Teaching the Nitrogen Cycle and Human Health Interactions
Margaret Townsend
Kansas Geological Survey, University of Kansas, 1930 Constant Avenue,
Lawrence, KS 66047, [email protected]
Audrey C. Rule
Department of Curriculum and Instruction, 250-G Wilber Hall, State University of
New York at Oswego, Oswego, NY 13126, [email protected]
Mary Ann Meyer
Thomas M. Cooley High School, Detroit Public Schools, Detroit, Michigan,
[email protected]
C. Jolene Dockstader
Jerome School District, Jerome, Idaho, [email protected]
atmosphere is made of nitrogen gas. However, because
of the chemical structure of nitrogen - a strong triple
An overview of components of the nitrogen cycle with covalent bond between the N atoms in N2 gas, the
Internet resources for students to explore is presented to molecule is relatively inactive (Equation. 1).
discuss the ways this important cycle affects life.
N≡N
(1)
Beneficial uses include fertilizers, explosives, aerosol
propellants and food packaging, and anesthetics;
For plants and animals to be able to use nitrogen, N2
problems associated with nitrogen include NOx
emissions, water pollution, and potential health effects. gas must be converted to a more chemically available
A learning cycle lesson on the nitrogen cycle is provided, form such as ammonium (NH4+), nitrate (NO3-), or
along with pretest-posttest data (N-cycle drawings and organic nitrogen (e.g. urea - (NH2)2CO). These forms are
responses to a 25-question test) from rural sixth grade available only with the assistance of microbial action or
students and urban high school students who inorganic forms manufactured by humans. This means
participated in the activities. Both groups were that biologically available nitrogen is often in short
enthusiastic about the lessons and showed significant supply, limiting plant growth and biomass accumulation
improvement, although final scores of the sixth graders (Illinois State Water Survey, 2004; Harrison, 2003).
The different forms of nitrogen enable it to be used
were low. Results of an additional experimental
group-control group pretest-posttest study with for a variety of purposes such as fertilizer, explosives,
undergraduate preservice elementary teachers indicated propellants, preservatives, and as an anesthetic. The
that students learned more when using the hands-on form of nitrogen often determines how it is used and
nitrogen cycle cards with objects and by writing related what possible ecologic and human health impacts may
poetry (experimental condition) than by creating a occur.
nitrogen cycle diagram online through Internet searches
for information and writing summary essays of cycle Beneficial Uses of Nitrogen - The beneficial uses of
interactions. The high school and college students were nitrogen include nitrogen fertilizers, explosives, aerosol
highly motivated by the lessons and showed larger gains propellants and food packaging, and anesthesia.
than sixth graders, indicating that the lessons are most Fertilizers, such as anhydrous ammonia manufactured
by the Haber-Bosch process, aid farmers in the
appropriate for older students.
production of crops for animal and human consumption
and plants such as flax and cotton for fabric production
(USGS, 1999; Zmaczynski, 1985; Eckert, 2004; Deacon,
INTRODUCTION
2004; Barbarick, 2003; Keleher, 1996). Legumes, bat
This article describes research-supported teaching guano, and animal waste are additional sources of
materials for the nitrogen cycle, an important system nitrogen to the soil system. Legumes permit scavenging
affecting environment, life, and human health. During of excess nitrogen in the soil or production of nitrogen
May 2004, the National Association of Geoscience from air using rhizomes in the root systems. Explosives
Teachers hosted a workshop on "Geology and Human aid in the mining industry and construction and
Health" to address the need to include more instruction demolition industry and are also used in the
in geoscience classes on this important topic. The first manufacture of fireworks and armaments (Pafko, 2000;
two authors of this paper attended the workshop and Organ Cave, 2000; USNPS, 2000). Aerosol propellants
began development of these materials at that time. In this and food packaging are among the most useful products
article, we first describe the nitrogen cycle including its in terms of delivery of products such as whipping cream
geoscience connections and importance to human health; and protection of food products from bacteria and
secondly, we present the set of teaching materials with a disease by use of nitrite as a preservation and by
classroom-tested lesson plan, and finally, we describe the freezing. Use of nitrous oxide as an anesthesia
(Heitmiller, 2006) is one of the most useful discoveries for
findings of studies validating these materials.
the dental industry (Cameron and May, 2004). More
detailed summary of the beneficial and non-beneficial
THE NITROGEN CYCLE
uses of nitrogen are provided by the web sites and
The nitrogen cycle is one of several major articles cited previously and on the website
biogeochemical cycles (e.g., the water cycle, the carbon http://serc.carleton.edu/NAGTWorkshops/health/int
cycle) that exist in the world. The nitrogen cycle affects ernet.html.
many aspects of life. Nitrogen is one of the basic elements
necessary for life to exist. Approximately 78% of the
ABSTRACT
158
Journal of Geoscience Education, v. 55, n. 2, March, 2007, p. 158-168
Potential Non-Beneficial Effects of Nitrogen Use Although nitrogen has many beneficial uses as discussed
previously, the use of nitrogen and the presence of
nitrogen byproducts from industrial processes,
agriculture, and population sources can result in
contamination of air and water sources as well as cause
health issues. Some of the issues are (1) nitrogen oxide
(NO x) emissions from cars and industrial processes can
cause increased deposition of nitrogen on land and
water, interfere with the production of ozone in the
atmosphere (Uhereck, 2004), or contribute to respiratory
ailments, heart disease and several cancers (Townsend et
al., 2003) and (2) nitrate contamination of surface and
ground water where overabundance of nitrogen in the
environment can result in hypoxia such as is observed in
the Gulf of Mexico, Oregon, the Black Sea, and the Baltic
Sea (USGS, 2004; ESA, 2004; Vitousek et al., 1997a, b;
Science Museum of Minnesota, 2004), algal blooms
(Spokes, 2003), excess weed growth, and leaching of
nitrate to ground water, as well as health effects to
humans and animals such as methemoglobinemia or
possible cancers (U.S. EPA, 2001).
Potential Health Effects - Use of nitrogen can have
beneficial and non-beneficial effects as discussed above.
An article by Townsend et al. (2003) discusses the global
impacts of excessive use of nitrogen products,
population growth, and health effects. Vitousek et al.
(1997a, b) along with Harrison and Pearce (2001) also
discuss sources of nitrogen, impacts on ecosystems, and
human use of resources. An article by Anonymous (2003)
in Science and Children stresses the impact of overuse
and overexposure to high concentrations of nitrogen on
both human health and on the ecosystem.
High nitrate in surface and ground water can impact
human and animal health. Infants who drink water or
formula mixed with high nitrate water can develop
methemoglobinemia otherwise known as blue baby
syndrome (ATSDR, 2004; McCasland et al., 1998). Young
livestock also will develop health problems if they drink
water with nitrate-nitrogen (NO3-N) higher than 100
ppm (Self and Waskom, 1998; Robson, 2003). Ingestion of
high nitrate foliage can also poison young animals
(Allison, 1998).
