Fire may have impact on Lake Tahoe’s clarity | SierraSun.com
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Fire may have impact on Lake Tahoe’s clarity

Charles Levinson, Sun News Service

Though none of the watersheds affected by the Martis Fire drain into Lake Tahoe, the lake’s water quality could still be adversely affected from smoke, ash and other atmospheric fallout from the fire.

In 1985, 123,000 acres of brush burned in Los Padres National Forest in southern California, when smoke from the fire drifted northwards into the Lake Tahoe Basin. Algae growth in the lake increased three fold and lake clarity was noticeably affected.

“During that fire there was quite a dramatic effect on the lake,” said Dr. John Reuter, a University of California, Davis, researcher who oversees many of the Tahoe Research Group’s lake studies. “It really had a big affect and what we saw was a lot of algae growth.”

The 1985 fire was a brush fire, which studies suggest affect water quality more so than coniferous forest fires, such as the Martis Fire. Still, Reuter warns, there is the potential for fires to impact the lake.

“In a lake like Lake Tahoe, it’s really not surprising that what’s falling out of the air could have a significant impact,” he said. “What’s going to happen during controlled burns, or what would happen if a small fire got out of hand? These are all issues of concern.”

The Lake Tahoe Watershed Assessment published last year, allocated several pages to address the affect of fires on lake quality and concluded that there was a link between atmospheric pollution from fires and Lake Tahoe water quality. The report states that isolated fires have minimal long-term affects but warns that “increased fire frequency is likely to have an effect.”

The smoke and ash from fires affects water quality by stimulating algae growth. Ash from a fire provides nutrients, such as nitrogen and phosphorous, which algae needs to grow and the smoke from a fire filters harmful UV rays from the sun, which in turn promotes more photosynthetic activity in algae. In other words, the algae eats more and burns less.

The likelihood of the lake being significantly impacted by the Martis Fire is not great since prevailing winds have generally pushed smoke away from the basin. The biggest threat to the lake from future fires is from erosion, warns Dr. Charles Goldman with the Tahoe Research Group. Due to the erosion issues left in its wake, the Martis Fire is expected to have troublesome consequences for the watersheds it affects, namely the Truckee River which supplies Reno with 60 percent of its water supply.

“If we had a similar fire [to the Martis Fire] in the basin it could be catastrophic,” Goldman said. “Once you get vegetation off the ground erosion rates skyrocket.”

Supporting Goldman’s claim one need only look to studies performed by Dr. Alan Hayvaert. A specialist in paleo-limnology – reconstructing the lake’s history by examination of its sediments – Hayvaert has documented the rise and fall of sedimentation rates. Sedimentation rates are the number of particles in the water. High sedimentation rates adversely affect lake clarity.

During the Comstock mining period when the basin was stripped of its timber, sedimentation rates rose to 450 grams per square meter of water. When revegetation started around the turn of the century, those rates dropped to 90 grams per square meter. When development on the lake picked up in the 1950s those rates increased again to 270 grams per square meter, and remains there today.


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