Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Ohio Standards
Connection:
Earth Sciences
Benchmark D
Describe the finite nature
of Earth’s resources and
those human activities that
can conserve or deplete
Earth’s resources.
Lesson Summary:
Students will learn about two related scenarios that
examine human impact on the nitrogen cycle. In the first
example, students examine farm fertilizer runoff and its
effect on a lake. In the second example, students will
examine the link between salmon, trees and bears as
nitrogen passes through the food web in the Pacific
Northwest stream-forest ecosystem.
Estimated Duration: Two hours
Indicator 6
Describe ways that human
activity can alter
biogeochemical cycles
(e.g., carbon and nitrogen
cycles) as well as food
webs and energy pyramids
(e.g., pest control, legume
rotation crops vs. chemical
fertilizers).
Commentary:
This lesson incorporates open-class discussion of questions
to stimulate discourse among students. As students discuss
the Pacific Northwest ecosystem and the effect of
agriculture on nitrogen cycling, they remodel and refine
their own schemas of food webs and biogeochemical cycles.
Internet resources are integrated into the lesson to help
students access scientifically reliable information about
human activities that affect the Earth's resources.
Pre-Assessment:
Distribute copies of Attachment A, Pre-Assessment / PostAssessment and instruct students to complete the questions.
You may choose to complete only some of the questions for
the Pre-Assessment if time is limited.
Scoring Guidelines:
See Attachment B, Pre-Assessment /Post-Assessment Key to
assess student work.
Post-Assessment:
Distribute copies of Attachment A, Pre-Assessment / PostAssessment and instruct students to complete the questions. It
is suggested that all questions are completed for the postassessment.
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Scoring Guidelines:
See Attachment B, Pre-Assessment /Post-Assessment Key to assess student work.
Instructional Procedures:
1. Review the following points of the nitrogen cycle.
 Nitrogen is found in the atmosphere as a chemically stable gas (N2). Seventy-eight
percent of the Earth’s atmosphere is nitrogen gas.
 Nitrogen is a major component of amino acids which make up proteins.
 Animals must get all their nitrogen from the food they eat. They cannot use
atmospheric nitrogen or N2.
 Plants must get their nitrogen from the soil. Plants cannot use atmospheric nitrogen
or N2 and must use nitrogen which is combined with oxygen (NO3 nitrate) or
hydrogen (NH4- ammonium). Various bacteria convert atmospheric nitrogen and
nitrogen from the bodies of plants and animals into forms which plants can use.
 Nitrogen is often a limiting factor in plants. (A limiting factor is any factor which if in
short supply limits the size of a population.)
 Excess nitrogen can lead to increased numbers of plants especially algae in aquatic
systems.
2. Give each student Attachment C, Farm Scenario and Attachment E, Salmon-Tree-Bear
Scenario and have them complete the questions on each. Attachment C contains two
scenarios of man’s influence on the nitrogen cycle. Attachment E examines the flow of
nitrogen in the ecosystem of the Pacific Northwest.
Instructional Tip:
This activity can be done individually, in small groups, or as a whole class activity.
3.
4
5.
6.
Reconvene the class as a whole and lead a large group discussion of the questions they
have answered using Attachments D, Farm Scenario Key and F, Salmon-Tree-Bear
Scenario Key to guide the class.
Have students individually summarize their understandings of human impact on the
nitrogen cycle from one scenario in an essay or graphic organizer. Ask students to focus
on the potential changes in the nitrogen cycle caused by human intervention, and how
these changes have effects that ripple through the ecosystem.
As a class, invite students to hypothesize ways to address the issues that they identified
in their essays or graphic organizers. Pose the question, “What could be done to preserve
the functioning of the food web and the ecosystem?”
Proceed to the post-assessment.
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Differentiated Instructional Support:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
 You may allow students working beyond the indicator to research a food web that is
found in Ohio. Ask these students to trace the nitrogen through this cycle, and compare
and contrast the Pacific Northwest cycle with the Ohio example they have studied.
 Hang posters of a generalized nitrogen cycle in the classroom that students can use as
reference when considering the problems in this lesson.