High-nitrate water may be responsible for some
cancers such as bladder cancer. A long-term study in
Iowa indicates that more cases of bladder cancer
occurred in areas in Iowa with long-term exposure to
drinking water with nitrate  N greater than 2.5 ppm
(Lynch, 2001; Waternet.com, 2001).
In Scotland, research indicates the possibility that
high nitrate fertilizer use with vegetables can be related
to observed increases in gullet cancer. Research in this
area is still ongoing. Areas with lower sunlight exposure
and where vegetables are grown in greenhouses may be
more at risk (BBC News, 2002).
Medical studies suggest that a diet high in animal
sources of nitrite may result in cancer. Dietary nitrite
comes from nitrite used to preserve meats or it may form
in the body from high nitrite or nitrate sources in
drinking water or tobacco products. The evidence for the
relationship between nitrate/nitrite/nitrosamines and
cancer is still being researched and is not definite at this
time (Scanlan, 2003). A number of references are given in
the web references on studies dealing with nitrogen
compounds and cancer issues (Kendall, 1997; ACS, 2006,
McCasland et al., 1998).
Townsend et al. - Teaching the Nitrogen Cycle
LESSON MATERIALS
A survey of literature on teaching the nitrogen cycle
indicates that most materials are geared towards upper
high school and college level programs and not towards
younger students. The work by Savanick and Perry
(2006) showed a good methodology for using a college
campus nitrogen budget to teach about the nitrogen
cycle but the process is much too involved for upper
elementary, junior high, or high school students. Work
by Ambler et al. (2001) examined the oxic and hypoxic
role of soils and sediments on the nitrogen cycle and
emphasized the role of denitrification. Schipper et al.
(1996) presented a set of experiments to help junior high
and high school students understand the nitrogen cycle
but no controlled study was conducted to determine if
the experimental approach improved learning. Raun et
al. (1997) awarded a Nitrogen cycle Ninja card to college
students for use as a reference on future quizzes as a
reward for correctly drawing the nitrogen cycle.
Responses by the students indicated that receiving a
tangible reward and working together in groups to help
everyone achieve the reward was an added bonus to the
class and reinforced learning of the nitrogen cycle. An
article by Hollenbeck et al. (2006) discussed using
concept maps as a substitute for essay writing on the
water, carbon, and nitrogen cycles. Statistical evaluation
of the results showed that the essay writing and concept
maps each emphasized different aspects of learning and
should be used together rather than trying to substitute
one for the other.
The Learning Cycle - Lord (1999) showed that college
students learning about the nitrogen cycle in an
environmental science course performed significantly
better on exams, rated the course higher, and
volunteered for more local environmental support
efforts when taught using a constructivist lesson format
incorporating the Learning Cycle teaching model than
students taught using a more traditional lecture style.
The set of teaching materials we present here coordinates
with a lesson in the Learning Cycle format of three
phases: exploration, explanation, and expansion (Atkin
and Karplus, 1962; Karplus and Lawson, 1974). This
lesson format is a widely used teaching model based on
Constructivist Learning Theory, which has its
foundation in the work of Jean Piaget (1896-1980). Piaget
believed that learning was not the result of passively
listening to a teacher, but arose from interacting with
objects to construct knowledge. This action provides
knowledge of those objects (Sigel and Cocking, 1977).
The Constructivist learning approach is currently
accepted as best teaching practice by national science
teaching organizations such as the American Association
for the Advancement of Science (1993) and the National
Research Council (1996).
Exploration Phase - During this phase of the Learning
Cycle, the teacher focuses student attention on the topic,
finds out what students already know, and activates
students' prior knowledge. The teacher begins by
showing a diagram of a familiar cycle, such as the water
cycle, to students and tells students that many earth
materials undergo cycles (another common example is
the rock cycle). The teacher explains that the topic of the
current lesson is the nitrogen cycle. What do students
know about nitrogen or any part of the nitrogen cycle?
Where can nitrogen be found (sources)? What are its
159
Figure 1. Possible cyclic arrangement of cards from the nitrogen cycle curriculum materials (Rule and
Townsend, 2006).
uses? What are its effects on humans, animals, plants,
and the environment?
This phase of the Learning Cycle fits with
Constructivist Learning Theory in the following way.
When students consider a cycle diagram for nitrogen,
they may be thrown into a state of disequilibrium, a state
in which the current situation does not match the
student's previous view of reality (called organization of
the mind). Perhaps students had never thought there
could be other cycles than the one or ones with which
they are familiar. Perhaps they have very little
knowledge of nitrogen. This state of disequilibrium is a
necessary component in acquiring new knowledge. If the
learner is comfortable with his or her current knowledge
state, then there is no need to learn - no need to change the
current organization of the mind - no need to construct
new knowledge. As the learner questions his or her
current understandings of nitrogen, he/she prepares for
new information that will be available during the next
phase.
The teacher writes students' ideas on the board as
they are suggested, forming a web of ideas. As this
occurs, the teacher is able to diagnose what students do
and do not know about the topic, thereby enabling the
teacher to alter the lesson to fit students' needs. If
misconceptions or lack of necessary background
information (possibly chemistry) become apparent, the
teacher can modify the lesson to make sure these are
adequately addressed during the next phase.
160
Alternatively, students may indicate a deep
understanding of the nitrogen cycle and the lesson may
be shortened.
Looking for possible similarities between the water
cycle and the nitrogen cycle may activate prior
knowledge and help students make connections
between old and new ideas. Both cycles involve the same
parts of the earth system of atmosphere, biosphere,
hydrosphere and lithosphere. Do students know the
names of any substances that have the root "nitri" "nitra"
or "nitro" in them? What do students know of the
element nitrogen? What is its atomic number (7) and
charge (-3)? What compounds does it form? (Sodium
nitrate NaNO 3; potassium nitrate KNO3; nitric acid
HNO3; ammonia NH 3; nitrate NO3; and oxides NO, NO 2,
N2O4, N2O).
Explanation Phase - During this phase, students
participate in activities that lead them to discover new
information and understandings. The teacher guides
students back to equilibrium (a state in which the
student's view of reality matches the information with
which he/she is presented) through explanations and
examples.
Activity 1. Students conduct an Internet search to find
information about different parts of the nitrogen cycle.
Suggested web sites were presented in the previous
sections and are listed in the references. Students may
Journal of Geoscience Education, v. 55, n. 2, March, 2007, p. 158-168
Bathroom “Sink” Limerick
By Audrey Rule
Green Fiend Limerick
By Margaret Townsend
Our town has a nitrogen sink,
Where septic tanks leak all their stink.
Now nitrates do dwell,
In our drinking well,
And baby looks bluish not pink.
