i
A
e cT on.4
ChainR
plants,
animals, and people
Get to know the
Urban
Ecology
Stories of Science and Learning from Arizona State University
of your
What do
you
Breathe?
When
water
Stinks
Birds in your neighborhood
The problem
with studying air pollution
is that it just won’t stay put.
It blows in the wind.
It rises with the sun’s warmth.
It slips between buildings
and slides along mountain slopes
in a dusty dance of particles and gas.
Pollution doesn’t respect neighborhood divisions, state lines,
or even national borders. The people making the stuff
never notice its bad effects. But their neighbors downwind
Flow
could face some nasty results.
Follow the
B y D i a n e B o u d re au
Pa rt i c l e i m ag e s by H ua X i n , P h . D .
C h a i n R e a c t i o n . 4
2
by Diane Boudreau
Air pollution moves through the
Phoenix area. For example, ozone
from Tempe freeways bothers people
living to the far east in Fountain Hills.
Particles from a power plant miles
out of town slink south into Phoenix.
Scientists at Arizona State University are
tracing pollution’s trail throughout the Phoenix metropolitan area.
They want to learn how it f lows in urban areas. “This is one of the areas where
we can really excel,” explains Joe Fernando, an ASU professor of engineering.
“We live in complex terrain. Because of that, we have a pollution problem.
Here at ASU, we have experts in geography, mathematics, chemistry,
and engineering who are able to study the problem.”
Fernando leads a group of scientists who study air f low in cities that
have what is called “complex terrain.” Complex terrain includes mountains
and other irregular features.
The ASU researchers measured particulate matter and ozone, the main
pollutants in the Phoenix area. Because pollution patterns change with
the seasons, they conducted experiments in both summer and winter.
Summertime is ozone season. Ozone is a gas that can irritate your lungs
with every breath you take. Phoenix has all the right ingredients for making
ozone. Lots of cars and year-round sunshine make Phoenix a perfect
ozone factory. Ozone forms when chemicals called volatile
organic compounds combine with oxides of nitrogen (NOx).
Gasoline is a volatile organic compound.
NOx is produced by combustion engines
like the ones that power cars, trucks, and airplanes.
These chemicals mix in a reaction that is triggered
by sunlight. The final result is ozone.
The researchers found that most of the ozone
in the Phoenix area comes from the place where several
major freeways—Interstate 10, U. S. 60, and the Loop 101—come together.
“This is the area where you expect a lot of morning traffic and a lot
of production of nitrogen dioxide. We think that’s the source,” says
Andrew Ellis, an ASU climatologist.
Ozone doesn’t form right away, however. The chemical reaction can
take up to four hours. Jim Anderson is an atmospheric chemist at ASU.
He describes the pollution plume as “a big reaction chamber” that moves
eastward as the day progresses. “Ozone is forming all along. By the time it
gets to East Mesa, the ozone concentration is actually higher. It also goes up
to Fountain Hills. At 6 p.m. in Fountain Hills we find a higher concentration
of ozone than is found anytime in downtown Phoenix,” he says. ›››
All About Ozone
What is ozone? Ozone is an invisible
gas. The ozone molecule is made up
of three oxygen atoms (O3). It is very
unstable and highly reactive. Ozone
is sometimes used as a bleach and
a sterilization agent for air and
drinking water.
Why is ozone pollution bad?
Breathing ozone regularly can irritate
your lungs and cause respiratory infections. Ozone can aggravate asthma,
reduce your capacity for exercise, and
cause chest pain and coughing. Ozone
is most dangerous to young children,
the elderly, and people with respiratory
conditions like asthma. Ozone can also
damage trees and plants.
If ozone is harmful, why do we want
to protect the ozone layer? The ozone
layer is located miles above us in the
stratosphere. It is much too high up
for humans to breathe. The ozone layer
of the atmosphere actually helps protect the Earth’s surface from dangerous
ultraviolet light from the sun.
How can we reduce ozone pollution?
In the Phoenix area, peak ozone times
occur in the afternoon and early
evening during the late spring, summer, and
early fall. Avoid the following activities
during those peak ozone times as much
as possible:
Driving a car
Fueling your car
Using gasoline-powered lawnmowers
Lighting fires or outdoor grills
Diane Boudreau
3
h t t p : / / c h a i n re a c t i o n . a s u . e d u
10 pm
3:30 am
Mathematical
Models
In studying air pollution, measuring
what is in the air is only part of the job.
Scientists also have to find out where
it comes from and where it will go.
The flow of air involves many factors,
such as wind speed, wind direction,
temperature, humidity, and landscape,
to name a few. ASU researchers enter
this information into a computer and
use mathematical formulas to create
a model of how air flows through
space and time. The models are 3D
animations of how air should flow
through the region. These models help
them learn all kinds of information.
For example, they tracked down the
source of coal burning particles found
in Phoenix-area air.
As they find out new information,
the scientists go back and improve
their models, making them more
accurate all the time. “Models are
not perfect. We keep on updating them
when they don’t work. They keep on
changing,” says ASU’s Joe Fernando.
In that sense, they are a lot like
the air flow patterns they represent.
Diane Boudreau
Micron?
A micron is one-millionth of a meter.
A human hair is between 25 and 100
microns wide. So a particle less than
2.5 microns wide is very small indeed!
C h a i n R e a c t i o n . 4
8 am
Phoenix is not a windy city. It also is surrounded by mountains.
These facts makes it hard for the ozone to escape the area once is has formed.
Did you ever see a bug trying to climb out of a plastic cup? It crawls up
a little way, then slips and falls back down into the bottom. Because Phoenix
is in a valley, it resembles a cup. The ozone starts to climb up the sides of
the cup—the mountains—but it slides back down again before it can escape.
During the day, rising temperatures heat the slopes of the Superstition
Mountains east of Phoenix. The heat causes the air around the mountains
to rise. As the air rises out of the valley, it pulls more air in from the west.
Before the ozone can slip over the mountains, however, the sun goes down.
This causes the mountains to cool. The air slides back down into the valley.
“As the air slides up the Superstitions we can watch the ozone level peak
in Mesa at 4 in the afternoon. We also see a peak on high ozone days
at about 10:30 at night. That is when the air slides down the Superstitions
and back into the valley,” says Ellis.
The other major pollutant in the Phoenix area is particulate matter.
Particulate matter is defined as tiny airborne particles that can be dangerous
when they are inhaled. The researchers measured these pollutants during
their winter experiments.
The Environmental Protection Agency (EPA) records the air concentration
of all particles less than 10 microns wide. They have also started tracking
particles under 2.5 microns. Scientists believe that these smaller particles
may be the most dangerous to human health. The EPA only tracks the size
of particles, not what they are made of. But certain kinds of particles are
more dangerous than others.
The ASU researchers collected particles from the air and studied them
using a scanning electron microscope. The microscope bombards the samples
with high-energy electrons. This makes the samples emit an X-ray signal.
4
Atmospheric scientists often gather information using
balloons like this one. The balloon carries instruments
below it that measure temperature, humidity, wind speed,
and direction. An optical device is used to determine the
amount of particles in the air. The device measures light
scattered from the particles.
Each different element gives off its own X-ray “signature.” A computer
connected to the microscope figures out what the particle is made of
by “reading” the X-ray signature. It also measures the size and shape
of the particle. This information helps the researchers find out what
harmful particles are out there, and where they might come from.
Exactly what kinds of particles are f loating around in Phoenix area air?
The scientists found some surprises. “We saw distinctive particles that
come from the burning of coal. But there aren’t any coal-fired power plants
in Phoenix,” says Anderson.
The most likely source turned out to be a coal-burning power plant near
Joseph City, Ariz., located more than 100 miles northeast of Phoenix.
“We suspect that’s where they come from,” says Neil Berman,
a professor of chemical engineering. “The model shows that
it’s possible.” The team found that air from higher mountains
north of Phoenix f lows down into the Phoenix area after sunset.
Of course, local sources create plenty of particulates of their
own. For example, the researchers discovered spheres of toxic iron
oxide in the air. “Some company is putting out a tremendous
amount of these particles,” says Anderson. Unfortunately,
the scientists could not find their source.
Traffic contributes particles by spewing exhaust and kicking
up dirt. In the mornings, lots of these particles appear just downwind
of the interchange between Interstate-10 and Interstate-17 in Phoenix.
With help from the Arizona Department of Transportation, ASU scientists
are studying how traffic contributes to air pollution. They are taking air
samples and measuring wind direction at various places along Phoenix-area
freeways. They are separating particles that come from different directions
to find out where those particles are created.“I don’t think anybody’s ever
done this before. I’m interested in whether the speed and number of large
trucks affects the emissions,” says Anderson, who leads the study.
Ultimately, the goal of studying pollution is to figure out how to reduce
the amount of pollution and to minimize its health effects. By figuring out
where pollutants are created, and how they move through the area,
the ASU scientists are moving closer to answers.
All About
Particulates
What is particulate matter? Particulate
matter is a general term for a variety
of solid particles and liquid droplets
found in the air. Some particles are
large or dark enough to be visible as
soot or smoke. Others are so small you
cannot see them without an electron
microscope. These particles come from
many different natural and humanmade sources.
Why are particulates dangerous?
Particulates are small enough to be
inhaled when you breathe. They can
collect in your respiratory system.
Larger particles can aggravate
respiratory conditions like asthma.
Tiny particles contribute to heart and lung
disease and decreased lung function.
Particulate matter is most dangerous
to young children, the elderly, and
people with cardiopulmonary diseases.
Particulates create ugly smog. They also
damage paint and building materials.
Diane Boudreau
How can we reduce particulates?
