Number 18

The

Edition

7

25

41

58

74

90

105

WHAT’S INSIDE

Green Means Clean!

What’s the Nonpoint?

Caribbean Cruise

Sediment-al Journey

Mussel Mania!

Timed Travel

Under Where?
Natural Inquirer

Freshwater Edition • Number 18 • Fall 2015

Produced by

Forest Service

Production Staff

Babs McDonald, Forest Service

Jessica Nickelsen, Cradle of 

Forestry in America Interpretive 

Association

Brian Cooke, Cradle of Forestry in 

America Interpretive Association

Michelle Andrews, University of 

Georgia

Samantha Dean, Cradle of 

Forestry in America Interpretive 

Association

Amber Painter, Cradle of Forestry 

in America Interpretive 

Association

Stephanie Pfeiffer, Illustrator

Carey Burda, Cartographer

Lindsay Gnann, Cartographer

Forest Service Scientists 

Highlighted in the 

Journal

Dr. Thomas Brown, Rocky 

Mountain Research Station

Ms. Pamela Froemke, Rocky 

Mountain Research Station

Dr. Wendell Haag, Southern 

Research Station

Dr. Carolyn Hunsaker, Pacific 

Southwest Research Station

Dr. Ariel Lugo, International 

Institute of Tropical Forestry

Mr. Samuel Moya, International 

Institute of Tropical Forestry

Dr. Richard Pouyat, Northern 

Research Station

Dr. Kurt Riitters, Southern 

Research Station

Dr. Tamara Heartsill Scalley, 

International Institute of 

Tropical Forestry

Dr. E. Ashley Steel, Pacific 

Northwest Research Station

Mr. Ian Yesilonis, Northern 

Research Station

Collaborating Scientists 

Dr. Daniel Bain, University of 

Pittsburgh

Dr. Roger Bales, University of 

California, Merced

Dr. Brian Beckman, National 

Oceanic and Atmospheric 

Administration

Mr. Keith Denton, University of 

Washington

Ms. Aimee Fullerton, National 

Oceanic and Atmospheric 

Administration

Dr. Donald Larsen, National 

Oceanic and Atmospheric 

Administration

Dr. Fengjing Liu, Lincoln 

University

Dr. Andrew Rypel, University of 

Alabama

Ms. Abby Tillotson, National 

Oceanic and Atmospheric 

Administration

Mr. Timothy Wade, U.S. 

Environmental Protection 

Agency

Dr. James Wickham, U.S. 

Environmental Protection 

Agency

Forest Service

Thomas L. Tidwell, Chief

Dr. Carlos Rodriguez-Franco,

Acting Deputy Chief, 

Research and Development

James E. Hubbard, Deputy Chief, 

State and Private Forestry

Michael Rains, Director, 

Northern Research Station and 

Forest Products Laboratory

Vacant, Staff Director, 

Knowledge Management 

and Communications

Michiko Martin, Staff Director, 

Conservation Education

Dr. Katherine L. Smith, Assistant 

Director, Pacific Northwest 

Research Station

Kimberly Winter, NatureWatch 

Program Coordinator

Vicki Arthur, Conservation 

Education Specialist

Sandy Frost, Partnership Liaison 

Specialist

Cradle of Forestry in 

America Interpretive 

Association

Hope Ascher, Chairperson

Carlton Murrey, Executive Director

Adam DeWitte, Director of 

Education

With thanks to 

FreshWaterLIVE, 

http://www.freshwaterlive.org/

Project Learning Tree, 

http://www.plt.org/

Natural Inquirer is reproduced on 

recycled paper with soy-based inks.

Please pass this journal along or 

recycle it when you have finished 

using it.
1

Natural Inquirer • Number 18

Contents

Editorial Review Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

About Natural Inquirer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Who Are Scientists? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Welcome to the Natural Inquirer Freshwater Edition! . . . . . . . . . . 4

Features

Green Means Clean! Assessing the Condition of U.S.

Drinking Water Watersheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

What’s the Nonpoint? Assessing Nonpoint Source Water 

Quality Threats Nationwide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Caribbean Cruise: Examining the Movement and Quality of 

Organic Matter Over Time From Two Caribbean Watersheds . 41

Sediment-al Journey: Measuring Metal Concentrations in 

Soils Beside Urban Waterways . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Mussel Mania! How Streamflow Affects Freshwater Mussels 

Over Long Time Periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Timed Travel: Measuring the Relationship Between Stream 

Temperatures and the Development of Salmon . . . . . . . . . . . . 90

Under Where? Underground Water and Its Contribution 

to Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 

Freshwater eyeChallenge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Freshwater Crossword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

National Education Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

What Is the Forest Service? . . . . . . . . . . . . . . . . . . inside back cover

What Is the Cradle of Forestry in America 

Interpretive Association? . . . . . . . . . . . . . . . . . . . . inside back cover

What Is FreshWaterLIVE? . . . . . . . . . . . . . . . . . . . . inside back cover

Web Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . back cover

Join us in being green! The following Educator Resources 

are now available exclusively on the Natural Inquirer

Web site, http://www.naturalinquirer.org. These resources 

can be found with the “Freshwater” journal and on the 

“Educational Resources” pages.

• Note to Educators

• Lesson Plan

• Reflection Section Answer Guide

• National Education Standards (specific to each article), 

including:

- Next Generation Science Standards

- National Science Education Standards

- National Curriculum Standards for Social Studies

- Common Core State Standards

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58

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Freshwater Edition, http://www.naturalinquirer.org

Editorial Review Boards

Natural Inquirer editorial review boards hard at work.

Editorial Review Boards’ Comments

Bemidji Middle School, Minnesota: Ms. Henry’s 7th Grade Life Science Classes

The glossary is helpful. Including color pictures inside 

the magazine would make it more interesting. 

The most important thing I learned was what kinds of 

things scientists work on. 

I think it is cool that you put the scientist’s names and 

told us what they study but I think you should add 

some fun facts. 

The most important thing I learned was that our 

water that we drink now comes from way back before 

dinosaurs existed and that water is good for you. 

If these magazines are for teenagers, you should give 

them more excitement like people’s opinions or fun facts. 

I thought the magazine was going to be boring, but it wasn’t. 

It was fun and educational. 

I liked that there were a lot of pictures to show me what the 

parts of the article were about. 

I think that it was a good learning tool but very long so it 

made it kind of boring at points. 

I learned about the water cycle before, but never in detail! It 

was pretty cool to know exactly where my water comes from!

I think that a little more of what I like to call “pop!” would be 

appreciated; as well as some simpler summaries at the 

bottom of each article.

I think you should have more activity pages.
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Natural Inquirer • Number 18

About Natural Inquirer

Scientists report their research in journals, 

which are special booklets that enable 

scientists to share information with one 

another and with others. This journal, Natural 

Inquirer, was created so that scientists can share 

their research with you and other middle school 

students. This journal presents the research 

of scientists with the Forest Service and other 

cooperating organizations. The Forest Service is 

an agency of the U.S. Department of Agriculture.

If you want to know more about the Forest 

Service, you can read about it on the inside back

cover of this journal, or you can visit the Natural 

Inquirer Web site at http://www.naturalinquirer.

org. Information is also available at http://www.

fs.fed.us.

All of the research in Natural Inquirer is focused

on nature, such as trees, forests, animals, insects, 

outdoor activities, and water. First, you will 

“Meet the Scientists” who conducted the 

research. Then, you will read something special 

about science and about the natural environment. 

You will also read about a specific research 

project, which is written in the format that 

scientists use when they publish their research in 

journals. Then, YOU will become the scientist 

when you conduct the FACTivity associated 

with each article. Don’t forget to look at the 

glossary and the special sections highlighted in 

each article. At the end of each section of the 

article, you will find a few questions to help you 

think about what you have read. Your teacher 

may use these questions in a class discussion.

Be sure to try the Freshwater eyeChallenge 

and Crossword on pages 124–126!

Who Are Scientists?

Scientists collect and evaluate 

information about a wide range 

of topics. Some scientists study 

the natural environment. To be 

a successful scientist, you must:

b Be curious—Are you interested in learning?

b Be enthusiastic—Are you excited about a 

particular topic?

b Be careful—Are you accurate in everything you do?

b Be open-minded—Are you willing to listen to new 

ideas?

b Question everything—Do you think about what 

you read and observe?

To learn more about scientists and their work, you can find cards and posters for Natural Inquirer

scientists online at http://www.naturalinquirer.org.
4

Freshwater Edition, http://www.naturalinquirer.org

Welcome

to the Natural Inquirer Freshwater Edition! 

Clean water is one of Earth’s most 

important natural resources (figures 1, 

2, and 3). All the planet’s organisms 

need water. You may know that some small 

amounts of water can come to Earth from 

extraterrestrial sources such as meteors. 

Practically speaking, however, water found 

today across Earth’s environment is also Earth’s 

supply of water for the future. The water you 

drank today was on Earth even before the 

dinosaurs lived! Water moves from Earth’s 

atmosphere to its surface and underground, 

and then back to the atmosphere in a 

continuous cycle (figure 4).

Earth has been called a water planet. Nearly 

70 percent of Earth’s surface is covered by 

water. Of this surface area, 97.5 percent is 

saltwater. Take a look at a globe or a map of 

Earth. You will see for yourself just how much 

saltwater is found on our planet.

The remaining 2.5 percent of Earth’s 

water is freshwater. Humans must have clean 

freshwater to live. Urban and industrialized 

(in dəs trē ə līz(d)) societies must provide clean 

freshwater for a growing human population. 

Industrialized societies build and operate 

factories and businesses in a city, region, or 

country. To provide freshwater, people have 

developed ways to collect large quantities of 

freshwater for human use. People have also 

developed ways to clean polluted freshwater 

(figure 5). Humans unfortunately have also 

wasted and polluted some of their freshwater 

resources, and they have neglected to properly 

protect many of Earth’s water resources.

Figures 1, 2, and 3. Water is necessary for all of 

Earth’s organisms.
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Natural Inquirer • Number 18

Figure 4. The water cycle. Illustration by Stephanie Pfeiffer.

Figure 5. Wastewater treatment plants clean 

used water and release it back into waterways.

The Middle Oconee Water Reclamation (re klə 

mā shən) Facility is in Athens-Clarke County, GA.

Photo courtesy of Elizabeth Cason.

Human activities are changing rainfall and 

snowfall patterns, resulting in unexpected 

droughts and floods. It is important, therefore, 

to understand how human use of large 

freshwater quantities fits into the water cycle 

(figure 6).

In this Natural Inquirer Freshwater edition, 

you will learn many new things about Earth’s 

freshwater. In “Green Means Clean,” you 

will learn how scientists and managers are 

protecting U.S. drinking water supplies 

using better land management practices. 

Water pollution that cannot be traced to a 

particular source is the subject of “What’s the 

Nonpoint?” You will learn how the amount 

and type of living, or once-living, matter in a 

waterway changes over time in “Caribbean 

Cruise.” Have you ever wondered whether 

chemicals flowing into urban waterways are 
6

Freshwater Edition, http://www.naturalinquirer.org

Figure 6. Humans have modified Earth’s natural water cycle by collecting and using large quantities 

of freshwater for household and industrial use. Illustration by Stephanie Pfeiffer.

dangerous? You will learn whether those 

chemicals are dangerous in “Sediment-al 

Journey.” The fascinating world of freshwater 

mussels and what they tell us about water 

quality is revealed in “Mussel Mania.” “Timed 

Travel” will introduce you to the importance 

of water temperature to young salmon. In 

“Under Where?” you will explore the unseen 

but important movement of groundwater 

below your feet.

As you read each article, think about your 

daily water use. You use clean freshwater for 

drinking, bathing, and cooking. Did you know 

that up to 60 percent of your body weight is 

water? Water not only keeps you healthy, it 

keeps the planet healthy!

Be Water Wise!

Here are some tips to help you and your 

family conserve freshwater:

 Turn off the faucet when you brush your 

teeth and only turn it on as you need it.

 Install low flow toilets and showerheads to 

reduce the amount of water used.

 Put a rain barrel outside to collect rainwater. 

Use this water for your plants.

For more great ideas about what you can do to 

conserve freshwater, visit http://www.epa.gov/

WaterSense/kids/.

Are you interested in learning more about freshwater? Check 

out “FreshWaterLIVE: A Distance Learning Adventure!” 

FreshWaterLIVE will be available in 2015–2016 at http://

www.freshwaterlive.org/. Also read the inside back cover 

of this Natural Inquirer for additional information about 

FreshWaterLIVE.
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Natural Inquirer • Number 18

Green Means Clean! 

Assessing the 

Condition of U.S. 

Drinking Water 

Watersheds

Photo courtesy of Babs McDonald
8

Freshwater Edition, http://www.naturalinquirer.org

Meet the Scientists

Dr. James Wickham, Biologist: My favorite science 

experience is studying Earth’s environment from space.

Mr. Timothy Wade, Geographer: 

My favorite science experience is using 

Geographic Information Systems (GIS) 

to uncover environmental patterns that 

were not previously known.

Dr. Kurt Riitters, Ecologist: 

My favorite science experience 

is asking and answering 

questions that have not been 

asked before.

Glossary words are bold and are defined on page 21.

t

t

t
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Natural Inquirer • Number 18

What Kinds of 

Scientists Did 

This Research?

biologist: This scientist studies living 

organisms and living systems.

ecologist: This scientist studies the 

relationship of living things with each other 

and with the nonliving environment.

geographer: This scientist studies 

the relationship between Earth’s natural 

environment and human society.

Thinking About 

Science

Look at the section entitled, 

“What Kinds of Scientists Did 

This Research?” What do 

you notice about the kinds of 

scientists who are involved with 

this study? You probably noticed 

that three different kinds of scientists worked 

together to study drinking water watersheds in 

the United States. You might have also noticed 

that two of the scientists study relationships. 

When different kinds of scientists come 

together to conduct a study, each scientist 

brings a different perspective, a different kind 

of knowledge, and perhaps different scientific 

methods. These differences strengthen the 

study. One person may see or understand 

things that another person may not.

If you are holding a hard copy of Natural 

Inquirer, take a moment to look at the “What 

Kinds of Scientists Did This Research?” section 

of the other articles within the journal. You may 

also look at this section in more articles by viewing 

Natural IQ: Southern United States Climate 

Change edition at http://www.naturalinquirer.

org. Notice that a variety of scientists came 

together to conduct the other studies. Relate 

this characteristic of scientific research 

to your own experiences. Share an experience 

of when having many different perspectives 

was an advantage for you. 

Thinking About the 

Environment

A watershed is an area of 

land where all the water that 

is underground within the area 

and all the water that drains off 

of its surface goes to the same 

place (figure 1). 

Figure 1. What do you notice about watersheds? 

Illustration by Stephanie Pfeiffer.

Watersheds contain streams or rivers that 

carry surface water toward the oceans, and 

they may contain lakes or reservoirs (re zə 

vwärz) (figures 2a and 2b). Watersheds hold 

groundwater, which also flows into streams 

and rivers. In the United States, the largest 

watersheds are defined by the Continental 

Divide (figure 3). One of these large watersheds 

drains into the Pacific Ocean. The other large 

watershed drains into the Atlantic Ocean, the 

Gulf of Mexico, and the Caribbean Sea. Smaller 

watersheds are contained within each larger 

watershed in a nesting pattern (figure 4).
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Freshwater Edition, http://www.naturalinquirer.org

Figure 2a. Reservoirs are formed when a river is 

dammed. Reservoirs are built for many reasons, 

such as flood control or power generation. Photo 

courtesy of Babs McDonald.

Figure 2b. Many reservoirs are built to hold water 

that will be used as drinking water. Notice the 

drinking water treatment plant on this reservoir 

in northeast Georgia. For more information on 

water treatment plants, see page 16. Photo 

courtesy of Babs McDonald.

Figure 3. The Great Continental Divide defines two large U.S. watersheds. Notice the 

other large watersheds of North America. Identify which direction the water flows from the 

boundary of each watershed. Map by Lindsay Gnann and photo courtesy of Babs McDonald.
11

Natural Inquirer • Number 18

Figure 4. Smaller watersheds may be contained 

within larger watersheds. Illustration by Stephanie 

Pfeiffer.

Introduction

Scientists estimate that 80 percent 

of all U.S. freshwater resources begin in 

forests. Approximately 60 million U.S. 

citizens rely directly on national forests 

for their water. About two-thirds of 

the U.S. population use drinking water 

from surface sources. Surface sources 

of drinking water include streams, 

rivers, lakes, and reservoirs (figure 5). 

People who manage drinking water 

sources have recognized the relationship 

between conservation of natural land 

and improved drinking water quality. 

When land is covered with vegetation, 

surface water is cleaner. Cleaner water 

means lower water treatment costs and 

safer drinking water.

Managers take a number of actions 

to protect drinking water. Starting 

in 1974, with the passage of the Safe 

Drinking Water Act, managers focused 

on detecting sources of water pollution. 

By 1996, people had begun to think 

differently about how to provide clean 

Figure 5. Rivers, as well 

as lakes and reservoirs, 

are surface sources of 

drinking water. Photo 

courtesy of Babs 

McDonald.
12

Freshwater Edition, http://www.naturalinquirer.org

drinking water. People realized that protecting 

surface source water was more effective 

and efficient than just detecting pollution. 

In 1996, amendments to the Safe Drinking 

Water Act shifted the focus from detection of 

pollution to protection of source water. A big 

part of protection is managing drinking water 

watersheds so that the surface water is clean. 

This kind of management means that the land is 

purposely managed to protect surface sources 

of drinking water.

The 1996 Safe Drinking Water Act 

amendments also required each State to 

assess the condition of its source water. These 

assessments are important, as they alert 

managers to the condition of drinking water 

watersheds. If a watershed’s natural condition 

becomes degraded or the land is developed 

for other uses, for example, managers can 

address the problem to protect water quality. 

Unfortunately, State-by-State assessments do 

not provide a regional or national understanding 

of drinking water watersheds. Each State might 

do its assessment a little differently. Watersheds 

often cross State boundaries, and watersheds 

are managed across State boundaries (figure 6). 

The scientists in this study, therefore, were 

interested in conducting a national assessment 

of drinking water watersheds that crossed State 

boundaries.

Figure 6. The U.S. Geological Survey divides the United States into 21 hydrologic regions. These 

regions contain either the drainage area of a major river, such as the Missouri region, or the combined 

drainage areas of a series of rivers, such as the Texas-Gulf region. In which hydrologic region do you 

live? Map by Lindsay Gnann.

Alaska, Hawai`i, and Puerto Rico are not drawn to proper scale or location.
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Natural Inquirer • Number 18

What Is the Safe Drinking Water Act?

Congress passed the Safe Drinking Water Act 

in 1974 to protect public 

health by regulating the 

Nation’s public drinking 

water supply. The law was 

amended in 1986 and 1996 

and requires actions to 

protect drinking water and 

its sources. These sources 

include streams, rivers, lakes, 

reservoirs, springs, and 

groundwater wells. Springs 

and groundwater wells are 

belowground sources of 

drinking water. In this study, 

the scientists were interested 

in surface drinking water 

sources.

The Safe Drinking Water 

Act identifies risks to safe 

drinking water. These 

risks include, for example, 

pesticide application, mining, 

and landfills (figure 7a). The 

act also identifies the many 

ways drinking water can be 

protected. These protective 

actions create barriers to 

water pollution (figure 7b).

Examples of barriers to water 

pollution include sustainable 

land management and 

public education programs.

Figure 7a. The Safe Drinking Water Act identifies risks to safe 

drinking water. Illustration by Stephanie Pfeiffer, adapted from 

the Safe Drinking Water—Protecting America’s Public Health 

Poster (EPA 816-H-02-001 January 2002).

Figure 7b. The Safe Drinking Water Act identifies barriers 

to water pollution. These barriers are protective actions that 

directly and indirectly protect water quality. Illustration by 

Stephanie Pfeiffer, adapted from the Safe Drinking Water—

Protecting America’s Public Health Poster (EPA 816-H-02-001 

January 2002).
14

Freshwater Edition, http://www.naturalinquirer.org

Reflection Section

b	 Do you knowwhere your drinkingwater comes from? If so,whatis the source? If you are not sure

ofthe source of your drinkingwater, do some research to identify the source. Your sourcemight

be a stream,river, lake, orreservoir. Youmay also have a spring, an individualwaterwell at your

home, or a communitywell.

b	 Look atfigure 7a.Why do you thinkwastewatertreatment plants are identified as a risk to safe

drinkingwater?

b	 Explain in your ownwordswhy the scientistswanted to conduct a national assessment of

drinkingwaterwatersheds.

Methods

First, the scientists located all surface 

drinking water intakes. A surface drinking water 

intake is a pipe in lakes, streams, rivers, or 

reservoirs that takes water from the source and 

carries it to a water treatment plant (figures 8, 

9a, 9b, and 9c). The scientists found 5,265 of 

these intakes across the United States.

The scientists then used maps to trace 

backwards from the water intakes. Tracing 

backwards from the intakes enabled scientists 

to identify the watershed for each intake. Each 

watershed included all the land area supplying 

water to the intake. Then, the scientists 

identified in which of the 21 hydrologic regions 

of the United States each watershed belonged 

(see figure 6).

Figure 8. Water enters a 

water treatment system 

through drinking water 

intakes. In this photo, 

water enters through a 

grate at a river’s edge 

and into a pipe for 

transport to the water 

treatment plant. This 

photo was taken from 

above the water intake.

Photo courtesy of Babs 

McDonald.
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Natural Inquirer • Number 18

Figures 9a, 9b, and 9c.

Water treatment plants 

clean the water received 

from watersheds and 

water intakes. Photos 

courtesy of Babs 

McDonald.
16

Freshwater Edition, http://www.naturalinquirer.org

How Is Water Treated So That It Becomes 

Clean Enough To Safely Drink? 

Figure 10. Water entering a drinking water treatment system 

is treated using a number of steps. Illustration by Stephanie 

Pfeiffer.

Water entering a drinking water treatment system is treated 

using a number of steps (figure 10).

When water is taken from a river 

(and before it reaches the water 

treatment plant), the water is filtered 

through screens to remove sticks 

and leaves. Water taken from a 

reservoir does not usually need to 

be screened. When water reaches 

the plant, coagulation is often the 

first step in treatment. Chemicals 

with a positive electrical charge 

are added to the water. The 

positive charge of these chemicals 

neutralizes the negative charge of 

dirt and other dissolved particles 

in the water. When this process 

occurs, the particles bind with the 

chemicals and form larger particles, 

called floc.

Due to its weight, floc settles 

to the bottom of the water supply.

This settling process is called 

sedimentation.

After the floc has settled to the 

bottom of the water supply, the 

clear water on top passes through 

a filtration process. Filtration uses 

materials such as sand, gravel, and 

charcoal to filter the water. Filtration 

removes dissolved particles, such 

as dust, parasites, bacteria, viruses, 

and chemicals.

After the water is filtered, a 

disinfectant (such as chlorine) is 

usually added to kill any remaining 

parasites, bacteria, and viruses.

Disinfectant also protects the water 

from germs when it is piped to 

homes and businesses.
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Natural Inquirer • Number 18

Water is stored at the water treatment plant 

in a clearwell before being piped to homes and 

businesses. Some of the water is piped to and stored 

in water towers located throughout the community.

Most of the water is piped directly to homes and 

businesses (figure 11). Water travels through these 

pipes and into a building’s plumbing system.

Figure 11. Water pipes are laid underground near 

roads. These pipes bring clean water from the water 

treatment plant to homes and businesses, including 

your home and school. The next time you turn on a 

faucet, think about the journey each drop of water 

has taken from its surface water source to your 

faucet. Photo courtesy of Babs McDonald.

The scientists needed more information 

to do their analysis. The scientists used 

information from an existing national database 

on land cover. This database is made up of 

satellite photographs taken of Earth’s surface 

(figures 12 and 13). Land cover is the physical 

cover at Earth’s surface. Examples of land 

cover include forest, grass, asphalt, water, 

and buildings. Some of these land covers are 

classified as urban, such as buildings. Some of 

these land covers are classified as natural, such 

as forests.

Using this database of photographs, the 

scientists noted changes between 1992 and 

2001 in land cover for areas identified as 

urban, natural, agricultural, and water. 

Figure 12. Landsat satellites take images of 

Earth’s surface. The photographs are used for 

many purposes. Photo courtesy of National 

Aeronautics and Space Administration.

Figure 13. Landsat images are commonly used 

today. Landsat images help us understand 

how Earth’s surface is changing over time.

This Landsat image is of the Island of Hawai`i.

Image courtesy of http://www.geology.com.
18

Freshwater Edition, http://www.naturalinquirer.org

They identified, for example, whether the 

amount of urban land expanded or got smaller 

between 1992 and 2001 for each of the drinking 

water watersheds.

Next, the scientists looked at another 

database called the Protected Areas Database 

of the United States. This database identifies 

land that is protected from development. 