Extension:
 Have students investigate the impact of human activity on the carbon cycle.
Students can prepare a written report on their findings. If time permits, the findings can be
shared with the class. If time is short, select only a few to be reported to the class.
 Have students research and expand on the food web of the Pacific Northwest forest
ecosystem. This could include other organisms which prey on the salmon or insects
which feed on the trees.
 Have students research Ohio organisms to see if there is any published research on the
cycling on nitrogen or carbon in Ohio ecosystems.
Homework Options and Home Connections:
 Students could research local waste treatment facilities or farms, attempting to answer the
question “Where does the nitrogen go?” Library or Internet research could be done
examining the problem with nitrogen fertilizers or nitrogen flow through various
ecosystems or energy pyramids.
Key Vocabulary:
 Biogeochemical cycle
 Nitrogen
 Amino acid
 Nitrate
 Ammonium
 Isotopes
Technology Connections:
Have students access websites to locate information about the nitrogen cycle and its
movement through the ecosystem. Beginning resources are;
 http://www.epa.gov
 http://www.noaa.gov
 http://www.fs.fed.us
 http://www.epa.gov
 http://www.wdfw.wa.gov
 http://www.dnr.state.oh.us
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Research Connections:
Marzano, R., Pickering, D., Pollock, J. (2001).Classroom Instruction that Works: Researchbased Strategies for Increasing Student Achievement, Alexandria, Va.: Association for
Supervision and Curriculum Development.
Summarizing and note-taking are two of the most powerful skills to help students
identify and understand the most important aspects of what they are learning.
General Tips:
See the following citations for further information on human impacts on the nitrogen cycle
and on the roles of bear and salmon in the nitrogen cycle.
 Vitousek, Peter M. et al. 1997. Human Alteration of the Global Nitrogen Cycle: Causes
and Consequences. Issues in Ecology 1: 1-15.
 Reimchen, T. E. 2000. Some ecological and evolutionary aspects of bear - salmon
interactions in coastal British Columbia. Canadian Journal of Zoology, 78: 448-457
Attachments:
Attachment A, Pre-Assessment / Post-Assessment
Attachment B, Pre-Assessment / Post-Assessment Key
Attachment C, Farm Scenario
Attachment D, Farm Scenario Key
Attachment E, Salmon-Bear-Tree Scenario
Attachment F, Salmon-Bear-Tree Scenario Key
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Attachment A
Pre-Assessment / Post-Assessment
Answer the following questions on a separate sheet of paper or in your science journal.
1. Explain how an increase in nitrogen can have a negative effect on a lake ecosystem even
though nitrogen helps plants grow.
2. What human farming activity can alter the biogeochemical nitrogen cycle in a local
environment?
3. Explain and give an example of how man can alter the nitrogen cycle on a global scale.
4. Explain the link between the life cycle of Pacific salmon, bears and the tree species
growing along rivers and streams in the Pacific Northwest.
5. Describe man’s impact on the trees, bears, or salmon. What impact does this action have
on the populations of the other organisms?
6. Predict the long-term consequences to wildlife of the Pacific Northwest if man continues
to have the same impact on salmon and bears.
7. Trace the path of nitrogen from crustaceans living in the northern Pacific to trees growing
within several hundred meters of streams in Coastal Western Canada by using a diagram or
description.
8. Describe a way human activity can alter a biogeochemical cycle and how the altered cycle
impacts a food web or energy pyramid.
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Attachment B
Pre-Assessment / Post-Assessment Key
The following key provides idealized answers, but other answers from students may be
equally valid. When reviewing student responses, assess them for evidence of understanding
of the concepts of the nitrogen cycle, and how human intervention can disturb the nitrogen
cycle.
1.
Explain how an increase in nitrogen can have a negative effect on a lake ecosystem even
though nitrogen helps plants grow.
Plants, particularly aquatic algae, can grow so much that in the fall or winter when they
die and begin to decompose, the decomposing bacteria use up the oxygen. As a result,
fish and other aquatic organisms die.
2.
What human farming activity can alter the biogeochemical nitrogen cycle in a local
environment?