Drive less. Try walking, biking,
riding the bus or carpooling instead.
Drive slowly on unpaved roads
to avoid kicking up lots of dust.
Avoid using a wood stove or fireplace
on days with poor air quality.
Avoid using leaf blowers and other
equipment that kicks up dust.
5
h t t p : / / c h a i n re a c t i o n . a s u . e d u
CO2Questions
Carbon Dioxide
is the second
most common
greenhouse gas.
Water vapor is first.
Greenhouse gases act
like a blanket around
the Earth. They trap
in the sun’s heat.
Without greenhouse
gases, we could not
survive. Earth would
be way too cold.
We don’t have to worry
about that, however.
CO2 levels in the
atmosphere are rising.
So is the average global
temperature. If CO2
continues to increase,
what will it mean for
Earth’s climate?
BY
DIANE BOUDREAU
C h a i n R e a c t i o n . 4
You can’t see it. You can’t smell it. You can’t taste or feel it.
It enters your body with every breath and you don’t even know it.
Carbon dioxide (CO2) has no direct effect on people. Most of us hardly
think about it at all. But climate scientists think about it a lot, because
it does affect our planet, and it’s on the rise.
Scientists aren’t exactly sure how this rise will change the planet, but
most researchers believe it will be bad. They predict the Earth’s temperature
will go up, and rising sea levels will f lood whole islands and coastal cities.
Entire forests, like the Amazon, could be destroyed. A few scientists,
however, claim that global warming will actually slow the rise in sea levels.
They say that high levels of CO2 will help plants and trees.
These theories are very different, but they do have something in common.
Both theories are based on computer models.
“Most future climate predictions are based on mathematical models,”
explains Craig Idso, a climatologist at Arizona State University. “You can’t
just double the CO2 concentration and see what happens in the real world.
We don’t have the technology to do that.”
Computer models are not perfect. But they have been the only way
to study the effects of CO2 in the atmosphere. Until now.
In 1998, Idso discovered that Phoenix lies under a carbon dioxide “dome.”
The city has CO2 levels up to 50 percent higher than the global average.
Those high levels are what scientists expect to see around the world in about
50 years. Because Phoenix is ahead of the game, scientists can use the city
as a natural “laboratory” to study the effects of these changes.
“People are running around saying we’ll double carbon dioxide sometime
in the next century,” says ASU climatologist Robert Balling. “We are saying
that we’ve already come close to doing it in Phoenix. You don’t have
to wait around.” This type of CO2 dome hasn’t been seen in any other city,
says Balling. Very few cities have even measured CO2 levels. Those that have
show only small increases of CO2 over urban areas.
Where does all that carbon dioxide come from?
6
ASU scientist Craig Idso and other students attached tubes to their cars to pipe
air inside to a CO2 sampling instrument. The map of the Phoenix area shows CO2
concentrations measured by researchers. Blue-colored areas indicate how much CO2
was found in air at ground level. Darker blue areas show the highest concentrations.
Phoenix
Mountains
Salt River Indian
Reservation
Downtown
Phoenix
There are many sources of CO2.
Tempe
mesa
Gila River
“It looks like everything comes together in Phoenix to produce this
carbon dioxide dome,” says Balling. For one thing, the desert does not
have many trees or other plants. Trees and green plants normally absorb
lots and lots of CO2. Also, people in Phoenix drive a lot. Cars, trucks,
and buses spew tons of CO2 from their tailpipes as they go. Finally,
Phoenix has very little wind compared to other cities. As a result,
he CO2 in Phoenix doesn’t get blown away.
Balling leads a group of scientists who study the relationship between
CO2, humans, and the environment. The team has found that CO2 levels
change throughout the day, week, and year. For instance, CO2 levels before
dawn are higher than they are in the middle of the afternoon.
ASU ecologist Jeff Klopatek suggests reasons for this difference. “CO2
is heavy. At night, it tends to settle in,” he says. “During the day we think
the CO2 may just be rising with the warmer air. It could also be a function
of vegetation. In most natural ecosystems the CO2’s going to be a lot lower
during the day because the plants are taking in the gas for photosynthesis.”
The team also found that CO2 levels are higher on weekdays than
on weekends, and higher in mid-winter than in the summer.
Vegetation is one of the trickiest pieces of the CO2 puzzle. Plant life
affects the CO2 dome but is affected by it as well. At night, plants give off CO2.
But during the day, plants take in CO2 to use for photosynthesis.
Photosynthesis is the process plants use to turn sunlight into food. ›››
Cars, power plants, and anything else
that burns fossil fuels will produce CO2.
Cement production also releases
the gas. Rotting materials produce CO2,
so landfills may be a big contributor.
And plant life gives off CO2 at night.
Even people are a source, because
we all exhale CO2. “You’re producing
carbon dioxide right now, never forget
it,” says ASU scientist Robert Balling.
“We have plans sometime in the next
year to go out in Sun Devil Stadium.
We want to measure the carbon dioxide
dome around that stadium when 70,000
great Sun Devil fans are out there
screaming and yelling. We think that
the level probably goes way up.”
ASU students, led by researcher Craig
Idso, have measured CO2 over time and
space. They drove all over the Phoenix
metropolitan area taking air samples
and measuring their CO2 content.
They also set up several permanent
sampling sites.
So far, the results all support Idso’s
earlier findings of a huge CO2 dome over
Phoenix. They also found that CO2 levels
in the heart of Phoenix are higher than
those on the outskirts of the city.
E ACH CARBON DIOXIDE MOLECULE IS MADE OF
ONE PART CARBON (C) AND TWO PARTS OXYGEN (O2)
7
h t t p : / / c h a i n re a c t i o n . a s u . e d u
John C. Phillips photos
<ASU plant biologist Tad Day studies the relationship between plants and the CO2 dome.
He is looking at CO2 levels over four types of land: turf (grass) outside the CO2 dome, turf inside the
dome, desert remnant outside the dome, and desert remnant inside the dome. There is a wider daily
range of CO2 levels over turf than over desert areas. Over turf, nightly spikes are higher than over desert.
Daily lows are lower over turf. “This makes sense because turf vegetation draws in much more CO2
per ground surface area [during the day],” says Day.
Thought questions:
Why might global warming cause sea levels to rise?
Why are CO2 levels higher in winter than summer?
Why are CO2 levels lower on weekends than weekdays?
Jeff Klopatek digs deeper into
the vegetation issue. He studies
underground and soil contribution
to the CO2 dome. “In most ecosystems,
about 80 to 90 percent of the CO2
in the system is being emitted from
the soil,” he says.
Soil CO2 comes from root and fungal
activity. It also comes from rotting
organic matter. Klopatek is comparing
these below-ground sources of CO2
across Phoenix, especially in landfills.
“We expect that they’re significant
sources,” he says. “When the organic
matter buried in landfills starts
to decompose, it also starts to
release carbon dioxide.”
C h a i n R e a c t i o n . 4
Human activities are at the heart of Phoenix’s CO2 dome. It’s easy to see
that CO2 levels spike over areas where the most people live. The researchers
want to know which human activities produce the most CO2.
Tim Hogan is the director of ASU’s Center for Business Research.
He provides information on human-made sources of CO2. Hogan and
his co-workers locate major CO2 sources in Phoenix. They find out just
how much electricity the power plants are producing, or how many miles
people are driving, to learn how much CO2 is being produced. He also looks
at how these numbers vary over time. As the Phoenix area grows, so will
the carbon dioxide dome. Hogan works to predict how the CO2 dome will
change, and how it will affect the area.
Collecting data is the first step. That takes lots of time. The work to
understand it all starts once the data is collected. The researchers have
to put it all together and try to figure out what it means.
Patricia Gober and Elizabeth Wentz are geographers. They collect data
on traffic patterns, population, land use, and employment. They use numbers
from Hogan’s office, along with other local and national sources. They also
gather the CO2 data from the other researchers. Then they plug all the
information into Geographic Information Systems software and use
the computer to look for patterns among the jumble of numbers.
For example, they can make a map showing where the highest CO2
levels occur in the Phoenix area. They can overlay that map onto a map
of traffic patterns to see if there is more CO2 over high-traffic areas
such as freeways. Their findings will help researchers answer some of
the important questions about carbon dioxide.
“There are all these linkages,” says Balling. “We’re working together as a
grand team. The goal is to better understand the carbon dioxide all around us.”
8
COAL
Coal is formed mainly from
the carbon in ancient plant material
WHERE DOES ALL THE CARBON GO?
Carbon is an element with many forms. Those different forms flow between the biosphere,
the atmosphere, and the oceans. This global flow is called the
carbon cycle. Scientists study
how carbon is exchanged between these elements. They also look at where carbon is stored
for long periods of time. Because the amounts of carbon involved are so huge, scientists
use the term gigaton as a unit of measure. One gigaton is equal
to 1 billion tons of carbon!
The largest stores of carbon lie underground. The carbon is part
of fossil fuels like oil and coal, and in sedimentary rock deposits.
Other huge amounts are found at the bottom of the oceans. About
44,000 gigatons of carbon is trapped in these stores. When humans
burn fossil fuels and clear land they release huge amounts of carbon into
the atmosphere. These activities release about 6 gigatons of carbon each year.
The atmosphere holds about 750 gigatons of carbon in the
form of carbon dioxide. Scientists say that the amount
of CO2 in the atmosphere is on the rise.
Current levels are 25 percent higher than
they were before the Industrial Revolution
began in the late 1700s.
GRAPHITE
Many sea creatures–
some of microscopic size–
build shells of carbon
minerals.
The “lead” in pencils is really a form of carbon called graphite.
