Air pollution from Asia's coal-powered energy plants and Gobi Desert dust storms could be minor factors in Lake Tahoe's declining clarity. But scientists believe a lot of the lake's pollutants come straight from rush-hour traffic in the Tahoe Basin.
The effect of air pollution on the lake came up at a recent
meeting between California's air and water quality boards, held to
discuss how their mandates overlap.
The California Air Resources Board is primarily concerned with
health problems such as asthma in children, while the Lahontan
Water Quality Control Board looks for impacts to wildlife, safe
drinking water or Tahoe clarity.
It's been known for years that air pollution affects the lake,
but scientists are still figuring out exactly where that pollution
comes from, according to Dave Roberts, an environmental scientist
with the Lahontan water board.
More than half of the nitrogen feeding algae growth in the lake
comes from air pollution, and much of the nitrogen is in the form
of nitrous oxide emitted by vehicles. Roberts said studies have
shown that periods of rush-hour traffic in Lake Tahoe correspond
directly to peaks in air pollution noted by detection instruments.
"It's been documented more and more that what's coming from the
sky is significant and problematic," Roberts said. "It's
certainly going to be gaining attention in the next couple of
Another problem is fine sediment, which is dirt that is so small
it can take years to sink to the bottom of Tahoe. While a lot of
the sediment comes from stream bank erosion, studies show road dust
is turning out to be a significant factor, Roberts said.
He added that phosphorous is found in the fine sediments, and
nitrogen combined with phosphorous can stimulate algae growth in
The impact of Sacramento's smog also is under debate. Monitoring
systems on the west slope of the Sierra have shown the smog usually
is contained in the Central Valley, although storms from the West
can bring more of it into the Tahoe basin.
The San Francisco Bay is a classic example of air impacting
water: almost 60 pounds of mercury enter the bay each year from the
air. The metal gets into the air in vapor form through coal-fired