Erosion from Tahoe fire may hurt lake's health
Last week's fire occurred in a key watershed responsible for a quarter of all the pollutants entering the lake.
South Lake Tahoe, Calif.
With the Angora wildfire contained, officials are now racing to stave off damage to the famous, cobalt-blue Lake Tahoe.
In just over a week, the fire burned 3,100 acres, forced the evacuation of 3,500 people, and cost $11.3 million to fight. Property losses from more than 325 homes and structures could tack another $150 million onto the tab.
Long after the embers fade, the fire is expect to impact the clarity and health of North America's largest alpine lake. Its stewards are scrambling to prevent runoff from the burn area, an effort that could be complicated by community frustration with past antierosion regulations.
"Lake Tahoe is revered for its cobalt blue, clear water," says Charles Goldman, a lake researcher at the University of California at Davis. "It's one of the clearest large lakes in the world, even with the transparency loss [in recent years]."
The lake has lost a third of its transparency since Dr. Goldman began monitoring it in 1959. Visitors can still see 22 meters down, but that figure shrinks about one foot each year. Human impacts are to blame: auto exhaust, smoke, road dust, and runoff from nearby development.
That runoff may be accelerated by the fire's destruction of the vegetation that holds soils in place, bringing fine particles into the lake. And nitrogen and phosphorous from the fire threaten to turn the lake green by spurring algae blooms.
These effects aren't merely aesthetic. In the long run, such impacts could diminish the deep-water oxygen needed for the lake's trout, says Goldman.
"It's kind of like the canary in the coal mine: We've used water clarity as a symbol of whether the whole lake ecosystem is getting better," says Michael Donahoe, conservation co-chair with the Tahoe Area Sierra Club.
A greater threat, however, is erosion. The burn area covers 10 percent of the Upper Truckee River watershed, and 25 percent of all water and pollutants entering the lake come from that river, says John Reuter with the Tahoe Environmental Research Center at UC Davis.
The forest service, state officials, and local planners are working on erosion mitigation strategies. Even during the firefighting effort, trenches known as water bars were dug to manage runoff. Next steps include planting trees, such as willows, to hold together steep, burned-out slopes. Another possibility, says Dr. Reuter, is diverting the flow of Angora Creek through a nearby meadow that could act as a natural water filter.
"The critical time is between now and when we get the rains in the fall. We need to get the planting done," says Donahoe.
While most of the burned land is public, experts say homeowners also have a role to play by replanting properties with vegetation that isn't highly flammable and that retains moisture.
Tahoe residents are familiar with such calls: For decades the Tahoe Regional Planning Agency (TRPA) has strictly managed building and landscaping on properties around the lake with an eye to conserving lake water quality.
The fire stirred up local bitterness, with some residents feeling the TRPA exacerbated the fire with an antierosion measure that involved keeping a layer of pine needles or wood chips on properties.
Homeowner Jeff Glass raised concerns over the needles several years ago in a letter to a local newspaper after a fire marshal recommended he clean them up. Last week's fire destroyed his home. He says he doesn't know if cleaning up his needles would have made any difference.
As fire officials began reopening neighborhoods last week, some residents started angrily raking up the pine-needle layer.
"In the short term, people will feel more comfortable if they remove pine needles from their property, and we understand that," says Julie Regan, TRPA spokesperson.
The TRPA is working with many agencies on the restoration efforts and wants to work in harmony with homeowners, too. "Hopefully we can keep the lines of communication open to let them know they can still protect their land from fire while also reducing the potential for erosion – that the two are compatible," says Ms. Regan.
Many factors contributed to the fire, including drought, high winds, sluggish efforts to remove brush from local land, and human carelessness. Investigators are searching for those responsible for the illegal campfire that started the blaze.
"I think the level of pine needles had very little impact on the course of how this fire burned. This fire was a perfect storm," says Reuter. "The best we can do is try to educate people" despite the mistrust.