Plants absorb carbon dioxide from the atmosphere during photosynthesis.
That is the process plants use to turn sunlight into food.
Plants also release CO2 back into the air through respiration.
About 800 gigatons of carbon is dissolved in the surface layers of the world’s oceans.
Marine plants use that dissolved CO2. Plants and animals also store
carbon in their bodies. About half the weight of a mature tree is carbon.
Scientists believe that 550 gigatons of carbon exists in living plant and
animal matter. Another 1,300 gigatons of carbon is trapped in dead leaves,
twigs, branches, other ground litter, and soils.
Chalk– just like the kind teachers
use on blackboards– is formed from
the shells of ancient
sea creatures.
Plants decay into
soil and release
carbon into the
atmosphere.
These numbers are estimates,
of course. Scientists only have
a general understanding of the
carbon cycle. They have not totally
accounted for the rates of change
between the atmosphere, land,
and ocean. Scientists still can’t
account for about 20 percent
of the CO2 released each year.
That is between 1 and 2 gigatons.
Not a small amount! Scientists
are still working to discover where
this disappearing carbon goes.
Diane Boudreau
CHALK
SEAWATER
9
h t t p : / / c h a i n re a c t i o n . a s u . e d u
F i g h t i n g
f o r
A i r
The Homedale neighborhood in Phoenix is like a crystal hidden
Agency considers particles this size to be dangerous
inside a rough gray rock. The little group of houses is surrounded
to human health. A micron is one millionth of a meter.
by junkyards, piles of scrap tires, and giant warehouses.
On the southeast edge of the neighborhood sits a truck stop.
The third part of the survey includes recording social
and historical data about the neighborhood. The last
It is always filled with idling tractor-trailer rigs. To the north-
phase is hazard mapping. The team will create a map
west, a hulking power plant looms against the sky. Between
of the area that shows what facilities exist and how
truck stop and power plant lies a group of 440 houses.
close they are to the houses.
The area is spotted with sand lots and boarded-up windows.
Environmental risks often exist in or near low-income
But most of the homes are lovingly tended with soft green
and minority neighborhoods. In Homedale, 88 percent
lawns and bright flowers.
of residents are Latino. More than 36 percent live below
Many of the current homeowners grew up in this neighbor-
the poverty line. But these people are not powerless.
hood. Now they work to raise their own families here.
Years ago, they successfully fought an expansion
Homedale is the kind of place where people know each other.
of the local power plant. That plant would have
It is also the kind of place where neighbors band together
increased local air pollution. Unfortunately,
when something is wrong. They did just that in 2002.
the area still has problems.
Sara Grineski is an ASU graduate student in sociology.
The ASU students spent most of 2001 and 2002
She works with Homedale residents as part of a special
collecting data. Those numbers tell interesting
research training program for students. “There were a lot of
stories:
bad smells in the neighborhood. The residents were concerned
about air pollution,” she explains. “There’s a truck stop that
backs up into the neighborhood. The trucks idle all night long.”
Homedale’s leaders decided to find answers to their
problems. They presented their concerns to ASU scientists.
Grineski leads a team of students who study the neighbor-
Homedale residents appear to suffer from
a higher than normal rate of breathing
problems. They also have high rates
of allergies, irritated eyes and nose,
congestion, and chronic cough.
hood. Their project has four parts. First, the students devel-
Sixteen percent of Homedale adults have
oped a resident survey. They wanted to document health
asthma. So do 16 percent of their children.
conditions, symptoms of illness, and environmental concerns.
That compares with national averages
Students and residents crisscrossed the neighborhood
of 7.2 percent for adults and 7 percent
to give the surveys in both English and Spanish.
for children.
The second part of the study includes air quality monitoring.
The ASU team placed air monitors inside and on the rooftops
The ASU study results are not yet final.
of two Homedale houses. The monitors measure levels of
But Homedale residents already are
particulate matter in the air. They also measure elemental
seeing results. They hosted a special
carbon, sulfates, and nitrates. These are released into the air
conference last summer. As a result
when gasoline or diesel fuel is burned. Sulfates and nitrates
of that meeting, the neighborhood
are pollutants. Elemental carbon comes mainly from the
received a $90,000 Fight Back Grant
diesel engine exhaust of trucks.
from the City of Phoenix.
The community plans to use
matter in the air samples. They look for particles less than
the money to improve their
2.5 microns in diameter. The U. S. Environmental Protection
neighborhood.
C h a i n R e a c t i o n . 4
10
Diane Boudreau
Tim Tru
mble p
hoto
The scientists look closely at the amount of particulate
Making
Changes
BY DIANE BOUDREAU
At one time, people thought that only gods or magic could
Thought questions:
change the weather. Now we know that people can change
How could some of these human
developments change the climate?
it in many ways. The biggest example is global warming.
Scientists describe global warming as a rise in the Earth’s
Tall buildings
Parking lots
Golf courses Human-made lakes
Freeways
average temperature. They think that one cause might be
the addition of extra carbon dioxide in the atmosphere.
Carbon dioxide acts like a blanket. It holds the sun’s heat
How might rising temperatures
affect these?
close to the surface of the Earth. Many human activities
release carbon dioxide into the air. All of these activities
contribute to global warming.
Energy use
Global warming is a very slow change that affects the climate
Water use
Animal life
Plant life
all around the planet. “Climate” is the average of all the weather
conditions that occur in an area. It includes temperature, humidity,
rain, snow, and weather events such as El Niño or heat waves.
“Climate change occurs globally and locally,” says weather expert Tony Brazel.
Brazel is a climatologist and professor of geography at Arizona State University. “Phoenix is affected
by global climate patterns. But there are other climate patterns that happen only in this area.”
People have made changes to the Phoenix area environment. Brazel says that these changes
have also changed the local climate. “We have created a kind of artificial climate. We import water
that wasn’t here before, for example. That affects humidity,” he explains.
Average temperatures have climbed higher in Phoenix. Brazel says the rise in temperature is
due to the “heat island” effect. The city actually becomes warmer than the surrounding countryside.
The result is a little “island” of heat. “In downtown Phoenix the minimum average temperature in summer
has increased about 10 degrees Fahrenheit. This is one of the largest changes attributed to urban growth
anywhere,” Brazel says. “In the last 50 years or so, there’s been an increase in the minimum temperature.
It does not get as cold at night in Phoenix as it used to.”
So far, scientists haven’t found any major changes in the levels of precipitation (rain and snow) in the
Phoenix area. Humidity levels also have stayed about the same. “We take readings at Sky Harbor Airport.
Those readings have shown that there’s not much overall change in moisture over time,” says Brazel.
However, he says changes in humidity are hard to measure. They may be happening on a smaller scale.
“When the sky is clear, you can drive through town and hit moist areas and dry areas.
It’s like a patchwork quilt,” he says. Golf courses and lawns create little pockets of humidity, while
big shopping centers are dryer than average. “It’s hard to generalize that to what’s happened over time.”
Phoenix has never had much wind. Brazel says that some studies indicate that the increased heat
of the city could be causing more wind.
All of these changes have effects on the environment as a whole. For example, higher temperatures
can make ozone problems worse because ozone forms in hot weather.
Studying these connections is what urban ecology is all about, says Brazel. “We know
that an urban climate exists,” he adds. “Scientists want to know how this climate affects things
in the ecosystem. Is it affecting the comfort of people? Does it affect energy consumption?
Water use? All these questions are going to be linked with climate.”
11
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Urban
Ecology
[Latin urbanus, from urbs, a city]
adj. 1. Of, in, or constituting a city.
n. [Greek oikos, ‘house’] 1. The branch of biology
that deals with
the relationships between living things and their environment,
including all living and nonliving components.
What IS Urban Ecology?
C A T A L Y S T S
make things happen.
They speed up reactions
and make some
ingredients combine
that could not without them.
by Co n r a d J . Sto r a d
Ecology is all about relationships. No, not the relationships between
boys and girls. It’s bigger than that. Ecology is about studying the relationships
between all living and nonliving things in a particular area. The area might
be as big as a forest, a lake, a continent, or the entire planet. Or it might be
as small as a single grove of trees, a local pond, or a puddle in your backyard.
Scientists who study ecology once spent most of their time and work
in far-off, isolated, exotic locations. They studied groves of old trees in the
pristine forests of the far Northwest. They studied the plants and animals
of the tundra in Alaska or near the Arctic Circle. They went to Antarctica
to study penguins and other creatures that live in that icy wasteland.
They visited remote islands in the South Pacific. Or they went on expeditions
deep into the steaming rainforests of South America.
Today, ecologists stay close to home. They study cities, the places where
billions of people interact with living and nonliving things every single
day and night.
In Arizona, ecologists study the types of grasses and trees growing
in Phoenix parking lots. They study the birds living in your backyard.
They want to know how many and what kind of insects and arachnids
live on and around the playground at school. The projects are examples
of the new frontier of environmental study. It is called Urban Ecology.
Understanding
Urban Ecology
is a Big Job
Ecologists study how the environment
affects plants and animals. Biologists study bacteria, plants, and animals.
Meteorologists study the atmosphere and weather.
Climatologists study long-term weather patterns.
Geologists study how landforms change over long periods of time.
C h a i n R e a c t i o n . 4
12
2002 – Largest cities in the world: Tokyo, Mexico City, Sao Paulo, New York City, Mumbai (Bombay)
2015 – Largest cities in the world: Tokyo, Dhaka, Mumbai, Sao Paulo, Delhi
Source: National Geographic Magazine, November 2002
Urban ecologists study people, plants, and
●New York City
animals living in and near cities. More impor●Mexico City
tantly, they study the relationship between all
those living things and the nonliving things in
and around cities. They study the air and water
●Sao Paulo
and soil. They study how people change those
nonliving things. And they study how those changes
can come back to affect people and other living things.
