Environmental Engineering Reference
In-Depth Information
15
Air
Purification
Air Pollution
Air
CASE STUDY
When Is a Lichen Like
a Canary?
Some lichen species are sensitive to specific air-pol-
luting chemicals. Old man's beard ( Usnea trichodea, Fig-
ure 15-1, left) and yellow Evernia lichens, for example,
sicken or die in the presence of excess sulfur dioxide.
Because lichens are widespread, long lived, and
anchored in place, they can also help track pollution
to its source. Isle Royale in Lake Superior is a place
where no car or smokestack has ever intruded. The sci-
entist who discovered sulfur dioxide pollution there
used Evernia lichens to point the finger northward to
coal-burning facilities at Thunder Bay, Canada.
In 1986, the Chernobyl nuclear power plant in
Ukraine exploded and spewed radioactive particles
into the atmosphere. Some of these particles fell to the
ground over northern Scandinavia and were absorbed
by the lichens that carpet much of Lapland. The area's
Saami people depend on reindeer meat for food, and
the reindeer feed on lichens. After Chernobyl, more
than 70,000 reindeer had to be killed and the meat dis-
carded because it was too radioactive to eat. Scientists
helped the Saami identify which of the remaining
reindeer to move by analyzing lichens to pinpoint the
most contaminated areas.
We all must breathe air from a global atmospheric
commons in which air currents and winds can trans-
port some pollutants over long distances. Lichens can
alert us to the danger, but as with all forms of pollu-
tion, the best solution is prevention.
Nineteenth-century coal miners took canaries with
them into the mines—not to enjoy their songs but to
listen for the moment when they stopped singing.
Then the miners knew it was time to get out of the
mine because the air contained methane, which could
ignite and explode.
Today we use sophisticated equipment to moni-
tor air quality, but living things such as lichens (Fig-
ure 15-1) can also warn us of bad air. Lichens consist
of a fungus and an alga living together, usually in a
mutually beneficial (mutualistic) partnership. You
have probably seen lichens growing as crusts or leafy
growths on rocks (Figure 15-1, right), walls, tomb-
stones, and tree trunks or hanging down from twigs
and branches (Figure 15-1, left).
These hardy pioneer species are good biological
indicators of air pollution because they continually
absorb air as a source of nourishment. A highly pol-
luted area around an industrial plant may have no
lichens or only gray-green crusty lichen. An area with
moderate air pollution may have orange crusty
lichens on walls. Walls and trees in areas with fairly
clean air may support leafy lichens.
Figure 15-1 Natural capital: red and yellow crustose lichens grow-
ing on tundra rock in the foothills of the Sierra Nevada near Merced,
California (right), and Usnea trichodea lichen growing on a branch of
a larch tree in Gifford Pinchot National Park, Washington (left). The
vulnerability of various lichen species to specific air pollutants can
help researchers detect levels of these pollutants and track down
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