Development is what happens when land is 

converted from natural to urban or agricultural 

uses. The Protected Areas Database identifies 

public land and conservation land. The scientists 

figured out how much land in each of the 

drinking water watersheds was protected. Land 

that is protected is less likely to be developed 

into roads and buildings, or used for agriculture.

Finally, the scientists put all of this 

information together into a computer. For each 

of the drinking water watersheds, the scientists 

figured out how much of the land was urban, 

natural, agricultural, or covered in water. They 

figured out percentages for 1992 and 2001. By 

looking at data for 1992 and 2001, the scientists 

figured out if each watershed was becoming 

more urban, more agricultural, more natural, or 

had not changed. Then, the scientists calculated 

the percentage of land in each watershed 

that was protected from further urban and 

agricultural growth.

Findings

Most major U.S. rivers are used to supply 

drinking water to Americans. The scientists 

discovered that about two-thirds of surface 

drinking water intakes are in rivers. Onethird of the intakes are in lakes and reservoirs. 

Nationwide, most of the land in drinking 

water watersheds is covered with plants and 

trees. The scientists found that the median

watershed percentage of natural land cover 

nationwide was 77.1 percent (table 1).

Land Cover Median Percentage

Natural 77.1

Agricultural 8.1

Urban 5.2

Table 1. Comparison of the median amount of 

land characterized as natural, agricultural, and 

urban in U.S. drinking water watersheds.

Number Crunch

b	 Whatis the totalpercentageofdrinkingwater

watershed land accounted forin table 1?

What could be one reason these numbers

do not add up to 100percent?

Reflection Section

b Explainwhatkindofinformationthe

scientistscomparedforeachofthe

drinkingwaterwatersheds.

b Whatistherelationshipbetweenland

coverchangeanddrinkingwater

quality?

The scientists also discovered that about 

3 percent of the land in U.S. drinking water 

watersheds was protected from development. 

The Western United States, however, has a 

higher percentage of protected land in drinking 

water watersheds. This higher percentage is 

due to the large amount of public land in the 

Western United States (figure 14). Public land 

is generally kept in a natural condition with 

limited development.

Between 1992 and 2001, land cover changed 

in some of the drinking water watersheds. 
19

Natural Inquirer • Number 18

Figure 14. Observe the difference in the amount of western public land as compared with the amount 

of eastern public land. What do you notice? Map by Lindsay Gnann.

About 23 percent of the watersheds lost at 

least 1 percent of their natural vegetation. 

About 5 percent of the watersheds gained at 

least 1 percent in natural vegetation. In the 

Southeast and Ohio hydrologic regions (see 

figure 6), 42 percent of the watersheds lost at 

least 1 percent of their natural vegetation.

About 9 percent of the drinking water 

watersheds had at least a 1-percent increase 

in urban land between 1992 and 2001. Most of 

this increase was in the Eastern United States. 

Three-fourths of all watersheds nationwide, 

however, increased in urban land by some 

percentage between 1992 and 2001.

Number Crunch

b	 Consider awatershedwith a 1-percent

increase in urban land. Thiswatershed

contains 30,000hectares. To find out how

many acres are in thiswatershed,multiply

30,000times 2.471.Following a 1-percent

increase in urban land, howmanymore

hectares (and acres) are nowin urban

land? Is a 1-percentincrease ofland a large

amount ofland?Why orwhy not?
20

Freshwater Edition, http://www.naturalinquirer.org

Reflection Section

b Whatnationaltrendsinlandcoverchangewere

discoveredforthedrinkingwaterwatersheds?

b Basedonwhatyoulearnedinthisarticle,would

yousaythatfuturethreatstodrinkingwater

qualityareequalacrosstheUnitedStates?Why

orwhynot?Providereasonsforyouranswer.

Did You Know?

The average U.S. household uses about 94,000 gallons of water each year. That 

amount is about 257 gallons used per household each day, or about 11 gallons each hour.

In 2010, the U.S. Census Bureau estimated 

that an average U.S. household has 2.58 

people. Based on this information, do you 

think your household uses more or less than 

94,000 gallons of water every year?

Discussion

The scientists found that drinking water 

watersheds are mostly covered with natural 

vegetation. In some areas of the United States, 

however, watersheds contain a high percentage 

of urban land. Twenty percent of the Nation’s 

drinking water watersheds have less than 

50 percent natural vegetation. In addition, 

8 percent of the Nation’s drinking water 

watersheds contain at least 20 percent urban 

land. Over time, drinking water watersheds 

are losing natural vegetation and are becoming 

more urbanized. These trends indicate that 

many surface sources of drinking water may 

become more exposed to pollutants.

This study shows the importance of taking 

a regional and national look at U.S. drinking 

water supply. U.S. population increases will 

put more land use demands on drinking water 

watersheds. As more land becomes urbanized, 

drinking water source protection will likely 

become more difficult unless the percentage 

of protected lands increases as well.

Reflection Section

b Thescientistsdiscoveredthat8percentoftheNation’sdrinkingwaterwatershedscontainatleast20

percenturbanland.DoyouthinkthesemoreurbanizedwatershedsaremostlyfoundintheEasternUnited

StatesortheWesternUnitedStates?Why?

b Basedonthisarticle,doyouthinkthatdrinkingwatersourceswillfacemorechallengesfrompollutionin

thefuture?Why?

Adapted from Wickham, J.D.; Wade, T.G.; Riitters, K.H. 2011. An environmental assessment of United States 

drinking water watersheds. Landscape Ecology. 26: 605–616. http://www.srs.fs.usda.gov/pubs/ja/2011/ja_2011_

wickham_001.pdf.
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Natural Inquirer • Number 18

Glossary

amendment (ə men(d) mənt): A change in 

wording or meaning especially in a law, bill, or 

motion.

conservation (kän(t) sər vā shən): The care and 

protection of natural resources such as forests 

and water.

database (dā tə bās): A collection of related 

data organized for convenient access, generally 

in a computer.

degrade (di grād): To make the quality of 

something worse.

efficient (i fi shənt): Bringing about the result 

wanted with the least amount of time, waste, or 

materials.

groundwater (grau̇ nd wä tər): Water that sinks 

into the soil and is stored in aquifers.

hydrologic (hī drä lə jik): Relating to the properties, distribution, and circulation of water on 

and below Earth’s surface and in the atmosphere.

indirect (in dī rekt): (1) Not straightforward 

and open; (2) Not directly aimed at.

median (mē dē ən): A value in an ordered set 

of values below and above which is an equal 

number of values or which is the arithmetic 

mean of the two middle whole values if there is 

not one middle whole number.

pesticide (pes tə sīd): A substance that is used 

to kill animals or insects that damage plants or 

crops.

regulate (re gyə lāt): (1) To control according 

to a system; (2) To bring under control of law or 

some authority.

wastewater (wāst wä tər): (1) Water that has 

been used; (2) Sewage.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriam-webster.

com. Definitions are limited to the word’s meaning 

in the article.

How does this scene relate to this article?
22

Freshwater Edition, http://www.naturalinquirer.org

FACTivity

Time Needed

One class period

Materials

(for each student or group of students)

• Three paint roller pans

• One shovel

• 3/4 cup liquid kitchen oil, such as 

canola oil

• 2 gallons of water in plastic jugs

• One garden sprinkler can

• Blue or red food coloring

The questions you will answer in this 

FACTivity are: Which land cover surface 

best protects water quality and why?

Methods

Identify an area of thick grass near 

the edge of a grassy area. Ask an adult 

if the area you have chosen is a good 

location. Using the shovel, dig up an area 

of grass the size of one-half of the paint 

roller pan, including 1⁄2 to 1 inch of the soil 

underneath. Brush off the loose soil and 

place the grass into one of the paint roller 

pans. The roots of the grass should be 

holding the soil together. Make sure that 

the area of grass that you remove is away 

from the main lawn area.

Identify an area of bare soil. Bare soil 

is dirt with little or no vegetation. Dig up 

a shovelful of bare soil and place it into 

the second paint roller pan, to about 

1-inch deep. If it is not possible to find the 

grass or bare soil in your schoolyard, your 

teacher will bring them to class. Leave the 

third paint roller pan empty. Line up the 

three paint pans so that you can easily 

compare them (figure 15).

During your experiment, use the graphic 

organizer in the next section to answer the 

following questions. What do think each 

of the paint pans represents? (Hint: Think 

about the different land covers studied in 

the research you just read.) What do the 

water and oil represent? (The answers 

are given after the graphic organizer.) Based 

on your reading of this article, what do you 

predict will happen when oil is added and 

water is poured across each of the paint roller 

pans? Write your prediction in the form of a 

complete sentence in the graphic organizer.

Pour 1/4 cup of oil over the contents of 

each pan. Wait 5 minutes.

Add food coloring to the water. Mix the 

water and food coloring together until it 

makes a bright color. Add the water to the 

garden sprinkler can. Using the sprinkler can, 

pour an equal amount of water over each of 

the three paint pans. As the water drains into 

the bottom of each pan, observe the drained 

water in each of the pans. What differences do 

you see between the water in each pan? What 

has happened to the water in each case? 

What do you think is the reason for the water’s 

appearance in each of the pans?

Figure 15. How to set up the paint roller pans.

Illustration by Stephanie Pfeiffer.
23

Natural Inquirer • Number 18

Graphic Organizer

Note: Write using complete sentences, proper grammar, and appropriate punctuation.

The grass represents:

The soil represents:

The bare aluminum represents:

Write your predictions 

about how the water 

will look after oil is 

added and the water 

drains into each pan.

Bare aluminum:

Grass:

Soil:

Describe your 

observations of the 

water in each pan.

Bare aluminum:

Grass:

Soil:

Explain why you think 

the water looks like 

it does in each pan.

Bare aluminum:

Grass:

Soil:

How does this experiment relate to the research you read about in the article?

Based on what you learned, what are your conclusions about land cover and water quality?
24

Freshwater Edition, http://www.naturalinquirer.org

In this FACTivity, each paint roller pan 

represents a different watershed land cover. The 

grass represents a watershed with vegetation.

The soil represents a watershed with agricultural 

land. The bare aluminum represents an urban 

watershed with pavement, such as roads and 

parking lots. The oil represents pollution coming 

from cars, industry, and agriculture. The water 

represents rain.

Now answer the question posed at the 

beginning of this FACTivity: Which land cover 

surface best protects water quality and why? 

Share your answer with your class.

FACTivity Extension

To better understand how water treatment plants clean water, do the U.S. Environmental 

Protection Agency water filtration activity found at http://www.epa.gov/ogwdw/kids/flash/

flash_filtration.html.

If you are a trained Project 

Learning Tree educator, you may 

use “Water Wonders” as an 

additional resource.

Safe Drinking 

Water Hotline

The Safe Drinking Water Hotline provides information about drinking water and 

groundwater programs authorized under the 

Safe Drinking Water Act.

800–426–4791

http://water.epa.gov/drink/hotline/

Web Resources

U.S. Environmental Protection Agency: Learn 

About Water

http://www2.epa.gov/learn-issues/learn-about-water

U.S. Environmental Protection Agency: Surf Your 

Watershed

http://cfpub.epa.gov/surf/locate/index.cfm

U.S. Environmental Protection Agency Video: After 

the storm: The impact of storm water runoff on 

drinking water supply

http://water.epa.gov/action/weatherchannel/index.cfm

U.S. Environmental Protection Agency Water: 

Educator Resources

http://water.epa.gov/learn/resources/nationswaters_

index.cfm

U.S. Environmental Protection Agency Water: 

Educator Resources: What Can I Do?

http://water.epa.gov/learn/resources/projects.

cfm#projects
What’s the Nonpoint? 

Assessing 

Nonpoint Source 

Water Quality 

Threats Nationwide

Photo courtesy of James Holland
26

Freshwater Edition, http://www.naturalinquirer.org

Meet the Scientists

Dr. Thomas Brown, Economist: My 

favorite science experience happened 

before I was a scientist. I was a Peace 

Corps (kȯr) volunteer in rural Paraguay, in 

the heart of South America. I had grown 

up in the suburbs. When I arrived in 

Paraguay, therefore, I didn’t know much 

about rural life and the natural resources 

that are so important to people who live off 

the land. In Paraguay, I learned first-hand 

about water supply and water quality. I also 

learned how essential it is that our water 

resources be protected. My experience in 

Paraguay pointed me in the direction that, 

several decades later, I am still following.

Now, I study how our success as a society 

depends on the availability and quality of 

our water resources.

Ms. Pamela Froemke, Computer Specialist: 

Being constantly exposed to the great outdoors 

when I was young led me to love and appreciate 

the natural world. I always felt the best when I 

was outside. So, my favorite science experience 

is just what I’m doing now. I work with scientists 

to provide information that helps to protect 

our natural resources. I feel like I contribute to 

society and make a difference by helping to 

protect our water and other natural resources.

t

t
27

Natural Inquirer • Number 18

What Kinds of 

Scientists Did 

This Research?

computer specialist: Computer

specialists provide help and advice to people 

and organizations using computer software 

or equipment.

economist: This scientist studies 

economics. Economics is a social science 

that addresses the production, distribution, 

and use of goods and services. Goods 

and services include purchased items and 

services, such as clothes and car repair.

Goods and services also include those that 

are difficult if not impossible to buy and sell, 

including for example, clean water, clean air, 

and pollination.

Thinking About 

Science

When scientists want to 

figure out the total impact of 

a number of unlike variables

on another variable, they 

need a standard way to 

measure the variables. In this research, for 

example, the scientists wanted to know how 

a combination of variables might impact the 

level of water pollution risk in an area. These 

variables had different units of measurement. 

A unit of measurement is a standardized 

quantity of a physical property, such as inches, 

meters, degrees Celsius, etc. Different units 

of measurement cannot be added together. 

As an example, consider how we measure 

percentage of cloud cover and air temperature. 

Adding the percentage of cloud cover to the air 

temperature produces a senseless number.

In this research, the scientists divided the 

range of measurement for each variable into 

five equal categories. Each category represented 

20 percent of the entire range of values. A 

category representing an equal percentage 

of the whole is called a percentile. Then, the 

scientists assigned a number from 1 to 5 for 

each measured value. A value in the lowest 

20 percent of the range, for example, was 

given a score of 1. A measurement in the highest 

20 percent of the range was given a score of 5 

(figure 1). This process standardized the 

relative value of each variable so that the values 

could be compared and summed.

Glossary words are bold and are defined on page 35.

Figure 1. The units of measurement for percentage of cloud cover and air temperature are not 

comparable. Placing each value within a percentile enables scientists to compare and sum 

measurements. Illustration by Stephanie Pfeiffer.
28

Freshwater Edition, http://www.naturalinquirer.org

Thinking About the 

Environment

Congress passed the Federal 

Water Pollution Control 

Act in 1972. Since the act’s 

passage, water pollution 

coming from point sources 

has been reduced. Point sources of pollution 

are those that directly release pollution into a 

water source and may include factories and 

wastewater treatment plants. This reduction 

was possible because it is easy to identify point 

sources of pollution (figure 2).

Figure 2. Although point sources of water 

pollution have been reduced, they have not 

been completely removed. This photo, taken 

in 2012, shows point source pollution of the 

Altamaha (ȯl tə mə hä) River in Georgia. The pipe 

coming from an unseen factory is the source 

of the dark effluent. Photo courtesy of James 

Holland.

Nonpoint sources of pollution, in contrast, 

are not easily identified or controlled. These 

sources are not easily identified or controlled 

because nonpoint sources of pollution include 

things like farms, roadways, and urban and 

suburban communities (figure 3).

The scientists in this study were interested in 

better understanding the risk of water pollution 

from nonpoint sources across the entire United 

States.

Figure 3. This highway is a nonpoint source 

of water pollution. The pollution from cars and 

trucks is spread out over the entire highway, 

rather than coming from a few points. Photo 

courtesy of Babs McDonald.

Introduction

Nonpoint source water pollution still remains 

a problem in the United States, even decades 

following the passage of the Federal Water 

Pollution Control Act of 1972. Nonpoint source 

water pollution comes from large areas or 

landscapes. These areas include roadways, 

farms, and urban and suburban communities. 

Scientists know that nonpoint sources of 

pollution exist. It is difficult, however, to identify 

and control such diffuse sources of pollution.

The scientists in this study were interested in 

how the threat from nonpoint sources of water 

pollution varies in watersheds across the United 

States (figures 4 and 5).
29

Natural Inquirer • Number 18

What Is the Federal 

Water Pollution 

Control Act of 1972?

The Federal Water Pollution Control Act is the primary Federal law in the United 

States governing water pollution. The Federal 

Water Pollution Control Act is commonly 

referred to as the Clean Water Act. The 

act’s objective is to restore and maintain the 

chemical, physical, and biological health of 

the Nation’s waters. Restoring and maintaining 

water quality is accomplished by limiting point 

and nonpoint pollution sources, by improving 

publicly owned wastewater treatment plants, 

and by maintaining the health of wetlands and 

watersheds. Figure 4. A watershed is an area of land where 

all the water on it or under it drains to the same 

place. Illustration by Stephanie Pfeiffer.

Figure 5. The scientists began with 18 watersheds identified by the U.S. Geological Survey. The 

scientists studied watersheds only in the 48 contiguous States. Those large watersheds each contain 

many smaller watersheds (figure 6). The scientists studied 15,272 watersheds contained within the 

18 watersheds. Map by Lindsay Gnann.

Alaska, Hawai`i, and Puerto Rico are not 

drawn to scale or in correct locations.
30

Freshwater Edition, http://www.naturalinquirer.org

With information based on regions 

of the country, scientists and managers 

will have a better idea what and where 

are the greatest threats to U.S. water 

quality.

Reflection 

Section

b Whymightunderstandingthe

nonpointsourcewaterpollution

threatbyU.S.watershedregionbe

helpfultothosetryingtobetter

understandwaterpollution?

b Intheyearssincepassageofthe

CleanWaterActof1972,onetypeof

threattowaterqualityhasnotbeen

adequatelyaddressed.Explainin

yourownwordswhyitisdifficult

toidentifyandaddressnonpoint

sourcepollution.

Figure 6. Each large watershed contains many smaller, 

nested watersheds. Illustration by Stephanie Pfeiffer.

Methods

The scientists studied three problems affecting water 

quality. These problems were sediment, nutrients, and 

toxic chemicals (figure 7). Then, scientists considered 

each of these problems and some of their contributing 

factors (figure 8).

Problem Description

Sediment Sediment contains soil particles carried along in streams and rivers. Some particles 

settle to the bottom of streams, reservoirs, lakes, canals, and pipes. Some particles 

move with the current. All rivers naturally receive and carry sediment. Too much 

erosion, however, can cause too much sediment to enter waterways. Too much 

sediment decreases water clarity and may carry attached nutrients, toxic chemicals, 

and other pollutants. Too much sediment reduces drinking water quality and makes 

water more expensive to treat.

Nutrients Nutrients found in water are primarily nitrogen and phosphorus. These nutrients are 

essential for aquatic plant life. If too much nitrogen and phosphorus are found in 

waterways, however, they begin to destroy water quality. Too much nutrient content 

causes too much algae growth and reduces water clarity. Too much nutrient content 

also reduces the amount of oxygen in the water, which fish and other organisms need 

to live.

Toxic 

chemicals

These chemicals cause damage to plants and animals. These toxic chemicals include 

heavy metals such as mercury, lead, cadmium, and arsenic. Toxic chemicals may be 

contained in pesticides and herbicides, industrial chemicals, medical chemicals, and 

some acids. Mining and abandoned mines are often sources of toxic chemicals.

Figure 7. The three problems of sediment, nutrients, and toxic chemicals are responsible for 60 

percent of water quality problems in U.S. rivers and streams.
31

Natural Inquirer • Number 18

Contributing 

Factor Measurement Problem

Sediments Nutrients Toxics

Housing density Housing units per square kilometer in 

year 2000 X X X

Road density Meters of road and railroad per square 

kilometer of watershed land X X

Agriculture Percent of watershed area in agricultural land 

cover

X X X

Livestock grazing Livestock animals per square kilometer in 

year 2007 X X

Confined animal 

feeding

Livestock animals per square kilometer in 

year 2007 X X

Mining land cover Percentage of watershed in mining land cover X

Potentially toxic 

mines

Total number of active and inactive mine sites 

potentially yielding toxics per 1,000 square 

kilometers of watershed

X

Potentially 

damaging wildfire

Percentage of area with a high risk of losing 

key ecosystem components, such as trees and 

other vegetation, in a wildfire

X

Atmospheric 

deposition

Average yearly deposition in kilograms 

per hectare of nitrates and sulfates in wet 

atmospheric deposition (acid rain) in years 

2000 through 2006

X X

Figure 8. Each water quality problem was associated with a number of contributing factors. In some 

instances, the same factor contributed to more than one problem. The scientists measured the 

contributing factors in all 15,272 watersheds.

How Do You Compare 

the Metric System With 

the U.S. Imperial System?

This chart will help you understand how the metric system compares with the U.S. imperial system. Scientists take and 

report their measurements using the metric system.

Metric System Multiplied by U.S. Imperial System

Meters 1.094 = Yards

Kilometers 0.6214 = Miles

Kilograms 2.205 = Pounds

Square kilometers 0.3861 = Square miles

The scientists used 

existing data to represent 

each contributing factor. 

These data had been 

collected and recorded 

by other scientists. 

For example, the U.S. 

Census Bureau collects 

information about the 

number of housing 

units per square mile 

for census regions. The 

Census Bureau posts this 

information on its Web 

site. When necessary, 

the scientists changed 

these and other data 
32

Freshwater Edition, http://www.naturalinquirer.org

from the U.S. imperial system to the metric 

system. You can see, however, that these 

contributing factors did not have the same 

measured value (see figure 8).

The scientists changed the contributing 

factor measurements to a common unit of 

value for each watershed. For each contributing 

factor in figure 8, the scientists divided the 

range of value into five equal categories, with 

each category representing 20 percent of the 

range. (See “Thinking About Science” for more 

information.) The scientists assigned a number 

from 1 to 5 for each measurement, depending 

into which of the 5 percentiles the measure 

fell. This number gave the scientists a common 

measure for all contributing factors. In this 

way, the scientists were able to compare and 

combine the contributing factors with one 

another.

The scientists calculated a single score 

for all the contributing factors in the 15,272 

watersheds. This single score enabled the 

scientists to identify the water pollution risk 

level, based on all the contributing factors, for 

each of the 15,272 watersheds.

Reflection Section

b Whatarethebasicsourcesofthethree

waterqualityproblems?(Hint:Lookatthe

contributingfactorsinfigure8.)

b Observethedifferent measuredvalues

usedforthedifferentcontributingfactors

infigure8.Asyoucansee,thesedifferent

measuredvaluescouldnotbeadded

together.Thinkaboutconvertingeachof

thesemeasuresto1of5percentiles.What

islostwhenthiskindofstandardization

processisused?(Hint:Reviewfigure1in

“ThinkingAboutScience”onpage27.)

Findings

The scientists 

created a map 

showing the threat 

to water quality for 

each contributing 

factor in the 15,272 

watersheds across 

the United States. 

They also combined 

all the contributing 

factors and created 

a map showing the 

overall threat to water 

quality for the 15,272 

watersheds in the 48 

contiguous States 

(figure 9). Figure 9. The overall threat to water quality across 15,272 watersheds 

in the 48 contiguous States in the United States. Map by Pam Froemke.

1 = Low Threat; 5 = High Threat
33

Natural Inquirer • Number 18

The scientists observed that water quality 

threats are greater in the Eastern United States 

than in the Western United States. The East, 

however, does contain some low-threat 

areas. These eastern low-threat areas include 

Michigan’s Upper Peninsula, Minnesota’s 

northern lake country, northern Maine, and 

the Florida Everglades. (Locate these areas in 

figure 9 or on another United States map.)

The West contains some high-threat areas. 

Most of the West, however, has a low waterquality threat. Western areas with high threat 

include large agricultural areas, urban areas, 

and places with a combination of urban and 

agricultural land. (Locate and identify one 

western urban area in figure 9.) The scientists 

observed that the United States’ water-quality 

threat level is roughly divided at the 100th 

meridian.

Reflection Section

b Lookcloselyatfigure9andlocatethe

areawhereyoulive.Whatisthenonpoint

sourcewaterpollutionthreatlevelfor

yourarea?Howdoesthethreatlevel

comparewithotherareas?Basedon

whatyouhavereadinthisarticleand

otherthingsyouknowaboutyourarea,

explainwhythethreatleveliswhereitis.

b ObservethelocationsoftheEastern

UnitedStates’low-threatareas.Name

onedifferencebetweentheFlorida

Evergladesandtheotherlocations.

b Whatissimilaraboutalltheseeastern

low-threatareas,includingtheFlorida

Everglades?

What Is the 100th Meridian?

The 100th meridian is an imaginary line with a longitude of 100° west.