Blue Baby Syndrome Limerick
By Sixth Grade Student
The pond in the park is all green,
With algae from fert’lizing extremes.
The ducks cannot land,
Kids can’t play in the sand,
‘Cause nitrogen now taints the scene.
Bat Guano Limerick
By Sixth Grade Student
Poor blue baby bathed in the sink,
Has nitrogen sickness - that stinks!
Some people survive it,
But others can’t thrive with it,
From finding a cure, please don’t shrink.
Bats eat and then make brown poo,
You’ll see quano is a good goo!
It can fertilize,
Don’t you now realize?
So use it as lawn or plant food.
Lightning Double Haiku
By Becky Reese
Dead Lake Limerick
By Barbara Banta
There once was a famer named Bill,
Who grazed his cows on a hill.
Dung run-off washed below,
Causing algal blooms to grow,
There’s no fish in that lake today still.
Blue Babe Double Haiku
By Stephanie Cilento
Baby cries for milk.
Mother mixes formula,
Nitrate-filled water.
Mother does not know,
She should have water tested.
Too late for blue babe.
Plants always growing.
Lightning is healthy for plants.
Storms create nitrates.
Nitrates help plants grow.
Without plants we all would die.
Now bring on the storms!
Sterile Food Packaging Diamante
By Melissa Schallmo
Nitrogen.
Sealed, air-tight,
Preventing, preserving, long-lasting,
Lets no oxygen in.
Breaking, opening, exposing,
Delicious, fresh,
Food.
Table 1. Example and sample student poems about the nitrogen cycle.
work on this in pairs or small groups. Alternatively, if
students do not have easy access to the Internet, the
teacher may print out pages of information from the
various websites and provide them for students to use.
Each group prepares a diagram for the overhead
projector, a poster, an electronic slide, or a list of three to
five facts to share their new knowledge with the class.
Activity 2. Students work in small groups to assemble a
diagram of the nitrogen cycle using the twenty card sets
(a set consists of a title card, a description card, a
photograph card and corresponding object, such as a dog
near a doghouse to represent "pet waste") available from
Rule and Townsend (2006). There is a large diagram title
card ("The Nitrogen Cycle") that is placed at the top of the
workspace. Six smaller heading cards ("Atmosphere,"
"Water," "Soils and Rocks," "Plants," "Animals," and
"Humans") are placed to form a circular arrangement.
Each smaller title card (e.g. "Blue Baby Syndrome") has
an accompanying picture card and description card.
Place the three cards together in the diagram near the
heading cards they best match. Use the arrow cards to
show possible pathways of nitrogen movement. A
possible arrangement of picture cards and titles
(accompanying objects and description cards have been
excluded from this figure) is shown in Figure 1. Note that
the cycle activity can be simplified for less proficient
learners by limiting the sets of cards used.
Ask each group of students to describe and explain a
nitrogen path using the nitrogen cycle card arrangement.
Discuss ways to avoid paths that lead to pollution or
Townsend et al. - Teaching the Nitrogen Cycle
negative health effects. The teacher provides closure by
highlighting the most important concepts about the
nitrogen cycle and reviewing any information with
which students struggled.
Expansion Phase - In this final phase of the learning
cycle, students practice their new learning to confirm the
new organization of their minds. They apply the learning
to a new situation to increase their general knowledge
and to enhance future transfer of the knowledge to new
problems. The teacher has three tasks during this phase:
1) helping students practice correctly, 2) providing the
opportunity for independent practice, and 3) evaluating
student learning.
Many different activities could be used to reinforce
students' learning about the nitrogen cycle. An excellent
example suggested by scientists at Ohio State University
(CMS, 2003) involves students in determining the
optimal amount of fertilizer for a small patch of grass
planted in a tray. This experiment provides the
opportunity for students to see the impact of fertilizer on
plants and sample water for runoff of nitrates. Other
experiments might involve students in testing local
stream or pond water for nitrates as prescribed for
students who participate in the GLOBE Program (2005).
In the protocol for this experiment, students use a test kit
to sample water and change nitrates in the water to
nitrites, detecting their presence through a color change
reaction with cadmium. Another nitrogen cycle practice
161
Number of Correct Items
Shown on Nitrogen Cycle*
Sex
N
Pretest
Posttest
Female
10
0.1 (0.3)
3.5 (2.2)
Male
13
0.0 (0.0)
3.8 (2.8)
Both
23
0.0 (0.2)
3.7 (2.5)
Statistically
Significant
Change from
Pretest to
Posttest?
Yes, F = 22.9,
df = 1/19,
p < 0.001
Yes, F = 93.8,
df = 1/61,
p < 0.001
Yes, F = 24.0,
df = 1/23,
p < 0.001
Percent Correct on
Assessment*
Pretest
Posttest
1.6 (2.8)
17.2 (6.0)
4.0 (6.5)
18.5 (12.1)
3.0 (5.3)
17.9 (9.7)
Statistically
Significant
Change from
Pretest to
Posttest?
Yes, F = 55.9,
df = 1/19,
p < 0.001
Yes, F = 26.4,
df = 1/61,
p < 0.001
Yes F = 28.0,
df = 1/23,
p < 0.001
Table 2. Pretest and posttest scores for sixth-grade students.
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Students took pretest.
Introduction to atoms and molecules. Class discussion.
Ionic/covalent bonding introduced. Laser disk presentation on bonding. Nitrogen compund bonds discussed
along with oxygen and hydrogen bonds.
Chart made with class - What do your know about the nitrogen cycle and what do you want to learn? Students
worked in small groups of three (tasks: reader, recorder, reporter) to read an Internet article about the nitrogen
cycle. They wrote three facts/ ideas on the white board learned from the article and presented them to the rest
of the class.
Students worked in groups of three to match title card, picture card, and description cards. To accomplish this,
students took turns reading the description, finding the corresponding picture, and finding the title card.
Students quickly reassembled the sets of cards. An example completely matched set was available on a front
table for students to check their work. Then students were given the twenty objects to match to the card sets.
Students read the section in their text (Johnson and Raven, 1998) that addressed the nitrogen cycle. They
defined terms and drew pictures of the nitrogen cycle in their notebooks by using a diagram in the text. The
teacher then read example limericks and explained the rhyming scheme. Students wrote nitrogen cycle
limericks for homework.
Students used all the cards and objects to create their own nitrogen cycles. In one class of very low-achieving
students, the teacher helped groups do this step by step. Students placed arrows to show the path of nitrogen
through a complete cycle. Students copied the cycles they had made into their notebooks.
Students took the posttest.
Table 3. Schedule of nitrogen cycle-related activities for the urban high school biology students.
activity with connections to literacy is described in the
next section.