Phoenix is one of the fastest growing cities in North
America. Scientists are concerned about the rapid depletion of
its natural desert areas. The pressure continues to build. More people are
f locking to live in Phoenix and other cities in the West. Scientists who
study the cities have to team up and find ideas that help make them more
livable. That is what the Central Arizona-Phoenix Long Term Ecological
Research project based at Arizona State University is all about.
Scientists are learning that cities are interesting environments for study.
They have their own types of biodiversity. The more we understand these
environments, the better we can protect them. The more we know about
the places we live, the easier it will be to make them better places to live.
This map shows daytime temperature distribution in the Phoenix area.
Geographers study how the landscape
influences where plants and animals
live, including people. Theoreticians
model the environment with complicated
equations that are solved by powerful
computers.
Chemists study how
atoms and molecules
move through the
environment from
one chemical form
to another. Physicists
study how different kinds
of energy and forces work
in the environment.
●Tokyo
●Dhaka
●Mumbai
Delhi●
People, People,
Everywhere!
Why study the cities? The answer
is simple. More people live in cities
than ever before. In 1950, New York
City was the only city in the world
with a population of 10 million people.
By 2015, scientists say there will be
21 such cities. The number of urban
areas with populations between 5 and
10 million will increase from 7 to 37.
By 2030, two out of every three people
on Earth will live in the urban world…
in a city. For the first time in history,
60 percent of the world’s people
will be living in cities.
Source: United Nations,
World Urbanization Prospects (March 2002)
Population of urban areas of Earth in
2000— 2.9 billion people
Population of urban areas of Earth in
2030— 5 billion people
By 2007 the number of people living
in urban areas will equal that of rural
areas worldwide.
By 2030, about 83 percent of all
people living in the more developed
countries will live in cities.
By 2030, about 85 percent of all
people living in North America
will live in cities.
Chemists and physicists can use
electron microscopes like the one above
to make images of the particulates in our air.
13
h t t p : / / c h a i n re a c t i o n . a s u . e d u
When you think
about the environment,
you probably think
about plants and animals.
Perhaps you also think
about air and land
and water. But what
about people?
by Diane Boudreau
In urban areas, people have the biggest influence on the environment.
They build houses and roads, plant gardens, drive cars, and throw away tons
of garbage. People constantly reshape the landscape. Their activities affect
the plants, animals, air, and water around them.
Patricia Gober is a social geographer at Arizona State University.
She studies how people change the Earth’s surface. She is especially
interested in Phoenix, and how it has grown and changed over the years.
During the past 100 years, the population of the Phoenix area grew
tremendously. In 1900, only 20,457 people made their homes in Maricopa
County. By 2000, that number had risen to 3,072,149. All of those people
need places to live, work, and play. Gober studies how people in Phoenix
use the land for these activities. She also tries to predict how land
will be used in the future.
But how exactly do geographers predict where development
will happen in the future?
“They start with population predictions made by experts at the Department
of Economic Security,” explains Gober. “Geographers take those population
numbers and fill in where they think development will be.”
Where
thepeople
are
In the early 1900s, most of the land
in and around Phoenix was used for
farming. By the end of the century,
the area had become much more urban.
A lot of the land is now used for houses,
stores, and factories.
1912
During the 1990s, the Phoenix area
grew at lightning speed. Population
scientists predict that it will continue
to grow in the future. They look for
trends. They study maps of where
that population is distributed.
For example, Phoenix is much more
spread out than many other cities.
ASU geographer Pat Gober says this
happened because Phoenix was developed very recently. People have cars.
That means they don’t have to walk
everywhere. “If you look at the new
parts of Washington D.C., or Atlanta
or New York City, you’ll see a similar
pattern. It’s largely due to the newness
of development,” she says.
Central Phoenix✰
Urban area
Agricultural Area
C h a i n R e a c t i o n . 4
14
Recreational Area
They make assumptions based on what they know about
development trends and about the area in question. Developed
areas will probably get built up more. New development will happen
in areas physically suited to it, and also along transportation lines.
Scientists use these predictions. They try to figure out how
development will alter the landscape and affect pollution, traffic,
animal communities, and plant life. And that’s what ecology is all about.
Some people think that geography is just about memorizing
countries or capital cities on a map. Gober says that geography
involves much more, but those things are an important foundation
to build on.
Learning facts about countries and cities is much like memorizing
your multiplication tables. These facts are actually building blocks.
They help students to learn about geographic processes.
“We geographers are pretty good at tackling environmental
problems,” says Gober. “We know enough about both physical
and social processes. Geography is a place where a lot
of environmental issues are being addressed.”
Cities tend to develop along the routes
of major transportation systems.
“The early streets of Phoenix followed some
of the old trolley lines,” Pat Gober explains.
“The trolleys were built around 1890, and
then were phased out in 1948.” More recently,
development has followed the major highways
and roads. The population has spread out
along the major freeways such as
Interstates 10 and 17, and U.S. 60.
Astronauts see Phoenix like this.
Can you find your house?
2000
Pat Gober has predictions of her own.
She thinks that future development in and
around Phoenix will happen mostly in outlying
areas like Apache Junction and Avondale.
“In the 1960s and 70s most of the growth
in the Valley was in Phoenix itself. As the
century unfolded you got much faster growth
in the suburbs.” Gober thinks that both Phoenix
and suburban growth will taper off in the future.
“Most of the action is going to be in the
outlying areas,” she says.
Central Phoenix✰
co u n t ry a r e a s
suburbs
Growing
population
phoenix
15
h t t p : / / c h a i n re a c t i o n . a s u . e d u
The
Some birds prefer the view from a high tree branch.
Others like to sit on top of a cactus or along a power line. A team
of Arizona State University scientists found that birds also prefer to live
the high life in other ways, at least in the Phoenix metropolitan area.
For two years, ecologists Ann Kinzig and Paige Warren studied
the birds living in small Phoenix parks. What they found was a bit surprising.
They discovered that more birds and more types of birds actually live in
the city than in the surrounding Sonoran Desert.
The real surprise came when Kinzig and Warren took a look at exactly
where birds live in the city. In Phoenix, bird populations seem to prefer
high-income neighborhoods. The scientists found that more species of birds
live in wealthy neighborhoods than in middle and lower income areas.
The study was done as part of the Central Arizona-Phoenix Long Term
Ecological Research Project (CAP-LTER). Supported by the National Science
Foundation, CAP-LTER is an ongoing study of how humans interact with
ecological systems here in the Sonoran Desert of central Arizona.
The ASU scientists studied 15 small community parks in Phoenix.
by James Hathaway
The parks were located in a variety of residential areas. Some
were found in lower income areas. Others were in very wealthy
neighborhoods. Kinzig and Warren measured both the number
and types of birds and trees living in the parks. They chose to
look at parks rather than residential yards for a reason. The parks
provided comparable environments to study. Each site had similar
landscape. Each had grass, athletic fields, playgrounds, and scattered trees.
Together, the scientists counted birds living in about 2,000 trees.
These results also surprised them. They found that
Cactus wrens are a Sonoran Desert species.
The wren builds a nest to raise it’s chicks. But the bird stays and
an average of 30 different species live in the trees
roosts inside all year round. In the desert, the wrens build nests
in upper income parks. The average was spread
only on cholla cactus. In the city, the wrens build on a variety
of plants, and sometimes other places. Researchers found one
across one year. That compares to the 23 species
in a satellite TV dish. Madhusudan Katti
of birds they found living year-round in middle
Bird’s-eye view of Encanto Park in central Phoenix.
income parks. In the lowest income area parks
they found an average of only 18 bird species.
The findings are strange, but interesting.
“We can’t explain bird diversity in the
parks by the size of the parks, or the types
or sizes of trees in the parks,” says Kinzig.
“That is what we might expect. Instead,
the characteristics of the neighborhood,
including the income of the residents,
seem to play a significant role in
inf luencing the number of species
that live in the park.”
Good Life
for
Birds
C h a i n R e a c t i o n . 4
16
K
> inzig and Warren found more birds and more types of birds in upper
income neighborhood parks. They found fewer birds and fewer types of birds
in parks near middle and lower income neighborhoods. However, the amount
and types of trees were actually highest in lower income neighborhood parks.
The study eliminated park landscaping as a factor. But the scientists have
not yet found a good explanation for why birds like wealthy neighborhoods
best. “Something that happens near the park boundaries is inf luencing
the diversity of birds inside the parks,” Kinzig says. “We can’t explain it
with the park itself. The answer might be related to what people are planting
in their yards. It could be how often people feed the birds. Maybe the rich
people have more bird feeders.”
Other factors might be at work. The scientists say it could be something
as small as the number of bird-eating cats and other predators that live in the
neighborhoods. “Or it could be zoning,” Kinzig says. What does the city plant
along the median strips on near sidewalks? How much industrial activity
is allowed near the park? There are lots of questions that need answers.
“We don’t know the exact answer,” she adds, “but we know it’s related
to the differences in people’s lifestyles.”
The scientists want to look at other ecological factors that might
be important. “We still want to look at reproductive success in the parks.
There may be something that’s really inf luencing reproduction and
that has an inf luence on the bird community,” she says.
Kinzig and Warren plan to look at food sources
during the breeding season. What do people plant
in their yards that birds eat when they breed?
Birds love to eat bugs. Maybe some neighborhoods are better than others for insects.