Imaginary lines are drawn between the 

north and south poles of Earth to indicate 

longitude (figure 10). Longitude is 

measured from 0 to 180° east and 0 to 

180° west of the prime meridian. The 

prime meridian runs through Greenwich 

(grə nich), United Kingdom.

In the United States, the 100th 

meridian passes through North Dakota, 

South Dakota, Nebraska, Kansas, 

Oklahoma, and Texas. Roughly half of the 

country lies east of the 100th meridian 

and half lies west. The 100th meridian 

has traditionally been considered the 

dividing line between the moist eastern 

half of the United States and the dry 

western half. The 100th meridian is also 

the rough dividing line between the more 

populated Eastern United States and less 

populated Western United States.

Figure 10. Longitude consists of imaginary lines and 

provides a way to identify exact locations east and 

west across the planet. Longitude is measured from 

the Prime Meridian, located in the United Kingdom.

The Prime Meridian has a longitude of 0. Illustration 

by Samantha Bond.
34

Freshwater Edition, http://www.naturalinquirer.org

Discussion

The scientists noted the importance of the 

division at the 100th meridian. When colonists 

settled the United States, the wetter, gentler 

topography of the Eastern United States 

was more supportive of human habitation

and livestock grazing than other parts of the 

United States. Over time, a larger population 

led to greater demand for electricity and other 

resources, and to increased acid rain. These 

demands for natural resources, as well as urban 

growth and changing land uses, created more 

nonpoint source threats to water quality in the 

Eastern United States.

The much steeper and drier Western United 

States was less supportive of human habitation. 

Fewer people, along with less water and steeper 

topography, created an opportunity to protect 

large areas of western land. These protected areas 

include national forests, national parks, wildlife 

refuges, and other Federal and State-owned 

lands (figure 11). Steep topography, limited water, 

and large areas of protected land further limited 

population growth. Lower human population 

density resulted in fewer demands on natural 

resources and therefore in lower nonpoint 

source water pollution threats in the West.

The threat of nonpoint source water pollution 

is expected to rise if human population continues 

to rise. The human need for agriculture, housing, 

roads, and livestock feeding and grazing raises 

the importance of addressing nonpoint source 

water pollution threats. The Clean Water Act 

recognized that both point source and nonpoint 

source pollution are threats to water quality. The 

act, however, only requires the control of point 

source pollution. The scientists noted that 

progress on controlling nonpoint source pollution 

will require more effort and energy, and may 

even include more direction from Congress.

Figure 11. Federal lands, found mostly in the Western United States, are in a natural condition with 

limited human development. Map by Lindsay Gnaan.
35

Natural Inquirer • Number 18

Reflection Section

b FederalandStatelandshelptoprotect

waterresourcesbecausetheylimithuman

development.Nametwoothernatural

resourcesthatareusuallyprotectedby

FederalandStatelands.

b ThinkabouttheCleanWaterAct.Ifpopulation

continuestoriseasexpected,whatactions

mighthelpprotectAmericansfroma

reductioninwaterquality?

Glossary

aquatic (ə kwä tik): (1) Living or found in, on, or 

near water; (2) of or relating to the animals or 

plants that live in, on, or near water.

contiguous (kən ti gyü wəs): Used to describe 

things that touch each other or are immediately 

next to each other.

density (den(t) sə tē): The average number of 

individuals or units per space unit; for example, 

a housing density of 10 houses per acre.

deposition (de pə zi shən): The action of 

depositing something (such as sand, snow, or 

mud) on a surface or area, especially over a 

period of time.

diffuse (di fyüs): Spread out over a large space; 

not concentrated in one area.

effluent (ə flū ənt): Liquid that is released as waste.

emission (ē mi shən): Something discharged or 

sent out.

erosion (i rō zhən): The process or state of 

wearing or washing away.

habitation (ha bə tā shən): Living in a place.

herbicide (hər bə sīd): A substance that destroys 

plants or prevents plant growth.

land cover (land kə vər): Whatever is covering the 

land, such as trees, grasses, buildings, or roads.

pesticide (pes tə sīd): A substance that is used to 

kill animals or insects that damage plants or crops.

pollutant (pə lü tənt): (1) A substance that makes 

land, water, air, etc., dirty and not safe or suitable 

to use; (2) Something that causes pollution.

reservoir (re zə vwär): A place where water is 

collected and stored for use.

standardize (stan dǝr dīz): To change (things) 

so that they are similar.

suburb (sə bərb): A town or other area where 

people live in houses near a larger city.

topography (tə pä grə fē): Physical features that 

make up an area and include mountains, valleys, 

plains, and bodies of water.

variable (ver ē ə bəl): Something that is able or 

apt to vary.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriamwebster.com. Definitions are limited to the word’s 

meaning in the article.

Adapted from Brown, T.C.; Froemke, P. 2012. Nationwide assessment of nonpoint source threats to water quality. 

Bioscience. 62: 136–146. http://www.fs.fed.us/rm/pubs_other/rmrs_2012_brown_t001.pdf.
36

Freshwater Edition, http://www.naturalinquirer.org

FACTivity

Time Needed

One class period

Materials

• Graph provided in the FACTivity

• Blank paper for calculations

• Pencil

The questions you will answer in this 

FACTivity are: How do standardized 

units of measurement help scientists 

to answer questions? What are the 

advantages of using percentiles to 

standardize measurements? What are 

the disadvantages of using percentiles to 

standardize measurements?

Methods

Use figure 13 on page 40 and the 

graphic organizer (figure 12) on page 37 to 

answer the questions at the beginning of 

this FACTivity.

Look closely at figure 13. Notice the 

percentiles in the top bar. Then look at the 

next two bars.

The second bar shows the average 

number of clear days in each State over 

a year’s period. The third bar shows the 

average percent of each State’s surface 

waters (lakes, rivers, streams, and reservoirs) 

that contain clean water. The average 

number next to each State represents the 

alphabetical order of the State. The average 

number of clear days a year in Alabama 

(99), for example, is shown on the line at 

“99” with a “1.” Review figure 1 on page 27 

to help you understand figure 13.

If you do not understand figure 13, 

ask your teacher for help. It is important 

that you understand figure 13 to do the 

remainder of the FACTivity.

Pretend that you are a scientist interested 

in answering this question: What are the 

five least and five most desirable States 

for water-based outdoor recreation? 

Water-based outdoor recreation includes 

activities like swimming, boating, fishing, 

water skiing, and paddle boarding. You 

have determined that a combination of 

4 variables will enable you to identify 

these 10 States.

The 4 variables are:

• The number of clear (cloudless) days 

in a year

• The average yearly air temperature in 

degrees Fahrenheit

• The percent of the State’s area that 

has clean surface water

• The percent of the State’s surface 

waters (lakes, rivers, streams, and 

reservoirs) with reported pollution 

problems

Most desirable States for water-based 

outdoor recreation will have more clear 

days, a higher average air temperature, 

a larger percent of their area with clean 

water, and a lower percent of surface 

waters with reported pollution problems.

To determine the five least and five most 

desirable States for water-based outdoor 

recreation, you need to sum the values for 

the 4 variables listed above. The units of 

measurement for these 4 variables are not 

the same. To sum the values, you will need 

to standardize the units of measurement.

If you need more explanation, reread 

“Thinking About Science” on page 27.

In figure 13, the number of clear days 

and the percent of the State’s area with 

clean water have already been standardized 

using the method described in figure 1 on 

page 27.
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Natural Inquirer • Number 18

Using the two blank portions of the graphic 

organizer, plot the value for each State for 

the remaining two variables. You will find 

the variables in figure 13 on page 40. Write 

the number representing each State above 

the area on figure 13 that shows the State’s 

value. For example, for the average annual 

air temperature for Alabama, find the place 

on figure 13 that shows 63 degrees, and 

write a “1” above it. For Idaho, find the place 

on figure 13 that shows 44 for the average 

annual air temperature, and write a “12” 

above it.

After you have plotted all 100 values, take 

a ruler and draw lines from each percentile 

mark in the top bar through all 4 graphs.

Using figure 13 on page 40, write the score 

from 1 to 5 on the graphic organizer below 

for each State for each variable.

Then, sum the four values for each State 

and write the value in the right-hand column.

Locate the States with the lowest four values 

and the States with the highest four values.

Write these State names at the bottom of the 

graphic organizer on page 39.

What do you notice about the positions 

of the data points on each bar? From what 

you know of the United States, do the 10 

States’ rankings make sense, based on the 

standardized data? Why or why not?

Now answer the questions posed at the 

beginning of this FACTivity.

State

Percent of 

Surface 

Water 

With 

Problems

Average 

Yearly Air 

Temperature 

in Degrees 

Fahrenheit

Standardized Percentile Score (1 to 5)

Total 

State 

Score

Percent of 

Surface 

Water 

With 

Problems

Average 

Yearly Air 

Temperature

Number 

of Clear 

Days In 

a Year

Percent 

of State 

With 

Clean 

Surface 

Water

1. Alabama 14 63

2. Alaska Not 

Available

27

3. Arizona 1 60

4. Arkansas 4 60

5. California 15 59

6. Colorado 3 45

7. Connecticut 30 49

8. Delaware 49 55

9. Florida 18 71

10. Georgia 12 64

11. Hawai`i 5 70

12. Idaho 8 44

13. Illinois 7 52

14. Indiana 14 52

15. Iowa 6 48

16. Kansas 12 54
38

Freshwater Edition, http://www.naturalinquirer.org

State

Percent of 

Surface 

Water 

With 

Problems

Average 

Yearly Air 

Temperature 

in Degrees 

Fahrenheit

Standardized Percentile Score (1 to 5)

Total 

State 

Score

Percent of 

Surface 

Water 

With 

Problems

Average 

Yearly Air 

Temperature

Number 

of Clear 

Days In 

a Year

Percent 

of State 

With 

Clean 

Surface 

Water

17. Kentucky 10 56

18. Louisiana 22 66

19. Maine 9 41

20. Maryland 26 54

21. Massachusetts 18 48

22. Michigan 7 44

23. Minnesota 3 41

24. Mississippi 71 63

25. Missouri 4 55

26. Montana 11 43

27. Nebraska 5 49

28. Nevada 3 50

29. New Hampshire 17 44

30. New Jersey 42 53

31. New Mexico 3 53

32. New York 8 45

33. North Carolina 18 59

34. North Dakota 8 40

35. Ohio 14 51

36. Oklahoma 10 60

37. Oregon 13 48

38. Pennsylvania 15 49

39. Rhode Island 21 50

40. South Carolina 63 62

41. South Dakota 3 45

42. Tennessee 22 58

43. Texas 5 65

44. Utah 4 49

45. Vermont 15 43
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Natural Inquirer • Number 18

State

Percent of 

Surface 

Water 

With 

Problems

Average 

Yearly Air 

Temperature 

in Degrees 

Fahrenheit

Standardized Percentile Score (1 to 5)

Total 

State 

Score

Percent of 

Surface 

Water 

With 

Problems

Average 

Yearly Air 

Temperature

Number 

of Clear 

Days In 

a Year

Percent 

of State 

With 

Clean 

Surface 

Water

46. Virginia 13 55

47. Washington 3 48

48. West Virginia 14 52

49. Wisconsin 5 43

50. Wyoming 2 42

The Five Most Desirable States for Water-Based 

Outdoor Recreaction

The Five Least Desirable States for Water-Based 

Outdoor Recreaction

Figure 12. State values and standardized scores with associated number.

Draw a brochure for one of the most desirable States using the information from the chart.

In your brochure design, be sure to clearly illustrate why the State is considered one of the 

most desirable for water-based outdoor recreation.

Web Resources

U.S. Environmental Protection Agency: Water Is 

Worth It

http://water.epa.gov/action/cleanwater40/

Tennessee Valley Authority: Kids’ Guide to 

Protecting Water

http://www.tvakids.com/environment/cleanwater.htm

Happy Birthday Clean Water Act! Wisconsin 

Environmental Education for Kids (EEK!)

http://dnr.wi.gov/org/caer/ce/eek/earth/

cleanWaterActBirthday.htm

U.S. Environmental Protection Agency: 

Nonpoint Source Pollution

http://water.epa.gov/polwaste/nps/

If you are a trained Project Learning Tree educator, you may use 

“Pollution Search” and “Watch on Wetlands” as additional resources.
40

Freshwater Edition, http://www.naturalinquirer.org

Figure 13. Graph of five variables for determining the most and least desirable States for water-based outdoor recreation.The following States are listed in the above graph, in “Percent Clean Water,” from 0 to 10 percent:Alabama, Arizona, Arkansas, California, Colorado, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Mexico, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, and Wyoming.Thirty-six States are listed in this first percentile. What does this number of States tell you about the percentage of clean surface water in the United States?Hint: Use a magnifying glass to make it easier to read the State names.
41

Natural Inquirer • Number 18

Caribbean Cruise: 

Examining the Amount and 

Quality of Organic Matter 

Over Time From Two 

Caribbean Watersheds

Examining the Amount and 

Quality of Organic Matter 

Over Time From Two 

Caribbean Watersheds

Photo courtesy of Tamara Heartsill Scalley
42

Freshwater Edition, http://www.naturalinquirer.org

Meet the Scientists

Dr. Tamara Heartsill Scalley, Ecologist: One of my 

favorite experiences was sampling for aquatic fauna in the 

headwater streams at the highest elevations of the Luquillo 

(lü kē ō) Experimental Forest. The Elfin Cloud Forests have 

many small streams. Every surface is dripping wet, covered 

in all kinds of bryophytes, and the air is cool and humid.

These tiny streams have small pools where the modified 

minnow traps that we used for sampling barely fit. The 

streams were full of life—with very high densities of filter 

feeder shrimp such as Atya lanipes.

These streams were the headwaters where streams first 

emerge from the ground at the highest elevation possible 

in the forest (figure 1). It was a pleasant surprise, because 

we did not expect many shrimp to be in those pools at the top of the mountain where the river 

system begins. These shrimp are diadromous (dī a drə məs). Diadromous means that they came 

up the mountain by swimming upstream from the coast, where they were in the ocean saltwater.

The shrimp swim and crawl to the highest elevation possible in this mountain stream system.

Figure 1. Observe the 

change in elevation.

Illustration by 

Stephanie Pfeiffer.

Mr. Samuel Moya, Biologist: My favorite 

science experience is installing new scientific 

equipment and sensors on experimental sites.

New sensors allow me to see more accurate 

results using graphics and statistical methods.

t

t

t
43

Natural Inquirer • Number 18

Meet the Scientists

Dr. Ariel Lugo, 

Tropical Ecologist: 

My favorite science 

experience is 

interacting with 

other scientists 

and debating about 

science.

In this photo, Dr.

Lugo is on Mount 

Britton Tower. Mount 

Britton Tower is an 

observation tower 

located at high 

elevation in the middle of the El Yunque (yün kā)

National Forest. Cloud cover usually obscures

the view from the tower. The tower is named 

after Nathaniel Lord Britton (botanist) and his 

wife, Elizabeth G. Knight Britton (bryologist). The 

Brittons spent time doing research in Puerto Rico 

in the early 1900s. A botanist studies plants.

A bryologist is a type of botanist who studies 

plants like moss, liverworts, and hornworts 

(figure 2). Through the New York Botanical 

Gardens and the New York Academy of 

Sciences, the Brittons published the Scientific 

Survey of Puerto Rico in the 1920s.

Figure 2. Moss is growing in the forest.

Photo courtesy of Jessica Nickelsen.

Glossary words are bold and are defined on page 54.

What Kinds of 

Scientists Did 

This Research?

biologist: This scientist studies living 

organisms and living systems.

ecologist: This scientist studies the 

relationships of living things with each other 

and the nonliving environment.

tropical ecologist: This scientist studies 

the relationships of living things with each 

other and the nonliving environment in 

tropical regions. Tropical regions are areas 

located between the Tropic of Cancer and 

the Tropic of Capricorn (figure 3).

Figure 3. Tropical regions are areas located 

between the Tropic of Cancer and the Tropic of 

Capricorn. Illustration by Stephanie Pfeiffer.

t
44

Freshwater Edition, http://www.naturalinquirer.org

Thinking About 

Science

Sometimes it is useful for 

scientists to study something 

over a long period of time. 

The Forest Service created 

81 experimental forests and ranges with this 

idea in mind (figure 4). The Forest Service 

started setting up these experimental areas 

in 1908. Most of the experimental areas are 

at least 50 years old. These areas are useful 

for scientists because they provide scientists 

with the opportunity to observe and conduct 

experiments in an area over a long period of time.

When scientists are able to gather information 

over several years, they can gain a better idea 

of what is happening in the area. For example, 

think about a time in school when a student does 

not give his or her best effort with schoolwork. 

Then the student has several years in which he 

or she gives his or her best effort. If the student 

were given a choice to be evaluated over 

the short time period when they didn’t give 

their best effort or the longer time period, 

the student would want to be judged on the 

schoolwork done over the longer period of 

time. The longer time period would provide 

better information about the student. Similarly, 

scientists gain a deeper understanding of what 

is happening when they can review several 

years of data. Scientists are also able to identify 

trends in the data this way. In this article, you 

will learn about an experimental forest located 

in Puerto Rico (figure 5).

Figure 4. Experimental forests and ranges can be found throughout the United States. Find the one 

closest to where you live. Map by Carey Burda.
45

Natural Inquirer • Number 18

Figure 5. Puerto Rico is a territory of the United States 

located in the northeast Caribbean Sea. Map by Carey 

Burda.

Number Crunches

b	 The first experimentalforestwas Fort

Valley ExperimentalForestinArizona.

Itwas established in 1908.Howmany

years old is the experimentalforest

today?Howmany decades old is the

experimentalforest?

Thinking About the Environment

A watershed is the 

area that drains to a 

common waterway, 

such as a stream, lake, 

estuary, wetland, 

aquifer, or even the 

ocean (figure 6). 

Understanding the 

activities that occur 

within watersheds 

and the location 

of the watershed 

is important. The 

activities and location 

can affect the 

watershed’s water 

quality.

Figure 6. A watershed is the area that drains to a common waterway, such 

as a stream, lake, estuary, wetland, aquifer, or even the ocean. Illustration 

by Stephanie Pfeiffer.
46

Freshwater Edition, http://www.naturalinquirer.org

In this research, scientists studied two 

watersheds in Puerto Rico. The watersheds 

are located in tropical forests. Tropical forests 

are unique because they are located near the 

Equator (figure 7). These forests have a high 

degree of biodiversity and are characterized 

by a lack of a winter and the occurrence of 

only two seasons: a wet season and a dry 

season. In particular, the drainage areas for the 

watersheds the scientists studied are located 

in a tabonuco (tä bə nü kō) forest. This type of 

forest has tall trees and very little light reaches 

the forest floor. The tabonuco tree (Dacryodes 

excelsa) dominates the tabonuco forest. The 

tabonuco tree can grow up to 100 feet tall 

(figures 8a and 8b).

Figure 7. The Equator is an invisible line around 

the middle of planet Earth. It is located at zero 

degrees latitude. The Equator divides the planet 

into the Northern and Southern Hemispheres.

Illustration by Stephanie Pfeiffer.

Figure 8a. The tabonuco tree can grow up to 

100 feet tall. In Puerto Rico, the tabonuco tree is 

found mostly in lower elevations of mountainous 

areas. Photo courtesy of Jerry Bauer.

Figure 8b. The tabonuco tree oozes sap. Photo 

courtesy of Jerry Bauer.

Number Crunch

b Howtall can the tabonuco tree growinmeters? (Hint:1foot=0.3048meters.)
47

Natural Inquirer • Number 18

Introduction

The scientists chose to study two of the 

Bisley Experimental Watersheds in the Luquillo 

Experimental Forest (figure 9). Luquillo 

Experimental Forest shares its boundaries with 

El Yunque (ū(ng) kā) National Forest. Because 

the watersheds are located within the Luquillo 

Experimental Forest, the scientists could 

observe and record how things changed over 

a long period of time. For this research, the 

scientists studied particulate organic matter 

(POM).

POM consists of small pieces of twigs, 

leaves, soil, and other items found in the water 

(figure 10). POM measurements are important 

for several reasons. For example, POM is a 

source of food and energy for many animals. 

POM keeps some environmental pollutants 

out of the water by binding heavy metals and 

pesticides. POM also serves other roles in an 

ecosystem such as being an important part of 

the food web. POM is a part of the decomposition

process of the food web (figure 11).

In this research, the scientists examined the 

amount and types of a particular type of POM 

called coarse particulate organic matter

(CPOM). CPOM is the pieces of organic 

material that falls into or is carried into the river. 

CPOM is generally greater than 1 millimeter 

(mm) in size. Examples of CPOM are leaves, 

sticks, and other pieces of plant material. 

Because CPOM is an important component 

of an ecosystem and food webs, the scientists 

wanted to figure out how the amount and 

quality of CPOM changed over a period of time.

Figure 10. Particulate organic matter (POM) is an 

important component of an ecosystem and the 

food web. Photo courtesy of Babs McDonald.

Reflection Section

b Inyourownwords,whatisthequestionthe

scientistswantedtoanswerinthisstudy?

b Thescientistsstudiedtwowatershedsinthe

experimentalforest.Whatisonereasonthe

scientistswantedtostudytwowatersheds

insteadofonlyonewatershed?

Figure 9. Bisley Experimental Watersheds are 

located in the Luquillo Experimental Forest. Map 

by Carey Burda.

Number Crunch

b	 CPOMis generally greaterthan 1mmin size.

Is 1mmsmaller orlargerthan 1inch?Howdo

you know?
48

Freshwater Edition, http://www.naturalinquirer.org

Figure 11. Particulate organic matter (POM) is part of the decomposition process of the food web.

Illustration by Stephanie Pfeiffer.

Methods

The scientists collected data from the two 

watersheds from 1987 to 2005. The scientists 

collected mean annual rainfall, size of watershed 

area, stream channel length, as well as dates of 

hurricanes and other natural disturbances, such 

as drought (figure 12).

The scientists wanted to know how much 

CPOM was being exported from the watersheds. 

After CPOM is in the water, it undergoes some 

amount of decomposition. The amount that 

actually leaves the watershed is the amount 

that is exported. From 1987 to 2005, scientists 

collected CPOM that was trapped in metal 

mesh traps that they placed in the streams.

The scientists collected CPOM every other 

Tuesday and following large storms. The metal 

mesh traps were placed across the stream 

channels (figure 13). Scientists tested several 

mesh traps and sizes from 1987 to 1989. These 

test traps broke during periods of high water flow. 

Since 1989, however, the traps the scientists 

designed did not break. These traps recorded 

accurate measurements of CPOM by collecting 

all the CPOM going into the trap.

The scientists also completed chemical 

analysis on some of the samples to see what 

kinds of elements were in the CPOM. Elements 

are important to both living and nonliving things. 

For example, approximately 96 percent of the 

human body is made up of four elements: carbon, 

oxygen, hydrogen, and nitrogen. In this study, 

the scientists measured elements such as carbon, 

nitrogen, phosphorus, potassium, and calcium in 

the CPOM.
49

Natural Inquirer • Number 18

Figure 12. A lot of data change over time. In this graph, you can see what happened to the mean 

annual rainfall at the study site between 1988 and 2008. Illustration by Stephanie Pfeiffer.

Figure 13. Mesh traps were 

placed across the stream 

channels to collect coarse 

particulate organic matter 

(CPOM). Photo courtesy of 

Tamara Heartsill Scalley.
50

Freshwater Edition, http://www.naturalinquirer.org

The Periodic Table and Symbols

The periodic table (figure 14) is a table that arranges the chemical elements by 

atomic number. Each element has a letter 

or several letters that identify it in a simpler 

way and is called a symbol. For example, 

the symbol for carbon is C and the symbol 

for oxygen is O. Look at the periodic table and 

find the symbols for the elements the scientist 

studied: nitrogen, phosphorus, potassium, 

calcium, aluminum, magnesium, iron, and 

manganese.

Figure 14. This table is a shortened form of the periodic table of elements. For a full table, 

search the Internet for “periodic element table” or look for it in your science book. The 

complete periodic table contains 118 elements.

Reflection Section

b ThescientistscollectedCPOMafterlargestorms.

Whydoyouthinkthesecollectionswereagood

idea?

b Thescientistshadtotestseveraldifferenttypes

ofmetalmeshtrapstocollecttheCPOMuntil

theyfoundadesignthatworked.Thinkofatime

thatyouhavetriedtomakesomethingordo

somethinganditdidn’twork.Whatdidyoudo?

Whataresomecharacteristicsthatyouthink

areimportantforscientiststohaveinorderto

overcomeobstacles?(Hint:Takealookatsomeof

theNaturalInquirerscientistcardsathttp://www.

naturalinquirer.org/scientists-v-92.html.Lookat

thebackofthecardsandreadaboutimportant

scientistcharacteristics.Seeifyouthinkanyof

thosecharacteristicsapplytothissituation.)