EVALUATION STUDIES
Writing Nitrogen Cycle-Related Poetry - Students can
demonstrate their new knowledge and reinforce their
learning by composing poems that relay facts about the
nitrogen cycle's impact on the environment and human
health. Creative writing in earth science class as in the
Lusk et al. study (2006) of preservice teachers authoring
geoscience picture books and other studies on
poetry-writing (Bogina and Roberts, 2005; Kane and
Rule, 2004; Rule et al., 2004) has been shown to support
positive attitudes toward science learning along with
conceptual understanding of science content. We first
asked students to create limericks (see first two example
poems in Table 1) because this poetry form emphasizes
humor, which has been shown to have positive effects on
student
attitude,
attention,
engagement,
and
involvement in higher levels of thinking (Rule and Auge,
2005; Ulloth, 2002). However, the more complex rhyming
and rhythm scheme of limericks proved difficult for
some students, so we expanded the poetry forms to
double haikus and structured diamante poems. Example
poems and student-generated poems are shown in Table
1.
162
The nitrogen cycle curriculum materials described in this
article were used with three different grade levels of
students in different education settings: a class of sixth
grade students in rural southern Idaho, five classes of
urban high school students in Michigan, and four classes
of preservice elementary teachers in a science methods
class in New York State. All students drew a nitrogen
cycle and answered twenty-five questions (available
online from Rule and Townsend, 2006), most of which
were open-ended, about the nitrogen cycle as both
pretest and posttest assessments.
Rural Sixth Grade Students during Science Class One class of sixth grade students from southern Idaho
(10F, 13M) participated in the nitrogen cycle lessons
presented as described earlier in this article. Pretest and
posttest scores for drawing a nitrogen cycle and
answering the twenty-five questions are shown in Table
2. Female and male scores are shown separately and then
combined at the bottom of the table. In general, both
sexes scored similarly. While these scores show that
students' knowledge increased significantly, the scores
Journal of Geoscience Education, v. 55, n. 2, March, 2007, p. 158-168
Number of
Comments
Category and Examples of Student Comments
The lessons were fun: It was a fun assignment; We had a great time; I really enjoyed myself; the materials
were fun; I liked learning about the nitrogen cycle; I liked everything.
The objects helped learning: Understanding the objects and how well they showed what they represented; I
enjoyed that we used objects to help us learn; we actually had objects to act out the cycle; I liked that we used
example objects to help us.
Understanding was enhanced by the materials: Everything I needed was there to help me understand the
nitrogen cycle;Tthe materials made me understand more; I liked the way you designed the cards and objects
to help us learn; I could use the materials to figure out where each one goes in the cycle.
Matching cards with cards and objects was a good activity: We got to match the cards with pictures to learn;
I liked the way we had to match the titles and cards; I enjoyed the matching the most.
Learned about the nitrogen cycle: Now I know what the nitrogen cycle is; I learned stuff I did not know
before; I believe I know more about the nitrogen cycle now; Not only was I investigating, but I was learning
something about the nitrogen cycle and so I liked it.
Recognized the importance of nitrogen: Making the cycle showed us how everything connects with
nitrogen; The nitrogen cycle has a lot of organisms and parts; I learned that a lot of stuff has to do with
bacteria; The nitrogen cycle is very important to our way of life; A very interesting cycle because it tells how
nitrogen is transferred from one thing to another.
Assembling the cycle with cards was an effective way to learn: I enjoyed putting the cards and materials
where they were supposed to be in the cycle; I liked laying out the materials so I could see the cycle and how
it works.
The visuals helped learning: We used the visual aids to help us learn; Using the pictures on the cards helped
us set up everything; I liked the pictures.
The lessons were exciting and interesting: Laying out the cycle was the exciting part; It was very exciting to
learn about and interesting; The nitrogen cycle is one of the best lessons I ever did; It was very cool and
interesting,
Specific facts learned: I learned that nitrogen is part of gun ammunition; Certain foods contain nitrates; I
found out that N2 has a powerful triple bond that is hard to break; I never knew bat guano could be of so
much use; I didn't know a baby could get sick from drinking nitrates in water.
Perspectives were new: We got new materials and got to try something new; The materials let us look at it in
a different way; We were learning in many different ways.
Group work and cooperation: The class worked together to help each other; I enjoyed doing the group work;
we worked as groups; cooperating with classmates; we went over it together.
The cards helped me learn: The cards with notes on them helped; The explanations that went with the
pictures helped; The cards helped us with the nitrogen cycle.
Hands-on aspect: The fact that we used hands-on materials made it interesting and understandable; That we
had something to hold and arrange; Hands-on materials are best and easier and quicker instead of just
reading all the time - I really thought it was great.
Would like to continue to learn more: I would like to do it again; It was really great and I would love to do
more; I think we should do more on the nitrogen cycle.
Quality of the materials: The materials were nice and well-made; I liked the way the cards were all
laminated and rounded; I liked that some of the pieces were hand-made.
Creativity: The materials were very colorful and creative; Some of the objects were very creative; I like that
we got to arrange the cycle in different ways.
Total Positive Comments
31
25
23
20
14
14
14
13
13
12
12
10
10
9
6
6
6
238
Table 4. What students liked most about lessons on the nitrogen cycle.
are disappointing in that they are so low. There are two
main reasons for this. First, the lessons were conducted
on the last few days of school when students are
excitedly focused on the summer vacation time rather
than schoolwork. Secondly, the nitrogen cycle concepts,
especially the chemical reactions involved, are probably
too complex for sixth-grade students. However, the
teacher reported that students did enjoy the lessons,
particularly using the cards and objects to lay out a cycle,
and seemed to grasp the main ideas of the nitrogen cycle,
although the open-ended questions on the posttest
required students at this grade level to produce too many
facts. Several of the sixth graders, however, were able to
produce some effective limericks (See Table 1).
Townsend et al. - Teaching the Nitrogen Cycle
Urban High School Students in a Biology Class - Five
classes of ninth- and tenth-grade African American
students taught by the same teacher at an urban high
school in Detroit, Michigan, participated in the study.
The teacher used the general nitrogen cycle lesson plan
described in the previous section of this paper with some
modifications for the student population being taught
and for the short fifty-minute class periods. The schedule
of activities is shown in Table 3.
Because the class did not have easy access to the
Internet, the teacher prepared two- or three-page
printouts from Internet sites and gave each group a
different one. As described in Table 3, students worked
together to read the article and write three
nitrogen-related facts from it. Most of the students had
163
Category and Examples of Student Comments
Nothing: I did not least enjoy nothing- like I said I enjoyed it all; Nothing, I know it was just right; I did not
dislike anything.
Matching was difficult: It was kind of hard putting the pictures in the right places; When we couldn't find the
cards that matched; Matching pictures to words was hard; Figuring out the meanings of the pictures was hard.
Too much work and thinking: I didn't like the fact that we had to think to make the nitrogen cycle; I didn't like to
have to put the cards with the pictures because it required thinking; It was too much work; Getting up and going
to school on days we didn't feel like it.