Maybe the answer is related to available
water. Dog dishes are important water
sources for birds. Maybe rich neighborhoods
have more dog dishes and birdbaths.
Kinzig and Warren and other ecologists
have plenty of work to do. For the first
time in human history, most people
are living in urban environments.
Parks now provide more and
Mourning Dove Many types of doves
more people with their daily
live in suburban neighborhoods.
The mourning dove is very slender.
access to nature.
It has a pale blue ring around its eyes.
Brian Gersten
“We need to fundamentally
learn how these neighborhoods differ from each other,” Kinzig adds.
We want to understand what kind of nature people will have in their yards,
parks, and green spaces. We want to know what affects that nature.”
Trees and other
vegetation are important
to birds. They rely on trees
for food and shelter. So,
if you have lots of trees
in a park, you should see
lots more birds, right?
Sounds logical. But the
scientists actually found
the opposite to be true.
To learn more about urban parks research
or other CAP-LTER projects, visit the web site
at: http://caplter.asu.edu
Learn more about bird population studies:
http://caplter.asu.edu/PO12
17
h t t p : / / c h a i n re a c t i o n . a s u . e d u
A SHADY SITUATION
It’s an Arizona thing. People in other parts of the country just
don’t understand. Here in the Sonoran Desert, it’s pretty common
to pull into a parking lot and find the spots closest to the store
open and available. All the shoppers have parked at the far end
of the lot just to snag the few spaces half-shaded from the sun.
A long walk to the
store is far better
than driving home
in a car that has
baked for hours
in the desert heat.
BY
DIANE BOUDREAU
C h a i n R e a c t i o n . 4
Business owners plant trees around their parking lots to provide shade.
They often plant trees known to have a broad, full canopy—the leafy part
of the tree. But when the trees grow on the shores of an asphalt sea,
they don’t always live up to their potential.
“People plant trees for what they’re supposed to look like. But in a parking
lot they don’t always end up looking as they should,” says Sarah Celestian, an
ASU graduate student in plant biology. Celestian wants to know how parking
lots affect tree growth, and which kinds of trees do the best. She thinks that
the heat absorbed and ref lected by asphalt pavement is an important factor.
During a typical Arizona summer, parking lot surfaces can reach temperatures of more than 160 degrees Fahrenheit. The lots also hold onto their
heat well into the night. Natural desert surfaces cool down much more
quickly. Celestian studies the relationship between parking lot temperatures
and growth among six popular types of trees.
“I drove around town and looked for parking lots with a minimum of
five trees of one species located in the median, and five trees of the same
species on the perimeter landscape. I’m comparing the median trees to the
perimeter trees,” she explains. “The perimeter serves as my control group.”
18
The perimeter is the area surrounding the parking lot. This area is usually
covered with dirt, gravel, or grass instead of pavement.
During the summer of 2001, Celestian studied 15 parking lots in the
greater Phoenix area. The lots contained 149 trees.
Celestian took surface temperatures around each tree at several distances
from the trunk. She took readings in all four compass directions. She also
recorded surface types (e.g. asphalt, gravel, etc.) and whether or not the surface
had plants growing on it. Next she measured tree size using canopy volume,
height, and trunk diameter.
Celestian took her measurements from June to August between
1 and 4 p.m. “It was so hot! I did about three parking lots a day,” she says.
She found that parking lot surfaces
were up to 30 degrees hotter than the
perimeter. Parking lots had higher temperatures than any other type of surface.
Celestian’s parking lots contain six
different kinds of trees. She studied bottle
tree, Arizona ash, Chilean mesquite,
Aleppo pine, Canary Island pine, and
Chinese evergreen elm. Only three of
these trees—bottle, ash, and mesquite—
are native to hot, dry climates like that
in Arizona. Not surprisingly, these trees
did the best overall, especially the bottle
and mesquite trees.
All of the parking lot trees had smaller
canopies, heights, and trunk diameters than
the trees on the perimeter. But the mesquite
and bottle trees suffered the least.
The Aleppo pine and elm trees were the most reduced in parking lots in all
the size categories. However, elms were the most common parking lot trees
that Celestian found. They appeared in six of the 15 parking lots she studied.
“Elm seems to be a really good shade tree. It has a nice big canopy.
I worked in a nursery and if someone came in looking for a shade tree
for their yard, I’d say, ‘Buy an elm!’”
But Celestian wouldn’t recommend the elm for a parking lot. She also
wouldn’t recommend pines. In her study, the pines had an 80 percent
smaller canopy in parking lots than they do in other environments.
Celestian hopes that her work will help business owners make better
choices when planting trees around parking lots. Ultimately, the Arizona native
wants to help create more of those shady parking spots for desert drivers.
Bottle Tree
Brachychiton populneus
can have many different
shapes of leaves on one tree
Chilean mesquite
Prosopis chilensis
Arizona Ash
Fraxinus velutina
5 leaflets per leaf,
dark green leaves
evergreen elm
Ulmus parvifolia
leaves alternate
Aleppo Pine Pinus halapensis
2 needles per fasicle– the pinecone
is attached to the stem by a stalk
Canary Island pine Pinus canariensis
3 needles per fasicle–very long needles,
some nearly a foot in length.
Thought question:
Sarah Celestian says that
heat may not be the only
thing affecting tree growth
in parking lots. What other
effects could parking lots
have that would reduce
tree growth?
19
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Planting Water-Wise
Laziness is a virtue. At least, it can be when it comes
to caring for your yard. For desert plants, ASU plant
biologist Linda Stabler says that less work can be better
in terms of efficient water use.
Stabler studies the water use efficiency (WUE) of
desert plants. Water use efficiency describes how much
a plant will grow for every unit of water applied. When
a plant can grow a lot using a little bit of water, it has
high water use efficiency.
Water is scarce in the desert. Improving your yard’s
WUE helps the environment by conserving water.
It also can save you money, time, and effort.
Some types of plants need less water than others.
But other factors affect WUE as well. Stabler studies
Texas sage and oleander, two shrubs popular in desert
landscapes. She wants to know how irrigation and
pruning affect these plants’ WUE.
In the Phoenix area, these shrubs are often planted
close together and pruned often. Many times, you can
see Texas sage trimmed into square or rounded shapes.
Keeping these shapes neat requires a lot of work.
Oleander is often used as a natural fence because
it grows very tall. The plants are placed close together to
create a “wall.” These walls also need frequent pruning.
Both of these plants require little water. However,
Stabler found that many people get caught in a cycle
of heavy watering and pruning. Plants that are watered
heavily grow faster. They need to be pruned often to
control size. However, plants that are pruned frequently
use water less efficiently.
Stabler set up an experiment at the Desert Botanical
Garden in Papago Park. She created 14 mock landscapes.
Each was set up to look like a typical Phoenix yard.
Each 100 meter by 100 meter plot included trees, shrubs,
and ground covers.
Stabler divided the plots into groups based on how
often they are pruned. Some were pruned every six
C h a i n R e a c t i o n . 4
20
weeks, others every six months, and others
once a year or never. Then she measured
the WUE of plants in each of the groups.
“We found that plants given low volumes of
irrigation water and left unpruned had high water
use efficiency. Those given lots of water and pruned
often had very low water use efficiency,” says Stabler.
“A fully mature leaf is good at using the sun’s energy
to make the plant grow. Immature leaves require a lot
more energy to grow. If you’re constantly pruning a plant
it never develops a lot of good mature leaves to provide
energy for the rest of the plant. Also, it’s stressful on
the plant to constantly shear it.”
Not all pruning is bad. “Pruning is a rejuvenating
process,” she says. Occasional pruning is healthy.
Stabler says that people often buy new houses and
program their irrigation systems for young trees and
plants. Of course, young plants need more water than
older plants. Then they forget to change these levels
once the plants mature.
These people are wasting water. They may also be
harming their plants, causing problems such as root rot.
“When people see a plant failing they immediately think,
‘More water!’ That might not be the solution,” Stabler says.
Spacing of plants is another important part of the
equation. Many people place plants so close together
that they don’t have room to spread out. Then they
have to prune them more often.
A water-efficient yard is also low-maintenance,
says Stabler. “In Arizona you always see landscapers out
with their power hedgers and leaf-blowers,” she says.
These machines are quick and easy from a business standpoint. They are not very good for the environment or
for the customer’s pocketbook, Stabler notes.
“Fallen leaves are good for your yard. Your front lawn
is not your kitchen f loor. It doesn’t have to be spotless.”
Diane Boudreau
Where does our water come from?
The Phoenix area is a desert with limited amounts of water.
Yet the population keeps growing, using more and more water every year.
Where does this water come from?
> Local rivers The Salt and Verde rivers have been dammed in several places
to collect water in reservoirs for use by people.
> Groundwater sources Water that exists underground can be pumped
up through wells. Unfortunately, people are using more groundwater
than nature can replenish.
> Effluent Effluent is basically recycled wastewater. The water is treated
but not clean enough for drinking or bathing. However, it can be used
for things like watering golf courses and cooling power plants.
> Central Arizona Project Since 1985, water has been carried 336 miles
through CAP canals from the Colorado River to the Phoenix area
Photo courtesy Salt River Project
to supplement local water supplies.
How much water are we using?
In 1998, the Phoenix Active Management Area used 2.3 million acre-feet
4 4 % Fa r m i n g
of water. An acre-foot is the amount of water required to cover an acre
of land with one foot of water. It is about 325,851 gallons,
enough to serve a family of four for a year.
36% City
gallon
7% Industry
13% Other
MOST OF THE WATER (44 PERCENT) WAS USED FOR FARMING.
ANOTHER 36 PERCENT WENT TO CITY WATER SUPPLIES.