Findings

During the 18-year study period, 

the scientists found several things. 

The highest CPOM export through 

the watershed occurred before and 

during Hurricane Hugo. The scientists 

found that other tropical storms and 

hurricanes after Hurricane Hugo did 

not create as much CPOM export as 

during the time of Hurricane Hugo.

Relatively high exports of CPOM 

were recorded from 1995 to 2000 

(figure 15). The greatest export of 

leaves (which are part of CPOM) 

occurred during April, May, and 

September. These months have the 

most intense rain showers and the 

greatest number of plants with falling 

leaves. During this time, the leaves 
51

Natural Inquirer • Number 18

Figure 15. Scientists measured coarse particulate organic matter (CPOM) exports from 1995 to 

2000. What do you notice about CPOM export during this time? Graph by Stephanie Pfeiffer.

are mostly falling because of storms, wind, and 

rain, and they are still green when they fall. 

Therefore, these leaves have different nutrients 

and different chemical composition than leaves 

that fall in the dry season from natural aging.

Low CPOM export occurred during 1990–

1991, 1993–1994, and 2000–2002. The lowest 

amounts of CPOM export were during times 

of drought. The months of December, January, 

and February also show low CPOM exports.

Watershed 1 had higher values of potassium 

than watershed 2. Watershed 2 had higher 

levels of calcium, magnesium, aluminum, 

and iron. The scientists found no difference 

between the two watersheds for levels of 

nitrogen, phosphorus, and manganese. The 

scientists thought that the types of leaves 

and the amount of decay that the leaves had 

undergone may have affected the elements they 

found in the watersheds.

Reflection Section

b CPOMexportwaslowestduringtimesofdrought.Thinkaboutthestreamandthe

surroundingenvironmentduringthesetimes.Brainstormsomeideasastowhy

youthinkCPOMexportcouldhavebeenlow.Youmaywanttoresearchoneofyour

ideastoseewhatyoucanfindoutaboutit.

b December,January,andFebruaryhadlowCPOMexport.Whydoyouthinkthislow

levelmayhaveoccurred?
52

Freshwater Edition, http://www.naturalinquirer.org

Hurricane Hugo

Hurricane Hugo (figure 16), which made landfall in September 

1989, created some of the highest 

stormtide heights that had ever been 

recorded on the east coast of the 

United States. Hugo was a category 5 

hurricane in the Atlantic Ocean and 

then became a category 4 storm 

that went through the Caribbean.

Hurricane Hugo had maximum 

sustained winds of 135 to 140 miles 

per hour. During that time, Hugo 

was the strongest storm to hit the 

United States within a 20-year 

period, and it created approximately 

$7 billion ($7,000,000,000) in 

damage (figure 17). To learn more, 

visit http://www.weather.gov/chs/

HurricaneHugo-Sep1989.

The Saffir-Simpson Hurricane Wind 

Scale is a 1-to-5 rating based on a 

hurricane’s sustained wind speed 

(figure 18). The National Oceanic 

and Atmospheric Administration 

explains that “this scale estimates 

potential property damage. Hurricanes 

reaching Category 3 and higher are 

considered major hurricanes because 

of their potential for significant loss 

of life and damage. Category 1 and 

2 storms are still dangerous, however, 

and require preventative measures.”

Figure 16. Hurricane Hugo. Photo courtesy of National 

Oceanic and Atmospheric Administration.

Figure 17. Pre- and post-Hugo 

photos at Folly Beach, South 

Carolina. Photos courtesy 

of National Oceanic and 

Atmospheric Administration.

Pre-Hugo

Post-Hugo
53

Natural Inquirer • Number 18

Category Sustained Winds Types of Damage Due to Hurricane Winds

1 74–95 mph

64–82 kt

119–153 km/h

Very dangerous winds will produce some damage: Wellconstructed frame homes could have damage to roof, shingles, 

vinyl siding, and gutters. Large branches of trees will snap and 

shallowly rooted trees may be toppled. Extensive damage to 

power lines and poles likely will result in power outages that could 

last a few to several days.

2 96–110 mph

83–95 kt

154–177 km/h

Extremely dangerous winds will cause extensive damage:

Well-constructed frame homes could sustain major roof and siding 

damage. Many shallowly rooted trees will be snapped or uprooted 

and block numerous roads. Near-total power loss is expected with 

outages that could last from several days to weeks.

3 (major) 111–129 mph

96–112 kt

178–208 km/h

Devastating damage will occur: Well-built framed homes may incur 

major damage or removal of roof decking and gable ends. Many trees 

will be snapped or uprooted, blocking numerous roads. Electricity 

and water will be unavailable for several days to weeks after the storm 

passes.

4 (major) 130–156 mph

113–136 kt

209–251 km/h

Catastrophic damage will occur: Well-built framed homes can sustain 

severe damage with loss of most of the roof structure and/or some 

exterior walls. Most trees will be snapped or uprooted and power poles 

downed. Fallen trees and power poles will isolate residential areas.

Power outages will last weeks to possibly months. Most of the area will 

be uninhabitable for weeks or months.

5 (major) 157 mph or 

higher

137 kt or higher

252 km/h or 

higher

Catastrophic damage will occur: A high percentage of framed homes 

will be destroyed, with total roof failure and wall collapse. Fallen trees 

and power poles will isolate residential areas. Power outages will last 

for weeks to possibly months. Most of the area will be uninhabitable for 

weeks or months.

mph = miles per hour. kt = knots. km/h= kilometers per hour.

Figure 18. The Saffir-Simpson Hurricane Wind scale. Courtesy of the National Oceanic and 

Atmospheric Administration.

Discussion

The export of CPOM generally followed a 

seasonal pattern that was a combination of the 

monthly rainfall pattern and seasonal patterns 

for leaves falling from plants and trees. The 

scientists found that one of the greatest events 

of CPOM export was during Hurricane Hugo. 

The scientists also found that tropical storms 

and hurricanes after Hurricane Hugo did not 

create as much CPOM as during the time of 

Hurricane Hugo.

The scientists believe that this finding has to 

do with the fact that, during Hurricane Hugo, 

the forest was more mature. A more mature 

forest means that it is an older forest with 

larger trees and more growth. After Hurricane 

Hugo came through, parts of the forest were 

destroyed and fewer large trees remained. 

When tropical storms or other hurricanes came 

through the area after Hurricane Hugo, less 
54

Freshwater Edition, http://www.naturalinquirer.org

organic material was available to 

fall and export into the streams. 

Therefore, the frequency and 

intensity of hurricanes and tropical 

storms, along with the age of the 

forest, had a measurable effect on 

the export of CPOM through the 

watersheds.

Reflection Section

b Inyourownwords,whatdidthescientistslearnfrom

theirstudy?

b Whyarenaturaldisastersandotherlargeweatherevents

importanttostudy?Whatinformationcantheyprovide

forthefuturemanagementofthenaturalsystems?

Glossary 

analysis (ə na lə səs): A careful study of 

something to learn about its parts, what they do, 

and how they are related to each other.

biodiversity (bī ō də vər sə tē): The existence of 

many different kinds of plants and animals in an 

environment.

bryophyte (brī ə fīt): Any of a division 

(Bryophyta) of nonflowering plants comprising 

the mosses, liverworts, and hornworts.

coarse particulate organic matter (CPOM)

(kȯrs pär ti kyə lət ȯr ga nik ma tər): CPOM is the 

pieces of organic material that falls into or is 

carried into a river. CPOM is generally greater 

than 1 millimeter (mm) in size. Examples of 

CPOM are leaves, sticks, and other pieces of 

plant material.

decay (di kā): To break down, rot, or undergo 

decomposition.

decomposition (dē kəm pə zi shən): The slow 

destruction of something (such as dead plants 

and the bodies of dead animals) by natural 

processes, chemicals, etc.

dominate (dä mə nāt): To have a prominent 

place or position.

drainage (drā nij): (1) The act or process of 

draining something; (2) The act or process of 

removing water or liquid from a place or thing.

ecosystem (ē kō sis təm): Community of plants 

and animal species interacting with one another 

and with the nonliving environment.

export (ek spȯrt): To carry away.

fauna (fä nə): All the animals that live in a 

particular area, time period, or environment.

frequency (frē kwən(t) sē): The number of times 

that something happens during a particular period.

obscure (äb skyu̇ r): Not clearly seen or easily 

distinguished.

organic (ȯr ga nik): Of, relating to, or obtained 

from living things.

pesticide (pes tə sīd): A substance that is used 

to kill animals or insects that eat plants or crops.

statistical (stə tis ti kəl): Based on statistics, a 

branch of mathematics that deals with analyzing 

and interpreting data.

sustain (sə stān): Continuing for an extended 

period.

trend (trend): A general direction of change.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriam-webster.

com. Definitions are limited to the word’s 

meaning in the article.

Adapted from Heartsill Scalley, T.; Scatena, F.N.; Moya, S.; Lugo, A.E. 2012. Long-term dynamics of organic matter 

and elements exported as coarse particulates from two Caribbean montane watersheds. Journal of Tropical Ecology. 

28: 127–139. http://www.treesearch.fs.fed.us/pubs/41610.
55

Natural Inquirer • Number 18

FACTivity

Time Needed

One class period

Materials

(for each student or group of students)

• Pencil

• Graph paper

• “Caribbean Cruise” article in this 

Natural Inquirer edition

The question you will answer in this 

FACTivity is: What can you learn from data 

about gage height and streamflow for a 

stream for an extended period of time?

Methods

In the article you just read, the scientists 

examined a variety of different types of data 

from the Bisley Experimental Watersheds 

in the Luquillo Experimental 

Forest. The table of data 

provided in the following 

table is from the Rio Sabana in Luquillo 

Experimental Forest and El Yunque 

National Forest. The data have been 

collected for 33 years. The gage height is 

the height of the water above zero on the 

water gage. A water gage is an instrument 

used to find the depth or quantity of water 

or to indicate its surface height. Streamflow 

is the water released from a stream.

Streamflow is measured in cubic feet per 

second. Examine the data in table 1. On 

the graph paper provided (on page 123), 

create a graph for either the gage height 

data or the streamflow data (figure 19).

Figure 19. A sample graph of the peak streamflow data from Rio Sabana. Graph courtesy of the 

U.S. Geological Survey.
56

Freshwater Edition, http://www.naturalinquirer.org

Year Date Gage Height (feet) Streamflow (cubic feet per second)

1980 May 22, 1980 12.55 1,760

1981 May 19, 1981 15.77 4,480

1982 May 10, 1982 18.17 7,340

1983 Apr. 21, 1983 19.35 9,010

1984 Dec. 02, 1983 12.50 1,730

1985 May 17, 1985 14.73 3,470

1986 May 13, 1986 13.27 2,260

1987 May 25, 1987 14.16 2,970

1988 Nov. 27, 1987 15.23 3,940

1989 Sep. 18, 1989 18.77 8,170

1990 Aug. 13, 1990 16.08 4,660

1991 Jun. 30, 1991 15.80 4,520

1992 Jan. 05, 1992 19.74 9,600

1993 Dec. 29, 1992 16.11 4,840

1994 Feb. 19, 1994 14.00 2,830

1995 Nov. 07, 1994 12.62 1,810

1996 May 13, 1996 15.64 4,350

1997 Sep. 26, 1997 14.15 2,960

1998 Sep. 21, 1998 15.86 4,580

1999 May 08, 1999 14.56 3,310

2000 Aug. 23, 2000 14.24 3,030

2001 Aug. 22, 2001 15.79 4,500

2002 Nov. 09, 2001 13.91 2,760

2003 Apr. 17, 2003 18.69 8,050

2004 Sep. 15, 2004 16.55 5,330

2005 Oct. 29, 2004 15.41 4,120

2006 Apr. 05, 2006 13.07 2,120

2007 Oct. 20, 2006 13.35 2,320

2008 Apr. 27, 2008 18.99 8,480

2009 Jun. 12, 2009 13.67 2,570

2010 Apr. 13, 2010 15.58 4,290

2011 Aug. 22, 2011 14.50 3,260

2012 May 10, 2012 11.82 1,300

2013 May 10, 2013 12.89 1,990

Table 1. Gage height and streamflow data from Rio Sabana in Puerto Rico. Data courtesy of U.S.

Geological Survey.
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Natural Inquirer • Number 18

After you have created the graph, 

compare the data over the 33-year time 

period.

• Circle any points that seem to be 

very high or very low.

• Name at least two things from the 

data that seem important. Why do 

you think the data from these two 

times may be important? What do 

you think the data from these times 

may indicate?

• How did creating a graph from 

the data help you to analyze and 

understand the data?

• Share and discuss your results with 

your classmates. Did they notice 

similar points in the data? How were 

your graphs and analysis of the 

graphs similar and different?

Natural Inquirer

Connections

You may want to reference these Natural Inquirer articles for additional information 

and FACTivities:

• “Leaf Me Alone” in the Tropical Forest 

edition of Natural Inquirer.

• “Don’t Litter the Stream” in the Hawai`iPacific Islands edition of Natural Inquirer.

• “I’ll Huff and I’ll Puff and I’ll Blow Your 

Trees Down!” in the Tropical Forest 

edition of Natural Inquirer.

• “Swimming Upstream Without a Ladder” 

in the Tropical Forest edition of Natural 

Inquirer.

These articles, along with others, can 

be found at http://www.naturalinquirer.org/

all-issues.html.

What’s in a Word?

One of the many questions that people have asked from time to time is the 

spelling of the word “streamgage” versus 

spelling it with a “u” as in “streamgauge.”

Page 50 of the U.S. Geological Survey report, 

A History of the Water Resources Branch, U.S. 

Geological Survey: Volume I, From Predecessor 

Surveys to June 30, 1919 (http://on.doi.gov/

USGSWaterHistory) includes a reference 

giving credit to the change in spelling to F.H.

Newell around 1892. The author wrote:

At about this time, F.H. Newell 

adopted the spelling “gage” 

instead of “gauge.” As he informed 

the writer, “gage” was the Saxon 

spelling before the “u” was 

inserted as a result of Norman 

influence on the language.

Ever since then, the U.S. Geological Survey 

has spelled the word without the “u.”

Web Resources

International Institute of Tropical Forestry

http://www.fs.usda.gov/iitf/ 

U.S. Geological Survey Water Data for Rio Sabana

http://waterdata.usgs.gov/nwis/inventory/?site_

no=50067000&agency_cd=USGS

A Distance Learning Adventure: America’s 

Rainforests—Caribbean National Forest/Luquillo 

Experimental Forest

http://rainforests.pwnet.org/americas_rainforests/

caribbean.php

El Yunque National Forest

http://www.fs.usda.gov/elyunque

Luquillo Long-Term Ecological Research Program

http://luq.lternet.edu/

Tabonuco Trees

http://www.na.fs.fed.us/pubs/silvics_manual/volume_2/

dacryodes/excelsa.htm

University of California Museum of Paleontology: 

Tropical Forests

http://www.ucmp.berkeley.edu/exhibits/biomes/forests.

php#tropical

History of Fort Valley Experimental Forest 

http://www.foresthistory.org/ASPNET/Places/

ResearchSites/FortValley.aspx
Sediment-al Journey: 

Measuring Metal 

Concentrations in 

Soils Beside Urban 

Waterways

Photo courtesy of K.T. Belt
59

Natural Inquirer • Number 18

Meet the Scientists

Dr. Daniel Bain, Hydrologist: My favorite science experiences 

generally involve one of three things: (1) finding a clear pattern from 

data I have collected, (2) working in an urban stream or soil pit and 

having a local resident come up and ask a question or share an 

insightful observation about the area, and (3) contributing technical 

data to challenges created by interactions between humans and natural 

systems within neighborhoods.

Soils do a lot of things, like provide footing for 

plants to grow, homes for worms and insects, and filtration for water.

I enjoy playing in, learning from, and unlocking the mystery of soils.

My favorite science experience is when I am out in a field, with a soil 

corer in hand; ready to discover something new about soil. Often, I feel 

like a detective, investigating the soil structure below the surface to 

search for the unique story it has to tell. To figure out the story, I first 

survey the area and look at the landscape for markers like hills; I look at the rocks to see what 

they are made of; I look at the plants, the streams, and the rivers. All of these first insights give me 

an idea of how the soil developed and how it interacts with the current environment.

Next, I get out my auger, dig out a soil sample from the Earth, and lay the samples down 

systematically to create a soil profile on a ground cloth. Then, I feel the soil, look at its color, and 

shape, and sometimes I even smell it. Combined, this information can tell me a lot about the soil.

Using the soil profile, I can identify (1) if erosion took place hundreds of years ago, (2) if the area 

has been farmed or plowed, (3) how quickly water may or may not move through it, (4) if worms or 

mammals have made it their habitat, and (5) if the soil is old or young. For me, the best experience 

is going out into the field with my auger, on a nice sunny day, prepared to uncover the secrets of 

the soil.

Mr. Ian Yesilonis, Soil Scientist: Did you 

know more living individual organisms are in a 

tablespoon of soil than people are on Earth? 

Usually people don’t know a lot about soil, and 

without it, our lives on Earth would be very 

different. Soil is important to our daily health 

and holds the evolving history of our planet.

Dr. Richard Pouyat, Urban Ecosystem Ecologist: For me, science 

is most exciting when I have made a new discovery! If you practice 

science long enough, you too will make a discovery. One of my 

first scientific discoveries was when I found an invasive species of 

earthworm living in a forested park in New York City—a worm species 

from Asia! How did it get there? Why was this worm species not 

noticed before? Was it changing the soil? The species was probably 

brought to the United States with exotic plants and has had a dramatic 

effect on nutrient cycling.

Nobel-prize winner and Hungarian scientist Albert Szent-Gyorgyi 

(aul bǝrt sent gǝrj ē) once said, “Discovery is seeing what everybody 

else has seen and thinking what nobody else has thought.” Using his 

definition, every discovery you make is your own!

t

t

t
60

Freshwater Edition, http://www.naturalinquirer.org

Did You Know?

Dr. Pouyat found an earthworm that was an invasive species from Asia that 

was living in New York City parks. He was 

interested how it affected the environment.

The same earthworm species was found 

hundreds of miles away in Georgia. Scientists 

in Georgia conducted research to find out 

how this invasive species affected the ability 

of native earthworms to survive.

To learn more about these earthworms, 

read the Natural Inquirer Monograph 

“Worming Their Way In.” It can be found 

online at http://www.naturalinquirer.org/

all-issues.html.

What Kinds of 

Scientists Did This 

Research?

hydrologist: This scientist studies the 

distribution, movement, and quality of Earth’s 

waters.

soil scientist: This scientist studies soils as 

one of Earth’s natural resources.

urban ecosystem ecologist: This

scientist studies the interactions of people 

and other organisms with each other and with 

nonliving parts of urban environments.

Thinking About Science

In 1980, the National Science 

Foundation created a network of 

research locations to study how 

ecosystems change over a long 

period of time. This network is 

called the Long Term Ecological 

Research (LTER) Network. 

The United States has 26 of these areas, 

which includes one in Puerto Rico and two 

in Antarctica. The research being done 

at these locations is unusual because it focuses 

on changes that are happening over a long 

period of time. From a scientific perspective, 

long-term research provides information that 

is impossible to discover in any other way.

One of these research locations is the 

Baltimore Ecosystem Study. Scientists working 

with the Baltimore Ecosystem Study seek to 

understand metropolitan Baltimore as an 

ecological system. The Baltimore Ecosystem 

Study involves scientists from the biological, 

physical, and social sciences. The LTER 

network enables a variety of scientists to work 

together. By working as a team, these different 

scientists can provide a much more complete 

picture of what is happening over time and why 

it is happening.

What Is the National Science Foundation?

The National Science Foundation (NSF) is an independent Federal agency created by Congress in 1950. The NSF provides funding for scientific 

research. This research promotes scientific progress; advances national 

prosperity, health, and welfare; and aids in national defense. For more 

information, visit http://www.nsf.gov.

Glossary words are bold and are defined on page 70.
61

Natural Inquirer • Number 18

One goal of the Baltimore Ecosystem Study 

is to understand how urban and suburban 

ecosystems change over a long period of time. 

In this study, you will learn what scientists are 

discovering about changes in the riparian areas 

that drain into Baltimore’s Middle Branch of the 

Patapsco River. This body of water is also known 

as Baltimore Harbor (figures 1 and 2).

Figure 1. Baltimore is a large city in Maryland.

Locate Baltimore Harbor on this map. Map by 

Lindsay Gnann.

Figure 2. People enjoy water sports in Baltimore 

Harbor. Photo courtesy of K.T. Belt.

Thinking About the 

Environment

Riparian areas are transition

areas between waterways and 

land (figures 3 and 4). Riparian 

areas are ecologically important. 

They provide habitat for wildlife 

species and for plant species that 

grow in wet areas. When streams flow into 

rivers, the streams carry sediment into the 

rivers. Sediment is created by soil erosion. Soil 

erosion is caused by heavy rainfall from both 
62

Freshwater Edition, http://www.naturalinquirer.org

Figure 3. Riparian areas are found along waterways. When water levels are high, these areas may 

become flooded. When riparian areas are flooded, sediment being carried by the waterways is 

deposited onto the riparian area. Illustration by Stephanie Pfeiffer.

the lands through which streams and rivers 

flow and the riverbanks of the waterways 

themselves. Riparian areas protect waterways 

from too much soil erosion and sedimentation, 

and they protect upland areas from flooding.

Urban areas have a large amount of 

impervious (im pər vē əs) surface area. Concrete 

and asphalt are examples of impervious surfaces. 

Water cannot drain through impervious surfaces. 

Following rainfall or snowfall in urban areas, 

impervious surfaces cause rainfall or melted 

snow to enter waterways more quickly than it 

does in nonurban areas. Managers often take 

action to slow the rate of runoff into waterways 

and to protect streambanks from erosion 

(figure 5).

In this study, the scientists wanted to 

learn about changes in urban riparian areas in 

metropolitan Baltimore. The scientists studied 

the sediment that is deposited onto riparian 

areas during high streamflows. They wondered 

about the sediment’s chemical content, 

including trace chemicals like lead and plant 

nutrients like calcium. The scientists wanted to 

discover what the sediment’s chemical content 

indicates about urban land use.

Figure 4. This riparian area is located in 

metropolitan Baltimore. Photo courtesy of K.T. Belt.

Figure 5. Rocks may be placed along urban 

streambanks or riverbanks to protect waterways 

from soil erosion. This photo is of Silver Creek 

in Illinois. Photo courtesy of ENCAP, Inc., http://

www.encapinc.net.
63

Natural Inquirer • Number 18

Introduction 

Most urban areas include places that contain 

chemicals from automobile and truck emissions, 

industrial processes, and urban development. 

Two chemicals found abundantly in urban 

areas are calcium and lead. Calcium is abundant 

in urban areas because concrete contains 

calcium (figure 6). Lead is released to urban 

areas by industrial processes, from oil-based 

fuels, battery acid, and vehicle exhaust fumes, 

among other sources. Chemicals that bind to 

soil particles, such as calcium and lead, can 

be washed into waterways during periods of 

high rainfall (figure 7). Waterways carry this 

sediment downstream. When flooding occurs, 

the sediment is deposited on the riparian areas 

along the waterways (see “Thinking About the 

Environment”).

The scientists in this study wanted to answer 

the following questions: What is the chemical 

content of riparian sediment samples across 

an urban-suburban gradient? What does the 

chemical content tell us about urban land use?

Figure 6. Concrete is abundant in urban areas.

Concrete is used for sidewalks and for building 

and bridge foundations. Photo courtesy of K.T.

Belt.

Figure 7. Storm drains may carry chemicals from 

urban areas into waterways. Photo courtesy of 

Babs McDonald.

Reflection Section

b Concreteisusedformanybuildingprojects,

includingbridges,sidewalks,andbuildings.

Concreteismadefromcalcium.Whatpartof

yourbodycontainscalcium?Doesthisbody

partneedtobestrong?Whyorwhynot?

b Basedonwhatyouhavereadsofar,would

youexpecttofindmorecalciumandleadin

ripariansedimentclosertoorfartherawayfrom

thecitycenter?Why?
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Freshwater Edition, http://www.naturalinquirer.org

What Is the Urban-Rural Gradient?

Urban areas are not uniformly developed.City centers are areas with large buildings 

and a lot of people. Industrial sites are often 

found near city centers. In general, the farther 

away an area is from the city center, the less 

developed it is. Suburban areas are areas 

away from a city that have more homes and 

open space. Beyond suburban areas are small 

towns and rural areas. These areas have fewer 

people, more farms, and more forests. This 

change from urban city center to suburban 

land use, and then to rural areas, is called the 

urban-rural gradient (figure 8).

Figure 8. Urban areas have a lot of large buildings, roads, and people. Suburban areas have 

homes, shopping centers, and more open space. Rural areas are primarily open space. Photos 

courtesy of Babs McDonald.

