of their gas directly into the water.

A few watercraft companies were able to come out with new ban-compliant direct-fuel-injected motors that were used at Tahoe last summer; however, the presence of those kinds of watercraft decreased dramatically.

Last November researchers hailed the ban as a success, saying that the presence of gasoline constituents in the 23-mile-long, 12-mile-wide, 1,600-foot-deep lake decreased substantially, 50 percent in most places and 90 percent in others.

In addition to continuing to monitor for gasoline compounds, Miller said a big focus this year would be research on PAHs, or polycyclic aromatic hydrocarbons.

Those are large hydrocarbon molecules produced during combustion and are toxic to living creatures. It appears the new generation of quieter, fuel-injected engines that comply with the ban don’t burn PAHs much better than the banned carbureted two-stroke engines, Miller said.

Researchers this year are going to compare how different motor types burn PAHs and get a better idea of whether the molecules’ presence at Tahoe is a problem.

“We have no existing evidence showing whether this is a significant problem at Lake Tahoe,” Miller said. “But there are significant PAHs in high-use areas.”

PAH molecules are not soluble in water, and their toxicity increases when sunlight hits them. In a lake as clear as Tahoe, where sunlight can penetrate deep into the water, that makes PAHs even more of a concern.

The impact the molecules can have on fish ranges from damaging their gills to killing them.

Miller said it might be years before officials have an accurate idea of PAH effect at Tahoe.

“It’s a much more complicated problem than the other one (dealing with gasoline compounds),” he said. “There are not going to be any easy answers.”


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