INDUSTRY USED 7 PERCENT.
13 PERCENT WENT TO OTHER USES.
What is Xeriscaping?
Xeriscaping is a type of landscaping that uses water efficiently. ASU’s Linda Stabler
says that many people create desert-looking landscapes and believe they are xeriscaping.
“Putting out a bunch of gravel and putting in drip irrigation is not xeriscaping,” she says.
“Xeriscaping is a practice, not a style. It is founded on seven basic principles created
by the Denver Water Department.” Those principles are:
Plan and design for water conservation and beauty from the start.
Did you know?
It takes 8 gallons of water
to grow one medium tomato,
36 gallons to produce
a serving (2 ounces) of pasta,
and 1,232 gallons to produce
one 8-ounce steak.
Create practical turf areas of manageable sizes, shapes, and appropriate grasses.
Select plants that require low water. Group plants of similar water needs together.
Use soil helpers like compost or manure as needed by the site and type of plants used.
Use mulch, such as woodchips, to reduce evaporation and keep the soil cool.
Irrigate efficiently with properly designed systems. Apply the right amount
of water at the right time.
Maintain landscape by mowing, weeding, pruning, and fertilizing properly.
For more information on xeriscaping, visit Xeriscape Colorado! Inc.
(http://www.xeriscape.org/) or the Arizona Department of Water Resources
(http://water.az.gov/default.htm)
You save up to 4 gallons of water
per minute by shutting off the water
while you brush your teeth.
A seven-minute shower uses
9 to 12 gallons of water. Keep your
shower under 5 minutes and you'll
save about 1,000 gallons a month.
21
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Ahhh! Take a nice, long sip.
There’s nothing more refreshing on a hot summer day than a tall glass
of cold, sparkling water. But what if that water smells like mold and tastes like dirt?
The satisfied “Ahhh” can quickly turn into a disgusted “Ewww!”
Water
n
k
t
i
y
s
BY
DIANE BOUDREAU
L o t s o f p l ac e s o n E a rt h h av e na s t y d r i n k i n g wat e r .
Much is not fit for humans to drink . Drinking water in the Phoenix
metropolitan area is clean. However, sometimes it has a taste and
odor problem. Scientists at Arizona State University are trying to
figure out how to make the water more pleasant to drink.
“We knew that there were problems with how the water in our
area tastes and smells. Salt River Project has been trying to deal with
this problem for years,” says Milton Sommerfeld, a plant biologist at ASU.
Sommerfeld and his team decided to study stinky water in the Phoenix area.
However, they had a tough time finding good information about the
problem. Not much was written down.
There is a lot more information available now, thanks to Sommerfeld
and his research team. In 2002, the group finished a three-year study.
The work was funded by the City of Phoenix. The ASU scientists studied
water samples from reservoirs such as Saguaro Lake and Bartlett Lake.
They studied water from canals used to transport that water. They also
studied samples from the actual water treatment plants in Phoenix.
They found the cause of the stink. The funky water odor comes
from tiny plants called cyanobacteria. These plants live in the water.
“The cyanobacteria produce chemicals that leak into the water.
These chemicals cause the water to smell musty and moldy,”
explains Kirsten Hintze, a doctoral student on the research team.
F i e l dw o r k Fo i b l e s
Sometimes scientists work in a laboratory. Sometimes they work on computers.
Often, however, scientists must go out into the environment they study.
This is called fieldwork.
Kirsten Hintze studies cyanobacteria that live in Saguaro Lake. She must
collect samples of the bacteria to study in her lab. To make her collections,
Hintze takes a boat out on the lake and scoops water from several areas.
Unlike a carefully controlled lab experiment, fieldwork is full
of surprises and unexpected situations. “Field researchers have to be creative
in coming up with ways to answer questions,” says Hintze. “Sometimes they
have to be creative in dealing with unforeseen problems out in the field.
C h a i n R e a c t i o n . 4
22
Pseudanabaena collected from the Verde River.
This algae can produce 2-methylisoborneol (MIB)
which smells moldy and musty.
2-methylisoborneol (MIB)
The main chemical that causes problems is called MIB. Treatment plants
remove some of the MIB from the water using powdered, activated carbon.
However, it costs too much to remove all the MIB this way when levels are
very high. Instead, the researchers decided to track the problem to its source.
“We’re trying to better understand the organisms that produce the problems.
Maybe we can prevent or reduce the problem at the source,” says Hintze.
The first challenge was finding out what causes cyanobacteria to produce
MIB. Not all cyanobacteria produce MIB, and the types that do don’t produce
it all the time. The researchers wanted to know what causes cyanobacteria
to churn out high levels of MIB.
To find out, they measured different characteristics of the water itself.
They measured temperature, pH, nutrient levels, and the amount of salt
in the water.
The scientists already suspected that temperature affected MIB. Their
main clue was that taste and odor problems usually occur in late summer
and early fall. Sure enough, they were right. The hotter it gets, the more
the water begins to stink and taste bad. “We found that we don’t have
problems with organisms until the temperature exceeds 22 degrees Celsius
(71.6 degrees Fahrenheit),” says Sommerfeld. ›››
The weather, the wildlife, and even the
machines that researchers use do not
always cooperate.”
A plant biologist who works in the field
probably knows a lot more than biology.
She might be skilled at fixing cars, because
if her SUV breaks down in the wilderness,
no one is around to help. She probably
knows what to do when she encounters
a rattlesnake or bear, or how to treat
a case of poison ivy, and how to set up a tent.
She should also be handy at making things.
“Sometimes you have to make your own
tools. You have to devise ways to measure
things that haven’t been measured before,”
Hintze explains.
For example, researchers studying canal
water in Phoenix needed to measure how
much algae grew on the canal walls.
They needed a tool to scrape off the algae.
But they needed a way to get the same
amount each time without it being washed
away by the water current. They also needed
a tool that could reach down into the canal
to collect the sample. It’s dangerous for
people to climb into the canal itself.
The ASU scientists found a solution.
They got some pool cleaning poles and
attached a wire brush to the end. This let
them reach into the canal and scrape off
the algae. But there was still a problem
to solve. How could they collect what
they scraped off?
They made a box out of Plexiglas with
a fine mesh net on one side. When they
scraped the algae, they scraped it right
into the box.
Cyanobacteria are filamentous—
long and thin. In fact, they are less
than half the width of a human hair.
Some cyanobacteria are very small, but
they often clump together. When they
attach to a surface, like a canal wall,
they form a blue-green or brown fuzzy mat.
They can also float in the water as plankton.
geosmin
Oscillatoria collected from a canal.
It can produce a chemical called geosmin.
Geosmin smells like dirt.
The solution wasn’t expensive, high-tech
equipment, but it got the job done.
Besides poles and brushes, some of
the most important field tools are courage,
friendliness, and a good sense of humor.
“One time we were out on the far end
of the lake,” Hintze recalls. “We were way
past all the warning signs that say, ‘Danger!
Do not go any further!’ Of course, that is
where the motor of our boat decided to stop.
“The oars we had were pretty useless.
They were like toothpicks with plastic
spoons on the end,” she says. “Somehow,
we managed to get to shore, in case we had
to hike out of there. About a half hour later
another boat—as reckless as we were—
came near. After minimal begging and
pleading they agreed to tow us out.”
When the group got to shore, Hintze
and her companion asked how they could
repay their rescuers.
“Just give a tow to the next people
out there who need help,” was the reply.
23
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Phormidium filaments collected from rocks in Saguaro Lake.
This microscope image also shows round Synechocystis. Both are considered blue-green algae.
The team also found that MIB production goes up when nitrogen levels
in the water are high. So far, they have not found any other correlations.
Another key to tracking MIB is learning which strains of the bacteria
produce the chemical. There are many types of cyanobacteria, but only
some of them produce MIB. The only way to tell if a particular strain
will produce MIB is to take a sample and grow it in the laboratory.
Unfortunately, it’s hard to mimic lake conditions in the lab. Some bacteria
simply quit producing MIB under lab conditions.
“We spent three years trying to isolate a good MIB producer from
Saguaro Lake. It’s hard to replicate the exact conditions of the lake in a lab.
You can mimic the temperature. You can use lake water. But it’s still
a different environment,” says Sommerfeld.
Understanding cyanobacteria is helping the researchers to prevent
and treat the stinky water problem. The methods they use depend on where
the cyanobacteria are growing. “MIB can be produced in the lakes, canals,
or treatment plants,” says Sommerfeld. “There are large areas where these
organisms can grow and produce.”
Much of our drinking water
comes from Saguaro Lake.
It is transported to treatment plants through canals.
The ASU biologists have found several ways to help
area cities reduce the odor problems with drinking water:
Canals
Canals may be the easiest places
to combat MIB. One way to do this is to add copper to
the water. Copper kills the cyanobacteria so it cannot
Different kinds of algae grow on canal walls,
including green algae, blue-green algae, and
produce MIB. Another solution is to use a special brush
brown algae. Each kind contains different
that scrapes the cyanobacteria off the canal walls.
pigments used for photosynthesis, which
Both of these techniques are very effective. ASU’s Milton
gives them their different colors.
Sommerfeld says that there are 135 miles of canals winding
Blue-green algae are also called
cyanobacteria.
through the Phoenix area. It would be too time-consuming and
expensive to repeatedly treat and brush all of the canals. So the
researchers tried to find the hot spots that produce the most MIB.
They discovered that the highest production occurs between
the Squaw Peak and Deer Valley water treatment plants.
Other areas also produce large amounts of MIB, sometimes.
The researchers monitor the other areas and recommend
places for Salt River Project workers to brush or add copper.