Methods

The scientists studied riparian areas 

within the Gwynns Falls watershed 

(figures 9 and 10). Many scientists 

involved with the Baltimore Ecosystem 

Study are studying this watershed. 

During the study period, the headwaters 

of the Gwynns Falls watershed were less 

urban than the waterways downstream. 

This watershed, therefore, followed an 

urban-suburban gradient. The Gwynns 

Falls watershed does not include rural 

lands.

Another feature of the Gwynns Falls 

watershed is that it straddles a fall line 

(figure 11). This geographic feature is 

important, because it indicates a change 

in the types of underlying rock.

The scientists collected 26 soil 

samples from Gwynns Falls watershed 

riparian areas (figures 12 and 13). 

Figure 9. A watershed includes an area that drains 

to a common waterway, such as a stream, lake, 

estuary, wetland, aquifer, or even the ocean. The 

headwaters of a watershed is the area where water 

enters the watershed. Illustration by Stephanie Pfeiffer.
65

Natural Inquirer • Number 18

Figure 10. The Gwynns Falls watershed 

is located in northwest Baltimore City 

and southwestern Baltimore County. The 

watershed follows a northwest to southeast 

orientation. Baltimore’s city center is in 

the southeastern end of the watershed.

As you move to the northwest across the 

watershed, the land becomes less urban 

and more suburban. The Gwynns Fall 

watershed drains about 17,000 hectares 

of land. Map by Lindsay Gnaan.

Number Crunches

b	 Howmany acres is 17,000hectares?Multiply

the number of hectares by 2.47 to find out.

b	 Howmany square kilometers is 17,000

hectares?Divide 17,000by 100to find out.

Figure 11. The Gwynns Falls watershed straddles 

a fall line. A fall line is not really a line but an area 

where rolling hills meet the flatter Coastal Plain.

Photo courtesy of K.T. Belt.

Figure 12. The scientists took soil samples from 

areas near Gwynns Falls waterways. Each 

triangle on this map represents one of the areas 

from which a soil sample was taken. Why do you 

think some of the triangles are not close to the 

Gwynns Falls River? (Hint: What is missing on 

this map?) Map by Lindsay Gnaan.
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Freshwater Edition, http://www.naturalinquirer.org

Each sample was taken 10 meters from the 

water’s edge. The soil samples were taken 

between 0 and 15 centimeters from the soil 

surface. The scientists analyzed these samples 

for chemical content (figures 14 and 15).

Figure 13. Scientists take a soil sample in a 

suburban area. Photo courtesy of Dr. Richard 

Pouyat.

Figure 14. Scientists examine soil samples in the 

laboratory. Photo courtesy of Dr. Richard Pouyat.

Figure 15. The scientists used a Perkins-Elmer ELAN 6000 

ICP-MS to analyze the sediment samples. This equipment 

enabled the scientists to identify a wide variety of chemical 

concentrations in the sediment samples. Photo courtesy of 

Dr. Daniel Bain and the University of Pittsburgh.

What Is a 

Fall Line?

Afall line is the place where an upland region of rolling hills 

ends and the flatter Coastal Plain 

begins. The upland region of rolling 

hills is called the Piedmont. The 

underlying rock of the Piedmont 

is harder and the underlying 

rock of the Coastal Plain is softer.

Waterfalls, or a series of rapids, 

mark the fall lines. On the U.S. east 

coast, the Atlantic Seaboard Fall 

Line is 900 miles (1,400 kilometers) 

long. This fall line stretches from 

Massachusetts to Alabama. Is the 

Gwynns Falls watershed is a part 

of the Atlantic Seaboard Fall Line? 

How do you know? If you do not 

know, look at a map that includes 

the Eastern United States.
67

Natural Inquirer • Number 18

Number Crunches

b	 Howmany feet are equalto 10meters?

Multiply 10by 3.28 to find out.

b	 Howmany inches are equalto15 centimeters?

Multiply 15 by .3937 to find out.

Reflection Section

b Observefigure12.Whydidthescientiststake

samplesacrosstheentirewatershed,from

northwesttosoutheast?

b Whydidthescientiststakeeverysample10

metersfromthewater’sedge?

Figure 16. The percent of calcium found in the 

sediment samples was greater in areas closer 

to the city center. Each dot on this scatter plot 

represents a sampling site. When data are 

displayed in a scatter plot, scientists calculate an 

equation that shows a straight line. This straight 

line is mathematically determined to minimize 

the sum of the distances between the points and 

the line.

This line is called the line of best fit. A line of 

best fit shows the general trend of the data. A 

line of best fit may pass through some points, 

just one point, or all the points on a scatter plot.

It is possible, but not likely, that a line of best 

fit will not pass through any of the points. Does 

the line of best fit in this figure pass through any 

of the points? Explain in your own words what 

the line of best fit in this scatter plot is showing 

about the calcium content across the urbansuburban gradient. Illustration by Stephanie 

Pfeiffer.

Findings

The underlying rock structure changes at 

a fall line. The chemical nature of naturally 

occurring sediment, therefore, is usually different 

above and below fall lines. This difference is 

because the underlying rock above and below 

the fall line contains different chemicals. These 

chemicals are washed into the water and 

deposited onto riparian areas. When analyzing 

soil samples, scientists expect to see a change in 

the types of naturally occurring chemicals found 

in sediment above and below a fall line.

The scientists found that the level of calcium 

and lead in the soil samples increased as soil 

samples were pulled near increasingly urbanized 

land. The level of calcium did not change 

suddenly at the fall line, as it would have if it 

was occurring naturally. Instead, the scientists 

found an increase in calcium across the entire 

watershed from the northwest to the southeast 

(figures 16 and 17).

The scientists also tested the sediment 

samples for copper and zinc. These trace 

chemicals are often found in urban areas. 

Trace chemicals are chemicals found in small 

quantities. The scientists found that these 

chemical amounts also increased across the 

watershed’s urban-suburban gradient from the 

northwest to the southeast (figure 18).
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Freshwater Edition, http://www.naturalinquirer.org

Figure 17. Urban concrete could be a source 

of the increased calcium measured in riparian 

sediment samples. Photo courtesy of K.T. Belt.

Figure 18. The increase in concentration of 

the trace metals lead, copper, and zinc shows 

a strong relationship with the most urbanized 

areas of Baltimore. Compare this scatterplot with 

the map of Gwynns Falls watershed (figure 12).

Illustration by Stephanie Pfeiffer.

The scientists discovered something 

surprising about the amount of trace chemicals 

in the sediment. At four of the sampling sites, 

the amounts of trace chemicals were two to 

three times higher than those found at the other 

sampling sites. When comparing the sampling 

sites with maps of the watershed, the scientists 

observed something interesting. They observed 

that areas close to three of these four sampling 

sites were land areas created by adding fill dirt 

to existing low-lying land areas (figure 19). The 

scientists discovered that where these fill areas 

were created, high amounts of trace minerals 

were deposited onto nearby riparian areas.

Figure 19. Fill dirt is sometimes used to create 

land areas that are suitable for development.

Look carefully at this photo. Why might high 

rates of soil erosion be associated with fill dirt? 

Photo courtesy of Babs McDonald.
69

Natural Inquirer • Number 18

Reflection Section

b Scientistsprefertousemeasurementsto

describeconditions.Forexample,ratherthan

describingadayashot,ascientistwouldprefer

toreportthatthetemperatureis94°F(34°C).

Basedonthisstudy’sresults,whatmeasure

mightonedaybeusedtodescribetheamount

ofanarea’surbanization?Whatisoneadvantage

ofusingthismeasure?

b Thescientistsfoundarelationshipbetween

higherlevelsoftracechemicalsinriparian

sedimentandnearbyartificiallycreatedland

areas.Ifthatsamerelationshipisfoundinother

studies,whatmightyouconcludeaboutone

consequenceofusingfilldirttocreatenew

areasofland?

Elements and 

Symbols in the 

Periodic Table

Symbols of elements (chemicals) are written by capitalizing the first letter. Symbols are 

derived from names of the elements, name 

of the discoverer, place of discovery, or other 

characteristic.

In this research, the following elements, or 

chemicals, were studied:

Element Symbol

Calcium Ca

Lead Pb

Copper Cu

Zinc Zn

To examine a portion of the periodic table 

of elements, see page 50 in the “Caribbean 

Cruise” article of this Natural Inquirer journal.

Discussion

The scientists identified three important 

potential streamflow processes within urban 

watersheds. First, urban streams deposit 

sediment onto riparian areas. This sediment 

may contain chemicals found in roadways, 

industrial areas, and other developed areas. 

Second, the flooding of urban riparian areas 

during heavy rains may cause roadway, 

industrial, and development-related trace 

chemicals to enter waterways. Third, the 

process of creating new land areas from fill dirt 

placed in low-lying wet areas may introduce 

trace chemicals directly into waterways.

The scientists noted that little is known 

about the effects of increased chemical 

sediment deposited on riparian areas. Because 

urban riparian areas appear to have greater 

percentages of urban-related chemicals, this 

area deserves more scientific research.

Reflection Section

b Doyouagreewiththescientiststhatmore

researchisneededabouturban-related

chemicalsedimentdeposits?Whyorwhynot?

b Baltimoreisjustoneurbanareaamong

thousandsofurbanareasacrosstheglobe.

Ifthefindingsofthisstudyweretrueforall

urbanareaswithnearbywaters,whatlongtermchangemightyouexpecttofindinthese

waters,suchasrivers,lakes,andcoastalbays

aroundtheworld?Whatimpactwouldthis

changehaveonglobalhealth?(Hint:Reread

thefirstsentenceofthelastparagraphinthe

“Discussion”section).
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Freshwater Edition, http://www.naturalinquirer.org

Glossary

abundantly (a bun dənt lē): Marked by great 

plenty.

auger (ȯ gər): A sharp tool that is used for 

making holes.

chemical (ke mi kəl): A substance, such as an 

element or compound.

erosion (i rō zhən): The process or state of 

wearing or washing away.

exotic (ig zä tik): Strange, different, or foreign.

gradient (grā dē ənt): An ordering of something 

according to a value. In this article, the urbanrural gradient is an ordering of landscapes 

according to the number of buildings and 

population size.

invasive species (in vā siv spē shēz): Any plant, 

animal, or organism that is not native to the 

ecosystem it is in, and is likely to cause harm to 

the environment, the economy, or human health.

land use (land yüs): How people are using the 

land.

metropolitan (me trə pä lə tən): Of, or relating 

to, a large city and the surrounding cities and 

towns.

nutrient cycling (nü trē ənt sīk lɪŋ): The uptake, 

use, release, and storage of nutrients by plants 

and their environments.

open space (ō pən spās): Undeveloped land 

that is accessible to the public.

orientation (ȯr ē ən tā shən): Position or 

direction relative to other points or directions.

riparian (rə per ē ən): Areas along streams and 

rivers.

sediment (se də mənt): Soil particles carried 

along in streams and rivers, some of which may 

settle to the bottom.

sedimentation (se də mən tā shən): The natural 

process in which material (such as soil, stones, 

and sand) is carried to the bottom of a body of 

water.

social sciences (sō shəl sī ən(t)s is): Particular 

areas of study that relate to human behavior and 

society.

systematically (sis tə ma tik lē): Marked by 

thoroughness or regularity, or according to a 

system.

transition (tran si shən): The act or process of 

passing from one condition, form, or place to 

another.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriamwebster.com. Definitions are limited to the word’s 

meaning in the article.

What’s in a Name?

The title, “Sediment-al Journey,” was taken from a popular song called “Sentimental 

Journey.” This song was written by Les Brown 

and sung by Doris Day in the mid-1940s.

Adapted from Bain, D.J., Yesilonis, I.D., and Pouyat, R.V. 2012. Metal concentrations in urban riparian sediments 

along an urbanization gradient, Biogeochemistry, 107: 67–79. http://www.treesearch.fs.fed.us/pubs/40667.
71

Natural Inquirer • Number 18

FACTivity

Time Needed

One class period

Materials (for each student or 

group of students)

• Table on page 72

• Four blank pieces of graph paper 

(page 123)

• Pencils 

• Rulers

The question you will answer in this 

FACTivity is: What is the relationship 

between the level of chemicals in a city’s 

soils and level of the same chemicals in 

the city’s riparian areas?

Methods

Examine the table on page 72. This table 

contains actual data provided to you by the 

scientists in this study. The table presents 

the median and mean (average) levels 

of chemicals found in the Gwynns Falls 

watershed’s riparian areas. The table also 

presents the median and mean level of 

chemicals in Baltimore city soils.

You will construct bar graphs based on 

the data in table 1 to help you understand 

the data. You can use the graph paper on 

page 123 to help you construct your bar 

graphs. You will have to understand the 

difference between the mean, or average, 

and the median. The mean is the value 

of all the values summed and divided by 

the number of values. The median is the 

middle value in a list of values, ordered 

from the smallest value to the largest value.

Your teacher may hold a class discussion 

about what these two values represent.

Both values are summary values, intended 

to give you a feel for the entire list of 

values. The average, however, is sensitive 

to values that may be very different from 

most of the other values. The median, on 

the other hand, is not influenced by values 

that are very different from most of the other 

values.

• First, construct a bar graph for the mean 

value of the chemicals expressed as a 

percentage of a volume. Include both 

the Gwynns Falls Riparian Sediments 

and the Baltimore City Soils. Label the 

x-axis and y-axis.

• Next, construct a bar graph for the 

mean value of the chemicals expressed 

in ppm. Include both the Gwynns Falls 

Riparian Sediments and the Baltimore 

City Soils. Label the x-axis and y-axis.

How Much Is 1 PPM?

1 part per million (ppm) is 

roughly equal to:

1 inch in 16 miles

1 second in 11.5 days

1 minute in 2 years

• Now, observe your two bar graphs 

showing mean values. What do you 

notice about the amount of chemicals 

in Baltimore City Soils compared with 

the amount of chemicals in the riparian 

areas? What explanations do you have 

for your results?

• Now, construct a bar graph for 

the median value of the chemicals 

expressed as a percentage of a volume.

Include both the Gwynns Falls Riparian 

Sediments and the Baltimore City Soils.

Label the x-axis and y-axis.

• Next, construct a bar graph for the 

median value of the chemicals expressed 

in ppm. Include both the Gwynns Falls 

Riparian Sediments and the Baltimore 

City Soils. Label the x-axis and y-axis.

Blank graph paper is located on page 123.
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Freshwater Edition, http://www.naturalinquirer.org

• Now, observe your two bar graphs 

showing median values. What do you 

notice about the amount of chemicals 

in Baltimore city soils compared with 

the amount of chemicals in the riparian 

areas? What explanations do you have 

for your results? How do the two pairs 

of graphs compare? Did each statistical 

measure (mean and median) lead you 

to the same explanations?

What do you conclude about using 

different statistical measures? Your teacher 

will lead a class discussion about your 

class explanations and the effect of using 

different statistical measures to represent 

and summarize data.

Chemical Symbol Gwynns Falls 

Riparian Sediments

Baltimore 

City Soils

Unit of 

Measurement

(ppm = parts 

per million)

Median Mean Median Mean

Aluminum Al 1.9 1.8 1.4 1.4 %

Calcium Ca 0.29 0.46 0.025 0.043 %

Copper Cu 20 30 35 45 ppm

Iron Fe 2.2 2.0 2.2 2.3 %

Magnesium Mg 0.39 0.39 0.22 0.27 %

Manganese Mn 450 440 420 470 ppm

Lead Pb 35 76 89 231 ppm

Zinc Zn 63 120 81 141 ppm

Cadmium Cd 54 170 89 106 ppm

Cobalt Co 11 12 12 15 ppm

Chromium Cr 32 31 38 72 ppm

Potassium K 0.12 0.14 0.076 0.090 %

Molybdenum Mo 35 97 300 500 ppm

Sodium Na 150 150 96 120 ppm

Nickel Ni 26 40 18 27 ppm

Phosphorus P 300 330 460 530 ppm

Titanium Ti 110 110 197 282 ppm

Vanadium V 31 33 31 37 ppm

Table 1. Chemicals Measured in Gwynns Falls Watershed Riparian Areas and Baltimore City Soils.

Parts per million, or ppm, is a measure of how concentrated the chemical is in water. Percentage 

is a measure of the percent of a particular volume of liquid that contains the chemical.
73

Natural Inquirer • Number 18

Natural Inquirer

Connections

You may want to reference these Natural Inquirer articles for additional information 

and FACTivities:

• “Green Means Clean” on page 7 of this 

edition of Natural Inquirer. The FACTivity 

demonstrates the difference between 

runoff in vegetated, agricultural, and paved 

areas. You can modify this FACTivity by 

eliminating the agricultural option and 

assuming that the oil represents 

chemicals in the water.

• “Food for the Soil” Natural Inquirer

monograph. The FACTivity simulates how 

water flows onto streambanks during 

a flood and deposits materials on the 

streambanks.

These resources can be found at: http://

www.naturalinquirer.org/all-issues.html.

If you are a trained Project 

Learning Tree educator, you may 

use “Water Wonders,” “Field, Forest, 

and Stream,” and “Soil Stories” as 

additional resources.

Web Resources

The U.S. Geological Survey (USGS) Water Science 

School: Runoff

http://water.usgs.gov/edu/runoff.html

The U.S. Geological Survey (USGS) Water Science 

School: Sediment

http://water.usgs.gov/edu/sediment.html

When It Rains It Runs Off: Runoff in Urbanized 

Areas in Arizona

http://extension.arizona.edu/sites/extension.arizona.edu/

files/pubs/az1542.pdf

How does this scene relate to what you learned in this article?
Mussel Mania! 

How Streamflow Affects 

Freshwater Mussels 

Over Long Time Periods

Photo courtesy of Dr. Andrew Rypel
75

Natural Inquirer • Number 18

Meet the Scientists

Dr. Andrew Rypel, Applied Aquatic 

Ecologist: My favorite science experience 

is finding something totally unexpected that 

other people can’t believe, but also can’t 

argue with, because the data are so clear!

In this photo, I am using an increment 

(in krǝ mǝnt) borer to take a tree core. For 

more information on tree coring, see the 

sidebar on page 82.

Dr. Wendell Haag, Fisheries Biologist: 

When I was a kid, I loved to roam the fields, 

woods, creeks, and even my backyard, 

catching salamanders and crayfish and looking 

at plants and birds. In high school, I was lucky 

to have some great biology teachers who told 

me that I might actually be able to make a 

living doing these things. Now I think I have 

the best job in the world because I get to work 

with cool creatures every day, learn about 

how they live, and maybe even help to protect 

them.

Another great part of my job is working 

with other people who love animals and 

plants. People can be so generous and helpful 

when they’re doing something they love. That 

tells me they must be pretty happy, and I know 

that being a biologist certainly makes me 

happy.

Glossary words are bold and are defined on page 85.

t

t
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Freshwater Edition, http://www.naturalinquirer.org

What Kinds of 

Scientists Did This 

Research?

applied aquatic ecologist: This scientist 

studies the effects of man-made change on 

aquatic ecosystems .

fisheries biologist: This scientist studies 

fish and other aquatic organisms living in the 

wild, including what they eat, their habitat, 

and how they interact with their environment .

Dendrochronology is a field of study in 

which scientists learn about trees by studying 

the tree’s growth rings (figure 1). The field of 

sclerochronology similarly enables scientists to 

learn about any organism that leaves growth 

rings in hard tissues like bones or shells. Some 

scientists examine fish scales and mussel shells 

to learn more about the animal (figure 2). 

The growth rings in mussel shells can provide 

information about how fast the animal grew, 

how old it is, and how growth changes with 

changes in climate.

Thinking About 

Science

When scientists identify a 

problem they must sometimes 

find new methods to study the 

problem. Sometimes scientists 

come up with a new method based on some 

other method they know about or have used 

before. One new field of study is called 

sclerochronology (skler ə krə nä lə jē). This new 

field of study is based on dendrochronology. Figure 1. A tree’s growth rings can show times 

of fire, drought, and other events that the tree 

experienced. The rings also tell the age of the What’s in a Word? tree. Photo courtesy of Jessica Nickelsen.

Large words can be broken down into smaller words. Breaking larger words 

into smaller words helps to illustrate how the 

words were created and to understand why 

they are used. Sclerochronology is the study 

of chemical and physical changes in the 

gradual increase in hard tissue of organisms.

Break down the word “sclerochronology:”

sclero: hard, hardened, or hardening

chronos: time

logos: science

By piecing these smaller words together, 

you can see that the word sclerochronology 

comes from the science of how things harden 

over time, such as shells and bones.

Figure 2. A mussel has a hard exterior shell, and 

the animal deposits a ring of hard tissue each 

winter when its growth slows. Photo courtesy of 

Dr. Andrew Rypel.
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Natural Inquirer • Number 18

Thinking About the Environment

Bottomland hardwood 

forests are unique ecosystems

(figure 3). These ecosystems 

have a lot of diversity and 

are highly endangered. 

Bottomland hardwood forests 

are river swamps. These forests are 

found along rivers and streams and typically 

include large floodplains. The way in which 

water moves and flows through these rivers and 

forests has an effect on the entire ecosystem. 

Hydrology is the study of how water moves and 

flows. Changes to the hydrology of the rivers 

and streams may cause problems for the entire 

ecosystem.

times. The amount of water and the velocity, 

or speed, of water in a stream or river is called 

streamflow (figures 4a, 4b, and 4c). You 

will learn more about streamflow in the 

“Introduction” section. The scientists were 

particularly interested in how freshwater 

mussels responded to changes in streamflow.

Figure 3. Bottomland hardwood forests are 

river swamps. These forests are found along 

rivers and streams and typically include large 

floodplains. Photo courtesy of the U.S. Fish and 

Wildlife Service.

In earlier studies, scientists learned that 

periods of flooding are important to this 

ecosystem. One reason these periods of 

flooding are important is because carbon

deposits from the land, in the form of leaves and 

other organic matter, are transferred into the 

river during these periods. Carbon is important 

for the plants and animals in and along the river. 

The scientists in this study wondered if flooding 

provides other benefits for this ecosystem.

One way to study flooding is to look at the 

amount of water in a stream or river at different 

Figures 4a and 4b. Note the differences 

between the two illustrations. Which illustration 

has a high streamflow? How do you know? 

Illustrations by Stephanie Pfeiffer.

Figure 4c. This river currently has a low 

streamflow. Photo courtesy of Dr. Wendell Haag.

(4a)

(4b)
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Freshwater Edition, http://www.naturalinquirer.org

Introduction

An ecosystem is a community of plant and 

animal species interacting with one another 

and the nonliving environment. Ecosystems 

may change over time. Ecosystem changes are 

recorded in unique ways. For example, a tree’s 

growth rings show scientists which years of the 

tree’s life included drought and fire. Similarly, 

the shell of a mussel can show scientists the age 

and growth rate of the animal. In this study, the 

scientists wanted to use information from the 

mussels’ shells to help them better understand 

the environment in which the mussels lived.

The scientists in this study were interested 

in studying mussels in bottomland hardwood 

forest ecosystems. Streamflow is an important 

factor in bottomland hardwood forest 

ecosystems. Streamflow is the volume of water 

flowing through a stream at any particular 

place. The scientists wanted to figure out how 

streamflow affected mussels and plants near 

and in the rivers in these ecosystems. The 

scientists also wanted to compare streamflow 

with cypress trees along the river to see if 

streamflow affected mussels and trees the same 

way (figure 5).

North America has the highest diversity of 

freshwater mussels in the world (figure 6). 

Mussels are mollusks. They have two shells 

that are joined by a ligament (figure 7). Mussels 

have two small siphons used to draw in and 

expel water. This siphoning action helps to 

filter water of bacteria, algae, and other small 

particles, and it makes this material available to 

Figure 5. Bald cypress trees are found in 

bottomland hardwood forests because they 

are able to survive in areas that are seasonally 

flooded or that are covered in water a majority 

of the time. These bald cypress trees are found 

in Okefenokee National Wildlife Refuge. Photo 

courtesy of Babs McDonald.

Figure 6. North America is located in the Northern Hemisphere. Map by Carey Burda.
79

Natural Inquirer • Number 18

other organisms that live 

on the bottom. Mussels, 

therefore, help improve 

water quality.

The outer shell of a 

living mussel is a home to 

some organisms. Mussels 

are also a source of food 

for many animals. Some 

animals that eat mussels 

are muskrats, raccoons, 

otters, turtles, and fish 

(figure 8). In addition, 

the empty shells become 

homes for animals after 

the mussels are no longer 

living.

Figure 7. A mussel has many interesting features, such as a foot, 

a mouth, and teeth that help lock the shell together. Illustration by 

Stephanie Pfeiffer.

Figure 8. Raccoons and other animals use 

mussels as a source of food. Photo courtesy of 

Babs McDonald.