Too complex: There were so many cards; Too many cards- mind boggling to a certain degree; There were a lot of
things and it was hard keeping track of them.
Class periods were too short so had to repeat parts to keep continuity: Because we laid it out and had to then
put it all back in the bag; When you just get into it, it is time to put it away and leave; We put the cycle together
over and over; I hated that we did it 5 times; It was a long experiment.
Word and picture cards were small: The words were very tiny; Make the pictures bigger.
Reading was difficult: Hard to figure out the meaning of some of the words; Reading the cards was difficult;
Some cards were too hard and had too much to read.
Did not enjoy writing and drawing: It was hard to draw a nitrogen cycle; I didn't like writing down the
information; I didn't like writing the cycle in our notebooks.
Peers did not help in group work: When some students weren't helping us do the project; People were talking a
lot and not helping; I didn't like working in a group everyday.
Miscellaneous: Too cold in classroom; did not like the plastic covering on cards; Didn't enjoy learning about
atomic bonding; No milk as an object but cows.
Total Negative Comments (first category excluded)
N
15
13
12
11
10
6
6
5
5
4
72
Table 5. What students liked least about the nitrogen cycle lessons.
some difficulty with reading new vocabulary and
technical information - the teacher carefully chose the
materials and helped them interpret the text. Instead of
presenting students with the cards and objects all at once,
she broke the activity into several shorter lessons because
she thought the large amount of new information would
overwhelm students.
At the conclusion of the nitrogen cycle lessons,
students were asked to tell three things they enjoyed
most about the lessons and three things they enjoyed
least about their study of this topic. They were also asked
to write any additional comments. The responses to the
first question are tabulated in Table 4, along with
positive comments written in response to the third
question. Responses to the second question and negative
comments from the third question are tabulated in Table
5. Overall, students made more than three times as many
positive comments as negative comments. Many
students chose to respond only to the first question.
As can be seen in Table 4, students made numerous
comments about their enjoyment of the lessons and the
effectiveness of the materials. This corresponds well with
the teacher's account of how students reacted to the
lessons. She reported that students really enjoyed the
hands-on nature of the materials and marveled at the
quality of the heavy plastic coating on the colored cards
and the hand-made objects. Several students remarked
that the teacher must really like them to provide such
nice materials. The teacher observed that students were
very careful with the materials and were more
cooperative than usual.
Students enjoyed speculating on how objects had
been made and what they represented. They were
particularly interested in the baby representing blue
baby syndrome (had it been made with a Tootsie Pop
sucker for the head? No, a wooden bead covered with
paper was used), the bat (they had not heard of bat guano
previously), the outhouse (they did not know what an
outhouse was), and the dynamite (was it real?). As
164
shown in the recorded comments in Table 4, many
students benefited from the matching activity of finding
the title, picture, description, and object that supported
each component of the nitrogen cycle. The teacher
observed the students heavily engrossed in the matching
activity. Students enjoyed the puzzle-like nature of
finding the three cards that formed a set and the
corresponding object. Although the reading skills of
many students were poor, other group members read
and interpreted cards so that each group functioned
cooperatively. Table 4 shows that students recognized
the importance of learning about the nitrogen cycle and
several stated that they would like to learn more. An
additional observation for this activity was that it
worked very well for the many students in the classes
who had special learning needs and who qualified for
special education services. These students, who often
were left at the sidelines of other activities, were able to
participate fully.
Table 5 tabulates responses to what students liked
least about the lessons and other comments for
improvement. As reflected in the numerous positive
comments, many students did not have suggestions for
improvement or dislike of any part of the lessons. Their
next three responses (matching was difficult, too much
work and thinking, and too complex) show that much of
the information was overwhelming for these students.
However, the teacher reported that there were some
higher achieving students who were able to understand
the concepts well. Overall, the teacher thought that the
students did learn many new concepts and that the
motivational aspects of the lesson particularly made this
a valuable lesson in improving student interest in
science. She has continued to use these materials in
teaching about the nitrogen cycle in subsequent classes.
Student attendance (absences are a significant problem at
this school) during the hands-on parts of the lesson was
very high.
Journal of Geoscience Education, v. 55, n. 2, March, 2007, p. 158-168
Number of Correct Items
Shown on Nitrogen Cycle*
Sex
N
Pretest
Posttest
Female
39
0.3 (1.0)
7.9 (3.9)
Male
31
0.2 (0.8)
7.3 (4.0)
Both
70
0.2 (0.9)
7.6 (3.9)
Statistically
Significant
Change from
Pretest to
Posstest?
Yes, F = 141.6,
df = 1/77,
p < 0.001
Yes, F = 93.8,
df = 1/61,
p < 0.001
Yes, F = 236.6,
df = 1/139,
p < 0.001
Percent Correct on
Assessment*
Pretest
Posttest
23.5 (13.5)
38.6 (14.4)
27.0 (12.8)
41.8 (9.8)
25.0 (13.3)
40.0 (12.7)
Statistically
Significant
Change from
Pretest to
Posttest?
Yes, F = 22.8,
df = 1/77,
p < 0.001
Yes, F = 26.4,
df = 1/61,
p < 0.001
Yes, F = 47.2,
df = 1/139,
p < 0.001
Table 6. Pretest/posttest scores for 70 urban high school students. * Standard deviations given in
parentheses. N = number of students.
Mean Pretest Scores*
Exper.
Group
Control
Group
Significant
Difference
Between
Groups?
Mean Posttest Scores*
% Correct
Responses
to 25
Question
Test
%. Correct
Responses
to 25
Question
Test
Components
Placed on N
Cycle Sketch
Interactions
Shown on N
Cycle Sketch
Total Items
Noted on N
Cycle Sketch
11.1 (7.0)
13.0 (4.1)
5.8 (5.0)
18.9 (8.1)
53.3 (15.9)
0.2 (0.6)
11.4 (8.1)
8.1 (4.0)
1.4 (2.3)
9.5 (4.7)
37.3 (12.8)
No,
F = 3.96,
df = 1/79,
p = 0.36
No
F = 3.96,
df = 1/78,
p = 0.89
Yes,
F = 3.97,
df = 1/72
p < 0.001
Yes,
F = 3.97,
df = 1/72,
p < 0.001
Yes,
F = 3.97,
df = 1/72,
p < 0.001
Yes,
F = 3.97,
df = 1/71,
p < 0.001
Components
Placed on N
Cycle Sketch
Interactions
Shown on N
Cycle Sketch
Total Items
Noted on N
Cycle Sketch
0.3 (0.7)
0.0 (0.1)
0.4 (0.8)
0.2 (0.5)
0.0 (0.2)
No,
F = 3.96
df = 1/79
p = 0.27
No,
F = 3.96,
df = 1/79,
p = 0.80
Table 7. Pretest/posttest scores for preservice teachers. * Standard deviations given in parentheses
Table 6 shows pretest and posttest scores of those
high school students who took both pretest and posttest
(N=70). Students both drew a nitrogen cycle diagram
and completed a twenty-five question assessment. The
teacher modified the given open-ended assessment by
providing a randomized list of twenty-three possible
correct responses for the twenty-three short-answer
questions, thereby making it a matching test. Both
females and males scored similarly and displayed a
statistically significant change in scores from pretest to
posttest on the number of correct items drawn on a
nitrogen cycle diagram and the percent of assessment
questions answered correctly.