C h a i n R e a c t i o n . 4
24
Micrographs and photos courtesy Milton Sommerfeld, Ph.D.
In 2002, the ASU team began taking weekly water samples during high
odor months. They take samples at 10 different locations. The scientists
also send out a weekly newsletter with all the data they collect. They make
recommendations for how to deal with the problem. Workers at the treatment plants also contribute information.
Sommerfeld adds, “The cities of Chandler and Phoenix now have taste
and odor panels.” A group of people rate water samples based on their
smell and taste. It’s kind of like a wine tasting for stinky water.
All of these efforts help ensure that our water tastes good, without
costing a fortune. “I think this is one of the success stories of ASU
working with cities,” says Sommerfeld. “It allowed us to apply
the scientific method to a real-life problem.”
Lakes
Not all MIB is produced in the canals.
Some of it comes from the lakes that are used as reservoirs.
Treating lakes is more difficult than treating canals. “You can’t
scrape the sides in the rivers and reservoirs. There are no sides.
And you can’t dump in biocides (poison)—there are too many
Treatment Plants
All of this
drinking water goes through a water treatment plant before moving
other things that could be harmed,” says Kirsten Hintze.
However, the researchers made an important discovery that
on to homes and businesses. Cyanobacteria can grow in treatment plants,
helps them avoid stinky water from the lakes. Cyanobacteria tend
just as it grows in lakes and canals. Plant operators kill this cyanobacteria
to live in the upper layers of the water. It is warmer near
using copper, just as they do in the canals.
the top, and there is lots of light. “Think of when you jump
However, if MIB is already in the water when it flows into the plant,
copper will not have any effect. To remove existing MIB, plant operators
use powdered, activated carbon (PAC). They dump the PAC in the water,
in a lake and go swimming,” says Sommerfeld. “On top,
the water is warm, but down below, it’s cold.”
In Saguaro and Bartlett Lakes, drinking water is always
where it absorbs the molecules that cause the bad taste and smell.
pulled from the bottom of the reservoir. Lake Pleasant,
The PAC then sinks to the bottom. The plant operators skim the clean
however, has two outlets—one at the top and one at the bottom.
water off the top and dispose of the dirty carbon.
Now that the scientists know the bottom water has less MIB,
During high MIB months, this option becomes very expensive.
they can pull water from the bottom of Lake Pleasant during
However, Sommerfeld and his team have found ways to make it more
high MIB months. This helps reduce the amount of MIB
cost-effective. For example, they learned that some types of PAC work
that gets released.
better than others. “We evaluated the PAC used by treatment plants
to find out which were most cost-effective. It saved the cities
considerable money,” says Sommerfeld. “More recently, some of
the treatment plants have added activated carbon filters. The water
runs through beds of carbon. We continue to explore other technologies
that might help solve the problem,” he adds.
25
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Sneeze maps
cross
i k:
Big,
watery sneezes.
Red, itchy eyes.
Wheezing.
Runny noses.
That irritating tickle
in the back of the throat.
n
ink:
cros L
PALYNOLOGY
AND
ECOLOGY
Pollen grains are much too small
to see by eye. ASU biologists used
microscopes to make these images
of pollen. They also used a computer
system to add color to the images.
Color makes detail more visible.
Many types of plant pollen are
covered with sharp spikes. Spikes
help pollen stick to insects and
birds which carry it from plant
to plant. Allergic reactions are
not caused by the spikes, but
by chemicals on the surface
of pollen. Some types of
pollen that cause allergies
are round and smooth.
C h a i n R e a c t i o n . 4
We’ve all suffered those symptoms and others. We know that these
symptoms often are the result of our allergic reaction to something
in the air. That something is usually tiny bits of plant pollen.
Billions and trillions of bits of pollen fill the air in central Arizona
every spring and fall. Different types of pollen affect people in
different ways. Scientists know that the pollen is found in different
amounts in different parts of the Phoenix metropolitan area.
It might be helpful to have a large pollen map. The map would show
which parts of the city have the highest amounts of pollen. People with bad
allergy problems could use the map to choose the healthiest area to live.
It might also be nice to find a way to predict which areas of a city are likely
to change in terms of pollen count.
Glenn Stuart is working on both of those ideas. His research is done
as part of ASU’s Central Arizona-Phoenix Long Term Ecological Research
(CAP-LTER) project.
Stuart is a doctoral student in anthropology. He often uses pollen to help
find answers to anthropological questions. For example, he has studied old
pollen to study how people farmed the area of western Mexico a long time
ago. By looking at pollen found at different levels in the ground, Stuart can
reconstruct past environments. He looks at ecological change over time.
The work he does for CAP-LTER is different. He uses pollen to provide
a look at Phoenix as it is today and to predict how the whole area might
look in the future.
26
Palynology is the study of pollen deposits. Stuart’s work is a new use
for an old technique. In fact, his study is one of the most extensive pollen
mapping projects ever attempted. “Nothing like this has ever been done.
Not on this scale,” says Stuart. The ASU scientist has collected lots of data
and looked at lots and lots of plants.
Stuart has compiled some early findings. The pollen count of any
particular neighborhood in Phoenix is largely affected by how the land
immediately around it is being used.
For example, say a person is extremely allergic to ragweed. That person
might have a problem if he or she happens to live in a relatively expensive
home near one of the Phoenix mountain preserves. Levels of ragweed pollen
are very high in those areas. But in central Phoenix, the levels are low.
It might be reason enough to consider moving.
However, just living away from the mountain preserve might not protect
the person. Ragweed is a rapid colonizer. The plant likes to grow in areas
where the ground is churned and broken. People living anywhere near
a developing area, or a vacant lot, are more likely to suffer from the allergy.
At least until the development is complete.
No place is truly safe. Ragweed is a prolific pollen producer. The plant’s
pollen is found everywhere in the city. Some areas with well-maintained
landscapes simply have lower concentrations of the sneeze-producing grains.
Look at other parts of the Phoenix area and you’ll find other plants and
other kinds of pollen. Olive trees produce pollen that triggers particularly
harmful allergic reactions in many people. The olive pollen count is high in
older areas where these plants have been used as landscaping.
The same is true of pine trees. There are few natural pine trees in desert
areas. But developers planted lots of pines in Phoenix neighborhoods built
in the 1970s and 1980s. Landscaping patterns can tell a person much about
how he or she will suffer during allergy season.
Stuart’s findings come from the CAP-LTER 200 point survey.
The scientist looked at top layer soil samples from 200 locations in
and around Phoenix. These samples were less than 1 centimeter deep.
The pollen in these samples was deposited with the last few years.
Stuart analyzed the 200 soil samples for pollen content. He then mapped
how pollen types and levels of pollen vary across different parts of the city.
The plan is to continue taking new samples. Stuart will study how the pollen
count ref lects the actual number of plants and the changing uses of the land.
The information he collects might be used to help residents and future
home buyers. The data can be used to predict how types and concentration of
pollen might change in the future, depending on plans for neighborhood land
use. It will also help to refine the use of palynology in anthropology
and ecology. Matthew Shindell
The pollen grain at right comes from
a plant called Salsify, also known as
vegetable oyster (Tragapogon mirus).
Salsify is a cousin to another wellknown plant– the dandelion.
Photos by Charles Kazilek
27
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Cars, power plants, pesticides—
these are a few of the things responsible for today’s environmental problems.
But long before any of these technologies were invented, people were affecting
their environments. In some cases, scientists say they caused the
downfall of their own civilizations.
ECOLOGY
AND
HISTORY
People native to the Southwest often used a metate–
a smoothed flat stone– to grind corn and beans.
Above: Casa Grande Ruins National
Monument at Coolidge, Arizona.
Casa Grande means "Great House."
This structure was built by the Hohokam
people. It is considered to be the peak
architectural expression of their desert
culture. The ruins are located less than
two miles from the Gila River. This low
aerial view is to the south-southeast,
with the Picacho Mountains on the
horizon. © ADRIEL HEISEY. ALL RIGHTS RESERVED.
C h a i n R e a c t i o n . 4
“There’s a tendency to think that the establishment
of Earth Day in 1971 was the establishment of all our
environmental problems,”says Chuck Redman, an
archaeologist and ecologist at Arizona State University.
“But ancient people had their own problems. They also
dealt with monumental environmental change.”
Redman has written a book about ancient people’s effects
on the environment. He says even prehistoric cultures caused
environmental problems such as reduced soil fertility, erosion, and
deforestation. “Those problems are not the same as air pollution and
global warming, but they are things we still are dealing with.
Ancient cultures dealt with them, too. These problems affected
people’s productivity and their quality of life.”
When problems got too bad, people would have to leave the
area they had changed. “To us, it seems small—one valley they have
to move from. But after generations of living in the same community,
people had to leave and find a new home. This doesn’t generally
happen today,” says Redman.
The city of Phoenix was built on top of one of these ancient
civilizations. More than 1,500 years ago, the Hohokam people settled
this valley. They lived here for as long as 1,000 years—much longer
than modern Americans have lived here.
The Hohokam were irrigation farmers. They brought water
to their farms using canals, just like Arizona farmers do today.
Redman says the Hohokam may have been the most successful irrigation
farmers in all of prehistoric North America.
They were not successful enough to stop their own downfall, however.
In about 1350, the valley suffered a couple of really big f loods followed
by drought. The Hohokam were using all of their available resources.
They were very productive. However, that massive production depended
on the climate staying fairly stable.
“But against that background exists a climate that’s naturally variable.
There are wet years and dry years,” explains Redman. The Hohokam
had developed a very efficient farming system that gave them the most
productivity possible. However, their system was geared toward
the average rainfall, not to extremes.