Mussels are very sensitive to changes 

in rivers or lakes, and this sensitivity 

makes them good indicators of the 

health of aquatic ecosystems. Mussels 

are also interesting because they have a 

unique reproductive cycle (see sidebar 

on page 80). Due to the importance of 

mussels in the ecosystem, the scientists 

wanted to know how streamflow in the 

bottomland hardwood forest ecosystems 

affected the mussels. The scientists 

wanted to know specifically how 

streamflow affected mussel growth.

Reflection Section

b Stateinyourownwordsandintheformofquestionswhatthescientistswantedtolearn.

b Musselsareimportanttotheecosystem.Namethreewaysmusselsareimportantandwhyeach

functionisimportanttotheecosystem.
80

Freshwater Edition, http://www.naturalinquirer.org

Why Is the Mussel Reproductive Cycle 

Important?

Male mussels release sperm into the water, and the current carries the sperm to 

female mussels. After the eggs are fertilized, 

they hatch into tiny larvae inside the female’s 

gills. The females then release the larvae into 

the water where they must attach to a fish. The 

larvae are parasites that need nutrition from 

a fish to grow into young mussels. Different 

mussel species need different kinds of fish.

The female mussel must somehow make sure 

her larvae find the right kind of fish.

Mussels have different ways of attracting 

fish depending on what kind of fish their larvae 

need. For example, mussels whose larvae 

need big predators like bass have large lures 

that look like minnows. In this case, lures are 

something that attracts a fish. Other mussels 

whose larvae need smaller fishes have tiny 

lures that look like insects or snails. When a 

fish tries to attack the lure, the larvae attach 

to the fish and remain for several weeks. After 

they have developed into young mussels, they 

drop off, leaving the fish unharmed. Due to this 

interesting reproductive cycle, healthy mussel 

communities are dependent on a healthy and 

diverse fish community (figure 9).

Figure 9. A simplified version of mussel 

reproduction illustrates some of the interesting 

features of the reproductive cycle. Illustration 

by Stephanie Pfeiffer.

Methods

The scientists studied 13 mussel 

species. The scientists collected the 

mussels from Alabama, Arkansas, and 

Mississippi (figure 10). They collected 

mussels from two sites in Alabama on 

the Sipsey River, one site on the St. 

Francis River in Arkansas, and one 

site on the Little Tallahatchie River in 

Mississippi (figure 11).

The rivers that the scientists 

collected from were different from 

each other in several important ways. 

Some of the rivers were regulated and 

some were unregulated. A regulated 

river is a river whose water is 

Figure 10. The mussels were collected in three States: 

Alabama, Arkansas, and Mississippi. Map by Lindsay Gnann.
81

Natural Inquirer • Number 18

controlled by dams or other water storage 

methods (figure 12a). An unregulated river 

does not have any dams or other water storage 

methods (figure 12b). Unregulated rivers are 

free flowing.

Streamflow can be different for regulated 

and unregulated rivers. For example, a dam can 

be opened to release more water, which causes 

higher streamflow, or it can be closed, reducing 

the amount of water in the river. Changes 

in streamflow at certain times of year can 

have negative impacts on aquatic organisms. 

The scientists wanted to see if the difference 

between regulated and unregulated streams 

affected the mussels (figure 13).

Figure 11. The Sipsey River in Alabama goes 

through part of the Sipsey Wilderness, and 61 

miles of the river have been designated Wild and 

Scenic. For more information, visit http://www.

wilderness.net. Photo courtesy of Dr. Andrew 

Rypel.

Figure 12a. This river is regulated by a dam.

Illustration by Stephanie Pfeiffer.

Figure 12b. This river is unregulated. Illustration 

by Stephanie Pfeiffer.

Name of River Regulated or Unregulated Description of River

Sipsey River Unregulated The watershed is mostly forested. Water quality is 

high, and the river has one of the most complete 

aquatic communities in this region.

St. Francis River Mostly Unregulated This river was mostly unregulated at the study 

site and has a high diversity of mussels; however, 

much of the watershed is affected by large-scale 

agriculture and water diversion projects.

Little 

Tallahatchie 

River

Regulated The study site was just below a major storage 

reservoir, and another small dam is downstream of 

the study site.

Figure 13. The description of each river includes whether it is regulated or unregulated.
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Freshwater Edition, http://www.naturalinquirer.org

In order to understand how streamflow 

affected the mussels, the scientists had to 

collect a variety of data. The scientists used 

microscopes to examine thin sections of mussel 

shells (figures 14 and 15). The scientists took 

pictures of these shell sections with a digital 

camera, which allowed them to measure how 

fast the mussels grew in different years. They 

also took cores from cypress trees to measure 

how fast the trees grew.

The scientists gathered streamflow data for 

each of the rivers they studied. The scientists 

were able to obtain streamflow data for each 

day over several decades from data collected 

by the U.S. Geological Survey and other 

government agencies. They put all of this 

information into a computer program to help 

them analyze the data.

Figure 14. Ms. Cram, a Forest Service scientist, 

uses a microscope to study very small things.

Ms. Cram is studying different types of fungi 

with this microscope. Look at the “Meet the 

Scientists” section on page 75. You will see Dr.

Haag is using a microscope to study mussel 

shells. Photo courtesy of Jessica Nickelsen.

Figure 15. This thin piece of mussel shell 

provides the scientists with a lot of information.

For example, the number of rings in the shell 

tells how old the mussel is, and the width of a 

particular ring tells how fast the mussel grew in 

that year. Photo courtesy of Dr. Andrew Rypel.

What Is Tree Coring?

Obtaining a tree core is a way of getting information about a tree without cutting 

it down. Scientists, like the one pictured, use 

a tool called an increment borer to obtain 

the core.

The core looks like a long pencil with 

rings. Tree cores help scientists learn the age 

of the tree and how it grew over time.

Figure 16. 

Tree coring.

Photos courtesy 

of Scott Horn.
83

Natural Inquirer • Number 18

Reflection Section

b Thescientistscollecteddatafromthree

differentrivers.Doyouthinkitisagoodidea

tocollectdatafromdifferentareas? Whyor

whynot?

b Thescientistsincludedadescriptionofeach

riverinthestudy(seefigure13). Whydoyou

thinkthisinformationisuseful?

Findings

In the unregulated Sipsey River, mussels grew 

faster during times of low streamflow and slower 

during times of high streamflow (figure 17). 

Some mussel species in the St. Francis River also 

showed this relationship. The strongest and 

most consistent trend in the St. Francis River 

was a strong, positive relationship between 

mussel growth and hydrologic reversals.

A hydrologic reversal is when the river 

changes from a rising river to a falling river or 

from a falling river to a rising river. A greater 

number of reversals can mean that the water 

falling on the land winds up in the river and 

flows downstream very quickly. This rapid 

movement of water often happens in an 

agricultural landscape like the St. Francis 

River because much of the forest is gone. In 

a forested landscape like the Sipsey River, the 

water is absorbed by the forest and enters 

the river more slowly. This absorption of 

water influences things like the frequency and 

severity of floods.

River Name, Mussel Species Name, 

and Common Name 

Low 

Streamflow

High 

Streamflow

Number of 

Hydrologic Reversals

Sipsey River Mussels

Elliptio arca (Alabama spike) + – No change

Elliptio crassidens (Elephant ear) + – No change

Fusconaia cerina (Gulf pigtoe) + – No change

Fusconaia ebena (Ebonyshell) + – No change

Lampsilis ornata (Southern pocketbook) + – No change

Pleurobema decisum (Southern clubshell) + – No change

Quadrula asperata (Alabama orb) + – No change

Quadrula verrucosa (Pistolgrip) No change No change No change

Obovaria unicolor (Alabama hickorynut) + – No change

St. Francis River Mussels

Lampsilis teres (Yellow sandshell) No change No change A change

Potamilus purpuratus (Bleufer) No change – A change

Quadrula quadrula (Mapleleaf) No change No change A change

Little Tallahatchie River Mussels

Quadrula pustulosa (Pimpleback) No change No change No change

Figure 17. Mussel growth each year compared with low and high streamflow and number of 

hydrologic reversals. A plus sign means that growth was faster and a minus sign means growth was 

slower. What do you notice about the periods of low streamflow and high streamflow? You can see 

from the figure that mussels have very colorful names!
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Freshwater Edition, http://www.naturalinquirer.org

Unlike in the other rivers, mussel growth 

in the regulated Little Tallahatchie River was 

not significantly related to any streamflow 

measurements. This finding suggests that 

regulation of streamflow can disrupt the normal 

cycles of mussel growth found in unregulated 

streams. Interestingly, cypress trees behaved 

exactly the opposite from mussels. Cypress 

trees grew faster in high-streamflow years but 

slower in low-streamflow years.

is that high streamflow might make it more 

difficult for mussels to process their food. This 

difficulty is because the water is turbid and 

carries a lot of sediment that mussels must 

separate from edible material like algae and 

microbes. Finally, high water may dilute the 

food particles that mussels need to grow. The 

scientists would need to conduct additional 

studies to find out exactly why mussel growth is 

related to streamflow.

Even though the mussels experience 

lower growth during high streamflows, higher 

streamflows are needed periodically. Higher 

streamflows help keep the mussel habitat in 

good condition by removing fine sediment from 

the streambed. For some species of mussel, 

too much fine sediment may impact growth, 

feeding, and survival of young mussels. The 

different response of cypress trees also shows 

that a wide range of streamflows is necessary 

for the best growth for different organisms in 

the ecosystem.

The scientists found no relationship between 

streamflow and mussel growth in regulated 

streams. This finding suggests that dams or 

other forms of regulation disrupt the normal 

cycles of mussel growth. The scientists said 

that the potential relationships found between 

mussels and streamflow should be studied in 

other landscapes and rivers. This additional 

research is necessary so that the scientists will 

know if these relationships occur in many 

different places or only in the rivers they studied.

Reflection Section

b Howdoesmusselgrowthchangeintimesof

highandlowstreamflow?Howdoyouknow

basedonthedatainfigure17?

b Whatdidthescientistsfindoutabout

therelationshipbetweenregulatedand

unregulatedriversandmusselgrowth?

(Hint:Reviewfigures13and17.)

b Readthedescriptionsoftheriversinfigure13.

Doyouthinkanyoftheserivercharacteristics

couldinfluencemusselgrowth?Whatdoyou

thinkthescientistsmightsuggestasthenext

stepstotakeafterthisresearch?

Discussion

The scientists found that in unregulated 

streams, mussels showed higher growth in 

low-streamflow conditions. Low-streamflow 

conditions enable the growth of microbes and 

algae in the water, which make up much of 

an adult mussel’s diet. During periods of high 

streamflow, mussel growth slows.

The scientists think that the mussels’ growth 

pattern may be a result of several factors. One 

factor is that during times of high streamflow, 

mussels may require more energy to maintain 

their position in the riverbed. Another factor 

Reflection Section

b Doyouthinkitisimportanttostudytheimpact

ofstreamflowonmussels?Whyorwhynot?

b Whataretheadvantagesanddisadvantages

ofdamsonourrivers?Discusswithyour

classmates.
85

Natural Inquirer • Number 18

Glossary

agricultural (a gri kəl ch(ə) rəl): Of, relating to, or 

used in farming or agriculture.

aquatic (ə kwä tik): (1) Living or found in, on, or 

near water; (2) of or relating to the animals or 

plants that live in, on, or near water.

carbon (kär bən): A chemical element that 

forms diamonds and coal and that is found in 

petroleum and in all living plants and animals.

data (dā tə): (1) Factual information used as a 

basic for reasoning, discussion, or calculation; 

(2) Facts or figures studied to make a conclusion.

dendrochrononology (den drō krə nä lə jē): 

The science of dating events and variations in an 

environment in former periods by the study of 

growth rings in trees and aged wood.

diversion (də vər zhən ): The act of changing the 

direction or use of something.

diversity (də vər sə tē): A measure of the 

differences between the types and numbers of 

living things in a natural area.

drought (drau̇ t): A period of dry weather with 

little or no rain.

ecosystem (ē kə sis təm): Community of plant 

and animal species interacting with one another 

and with the nonliving environment.

endangered (in dān jər ed): Being in danger or 

peril.

floodplain (fləd plān): Flat land area next to a 

stream or river.

hydrologic (hī drə lä jik): Of or relating to the 

science dealing with the properties, distribution, 

and circulation of water on and below Earth’s 

surface and in the atmosphere.

larvae (lär vē): Wormlike feeding form that 

hatches from the egg of some animals.

mollusks (mä ləsks): Any one of a large group 

of animals (such as snails and clams) that have 

a soft body without a backbone and that usually 

live in a shell.

organic matter (ȯr ga nik ma tər): Substance 

which breaks down naturally and which comes 

from either plants or animals.

reservoir (re zə vwär): Place where water is 

collected and stored for use.

sclerochronology (skler ə krə nä lə jē): The 

study of chemical and physical changes in the 

gradual increase in hard tissue of organisms.

sediment (se də mənt): Soil particles carried 

along in streams and rivers, some of which may 

settle to the bottom.

siphon (sī fən): Tube-like organ in animals and 

especially mollusks or arthropods used for 

drawing in or ejecting fluids.

turbid (tər bəd): Not clear; foul or muddy.

velocity (və lä sə tē): Speed of movement.

watershed (wä tər shed): The area that drains 

to a common waterway, such as a stream, lake, 

estuary, wetland, aquifer, or even the ocean.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriamwebster.com. Definitions are limited to the word’s 

meaning in the article.

The definition for watershed is taken directly 

from the U.S. Environmental Protection Agency 

(http://www.epa.gov).

Adapted from Rypel, A.L.; Haag, W.R.; Findlay, R.H. 2009. Pervasive hydrologic effects on freshwater mussels and 

riparian trees in southeastern floodplain ecosystems. Wetlands. 29(2): 497–504. http://www.treesearch.fs.fed.us/

pubs/33529.
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FACTivity

Time Needed

One class period

Materials (Materials for each 

student or group of students)

• Three graphs on pages 86 and 87.

• Pencils

In this article, you learned about 

freshwater mussels and how they 

respond to streamflow. In this FACTivity, 

you will be the scientist and analyze 

real-time streamflow data from the three 

rivers that the scientists in this study 

studied.

The question you will answer in this 

FACTivity is: How do the three graphs of 

data from the rivers studied by the scientists 

compare with each other?

Look at the three graphs provided 

(figures 18, 19, and 20). Each graph 

represents the streamflow for each river 

during the same 8-day period. What is similar 

and different between the graphs? Look 

back at the findings about mussel growth 

and streamflow. Now, look at the three 

graphs. In which river or rivers do you think 

the mussels may grow the best during the 

8-day period? Why? Do you think an 8-day 

period provides enough information about 

the streamflow in a river? Why or why not?

Figure 18. Graph of stream discharge for the St. Francis River at Wappapello, MO. Graph courtesy 

of the U.S. Geological Survey.
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Natural Inquirer • Number 18

Figure 19. Graph of stream discharge for the Little Tallahatchie River at Etta, MS.

Graph courtesy of the U.S. Geological Survey.

Figure 20. Graph of stream discharge for the Sipsey River near Elrod, AL. Graph 

courtesy of the U.S. Geological Survey.
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Alternate FACTivity

First, you will need access to a computer 

to visit http://waterdata.usgs.gov/nwis/rt.

This Web site is the U.S. Geological Survey’s 

Web site for daily streamflow conditions 

across the United States (figure 21).

The three rivers that the scientists studied 

were the St. Francis, the Little Tallahatchie, 

and the Sipsey. Each of these rivers has 

a streamflow gage in it that records daily 

streamflow as well as other data.

1. Use the dropdown menu in the upper 

right hand corner to select a State. For 

each river, you will need to select the 

State. For example, for the St. Francis 

River, you would select Missouri (see 

bulleted list that follows).

2. After the Missouri Current Water Data 

page is displayed, then click on 

“Statewide Streamflow Table.”

3. After the “Statewide Streamflow 

Table” is displayed, select the specific 

locations provided in the following list.

• St. Francis at Wappapello, Missouri is 

07039500

• Little Tallahatchie at Etta, Mississippi 

is 07268000

• Sipsey River at Erod, Alabama is 

02446500

4. Compare the data between the three 

rivers during different time periods 

and seasons. You might want to create 

graphs or charts to help you make your 

comparisons. What similarities and 

differences do you notice?

5. Now, go back to the main page and 

click on your State. Explore some of 

the rivers around where you live. How 

do the data from these rivers compare 

to the three rivers in the study?

6. Share what you found with your 

classmates. If you have time, create 

a poster about a river in your area.

These posters can be hung up in the 

classroom or in the school to help 

others learn about streams and rivers 

in your area.

Figure 21. The U.S. Geological Survey Web site for daily streamflow conditions provides 

information about streams and rivers across the United States.
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Natural Inquirer • Number 18

What’s in a Word?

One of the many questions that people have asked from time to time is the spelling of the word “streamgage” versus spelling it with a “u” as in “streamgauge.” Page 50 of the U.S.

Geological Survey report, A History of the Water Resources Branch, U.S. Geological Survey: 

Volume I, From Predecessor Surveys to June 30, 1919 (http://on.doi.gov/USGSWaterHistory) 

includes a reference giving credit to the change in spelling to F.H. Newell around 1892. The 

author wrote:

At about this time, F.H. Newell adopted the spelling “gage” instead of “gauge.” As he 

informed the writer, “gage” was the Saxon spelling before the “u” was inserted as a 

result of Norman influence on the language.

Ever since then, the U.S. Geological Survey has spelled the word without the “u.”

Natural Inquirer

Connections

You may want to reference these Natural Inquirer articles for additional information 

and FACTivities:

• For more on turbidity, sediment, and 

pollution in water, read “What’s the 

Nonpoint?” on page 25 or “Sedimental Journey” on page 58 in this Natural 

Inquirer edition.

• To learn about another impact of 

regulated streams, see the sidebar 

on page 100 of “Timed Travel” in this 

Natural Inquirer edition.

• For more on the connectivity of stream 

habitats, read “Swimming Upstream 

Without a Ladder” in the Tropical edition 

of Natural Inquirer.

These articles, along with others, can 

be found at: http://www.naturalinquirer.org/

all-issues.html.

Web Resources

U.S. Geological Survey Water Data

http://waterdata.usgs.gov/nwis/rt

Bottomland Hardwood Forests

http://water.epa.gov/type/wetlands/bottomland.cfm

Fun With Freshwater Mussels!

http://www.uvm.edu/~pass/tignor/mussels/

America’s Mussels: Silent Sentinels

http://www.fws.gov/midwest/endangered/clams/

mussels.html

Florida Museum of Natural History: 

Sclerochronology

http://www.flmnh.ufl.edu/envarch/sclerochronology.htm

Freshwater Mussel YouTube Video from Virginia 

Department of Game and Inland Fisheries

https://www.youtube.com/watch?v=URHTrAAkpr0
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Timed Travel: 

Measuring the Relationship 

Between Stream Temperature 

and the Development of Salmon

Photo courtesy of http://www.iStockphoto.com
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Natural Inquirer • Number 18

Meet the Scientists

Dr. E. Ashley Steel, Statistician and Quantitative Ecologist: I have 

so many favorite science experiences! One cool science experience 

was when I was standing right in the middle of the Snoqualmie (snō 

kwȯl mē) River. I was thinking about how my 35 water temperature 

loggers were recording data all across the Snoqualmie River 

watershed at that very second!

Ms. Abby Tillotson, Fisheries Biologist: 

My favorite science experience so far has 

been participating in salmon surveys on 

the Yakima (yak ə ma) River near Cle Elum, Washington. We spent a few 

days floating the river on rafts, counting redds (salmon egg nests), and 

pulling over to the bank to count and measure salmon that 

died after spawning (laying eggs). This photo is of me holding 

a brown trout on the Sprague River in southeast Oregon.

Dr. Donald Larsen, Fisheries Biologist: My favorite science 

experience was rowing a raft down the Yakima River in Washington 

State. I was collecting data on spring Chinook salmon on a beautiful 

fall day and thinking... I can’t believe I get paid to do this.

Ms. Aimee Fullerton, Fisheries Biologist: 

It is tough to choose my favorite science 

experience. I’d have to say that it was watching 

nonnative fish use different habitats in the 

dark in a lab experiment. We marked fish with fluorescent paint and used a 

black light so the fish couldn’t see us observing them. This process was the 

subject of my Master of Science research in the late 1990s. You can earn 

a Master of Science degree after earning your Bachelor’s degree in college.

Mr. Keith Denton, Fisheries Biologist: 

My favorite science experience was capturing 

40-pound Chinook salmon in the newly 

restored Elwha 

River. The Elwha 

River is in Olympic 

National Park in 

Washington State.

I was measuring 

the impact of 

large-scale dam 

removal on salmon 

recovery.

Dr. Brian Beckman, Fisheries Biologist: 

I enjoy mentoring young scientists, helping 

them to develop useful and interesting 

questions and to form thorough and accurate 

answers. The 

curiosity and 

enthusiasm of 

these bright young 

people are amazing 

and I’m fortunate 

to be able to work 

with them.

t

t

t

t

t

t
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Freshwater Edition, http://www.naturalinquirer.org

What Kinds of 

Scientists Did 

This Research?

fisheries biologist: This scientist studies 

fish and how the environment and other 

outside forces affect fish throughout their life 

cycle.

statistician: This scientist uses statistical 

methods to collect and analyze data and 

help solve real-world problems in business, 

engineering, the sciences, or other fields.

Statistical methods include the collection, 

analysis, interpretation, presentation, and 

organization of data.

quantitative ecologist: This scientist 

applies statistical methods and mathematics 

to problems in ecology. Ecology is the study 

of the interactions of living things with each 

other and with the nonliving environment.

Thinking About 

Science

Part of a scientist’s job is to 

develop, establish, or improve 

methods of collecting, analyzing, 

organizing, or presenting data. 

Some scientists are particularly interested in 

helping to improve scientific methods. In this 

research, the scientists thought that a different 

method of collecting data might improve 

scientists’ understanding of fish development.

Have you ever thought of a better way to 

do something? Before you knew for sure that 

it was better, you would have to try your new 

way and compare it with an existing way. That 

is exactly what the scientists did in this research.

Glossary words are bold and are defined on 

page 101.

Thinking About the 

Environment

Over many years, decades, 

and thousands of years, 

organisms adapt to different 

factors in their physical 

environment. Temperature 

is one of the environmental factors to which 

organisms adapt. Many organisms live part, or 

all, of their lives in water. Water temperature, 

therefore, is a variable that affects the life 

cycle of many of Earth’s organisms.

In this research, the scientists studied the 

relationship of water temperature to the time it 

took Chinook salmon eggs to hatch and develop 

as young fish. The scientists also studied how 

water temperature affected the rate at which 

the fish developed. Water temperature can 

change over time as a result of global climate 

change, dams, irrigation, and changing land 

use. The scientists in this study, therefore, 

wanted to understand how variation in water 

temperature can affect the development of 

young Chinook salmon (figure 1).

Figure 1. An adult Chinook salmon leaps out of 

the water. Photo courtesy of http://iStockphoto.

com.
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Natural Inquirer • Number 18

How Are Salmon 

Important to the 

Ecosystem?

Salmon play an important role in their ecosystem. You probably know that 

salmon provide food for bears. Did you 

also know that salmon provide food for the 

soil? Salmon die after they lay their eggs, or 

spawn. During high water flows, the dead 

salmon are washed onto riverbanks. As the 

dead salmon decay, they provide important 

nutrients to the riverbank soils. To learn more 

about how salmon help riverbank soils in 

Alaska, read the Natural Inquirer monograph, 

“Food for the Soil,” http://www.naturalinquirer.

org/Food-for-the-Soil-i-37.html.

Figure 2. The Chinook salmon life cycle.

Illustration by Stephanie Pfeiffer.

Introduction

Water temperature helps regulate aquatic

ecosystems. Aquatic scientists, therefore, 

often measure water temperature. Scientists 

usually record daily water temperature by 

calculating the mean or average temperature 

over a 24-hour period. Scientists also calculate 

degree days. Degree days describe the total 

temperature units (TU) delivered. One 

degree day Celsius is equal to a temperature 

of 1 °Celsius (C) for 1 day. Temperature units 

describe the amount of energy or heat available 

to the fish. You will learn about temperature 

units and degree days in this article.

Aquatic organisms spend their lives in, on, 

or near water. For many aquatic organisms, 

life-cycle phases are tied to water temperature. 

Salmon eggs, for example, generally hatch when 

a certain number of degree days, or temperature 

units, have been accumulated. Scientists have 

figured out how many temperature units are 

required for Chinook salmon eggs to hatch and 

for young salmon to grow and emerge as young 

fish (figure 2). Scientists have focused their 

attention on total temperature units. Until now, 

they have not given a lot of attention to how 

those temperature units are delivered. Does it 

make a difference, for example, if the temperature 

is 3 °C one day and then 7 °C the next, or if it 

is just a stable 5 °C every day? Over a month, 

the same number of temperature units would 

be delivered but they would be delivered in 

different ways.