Although the posttest scores on the twenty-five
assessment questions were encouraging in that they
were significantly higher than the pretest scores, they
were also disappointingly low. This finding is most
likely an effect of the low socio-economic status and poor
academic backgrounds of the students at this inner-city
school serving students of poverty. The pretest-posttest
instrument, although modified into a matching test, still
asked students to recall too many details and new terms.
The nitrogen cycle drawings, shown on the left side of
Table 6, give a better view of what students learned.
Before the lesson, students had no knowledge of the
nitrogen cycle, whereas after the lesson, they were able to
place seven or eight items on their nitrogen cycle
drawings. This performance is twice as many concepts as
placed by the sixth-grade students.
Townsend et al. - Teaching the Nitrogen Cycle
Preservice Teachers - Four classes of preservice
elementary teachers from a mid-sized college in central
New York State participated in a pretest-posttest
control/ experimental group study with the nitrogen
cycle materials. Two classes comprised the experimental
group (N=47; 41F, 6M; 42White, 2Black, 2Hispanic,
1Asaian) with the two remaining classes forming the
control group (N=33; 29 F, 4 M; 28White, 4Hispanic,
1Asian). Both groups made nitrogen cycle drawings and
answered the written test questions six weeks before the
lessons were taught and completed identical exercises
for the posttest two weeks after lessons had concluded.
The posttest was unannounced; students did not spend
time in addition to the lessons in preparing for it.
Lessons for each of the two groups lasted three
hours. Pretest results (Table 7) showed that most
students had no knowledge of the nitrogen cycle. As an
exploratory activity in both the experimental and control
groups, students worked as partners to read printouts of
Internet websites that described various components of
the nitrogen cycle, then presented three interesting facts
from their reading to the class. Components from the
brief presentations were added to a nitrogen cycle sketch
on the board. During the explanation phase,
experimental group students worked in small groups
with the nitrogen cycle cards and objects to create a
nitrogen cycle. The instructor checked their work and
students each made a sketch of the layout of cards and
objects for their notes. As an expansion phase activity,
experimental group members composed three types of
poems: double haikus, limericks, and diamante165
structured poems that expressed information about a
nitrogen cycle component's effect on human health or the
environment and shared these with classmates.
The control group completed the explanation phase
using computers. Groups of two or three students were
given an electronic file of a diagram showing only the
titles of twenty components of the nitrogen cycle
arranged under the headings atmosphere, water,
soil/rocks, animals, plants, and humans. Preservice
teachers conducted Internet searches to retrieve an
image for each component to paste onto the diagram and
to find out more information concerning this
component's role in the cycle. They drew fifteen arrows
between the components and wrote a phrase about the
interaction on each arrow. The instructor met with each
group after the diagrams had been completed and
corrected any errors on the diagrams; students each
printed a copy of the diagram for their notes. As an
expansion phase activity, students wrote two-part
essays. In the first part of this assignment, students
described the direct and indirect effects of various
components of the nitrogen cycle on human health and
the environment; in the second part, they described
decisions and actions people can take related to the
nitrogen cycle to safeguard human health and the
environment.
Students
under
both
conditions
were
enthusiastically engaged with the work. In contrast to
Lord's study (1999), both conditions used a constructivist
approach so that the efficacy of the new materials could
be evaluated against another sound method of teaching.
Students using the cards and objects took delight in
examining the objects and discussing the possible
components each represented. In the control condition,
students enjoyed conducting Internet searches to locate
information and images. They stayed on task and took
pride in producing interesting, well-organized diagrams
that were factually correct.
Table 7 presents pretest and posttest data for both
the nitrogen cycle drawings and the twentyfive-question tests. An analysis of variance indicates that
there were no significant differences between groups on
the pretests, but significant differences favoring the
experimental group occurred on the posttests.
Experimental group preservice teachers drew almost
twice as many components on their nitrogen cycle
diagrams as control group students, and answered, on
average, more than half of the test questions correctly as
compared to the 37.3 % correctly answered by the control
group. The low scores on the twenty-five question test
are a result of three factors: first, students did not have
the opportunity to study or review for the unannounced
test because we wanted to measure the effect of the
lessons alone on knowledge of the nitrogen cycle;
second, the test was given two weeks after lessons had
concluded to measure longer term retention of concepts;
and third, the format of most questions was open-ended,
requiring students to produce information rather than to
merely recognize a correct response. Considering these
factors and the large number of components and
interactions placed on nitrogen cycle diagrams,
preservice teacher learning of nitrogen cycle concepts
during the experimental condition of using the new
materials presented in this paper was quite good.
We attribute higher student performance using these
materials to the following factors: the title-imageexplanation-object matching activity that focused
student attention and helped students remain on task;
166
the concise explanations on the cards that helped
students understand interactions between components;
the opportunity to arrange and rearrange components,
giving students ownership of their cycle configuration
and allowing students to easily consider other
interactions; attention-grabbing objects (baby doll with
pale blue features, outhouse, hotdogs on a grill, cow in
pasture, dog near doghouse) that allowed students to
recall various components of the cycle; and the
humorous poetry writing activity that motivated
students through laughter and sharing of ideas and
challenged them to apply their new learning. As in a
recent study of students learning about landforms
through different conditions (Rule, Graham, Kowalski,
& Harris, 2006), social learning and challenge as students
tried to figure out how to arrange and match complex
materials in the condition using cards and objects
contributed to higher learning outcomes.
CONCLUSION
The lesson materials we have provided here were of high
interest to students at all levels (upper elementary, high
school, college) and helped them gain knowledge of the
nitrogen cycle. The study conducted with sixth-grade
students indicates that nitrogen cycle concepts are
probably too complex for typical students at this grade
level. Students at an urban high school were able to recall
and correctly link more elements of the nitrogen cycle
and scored higher on the posttest than the sixth-grade
students. Students' and teacher's comments about the
lessons show that they found the activities interesting,
motivating and valuable. Data from the controlled
experiment with preservice teachers indicate that the
nitrogen cycle cards and objects lesson with
reinforcement through poetry-writing was more
effective than a lesson in which students constructed a
diagram by researching information on the Internet and
practiced their new knowledge by writing a
summarizing essay. Therefore, we recommend these
curriculum materials for students in high school and
above.