28
For more information on the Hohokam canal system, visit
http://www.srpnet.com/community/heritage/srphistory.asp
“If you really tune yourself to average rainfall, then much more
or less than average is bad. Too much or too little water is bad,” says Redman.
The Hohokam society could not withstand the extreme f loods and drought,
so they had to leave the valley. Nobody knows where they went.
Redman sees parallels between the Hohokam and today’s Phoenicians.
In fact, the name Phoenix refers to a mythical bird that lived for 500 years,
burned itself to ashes, and was reborn from those ashes to live another
500 years. Like the bird, the modern city of Phoenix rose from the ruins
of a former civilization. Early American settlers found the remains of the
Hohokam canal system and used them to build a new irrigation system.
The canals made it possible to produce large amounts of food here,
which attracted more settlers. Eventually, Phoenicians expanded the canals
beyond the old Hohokam system. Farming production increased.
“Our system here parallels the one built by the Hohokam. But they relied
solely on the Salt River for water,” Redman explains. “The early Americans
dammed rivers for reservoirs, and pumped groundwater. In 1985, Phoenix
also got access to water from the Colorado River.”
Like the ancient Hohokam, modern Phoenicians are using their resources
to the maximum. They don’t think much about whether they can sustain
those resources in the future.
“We are using all available water right now. There’s not a drop more.
That puts modern Phoenix in a position it’s never been in,” Redman says.
“We have a population of 3.2 million, and we have plenty of water.
But if the population doubles to 6.4 million, which it could, we would not
have enough water for everyone. We can survive a drought now, but what
about in 20 years? What if there’s a longer drought than we’ve ever seen?”
Unlike ancient people, modern humans have the technology to predict
their effects on the environment. This allows us to change our behavior so that
we don’t destroy our own homes. Redman wonders if human nature allows us
to do that. Can people stop their drive to constantly grow, grow, grow?
“Can Phoenix go low-growth? Will rapid growth destroy Phoenix?”
asks Redman. “The alternative is longer commutes from home to work,
bad air, and bad water. Then again, maybe it’s self-regulating.
As the conditions in Phoenix worsen, people will stop moving here.
Some might even move away,” he adds. “But that wouldn’t be good
for those of us who live here.” Diane Boudreau
The Hohokam canals were rediscovered
by early settlers in Phoenix. Some of
the canals were put to use again during
the 1870s.
The map shows how some of the canals
carried water from the Salt River.
ASU archaeologists dug this trench
across one of the old Hohokam canals.
The curved layers reveal the bottom
of the canal.
29
h t t p : / / c h a i n re a c t i o n . a s u . e d u
?
How do scientists study the environment?
The world around us is called the environment. Our environment is filled with things
to study. Physical scientists study the nonliving parts of the environment. Life scientists study
the living things. Ecologists study the relationships between the living and nonliving things.
All scientists use a special tool when they study. That tool is called the scientific method.
It kind of works like this:
BY
D AV I D W R I G H T
David Wright is an associate research
professional at ASU's Center for
Solid State Science. He visits schools
throughout Arizona doing demonstrations
as part of the Science is Fun! program.
Ask a question.
The goal of the research is to answer this question:
Does mercury pollute the environment?
two:
Explain why this question is important.
If mercury harms the living or nonliving things in the environment,
we need to be careful with how we use and discard mercury.
three:
Describe the system to be studied.
Scientists often collect many samples
over time so they may observe changes
in the environment. Sometimes nature
does the sampling for us. In animals and
people, hair absorbs substances from
the body as it grows. These substances
provide a record of any contamination
in the recent past.
Trees have growth rings that contain
substances absorbed by the tree each
year. A core sample from a tree reveals
the rings. The rings provide a history
of growth conditions over many years.
Core samples from glaciers, ice sheets,
and permafrost provide information
about environmental conditions
long ago.
In general terms for this case, the environment and pollution are the system.
The environment provides all that we consume. It receives all that we
discard. The environment is made of energy, air, water, land, and living things.
Pollution is anything that harms the environment. Pollutants come from
natural and human sources. Most pollutants circulate widely. They can become
diluted in the air, water, and soil. Most pollutants are present in trace amounts.
But even small amounts of very toxic substances can be harmful. And some
pollutants can build up in the food chain. This is called bioaccumulation.
four:
Describe the topic.
Mercury is a toxic metal. It is a liquid at room temperature and evaporates
quickly when heated. Mercury is extracted from the mineral cinnabar.
It reacts with other metals to form amalgams. It also reacts with other
substances to form compounds that can be very toxic. When handled
properly, mercury and its compounds are safe. However, accidental spills
or improper disposal can release mercury into the environment.
five:
Select a site to study and collect samples.
A good study site might be a lake near a factory where large amounts
of mercury are used.
Scientists collect samples of the air, water, soil, and plants. They also
collect tissue, f luids, or hair from animals and people. Each sample is stored
in a clean container and labeled with the date, time, and location.
The condition of plants and animals are recorded. If people are tested, the
scientists describe where these people live, what they do, and how they feel.
C h a i n R e a c t i o n . 4
30
six:
Examine the samples.
In this case, analyze them for mercury.
Samples are tested in a laboratory. Experts decide which testing methods
to use for each kind of sample. In some cases, samples can be tested at the
collection site with portable scientific instruments. A mercury detector blows
some air over a thin film of gold. If the air contains mercury vapor or dust,
it reacts with the gold film to form an amalgam. The electrical resistance
of the gold film changes. More mercury causes a bigger change.
This change is measured electronically. A computer in the detector calculates the amount of mercury in the amalgam. The amount of mercury in the
amalgam ref lects how much mercury was in the air sample. For convenience,
the computer reports only the final result of how much mercury was in the air.
seven:
Understand the results.
Scientists use quantitative analysis to measure
how much mercury is present in a sample.
When testing air, the concentration
is reported in micrograms of mercury
Air is sucked in through
per cubic meter of air (µg/m3).
the nozzle at the front of this
A microgram is one one-millionth
hand-held mercury vapor detector.
Molecules of mercury stick to
of a gram. A paper clip weighs
a small piece of gold film inside.
about one gram.
Mercury levels in air are
usually less than 0.02 µg/m3.
Near active volcanoes,
mercury levels in the air
might be as high as 18
micrograms per cubic meter.
In cinnabar mines with poor
ventilation, mercury levels
can climb to 5,000 micrograms
per cubic meter!
When testing water, soil,
plants, and animals, mercury levels
are reported in micrograms of mercury
per kilogram of sample (µg/kg).
One µg/kg is one part-per-billion (ppb).
Natural waters usually contain less than 0.01 ppb
of mercury. However, the sediment in the bottom
of a contaminated lake may have levels as high as 250 ppb.
Contaminated fish have levels as high as 10,000 ppb. Hair samples from
people who ate these fish and became sick had levels as high as 500,000 ppb!
One part per billion:
a drop of mercury this big dissolved
in an Olympic-size swimming pool.
Scientists use qualitative analysis
to identify what forms of mercury
are present:
Air samples may contain mercury
vapor or microscopic droplets of liquid
(mercury dust) floating in the air.
Air may also contain compounds that
evaporate easily. Water may contain very
small amounts of mercury compounds
that dissolve slightly in water. Soil may
contain mercury metal and compounds
of mercury. Mercury can accumulate
in plants, animals, and people.
31
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Scientists have found mercury in many
different chemical forms that appear
in different places. Each year, about
6,000 tons of mercury is released
eight:
naturally into the environment.
During eruptions, volcanoes spew gases
that contain mercury. Some mercury
Mercury is not normally present in the environment. But in contaminated
evaporates directly from seawater.
areas, mercury may be present in air, water, soil, plants, animals, and people.
Human activities release about 3,000
Mercury changes from one chemical form to another
tons of mercury every year. Some types
of bacteria can convert mercury into
as it moves through the environment.
C2H6
CH4
forms that are very toxic to living things. ethane
methane
Certain bacteria convert mercury to
Toxic forms of mercury can build up in
deadly organo-mercury compounds.
(CH3)2Hg
the food chain, especially in seafood.
dimethyl mercury
The process is called biomagnification.
These compounds can accumulate
Summarize the results.
Hg0
mercury metal
CH3Hg+
methyl mercuric ion
Hg2+
mercuric ion
CH3Hg+
methyl mercuric
ion
in the food chain. Plants and
animals can sicken and die.
If people eat food that
is tainted with mercury,
they can become very
sick for a long time.
Hg
CH3S-HgCH3
methyl methyl-mercuric sulfide
(CH3)2Hg
dimethyl mercury
CH3Hg+
Hg2(2+)
methyl mercuric
mercurous ion
ion
forms of
mercury in the
environment
CH3S-HgCH3
methyl methylmercuric sulfide
The chemical symbol for mercury
Hg0
mercury metal
nine:
Answer the question.
If present, mercury and its compounds pollute the environment.
HgS
This pollution harms living things.
mercury sulfide
Make a recommendation: Based on this answer,
we should avoid releasing mercury to the environment.
Share all the information. Scientists describe their research at
meetings and in written reports. Other scientists review the work to be sure
Mercury is a metal. It melts
it was done properly. Scientists all over the world read the published reports.
to a liquid at room temperature.
Mercury is heavy–the amount in this
They might try the same study in other locations. Or, they might try a brand
flask weighs about 7.5 pounds!
new study of the environment.
ten:
Hg2+
mercuric ion
Ask another question!
Good science always raises new questions to explore.
What would you ask next?
C h a i n R e a c t i o n . 4
32