The scientists in this study knew that stream 

and river water temperature varies in at least 

two ways. First, the temperature varies across 

each 24-hour period. Second, water temperature 

varies within and across seasons. The scientists 

knew that recent human actions were altering 

the patterns of water temperature where Chinook 

salmon laid their eggs. Dams, land-use changes, 

irrigation, and climate change can cause altered 

water temperatures (figures 3, 4, 5, and 6).

The scientists suspected that fish might 

respond to more than just total temperature 

units. They thought that it might matter whether 

the water temperature was stable or variable. 

Just knowing the number of total temperature 

units delivered does not enable scientists 

to understand how temperature variations 

affect the life cycle of Chinook salmon. The 

scientists asked this question: Do daily and 
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Figure 3. Dams can affect the water temperature, 

depending on the depth at which water is released 

downstream. Typically, surface water is warm 

and deep water is cold. When unnaturally warm 

or cold water is released, the change in water 

temperature can disrupt fish habitat. Illustration 

by Stephanie Pfeiffer.

Figure 4. When vegetation near waterways is 

disturbed, less plant cover can open waterways 

to more sunlight and result in higher water 

temperatures. Photo courtesy of Babs McDonald.

Figure 5. Irrigation withdraws water from 

waterways. This disturbance can cause water 

temperature changes. Irrigation usually causes 

the water temperature to rise. Photo courtesy of 

Babs McDonald.

Figure 6. Climate change can cause water 

temperature to change over time. The same 

factors that cause air temperature to rise can 

cause water temperature to rise as well. Photo 

courtesy of Babs McDonald.

seasonal water-temperature variations affect 

the development of salmon eggs and alevins 

(a lə vənz), or young salmon, before they become 

free-swimming fry?

To answer their question, the scientists 

did something new. The scientists observed 

Chinook salmon development in fish that 

were exposed to different water-temperature 

patterns. The scientists altered water 

temperature experimentally to explore how 

water temperature variability affects Chinook 

salmon development.

Reflection Section

b Whydoesstreamorriverwatertemperature

varyacrossa24-hourperiod?

b Imaginethatyouaregoingcampingover

theweekend.Youwillbesleepinginatent.

Theaveragedailyairtemperatureacross24

hourswillbe45°F(7.2°C).Doyouthinkitwould

bemorehelpfulforyoutoknowhowtheair

temperaturewillvaryacrossthe24-hour

period?Whyorwhynot?
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Natural Inquirer • Number 18

Methods

The scientists collected adult Chinook 

salmon near the Roza Dam on the Yakima 

River in June and July 2009 and took them 

to a hatchery (figures 7 and 8). The salmon 

spawned (laid eggs) while in the hatchery, 

and the scientists collected the fertilized eggs 

(figure 9). The scientists put 150 eggs into each 

of 64 chambers (figure 10). These chambers 

were set up so that the eggs would hatch and 

the alevins could develop into fry (figures 11 

and 12).

Figure 7. The Yakima River, named for the 

native Yakama people, has numerous dams and 

irrigation canals. The Yakima River is a source 

of water for the dry agricultural region of central 

Washington State. Photo courtesy of http://www.

iStockphoto.com.

Figure 8. The Yakima River is 

located in central Washington 

State. The Yakima River is a 

tributary of the Columbia 

River and is 214 miles 

(344 kilometers) 

long. Map by 

Carey Burda.

Figure 9. Fish hatcheries are large indoor or 

outdoor facilities where fish eggs are hatched and 

young fish are allowed to develop. Photo courtesy 

of Babs McDonald.

Number Crunch

b	 Howmany alevinswere observed overall?
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Freshwater Edition, http://www.naturalinquirer.org

Figure 10. The chambers 

were made with plastic pipe.

Each chamber enabled 

the eggs to hatch and the 

alevins to develop into fry.

The scientists were able 

to catch, measure, and 

count the young fry as they 

emerged from the chamber.

Photo courtesy of Dr. E.

Ashley Steel and illustration 

by Stephanie Pfeiffer.

Figure 11. Chinook salmon lay eggs in the gravel beds of 

a river. After hatching, the alevins, or young salmon, live 

among the gravel on the river’s bottom. While alevins are 

developing, they exist on a yolk sac. As they develop, they 

slowly absorb the yolk sac. When the yolk sac is gone, 

the alevins become free-swimming fry and they leave the 

graveled river bottom. Illustration by Stephanie Pfeiffer.

Figure 12. When an alevin’s yolk sac has been 

absorbed, it becomes a free-swimming fry.

Photo courtesy of Abby Tillotson.
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Natural Inquirer • Number 18

The scientists controlled the water

temperature in the chambers using very large 

aquarium heaters. They created eight different 

patterns of water temperature (figure 13). The 

different water-temperature patterns were 

meant to simulate stable temperatures, daily 

variation in water temperature, seasonal 

variation in water temperature, and daily plus 

seasonal variation in temperature. In two 

cases, the scientists also simulated completely 

unnatural patterns just to see if the fish would 

respond.

A: Water temperature 

stable at 5 °C

B: Water temperature 

varied daily from 

5 to 10 °C

C: Water temperature varied 

seasonally by reducing 

1 °C per week, then 

warmed 1 °C per week

D: Daily variation plus 

seasonal variation 

(combination of B and C)

E: Extreme seasonal 

variation by flip 

flopping 5 °C one 

week, then 10 °C 

the next week

F: Extreme daily 

variation by changing 

the temperature from 

5 to 10 °C twice daily

G: Water temperature stable 

at 10 °C

H: 10 °C with daily variation 

as high as 13 °C

Figure 13. The eight different water-temperature patterns.

Number Crunch

b	 The scientists divided the temperature

treatments equally across all 64 chambers.

Howmany chambers received each ofthe

eighttreatments?

The scientists recorded the water temperature 

every hour. The temperature patterns were 

designed so that the chambers with variable 

temperatures delivered about the same total 

temperature units every day as those with 

stable temperatures.

Number Crunches

b Temperature units (TUs) are usually thought of as degree days,the total amount oftemperature

delivered in one day. To design the temperature patterns,the scientists calculated TUevery hour

and then added the 24 hourlymeasurements togetherto determine the totaltemperature units

delivered in 1 day.

b Calculate the TUs delivered in 1 day for a stable pattern of10°C:(10/24 + 10/24 + 10/24 + 10/24...)

(Include all 24 hours TUs of10/24).What are the total TUs forthe day?Note thatfor a stablewater

temperature,the TUs for1 day is equalto thewatertemperature.

b Try calculating TUs for a temperature pattern that goes up and down every hour:

•	 Ifthewatertemperature fluctuated between 9 °C for1 hour and 11°C forthe next hour,

and this pattern repeated across 24 hours:(9/24 + 11/24...)(include all 24 of TUs in your

calculations),whatwould be the total TUs forthe day?

b Nowcalculate the TUs forthis temperature pattern:

•	 Ifthewatertemperaturewas 5 °C for 6 hours,10°C for10hours, and 7 °C for 8 hours,

whatwould be the total TUs forthe day?
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Freshwater Edition, http://www.naturalinquirer.org

At 11:00 a.m. every day, the total temperature 

units (TUs) for the past 24 hours were recorded 

for each chamber and the scientists checked to 

see if any fish had emerged. The scientists noted 

the day when most of the fish, 125 of the 150 

alevins, emerged as fry. At that point, the scientists 

calculated the total TUs that had accumulated 

in each chamber over all the days that the 

alevins had been developing in that chamber.

The scientists designed temperature patterns 

that delivered about the same daily total TUs 

but had different kinds of variability. By using 

these patterns, the scientists measured the 

impact of variation in water temperature on 

the development of Chinook salmon. Note 

that everything else was held constant in the 

experiment. Any differences between the TUs 

that had been delivered when most of the fry 

Reflection Section

b Explaininyourownwordshowthe

experimentwascontrolledsothatany

observeddifferencesinfryemergenceand

conditionwouldmostlikelyberelatedto

water-temperaturepatterns.

b Whatwerethescientiststryingtodiscover

inthisexperiment?

emerged, therefore, were likely related to the 

variability in the water-temperature patterns.

The scientists collected a sample of fry as 

they emerged from each chamber. The scientists 

weighed, measured, and determined the fry’s 

overall condition.

Now, answer the Reflection Section 

questions on this page.

Findings

The water-temperature patterns influenced 

when fry emerged. Eggs and alevins exposed to 

the most stable water temperature (5 °C and 

10 °C) had accumulated a mean of 1,160 (5 °C) 

and 1,153 (10 °C) TUs by the time most of the 

fry had emerged. Recall that the scientists used 

eight chambers for each of the eight temperature 

patterns. Therefore, the scientists calculated 

mean accumulated TUs for each of the eight 

patterns. The scientists expected these numbers 

to be similar. They expected this similarity because 

they knew that Chinook salmon eggs require a 

certain number of TUs to be ready to emerge.

The fry living in the chambers in which 

the water temperature varied by 5 to 10 °C 

once per day emerged after accumulating 

fewer TUs than when the water temperature 

was held stable (figure 14). The scientists 

Figure 14. The emergence of Chinook salmon fry based on accumulated temperature units for eight 

water-temperature patterns. Illustration by Stephanie Pfeiffer.
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Natural Inquirer • Number 18

discovered something different for the alevins 

exposed to water-temperature patterns with 

extreme daily or extreme seasonal variations. 

These alevins needed to accumulate more TUs 

than when the water-temperature was held 

stable for most of the fish to emerge as fry.

The scientists also discovered that fish exposed 

to the warmer patterns of water temperature 

emerged less fully developed than other fish. 

These fish were four times more likely to still 

have a visible yolk sac upon emergence.

Reflection Section

b Basedonthescientists’results,what

wouldyouconcludeabouttherelationship

betweenwater-temperaturevariabilityand

Chinooksalmondevelopment?

b Lookatfigure14.Whatdoyounoticeabout

fryemergencefromthisfigure?

How Does a Box Plot Show Interquartile Range?

Figure 14 is a box plot. Box plots are one way to display interquartile range.

Calculating an interquartile range helps 

scientists to understand the variation in their 

data. To find an interquartile range, the data 

must be listed in rank order, from the lowest 

value to the highest value. The middle value 

(the median) is identified. Then, the middle 

value of the bottom half and the middle value 

of the top half is identified. After this step is 

complete, the data have been divided into four 

parts or quartiles, called Q1, Q2, Q3, and Q4.

Q2 is the median. The interquartile range is the 

value of Q3-Q1.

In figure 14, the middle bar in each box 

is the median. The bottom of the box is Q1 

and the top of the box is Q3. The entire box 

for each temperature pattern represents the 

interquartile range.

Discussion

When scientists consider fish development 

based only on accumulated temperature units, 

they may be missing an important influence 

on fish development. This research shows that 

the timing of Chinook salmon development is 

dependent upon more than total accumulated 

temperature units. It matters how those total 

temperature units are delivered. Daily and 

seasonal water-temperature variability have 

an impact on how many temperature units are 

required for most of the fish to emerge.

The scientists estimate that variability in 

water temperature may affect fry emergence 

by as much as 1 week. Fish, like most wildlife 

species, have adapted to the availability of 

food sources in time. Emerging a few days 

early or late may cause fry to miss important 

food resources. If human changes to watertemperature patterns affect when fish emerge, 

fish might emerge at a time with fewer food 

resources. The possible lack of food resources 

could affect Chinook salmon survival.

Understanding the relationship between fry 

emergence and water variability is important 

now because humans are changing watertemperature patterns. Building dams, changing 

land cover, irrigating, and changing the global 

climate may have important impacts on the life 

cycle of Chinook salmon.
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Reflection Section

b Ifyouwereteachingyoungscientistshow

tostudyfishemergence,whatwouldyou

teachaboutconsideringwater-temperature

variability?

b Doyouthinktheresultsofthisresearchare

convincing?Whyorwhynot?

Adapted from Steel, E.A.; Tillotson, A.; Larsen, D.A.; 

Fullerton, A.H.; Denton, K.P.; Beckman, B.R. 2012. 

Beyond the mean: The role of variability in predicting 

ecological effects of stream temperature on salmon. 

Ecosphere. 3(11): 104. http://dx.doi.org/10.1890/ES12-

00255.1. http://www.fs.fed.us/pnw/pubs/journals/

pnw_2014_steel001.pdf.

Why Was the Elwha Dam Removed?

I

n 2014, the National Park Service 

completed the removal of two large dams 

on the Elwha River in Olympic National Park, 

Washington State (figure 15). For 100 years, 

the dams blocked all but the last 5 miles of 

the river. This blockage created reservoirs 

(large lakes) where a river once was, and 

stopped natural sediment flow and salmon 

migration. The dams had dramatically changed 

the Elwha River ecosystem. Removal of the 

dams has reopened more than 70 miles of 

important salmon spawning habitat, restored 

natural sediment flow, and begun the 

restoration of the Elwha River ecosystem.

Figure 15. The Elwha Dam in the midst of its removal. Photo courtesy of the National Park 

Service.
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Natural Inquirer • Number 18

Glossary 

accumulate (ə kyü m(y)e lāt): To increase 

gradually in amount as time passes.

aquatic (ə kwä tik): (1) Living or found in, on, or 

near water; (2) of or relating to the animals or 

plants that live in, on, or near water.

emerge (i mərj): To become known or visible.

fry (frī): Recently hatched or juvenile fishes.

habitat (ha bə tat): The place or environment 

where a plant or animal naturally or normally 

lives and grows.

land use (land yüs): How people are using the 

land.

mean (mēn): The average of a set of values.

migratory (mī grə tȯr ē): Having a characteristic 

of moving from one place to another on a 

periodic basis.

regulate (re gyə lāt): To set or adjust the 

amount, degree, or rate of something.

sample (sam pəl): A small subset group, 

representative of the entire group.

sediment (se də mənt): Soil particles carried 

along in streams and rivers, some of which may 

settle to the bottom.

simulate (sim yə lāt): To create the appearance 

or effect of something for purposes of evaluation.

tributary (tri byə ter ē): A stream that flows into 

a larger stream or river or into a lake.

variable (ver ē ə bəl): Subject to changes.

variability (ver ē ə bi-lə tē): The degree to which 

something is variable.

variation (ver ē ā shən): A change in the form, 

position, condition, or amount of something.

watershed (wä tər shed): The area that drains 

to a common waterway, such as a stream, lake, 

estuary, wetland, aquifer, or even the ocean.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriamwebster.com. Definitions are limited to the word’s 

meaning in the article.

The definition of watershed is taken directly 

from the U.S. Environmental Protection Agency 

(http://www.epa.gov).

FACTivity

Time Needed

• One class period for graphing data 

or 3 to 4 weeks for downloading and 

graphing data

• 3 to 4 weeks for observation involving 

5 to 10 minutes per day

• One class period for analysis, 

reporting, and discussion

Materials (for each small group)

• Observational tools appropriate for 

the event, such as binoculars or 

butterfly nets

• Graph paper and pencil

• Copy of the log sheet on page 103

• Daily access to a computer with 

Internet access (optional) or your 

teacher will provide daily data (from 

a Web site)

The question you will answer in this 

FACTivity is: How do air temperature 

patterns relate to a yearly natural event?

Your teacher will divide your class into 

groups. Your group will select an event to 

study. Identify a natural event that is at least 

partly dependent upon the air temperature 

for its occurrence. Your group may select 

an event from the following list, or identify 

a yearly natural event of your own:
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1. The emergence of a particular species 

of leaves.

2. The emergence of a particular species 

of flowers.

3. The first sighting of butterflies.

4. The first sighting of a particular 

migratory bird species.

5. The first occurrence of the developmental 

stage of an amphibian species.

6. The first leaf color change in the fall.

7. The first frost.

8. The first snowfall.

Identify a yearly natural event that you 

expect to occur in your area within the next 

3 to 4 weeks.

As a group, write down exactly what you 

will be looking for in the event. For example, 

you might write: “We are looking for the first 

sign of autumn color change in the maple 

tree in the front school yard, beside the front 

stairs. Color change means any change on 

any part of a leaf on that tree, from green to 

red, yellow, orange, or brown.”

After you have identified and described 

your event, look at the science log sheet on 

page 103. Your group will need three to four 

copies of the log sheet.

You will either access http://www.

weather.noaa.gov every day to record hourly 

temperatures, or your teacher will provide 

this information to you.

As an alternative, you may record your 

own hourly temperatures using an outdoor 

thermometer. If you choose this method, you 

may have to fill in nighttime temperatures 

and weekend temperatures from http://www.

weather.noaa.gov.

Observe daily, watching for your event 

to happen. When your event happens, 

record the date. At this point, you may stop 

recording the hourly temperature.

Using your completed log sheet, calculate 

the average daytime temperature and 

average nighttime temperature for each week.

For this FACTivity, daytime temperatures 

Plants are all around us. Changes 

in emergence of plants each year can 

tell scientists about changes in climate.

Contribute your observations of plants 

at home, at school, or at local parks with 

Project BudBurst (http://www.budburst.org), 

a citizen science project that 

allows you to become the 

scientist. Use the QR (Quick 

Response) code to start 

collecting data for science.

include those from 9:00 a.m. until 8:00 p.m.

Nighttime temperatures include those from 

9:00 p.m. until 8:00 a.m.

Make a graph of the two daily temperature 

averages across the weeks leading up to 

your event. (See figure 16 for an example.)

You may need to make three or four graphs, 

one for each week. Blank graph paper is 

located on page 123.

Your group will analyze your graphs as 

you think about your event. What patterns do 

you see in the air temperature in the weeks 

and days leading up to your event? How 

could these patterns affect the timing of your 

event? Write your observations and analysis, 

using complete sentences. Report your 

results to the class. Your teacher will hold 

a class discussion about the patterns you 

noticed in your data. Compare and contrast 

between different events.

To find hourly temperatures, visit http://

weather.noaa.gov. Select your State and then 

select your location. Select the location that 

is nearest to you.

This Web site displays hourly weather 

data for the past 3 days. Record the hourly 

temperatures using the log sheet. On 

Monday, record air temperature from over 

the weekend.
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Natural Inquirer • Number 18

Group Members: __________________________________________________________________________

Event: ____________________________________________________________________________________

__________________________________________________________________________________________

Log of Hourly Temperatures by Week

Week of __________________________________________________________________________________

Sun Mon Tue Wed Thurs Fri Sat

Degrees Fahrenheit

12 am

1 am

2 am

3 am

4 am

5 am

6 am

7 am

8 am

9 am

10 am

11 am

12 pm

1 pm

2 pm

3 pm

4 pm

5 pm

6 pm

7 pm

8 pm

9 pm

10 pm

11 pm 
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FACTivity 

Extension

As a class, compare and 

contrast this FACTivity 

with the salmon research 

in the article.

Figure 16. An example of a graph 

showing air temperatures over time.

Illustration by Stephanie Pfeiffer.

What’s in a Name?

Time travel is the concept of moving either forward or backward in time. In this article, the emergence of young fish from an earlier developmental stage was timed, in a way, by using 

a value called temperature units.

Web Resources

National Oceanic and Atmospheric Administration, 

Chinook Salmon

http://www.nmfs.noaa.gov/pr/species/fish/

chinooksalmon.htm

National Park Service, Elwha River Restoration

http://www.nps.gov/olym/naturescience/elwhaecosystem-restoration.htm

National Oceanic and Atmospheric Administration, 

Fisheries: Elwha Restoration 

https://www.youtube.com/watch?v=TP9z5S5oivo

Project Budburst/National Geographic Growing 

Degree Days Tool

http://budburst.org/documents/871408/1044448/FS_

Unit_3.pdf/5b4c635f-2d09-4055-a881-35a174d0085d

Project Budburst

http://www.budburst.org

USA National Phenology Network

https://www.usanpn.org/

Natural Inquirer

Connections

You may want to reference these Natural Inquirer articles for additional information 

and FACTivities:

• For more on the impact of dams, read 

“Mussel Mania” on page 74 of this 

edition of Natural Inquirer.

• For more information on salmon and 

their ecosystems, read “Food for the 

Soil” in the Natural Inquirer monograph.

These articles, along with others, can be 

found at: http://www.naturalinquirer.org/

 all-issues.html.
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Natural Inquirer • Number 18

Under Where? 

Underground Water and Its 

Contribution to Streams

Photo courtesy of the Forest Service, Pacific Southwest Region.
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Meet the Scientists

Dr. Fengjing Liu, Hydrologist: 

My favorite science experience 

is doing research to understand 

how water and contaminants

move and how they are linked 

within a watershed.

Dr. Carolyn 

Hunsaker, Ecologist: 

My favorite science 

experience was 

identifying a major 

gap in knowledge, 

and designing and 

implementing a largescale experiment 

with a diverse team 

of people. Our 

team believes this 

experiment’s findings 

will make a significant 

difference for forest 

health and water 

supplies in California.

In this photo, I am inside an instrument shed pouring 

a water sample from the automated sampler in the 

background. This sampler contains a computer that runs 

several instruments. These instruments measure streamflow

and turbidity and take automated water samples for later 

chemical analyses.

The instrument sheds, which are built deep in the 

forest, provide protection for the instruments. These small 

sheds also house the solar-powered batteries that run the 

instruments, and they provide shelter for research technicians 

during bad weather.

Dr. Roger Bales, Environmental Engineering Scientist: In 

my research, I switch between science and engineering. I 

get excited when our detailed, difficult measurements of the 

water cycle are successful and provide insight to predict how 

the measurements will change in the future. We measure 

snowpack, snowmelt, rainfall, shallow groundwater, 

streamflow, and vegetation water use. I am excited about 

this research because it provides the foundation to design 

solutions to the challenges posed by climate change, global 

population growth, and changing land cover. Photo courtesy 

of Roger Wynan.

Glossary words are bold and are defined on page 116.

t

t

t
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Natural Inquirer • Number 18

What Kinds of Scientists Did This Research?

ecologist: This scientist studies the relationship of living things with their living and nonliving 

environment.

environmental engineering scientist: This scientist combines biological, chemical, and 

physical sciences with the field of engineering to protect and restore the natural environment.

hydrologist: This scientist studies the distribution, movement, and quality of Earth’s waters.

Thinking 

About Science

Chemistry is a useful 

science tool. Environmental 

scientists can use chemistry to 

discover how water flows in an 

ecosystem. In this study, the 

scientists wanted to understand 

how much water in a particular stream began as 

rainfall or snowfall. They also wanted to know 

what percentage of the stream’s flow came 

from various locations.

The scientists knew that atoms of the same 

element can have different atomic weights. 

Different atomic weights are like a signature 

that helps scientists identify the atom. The 

scientists also knew that atoms can gain or lose 

electrons, resulting in a positive or negative 

charge. This gain or loss creates different chemical 

compounds, such as calcium or fluoride. These 

chemical compounds may dissolve in water, but 

they remain intact as chemical compounds. By 

testing the water in many places where it enters 

the ground, and then where water flows in the 

stream below, scientists can identify where the 

streamwater originated.

Thinking About the 

Environment

The water cycle describes 

the movement of water from 

Earth, to the atmosphere, and 

back (figure 1). You can see 

the water cycle at work in 

rainfall and snowfall, in rivers 

and streams, and in the oceans. You can 

observe evaporation by watching water slowly 

disappear from a wet roadway.

You cannot, however, see one mysterious 

part of the water cycle. Much of Earth’s 

precipitation moves into the soil, and, 

without your noticing, it flows underground as 

groundwater (figures 2, 3, 4a, 4b, and 5). 

This water can surface quickly or stay 

underground for thousands of years.

Underground water comes to the surface 

naturally through artesian wells, springs, 

and through seepage to streams and rivers. 

People bring groundwater to the surface by 

digging wells that pump water upward for their 

use. People use groundwater for irrigation, 

livestock, mining, public use (such as public 

swimming pools or water in public buildings), 

and individual household uses. Surface water, 

such as water in reservoirs, streams, rivers, 

and lakes, is also used for a variety of similar 

purposes. Plants use the water in the top 

several feet of soil for growth. This water is 

called shallow groundwater, or soil water.
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Figure 1. The water cycle. Illustration by Stephanie Pfeiffer.

Figure 2. Water moves underground as part of the water cycle. Notice that some water stays near 

the soil surface. This shallow groundwater, or soil water, may be a few feet deep or up to 20 feet deep 

below the soil surface. Deeper underground water is called deep groundwater or just groundwater.

Illustration by Stephanie Pfeiffer.
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Natural Inquirer • Number 18

Figure 3. Groundwater fills the spaces between soil particles and fractured rock underground. Notice 

that below the water table, all openings between soil particles and rocks are full of groundwater.

Above the water table, some water, held by molecular attraction, may surround particles and rocks.

Illustration by Stephanie Pfeiffer, adapted from the Groundwater Foundation and the U.S. Geological 

Survey.