ACKNOWLEDGEMENTS
We thank the following groups who kindly gave
permission to use photographs from their websites in
our materials: Texas Cooperative Extension photo by
Robert Burns, ComTec Computer Sales, Cresco - Resco
Restaurant Equipment and Restaurant Supply, United
States Department of Agriculture (USDA), the
University of Georgia Cooperative Extension Service, the
Arkansas Soil and Water Conservation Commission
(ASWCC), Alberta Environment, and StonCor Africa. In
addition we acknowledge Marla Adkins-Heljeson,
editor, and Mark Schoneweis, graphic artist, at the
Kansas Geological Survey who assisted with this project.
REFERENCES
Alberta Government, 2003, Environment, Algal Blooms good resource on causes of algal blooms, 2003,
http://www3.gov.ab.ca/env/water/swq/brochur
es/algalblooms.html (1 Dec. 2006).
Allison, C. D., 1998, Nitrate poisoning of livestock, Guide
B-807Allison,
http://www.cahe.nmsu.edu/pubs
/_b/b-807.html (1 Dec. 2006).
Journal of Geoscience Education, v. 55, n. 2, March, 2007, p. 158-168
Agency for Toxic Substances and Disease Registry
(ATSDR), 2004, Information on nitrate in water and
methemoglobinemia - Center for Disease Control
site:
http://www.atsdr.cdc.gov/HEC/CSEM/
nitrate/clinical_evaluation.html (1 Dec. 2006).
Ambler, J., Pelovitz, K., Ladd, T., and Steucek, G., 2001, A
demonstration of nitrogen dynamics in oxic and
hypoxic soils and sediments, The American Biology
Teacher, v. 63, p. 199-206.
American Association for the Advancement of Science
(AAAS), 1993, Benchmarks for science literacy,
Oxford University Press, New York, 418 p.
American Cancer Society (ACS), 2006, Secondhand
smoke,
http://www.cancer.org/docroot/PED/
content/PED_10_2X_Secondhand_Smoke-Clean_In
door_Air.asp (1 Dec. 2006).
Atkin, J. M., and Karplus, R., 1962, Discovery or
invention?, The Science Teacher, v. 29, p. 45-51.
Anonymous, 2003, Fertilizer and human health, Science
and Children, v. 41, p. 10-12.
Barbarick, K. A., 2003, Nitrogen sources and
transformations, Colorado State Extension Service
Circular no. 0.550, http://www.ext.colostate.edu/
pubs/crops/00550.html (1 Dec. 2006).
Bogina, M. A., and Roberts, B. R., 2005, The use of haiku
and portfolio entry to teach the change of seasons,
Journal of Geoscience Education, v. 53, p. 559-562.
British Broadcasting Company (BBC) News, 2002,
Cancer concern over vegetable nitrates (plants
grown in greenhouses), Scotland, http://news.
bbc.co.uk/2/hi/uk_news/scotland/1824156.stm
(1 Dec. 2006).
Cameron, E., and May, P., 2004, Molecule of the month,
nitrous oxide - laughing gas, School of Chemistry,
University of Bristol, http://www.chm.bris.ac.uk
/motm/n2o/n2oc.htm (1 Dec. 2006)
Curriculum Materials Service (CMS), 2003, OHIO
AgScience Lesson Plans, Unit 3. Environmental
Science, Lesson 3.04 Investigating factors affecting
nitrate in groundwater, Activity 3, Ohio State
University, http://www-cms.ag.ohio-state.edu/Ag
SciLPs.html#Unit3 (1 Dec. 2006).
Deacon, J., 2004, The microbial world: the nitrogen cycle
and nitrogen fixation, http://helios.bto.ed.ac.uk/
bto/microbes/nitrogen.htm (1 Dec. 2006).
Eckert, D., 2004, Efficient fertilizer use, nitrogen,
http://www.agcentral.com/imcdemo/05Nitrogen
/05-07.htm (1 Dec. 2006).
Ecological Society of America (ESA), 2004, Hypoxia fact
sheet, http://www.esa.org/education/edupdfs/
hypoxia.pdf (1 Dec. 2006).
GLOBE, 2005, Nitrate protocol, http://www.
globe.gov/tctg/hydro_prot_nitrate.pdf?sectionId=
156 (1 Dec. 2006).
Harrison, J. A., 2003, The nitrogen cycle: of microbes and
men, Visionlearning, EAS-2, no. 4, http://www.
visionlearning.com/library/module_viewer.php?
mid=98. (1 Dec. 2006).
Harrison, P. and Pearce, F., 2001, The AAAS atlas of
population and environment: American Association
for the Advancement of Science, http://
atlas.aaas.org/index.php?part=1 (1 Dec. 2006).
Heitmiller, E., 2006, How anesthesia works,
http://health.howstuffworks.com/anesthesia.htm
/printable (1 Dec. 2006).
Hollenbeck, K., Twyman, T., and Tindal, G., 2006,
Determining the exchangeability of concept map and
Townsend et al. - Teaching the Nitrogen Cycle
problem-solving essay scores, Assessment for
Effective Intervention, v. 31, p. 51-68.
Illinois State Water Survey, 2004, Nitrogen cycle
information, properties of nitrogen, http://www.
sws.uiuc.edu/nitro/biogeo.asp (1 Dec. 2006).
Johnson, G. B., and Raven, P. H., 1998, Biology principles
and exploration, Holt, Rhinehart Winston.
Kane, S., and Rule, A. C., 2004, Poetry connections can
enhance content area learning, Journal of Adolescent
and Adult Literacy, v. 47, p. 2-14.
Karplus, R., and Lawson, C. A., 1974, Science Curriculum
Improvement Study (SCIS) Teachers' Handbook,
University of California, Berkeley, California, 179 p.;
U. S. Government Educational Resources
Information Center (ERIC) Document No. ED 098
041.
Keleher, S. 1996, Guano: Bats' Gift to Gardeners, Bats, v.
14, p. 15-17, http://www.batcon.org/batsmag
/v14n1-7.html (1 Dec. 2006).
Kendall, P., 1997, Diet can reduce risk of cancer,
http://www.ext.colostate.edu/pubs/columnnn/n
n970430.html (1 Dec. 2006).
Lord, T., 1999, A comparison between traditional and
constructivist teaching in environmental science,
Journal of Environmental Education, v. 30, p. 22-27.
Lusk, M. G., Bickmore, B. R., Christiansen, E. H., and
Sudweeks, R. R., 2006, Use of a mentored creative
writing project to improve the geology education of
preservice elementary teachers, Journal of
Geoscience Education, v. 54, p. 31-40.
Lynch, C., 2001, Iowa women's health study links cancer
risk with nitrate levels in drinking water, National
Institute of Environmental Health, http://www.
niehs.nih.gov/dert/profiles/hilites/2001/nitrate.ht
m (1 Dec. 2006).
McCasland, M., Trautmann, N. M., Porter, K. S., and
Wagenet, R. J., 1998, Nitrate: health effects in
drinking water, Natural Resources Cornell
Cooperative Extension, http://pmep.cce.cornell.
edu/facts-slides-self/facts/nit-heef-grw85.html (1
Dec. 2006).
National Research Council, 1996, National Science
Education Standards: Observe, interact, change,
learn, National Academy Press, Washington, D.C.
262 p., http://newton.nap.edu/catalog/4962.html
(1 Dec. 2006).
Organ Cave, 2000, Civil War history and gunpowder,
http://www.organcave.com/CWHistory.htm
(1
Dec. 2006).
Pafko, W., 2000, Nitrogen: food or flames,
http://www.pafko.com/history/h_s_n2.html
(1
Dec. 2006).
Raun, W. R., Johnson, G. V., Hattey, J. A., Taylor, S. L.,
and Lees, H. L., 1997, Nitrogen cycle Ninja, a
teaching exercise, Journal of Natural Resources and
Life Sciences Education, v. 26, p. 39-42.
Robson, S., 2003, Nitrate and nitrite poisoning in
livestock, New South Wales Department of
Industries,
Agriculture,
Agfact
A0.9.67,
http://www.agric.nsw.gov.au/reader/an-health/a
0967.htm (1 Dec. 2006).
Rule, A. C., and Auge, J., 2005, Using humorous cartoons
to teach mineral and rock concepts in sixth grade
science class, Journal of Geoscience Education, v. 53,
p. 548-558.
Rule, A. C., Carnicelli, L., and Kane, S. S., 2004, Using
poetry to teach about minerals in Earth science class,
Journal of Geoscience Education, v. 52, p. 10-14.
167
Rule, A. C., Graham, L. E., Kowalski S., and Harris, M.,
2006, Learning landform vocabulary through
different methods: Object boxes, sand and dough
creations, or puppet plays, Journal of Geoscience
Education, v. 54, p. 515-525.
Rule, A. C., and Townsend, M., 2006, Nitrogen cycle
curriculum materials, geology and human health
topical resources, http://serc.carleton.edu/NAGT
Workshops/health/teaching.html (Materials will be
posted soon).
Savanick, S., and Perry, J., 2006, Using the campus
nitrogen budget to teach about the nitrogen cycle,
Journal of Geoscience Education, v. 54, p. 312-319.
Scanlan, R. A., 2003, Nitrosamines and cancer, The Linus
Pauling Institute, http://lpi.oregonstate.edu/f-w00
/nitrosamine.html (1 Dec. 2006).
Schipper, A., Schipper, L., and Horsby, A., 1996, The
nitrogen cycle, The Science Teacher, v. 63, p. 34-37.
Science Museum of Minnesota, 2004, Hypoxia for Kids,
http://www.smm.org/deadzone/ (1 Dec. 2006).
Self, J. R., and Waskom, R. M., 1998, Nitrates in drinking
water, Colorado State University Cooperative
Extension
00517,
http://www.ext.colostate.
edu/pubs/crops/00517.html (1 Dec. 2006).
Sigel, I., and Cocking, R., 1977, Cognitive development
from childhood to adolescence: A constructivist
perspective, Holt, Rinehart, and Winston, New York,
256 p.
Spokes, L., 2003, The oceans basics, unit 2-nutrients in the
ocean, ESPERE Encyclopedia, http://www.
atmosphere.mpg.de/enid/2a5b6a7b2ed6f3ac7bb6b
5ed88d6f3a8,55a304092d09/oa.html (1 Dec. 2006).
Townsend, A. R., Howarth, R. W., Bazzaz, F. A., Booth,
M. S., Cleveland, C. C., Collinge, S. K., Dobson, A. P.,
Epstein, P. R., Holland, E. A., Keeney, D. R., Mallin,
M. A., Rogers, C. A., Wayne, P., and Wolfe, A. H.,
2003, Human health effects of a changing global
nitrogen cycle, Frontiers in Ecology and the
Environment, v. 1, p. 240-246, http://ibl.colorado.
edu/Townsendetal_Frontiers2003.pdf (1 Dec. 2006).
Uhereck, E., 2004, Lower atmospheric basics, nitrogen
oxides - formation and relevance: Environmental
Science Published for Everyone Round the Earth
(ESPERE), http://www.atmosphere.mpg.de/enid
/23b.html (1 Dec. 2006).
Ulloth, J., 2002, The benefits of humor in nursing
education, Journal of Nursing Education, v. 41, p.
476-481.
168
U. S. Environmental Protection Agency Office of Water,
2001, Source water protection practices bulletin
managing septic systems to prevent contamination
of drinking water, EPA 816-F-01-021, 5 p.,
http://www.epa.gov/safewater/sourcewater/pub
s/fs_swpp_septic.pdf (1 Dec. 2006).
USGS, 1999, The quality of our nation's waters: U.S.
Geological Survey Circular 1225, Nutrients and
Pesticides, http://water.usgs.gov/pubs/circ/circ
1225/ (1 Dec. 2006).
USGS, 2004, Hypoxia in the Gulf of Mexico and related
USGS activities, U. S. Geological Survey, http://
toxics.usgs.gov/hypoxia/ (1 Dec. 2006).
U.S. National Park Service (USNPS), 2000, Glimpses of
our national parks (War of 1812, saltpeter), U. S.
National Park Service, http://www.cr.nps.gov
/history/online_books/glimpses1/glimpses25.htm
(1 Dec. 2006).
Vitousek, P. M., Mooney, H. A., Lubchenco, J., and
Melillo, J. M., 1997a, Human domination of earth's
ecosystems: Science, v. 277, p. 494-499.
Vitousek, P. M., Aber, J., Howarth, R. W., Likens, G. E.,
Matson, P. A., Schindler, D. W., Schlesinger, W.H.,
and Tilman, G. D., 1997b, Human alteration of the
global nitrogen cycle: Causes and consequences,
Ecological Society of America, Issues in Ecology,
Issue 1, p. 1-17, http://www.epa.gov/OWOW
/watershed/wacademy/acad2000/pdf/issue1.pdf
(1 Dec. 2006).
Waternet.com, 2001, Iowa - increased risk of bladder
cancer related to nitrate, http://waternet.com/
news.asp?mode=4&N_ID=21690 (1 Dec. 2006).
Wisconsin Paper Council, 2004, Paper in Wisconsin,
http://www.wipapercouncil.org/ (1 Dec. 2006).
Zmaczynski, R., 1985, Haber-Bosh Process for fertilizer
manufacture,
http://www.princeton.edu/~hos/
mike/texts/readmach/zmaczynski.htm
(1 Dec.
2006).
Journal of Geoscience Education, v. 55, n. 2, March, 2007, p. 158-168