Figure 4a and 4b. Aquifers are natural underground water storage areas. Coastal aquifers (4a) are 

different than aquifers found in hilly or mountainous areas (4b). Illustrations by Stephanie Pfeiffer.

(4a)

(4b)
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Figure 5. Groundwater provides water to underground aquifers or water storage areas. This water 

provision is called recharge. Most of the United States contains underground aquifers. This map 

shows the primary aquifers in the United States. Although the areas in white show no aquifers, these 

areas may have a shallow or more localized aquifer. Map courtesy of the U.S. Geological Survey.

Introduction 

When snow melts or rain falls, some of the 

water runs across the ground’s surface to nearby 

streams and rivers. This water movement is 

called surface flow. Much of the water, however, 

goes into the soil, and then seeps downward 

due to the force of gravity. The entrance of 

water into the soil is called infiltration, and the 

downward flow is called percolation (pər kə lā

shən). Some of the water stays in the soil near 

the soil’s surface, instead of percolating. This 

soil water flows laterally and down hillsides, 

especially in small, steep, forested watersheds 

called catchments (figure 6). This shallow 

underground water flow is called interflow. (See 

figure 2 in “Thinking About the Environment.”)

Snow is the main source of water in some 

of these catchments. These catchments are 

at higher elevations, where snow occurs more 

frequently (figures 9 and 10). In catchments 

at lower elevations, rain is the main source of 

water. As the global climate becomes warmer, 

the percent of total precipitation falling as snow 

will become less at these higher elevations.

The scientists in this study wanted to answer 

the following questions: (1) How much does 

soil water, compared with other water sources, 

such as rapid snowmelt, rainfall runoff, and 

groundwater, contribute to streamflow in these 

catchments? (2) Could underground water’s 

contribution to stream flow change as less snow 

falls in higher elevation catchments?
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Natural Inquirer • Number 18

Figure 6. Smaller watersheds 

may be contained within larger 

watersheds. The scientists in this 

study were interested in very 

small, steep, forested watersheds 

in the Sierra Nevada of California 

(figures 7 and 8). These small 

watersheds are called catchments.

Illustration by Stephanie Pfeiffer.

Figure 7. The Sierra Nevada is 

a mountain range in California.

Map by Carey Burda.

Figure 8. The 

Sierra Nevada has 

steep, forested 

slopes and clear 

mountain streams.

Photo courtesy of 

the Forest Service, 

Region 5.

Figure 9. Elevation is a measure of 

the height above the level of the sea.

Illustration by Stephanie Pfeiffer.
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Figure 10. As elevation increases, an area’s climate gets cooler and snow may fall often in the winter 

months. Illustration by Stephanie Pfeiffer.

Reflection Section

b Doeswaterflowundergroundinyourregion?Whydoyouthinkso?

b Whatissurprisingaboutfigure5?

b Doyouthinkotherareasacrosstheplanethaveaquifers?Whyorwhynot?

b Ifyouhavenotread“ThinkingAbouttheEnvironment,”dosonow.Usingtheinformationin“ThinkingAbout

theEnvironment”andinthe“Introduction”asclues,howdoyouthinkthescientistsansweredtheirfirst

researchquestion?

Methods

The scientists studied eight catchments in 

the Sierra Nevada. In particular, they studied 

catchments within the Kings River Experimental 

Watersheds. This area has been set aside 

especially to investigate watershed ecology in 

the Sierra National Forest in California (see 

figure 7). Four of the catchments were at high 

elevations in the mountains, and four were 

located at lower elevations (table 1).

The scientists collected water samples from 

the streams at each of the streams’ outlets 

within each catchment (figures 11 and 12). 

Watershed Name

Elevation 

Range 

(in m)

Size 

Range 

(in km2)

Percentage of 

Precipitation 

as Snowfall

Percentage of 

Precipitation 

as Rainfall

Average 

Annual Air 

Temperature 

(in °C)

Providence (four 

catchments)

1,479–2,113 0.49–1.32 20 80 7.8

Bull (four catchments) 2,055–2,490 0.55–2.28 75–90 10–25 6.8

Table 1. Characteristics of the catchments studied by the scientists.
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Figure 11. Dr. Hunsaker holds an instrument that 

measures water acidity, water temperature, and 

the amount of dissolved substances in a stream 

within the Kings River Experimental Watersheds.

A flume sits in the stream behind her. The flume 

creates a uniform streamflow so that scientists 

can measure the amount of water flowing in the 

stream. Solar-powered instruments automatically 

measure and record the amount of streamflow 

every 15 minutes. Photo courtesy of Dr. Carolyn 

Hunsaker.

How Do You Convert 

the Characteristics 

of the Catchments 

to the U.S. Imperial 

System?

meters (m) x 3.281 = feet

kilometers (km) x 0.6214 = miles

°Celsius (°C) x 9/5 + 32 = °Fahrenheit

centimeters (cm) x 0.3937 = inches

They collected these samples every other week 

from the fall of 2003 until the fall of 2007. The 

scientists collected soil water samples using 

pumps at depths of 13 cm and 26 cm into the 

soil (figure 13). These samples were taken 

upslope from the streams and at various 

locations throughout each catchment. The 

scientists collected snowfall samples using 

plastic bottles with funnels (figure 14). They 

installed these plastic bottles before winter and 

collected the melted snow water every other 

week after snowfall (figure 15).

Figure 12. All streamwater flowed to one 

stream outlet in each catchment. Illustration 

by Stephanie Pfeiffer.

Figure 13. This scientist is preparing vacuum 

pumps that enable him to collect soil water. The 

tip shown in the inset is inserted into the soil to 

collect the water. Photo courtesy of Dr. Carolyn 

Hunsaker.
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Figure 14. This snowmelt sampler is used to 

collect snowmelt. These samplers are buried in 

the soil up to the base of the funnel. An air line 

and a sample line are connected to the funnel.

When it snows and the snow melts, the water 

sample is pumped out by hand. Photo courtesy 

of Dr. Carolyn Hunsaker.

The scientists collected 2,239 streamflow, 

snowmelt, soil water, spring water, and 

groundwater samples (table 2). The scientists 

analyzed all the samples to determine which 

chemical compounds, and how much of each 

chemical compound, each sample contained.

The scientists used math to analyze the 

chemical characteristics of the water. This 

analysis enabled them to compare the water 

samples collected away from the streams 

with the streamflow samples collected at each 

catchment’s outlet. This procedure enabled the 

scientists to compare the chemical content of 

the water samples and to identify how much 

snowmelt and rainwater contributed to each 

stream.

Type of Water Sample

Number of 

Water Samples 

Collected

Streamflow (collected at the 

outlets)

1,342

Snowmelt 83

Soil Water 803

Spring Water 1

Groundwater (collected 

from drinking water wells)

10

Total Samples Collected 2,239

Table 2. The scientists collected five different 

types of water samples.

Figure 15. This scientist is pumping the 

snowmelt out of the sampler. Photo courtesy 

of Dr. Carolyn Hunsaker.

Number Crunches

b	 Howmany times did the scientists collect

water samples fromthe catchment outlets?

b	 On average, howmany streamflowsamples

did the scientists collect each time fromthe

catchment outlets?
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Natural Inquirer • Number 18

Reflection Section

b Whydidthescientistssamplecatchmentsat

twodifferentelevations?

b Lookatfigure14andrereaditscaption.Why

doyouthinkanairlinewasconnectedtothe

sampler?

Watershed Percent of Streamflow Coming 

From Underground Water

1 63

2 61

3 69

4 66

5 42

6 65

7 60

8 66

Table 3. The percentage of streamflow coming 

from underground water in each of the eight 

small catchments.

Findings

The scientists found that during the study 

period, over 60 percent of the streamflow came 

from water flowing underground (table 3). 

Snowmelt and rainwater moved rapidly through 

the soil to streams following a snowfall or 

rainfall. This rapid movement of groundwater to 

streams was likely due to the shallowness of the 

bedrock in this region of the Sierra Nevada.

Soil water above the water table (interflow) 

did not contribute much water to the 

streamflow. This finding was consistent with 

other studies that have found that soil water 

within 1 meter of the soil surface is taken up by 

trees and used for transpiration (tran(t) spə rā

shən) (figure 16).

The scientists found that the proportion 

of groundwater contributing to streamflow 

compared with surface flow was about the 

same for snowmelt water and rainwater.

Figure 16. Transpiration involves the flow of water into tree roots, 

up tree trunks, into branches, and out through pores in tree leaves.

Illustrations by Stephanie Pfeiffer and Nickola Dudley (inset).
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Number Crunches

b	 Whatwas the average percentage of

groundwater contributing to streamflowin

the eight catchments?

b	 In table 3,find thewatershedswith the

greatest and least percentage of streamflow

coming fromundergroundwater.Whatis

the percentage difference between these

two amounts of streamflow?

Reflection Section

b Whatforceisatworkintheunderground

movementofwater?Explainhowthisforce

affectsundergroundwatermovement.

b Readthelastsentenceinthe“Findings”

section.Basedonthisfinding,whatdoyou

thinkwastheanswertothescientists’second

researchquestion?(Hint:Seetheendofthe

“Introduction”section,page 110.)

Discussion

The scientists guessed that the shallow 

bedrock in this region contains large depressions. 

These depressions are like dimples in the bedrock. 

The depressions hold groundwater. Following a 

rainfall or snowfall, water percolates downward 

and the depressions fill up and spill over. Water 

then runs along the bedrock underground and 

into streambeds.

The total amount of streamflow coming 

from groundwater originating from snow and 

rain was about the same. The scientists expect, 

therefore, that a lower percentage of snowfall 

and a greater percentage of rainfall in the 

future will not affect streamflow in the higher 

elevation catchments.

Reflection Section

b Explainwhythescientistsexpectthata

lowerpercentageofsnowfallandahigher

percentageofrainfallinthefuturewillnot

affecttheflowofgroundwaterintostreams.

b Inachangingclimate,someareasmight

receivelessprecipitation.Imaginethatthe

scientistshadalsoconsideredthetrendinthe

totalamountofprecipitationfallinginthearea

overtime.Howmighttheirfindingschange

iftheydiscoveredatrendtowardlesstotal

precipitationovertime?

Glossary

artesian (är tē zhən): Involving, relating to, or 

supplied by the upward movement of water that is 

under pressure in rocks beneath Earth’s surface.

bedrock (bed räk): The solid rock that lies 

under the surface of the ground.

catchment (kach mənt): A small, steep 

watershed.

contaminant (kən ta mə nənt): Something that 

makes a place or a substance no longer suitable 

for use.

flume (flüm): A sloping channel for directing the 

flow of water.

groundwater (grau̇ nd wä tər): Water that sinks 

into the soil and moves or is stored underground.
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Natural Inquirer • Number 18

intact (in takt): Not broken or damaged.

land cover (land kə vər): Whatever is covering the 

land, such as trees, grasses, buildings, or roads.

laterally (la tə rəl lē): Side to side.

localized (lō kə līz(d)): Within a limited area.

precipitation (pri si pə tā shən): Rain, hail, snow, 

mist, or sleet that falls on Earth.

reservoir (re zə vwär): Place where water is 

collected and stored for use.

runoff (rən ȯf): The portion of rain or snow that 

flows over land and into streams.

snowmelt (snō melt): Water from melting snow 

that flows over the surface of the ground into 

streams and rivers.

snowpack (snō pak): A seasonal accumulation 

of slow-melting packed snow.

streamflow (strēm flō): The speed and volume 

of water flowing in a stream channel.

turbidity (tər bə də tē): A measure of the 

cloudiness or muddiness of a water body.

upslope (əp slōp): Being or moving to or toward 

the top of a slope.

watershed (wä tər shed): The area that drains 

to a common waterway, such as a stream, lake, 

estuary, wetland, aquifer, or even the ocean.

Accented syllables are in bold. Marks and 

definitions are from http://www.merriamwebster.com. Definitions are limited to the word’s 

meaning in the article.

The definition of watershed is taken directly 

from the U.S. Environmental Protection Agency 

(http://www.epa.gov).

How does this scene relate to the article you just read?
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FACTivity

Time Needed

• One class period for research (or 

assigned as homework)

• One class period for the FACTivity

Materials (for each student or 

group of students)

• Water cycle cube (see template on 

page 120)

• Plain or lined paper

• Pencils

• Scissors

• Tape or glue

Introduction

In this article, you learned about 

groundwater and the path water may take 

as it flows underground. Water may take 

a number of different paths, depending 

on the soil type, the type of underground 

rock, and the slope of the land. Water flow 

is also dependent upon the climate and 

recent weather. A drought, for example, 

may cause water to flow in a different 

pattern underground from its normal path.

Soil water may be taken up by trees and 

transpired.

In this FACTivity, you will use the 

knowledge you have gained from the 

reading “Under Where?” and other articles 

in this journal, as well as other sources of 

information about groundwater flow. You 

will answer the following question: What is 

one pathway a water droplet may follow as 

it moves through the water cycle?

Methods

Your teacher will have you work in 

pairs. To answer the question, you will 

need to refer to the following water cycle 

illustrations:

• Figure 1 on page 108, 

• Figure 2 on page 108,

• Figure 3 on page 109,

• Figure 4 on page 109, and

• Figure 6 on page 6 of the “Welcome 

to the Natural Inquirer Freshwater 

edition.” 

Take a moment now to review these 

illustrations. You should have a good idea 

of how water flows in the water cycle, 

including surface water as well as soil water 

and deep groundwater. If you need more 

information, read “Green Means Clean,” 

“What’s the Nonpoint?,” “Sediment-al 

Journey,” and “Welcome to the Natural 

Inquirer Freshwater edition” section in this 

Natural Inquirer. You may also do research 

in the media center. Your teacher may assign 

this reading and research for homework.

Next, you will build a water cycle cube 

using the template on page 120. Each 

side of this cube contains a portion of the 

illustration on page 119 (figure 17). Each 

pair of students should build one cube.

Locate the drop of water shown on each 

side of the cube. Alternatively, all student 

pairs in the class may take turns using one 

cube.

Adapted from Liu, F.; Hunsaker, C.; Bales, R.C. 2012. Controls of streamflow generation in small catchments across 

the snow—rain transition in the Southern Sierra Nevada, California. Hydrological Process, published online in Wiley 

Online Library, DOI: 10-1002/hyp.9304, http://www.fs.fed.us/psw/publications/hunsaker/psw_2012_hunsaker002_

lui.pdf.
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Figure 17. Water drops appear in many places throughout the water cycle. Illustration by Stephanie 

Pfeiffer.

Each student pair will roll the cube. (All 

student pairs may take turns rolling the same 

cube.) Each pair will work with whatever 

portion of the illustration lands on top. Identify 

the location of the water drop.

The water drop will be located in one of 

the following:

• In soil water

• In groundwater

• In an aquifer

• In a river

• In a lake or reservoir

• On the soil surface

Using a blank piece of paper, you will 

outline a story that traces the water drop’s 

journey. Each story begins with the water 

drop falling from the atmosphere. Trace the 

water drop’s journey to the location shown 

on the cube, and then eventually back to the 

atmosphere. Each of the six water drops’ 

journeys might be different. Remember that 

water is also collected and used by humans, 

and is used by other animals as a part of the 

water cycle. See figure 6 on page 6 of this 

journal.

You may tell your water drop’s story in song, 

rap, narrative, poetry, travel blog, a letter, or 

other form. Be creative and accurate about 

the journey your water drop will take.
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Natural Inquirer • Number 18

Alternate FACTivity

Time Needed • 10 minutes

• 1 day to wait

• 10 minutes for discussion

Materials • Potted houseplant with a hole in the 

bottom

• Saucer

• Small plastic bag, such as a lunch 

bag with a zip top.

• Water

• Paper

• Pencil

The purpose of this FACTivity is to 

demonstrate how houseplants use water 

and to compare this process with an 

outdoor plant’s use of soil water.

Methods

1. Place the plastic bag on one or 

more of the plant’s leaves and zip 

the bag as snug as possible without 

hurting the plant.

2. Water the plant thoroughly until 

some water flows into the saucer.

3. Empty the saucer.

4. Place the plant in a sunny window.

5. Wait 24 hours.

6. Observe the plastic bag. You may 

carefully remove the bag, being 

careful not to spill its contents.

7. Write down what you observed 

about the plastic bag.

Compare the potted plant with a plant 

outside. Think about what you learned in 

this article about underground water.

8. What does the saucer water 

represent?

9. What does the water inside the pot 

represent?

10. What do the bag’s contents show 

you about the plant?

11. Does this FACTivity support this 

article’s findings about soil water? 

Why or why not?

How does this scene relate to the water cycle?
122

Freshwater Edition, http://www.naturalinquirer.org

Natural Inquirer

Connections

You may want to reference these Natural Inquirer articles for additional information 

and FACTivities:

• For more on chemistry and energy flow, 

read “Don’t Litter the Stream” in the Hawai`iPacific Islands edition of Natural Inquirer.

• For more on chemistry in freshwater, read 

“Sediment-al Journey” on page 58 and 

“Caribbean Cruise” on page 41 in this 

Natural Inquirer edition.

• For more information on surface water, 

see “Green Means Clean” on page 7 in 

this Natural Inquirer edition.

These articles, along with others, can be found 

at http://www.naturalinquirer.org/all-issues.html.

Web Resources

U.S. Geological Survey: Groundwater

http://water.usgs.gov/edu/earthgw.html

U.S. Geological Survey: Infiltration

http://water.usgs.gov/edu/watercycleinfiltration.html

Kings River Experimental Watersheds

http://www.fs.fed.us/psw/topics/water/kingsriver/

U.S. Geological Survey: Aquifers

http://water.usgs.gov/edu/earthgwaquifer.html

U.S. Geological Survey: Water Basics

http://water.usgs.gov/edu/mwater.html

U.S. Geological Survey: Rivers Contain 

Groundwater

http://water.usgs.gov/edu/rivers-containgroundwater.html

U.S. Geological Survey Groundwater Map

http://www.usgs.gov/blogs/features/usgs_top_story/

the-quality-of-the-nations-groundwater/

If you are a trained Project Learning Tree educator, you may use “Rain Reasons” 

and “Water Wonders” as additional resources.
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Natural Inquirer • Number 18
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Freshwater Edition, http://www.naturalinquirer.org

Freshwater eyeChallenge

Explain what each of these photos represents. You may write your 

explanation or hold a class discussion. If you write your explanation, 

use complete sentences, proper spelling and grammar, and 

appropriate punctuation.
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Natural Inquirer • Number 18
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Freshwater Crossword

Across

2. To set or adjust the amount, degree, or rate of

something.

4. Of, relating to, or obtained from living things.

6. A measure of the cloudiness or muddiness of a water

body.

10. Something that makes a place or a substance no

longer suitable for use.

11. Flat land area next to a stream or river.

12. The area that drains to a common waterway, such as

Down

1. Speed of movement.

3. Water that sinks into the soil and is stored in aquifers.

5. An ordering of something according to a value.

7. A stream that flows into a larger stream or river or into

a lake.

8. (1) Water that has been used; (2) Sewage.

9. To carry away.

13. Liquid that is released as waste.

Untitled

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Across

2. To set or adjust the amount, degree, or rate of 

something.

4. Of, relating to, or obtained from living things.

6. A measure of the cloudiness or muddiness of a water 

body.

10. Something that makes a place or a substance no 

longer suitable for use.

11. Flat land area next to a stream or river.

12. The area that drains to a common waterway, such as 

a stream, lake, estuary, wetland, aquifer, or even the 

ocean.

14. The portion of rain or snow that flows over land and 

into streams.

Down

1. Speed of movement.

3. Water that sinks into the soil and is 

stored in aquifers.

5. An ordering of something according to 

a value.

7. A stream that flows into a larger stream or 

river or into a lake.

8. (1) Water that has been used; (2) Sewage.

9. To carry away.

13. Liquid that is released as waste.
127

Natural Inquirer • Number 18

National Education Standards 

A generic Common Core State Standards alignment, as well as alignment to the Next 

Generation Standards for these Natural Inquirer articles can be found on the “Education 

Standards” page under “Educational Resources” at the Natural Inquirer Web site, http://

www.naturalinquirer.org.

Green Means CleanWhat’s the Nonpoint?Caribbean CruiseSediment-al JourneyMussel ManiaTimed TravelUnder Where?

Science as Inquiry

 Abilities Necessary To Do Scientific Inquiry

 Understandings About Scientific Inquiry

Physical Science

 Properties and Changes of Properties in Matter

 Motions and Forces

 Transfer of Energy

Life Science

 Regulation and Behavior

 Populations and Ecosystems

 Diversity and Adaptations of Organisms

 Structure and Function in Living Systems

Earth Science

 Structure of Earth System

Science in Personal and Social Perspectives

 Risks and Benefits

 Science and Technology in Society

 Abilities of Technological Design

 Understandings about Science and Technology

 Personal Health

 Populations, Resources, and Environments

History and Nature of Science

 Science as a Human Endeavor

 Nature of Science

 History of Science

Which National Science 

Education Standards Can 

These Articles Address?
128

Freshwater Edition, http://www.naturalinquirer.org

Green Means CleanWhat’s the Nonpoint?Caribbean CruiseSediment-al JourneyMussel ManiaTimed TravelUnder Where?

 Culture and Cultural Diversity

 Time, Continuity, and Change

 People, Places, and Environments

 Power, Authority, and Governance

 Science, Technology, and Society

 Global Connections

 Individuals, Groups, and Institutions

 Civic Ideals and Practices

 Production, Distribution, and Consumption

 Individual Development, and Identity

Which National 

Curriculum Standards 

for Social Studies Can 

These Articles Address?

In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, 

offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, 

national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, 

income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity 

conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.

Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign 

Language, etc.) should contact the responsible Agency or USDA’s TARGET Center at (202) 720-2600 (voice and TTY) or contact USDA through the 

Federal Relay Service at (800) 877-8339.

To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at http://www.

ascr.usda.gov/complaint_filing_cust.html and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information 

requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to USDA by: (1) mail: U.S.

Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence Avenue, SW, Washington, D.C. 20250-9410; (2) fax: 

(202) 690-7442; or (3) email: program.intake@usda.gov.

USDA is an equal opportunity provider, employer, and lender.
What Is the Forest 

Service?

The Forest Service is part of 

the United States Department 

of Agriculture (USDA). The 

Forest Service is made up of 

thousands of people who care 

for the Nation’s forest land. The Forest 

Service manages 154 national forests and 

20 national grasslands. These are large areas 

of trees, streams, and grasslands. National 

forests are similar in some ways to national 

parks. Both are public lands, meaning they 

are owned by the public and managed for 

the public’s use and benefit. Both national 

forests and national parks provide clean 

water, homes for the animals that live in the 

wild, and places for people to do fun things 

in the outdoors. National forests also provide 

resources for people to use, such as trees 

for lumber, minerals, and plants used for 

medicines. Some people in the Forest Service 

are scientists whose work is presented in the 

journal. Forest Service scientists work to solve 

problems and provide new information about 

natural resources so that we can make sure 

our natural environment is healthy, now and 

into the future.

http://www.fs.fed.us.

What Is the Cradle of 

Forestry in America 

Interpretive 

Association?

The Cradle of Forestry 

in America Interpretive 

Association is a 501(c)(3) nonprofit 

organization based in Pisgah Forest, North 

Carolina. The interpretive association 

strives to help people better understand 

ecology through recreation and education 

opportunities. Their projects include the 

following:

• Campground and recreation area 

management

• Educational programs and services, 

including Natural Inquirer, Investi-gator, 

Natural Inquirer Reader Series, NSI: 

Nature Science Investigator, scientist 

cards, and Leaf Prints (formerly NatureOriented Parenting)

• Sales of forest-related gifts and 

educational materials

• Workshops, newsletters, and publications

• Partnership with the Forest Service to 

provide programming at the Cradle of 

Forestry Historic Site

http://www.cfaia.org

What Is FreshWaterLIVE?

The “FreshWaterLIVE: A Distance Learning Adventure” (http://www.

freshwaterlive.org) brings the mysteries of freshwater to classrooms 

grades 4 to 8 through FREE webcasts, webinars, and online resources 

about the origins, travels, and perils of water from green forests and 

grasslands to household faucets. Check out previous LIVE programs at 

http://www.FSNatureLIVE.org and register your class to participate in 

the 2015–2016 FreshWaterLIVE adventure.
United States 

Department 

of Agriculture

Forest Service

FS-1066

Fall 2015

Editorial Review Board—Bemidji Middle School, Minnesota: 

Ms. Henry’s 7th Grade Life Science Classes

Web Site Resources

Natural Inquirer

http://www.naturalinquirer.org

Forest Service Conservation Education

http://www.fs.usda.gov/conservationeducation

FreshWaterLIVE

http://www.freshwaterlive.org 

Follow us on Twitter (@naturalinquirer) and Facebook 

(http://www.facebook.com/NaturalInquirer)!