Adding too much fertilizer to a farm or adding it just before a rain can increase the
fertilizer in creeks, rivers, lakes and the ocean because of runoff. Another answer would
be raising cows, pigs or chickens in such numbers that the waste runs off into water
drainages.
3.
Explain and give an example of how man can alter the nitrogen cycle on a global scale.
Burning too much fossil fuel or using too much fertilizer can cause the amount of
nitrogen in the environment to increase. Many plants have evolved to live in nitrogenpoor environments. Those plants will die with high amounts of nitrogen and the animals
that are dependent upon those plants will also die. Too much algae in the ocean could
influence the temperature of the ocean or the oxygen content of the ocean or
atmosphere.
4.
Explain an interconnected link between the life cycle of Pacific salmon, bears and the
tree species growing along rivers and streams in the Pacific Northwest.
Salmon eat the small organisms in the ocean which contain nitrogen from the sea. The
salmon swim upstream taking the nitrogen with them. Bears eat the salmon, ingesting
the nitrogen from the ocean. Dead fish remains and bear feces decompose to fertilize the
trees. Nitrogen goes from the ocean to the trees through the fish and the bears.
5.
Describe man’s impact on trees, bears or salmon. What impact does this action have on
the populations of the other organisms?
Salmon: If the dams man has built cause the salmon to not be able to swim upstream
then the bears will not get the nitrogen they need from the fish and the trees will not get
the nitrogen from the fish or the bears.
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Bears: If the bears are eliminated only the trees near the waters edge will get the
nitrogen from the decomposing fish. Trees away from the water will not receive
nutrients from salmon transported in the digestive systems of bears.
Trees: If the trees are cut down the soil will erode into the water silting in the crevices
between rocks where salmon eggs are laid. Salmon eggs will not survive to hatch. The
lack of salmon will disrupt the nitrogen cycle.
6.
Predict the long-term consequences to the biodiversity of the Pacific Northwest if man
continues to have the same impact on salmon and bears.
If there are fewer nutrients such as nitrogen there will be fewer plants and fewer animals
living on them. Only those organisms which can survive on lower amounts of nitrogen
will survive.
7.
Trace nitrogen from crustaceans living in the northern pacific to trees growing within
several hundred meters of streams in Western Canada by using a diagram or description.
The crustaceans eat algae, which contain the nitrogen. The crustaceans gets eaten by a
larger fish or by the salmon directly. When the salmon migrate back upstream they
carry the nitrogen with them. If they die in the stream, they will nourish the trees along
the bank. A bear may also drag them a distance from the stream and deposit remains
near trees. Dead fish remains and bear feces will decompose to fertilize the trees.
crustacean fish- bear tree
8.
Describe a way that human activity can alter a biogeochemical cycle and how the altered
cycle impacts a food web or energy pyramid.
Answers may vary. Examples given could include, but not be limited to, man using too
much fertilizer or raising animals in concentrated areas resulting in too much animal
waste going into the environment. This action results in an increase of algae. When they
die, they use up the oxygen and kill animals that need that oxygen.
If man eliminates a level in a food web or energy pyramid then the flow of nitrogen
through the system will be slowed or stopped. Examples include removing bears, fish or
trees in areas where the three occur naturally. Removing any one will impact the others.
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Attachment C
Farm Scenario
Farmer A has a large farm on which he grows corn. Through his farm flows a small creek
which empties into a lake. This farmer sprays nitrogen fertilizer on his crops several times a
year. Due to the weather patterns where he lives it often rains within several days of the
application of the fertilizer. The lake near him has been a major recreation area with clear
water and good fishing. Recently, clear water has become brownish green with mats of algae
floating on the surface by late summer, resulting in fish kills. In the fall and winter there are
many dead fish floating on the surface of the lake and drifting to shore. Recreation at the
lake is coming to a halt because of the murky water and the dead fish.
Farmer B has a similar large farm in which he grows corn one year and soybeans the next.
Through his farm also flows a small creek, which empties into a similar lake. This farmer
does not spray any nitrogen fertilizer on his crops. He knows that soybeans have bacteria on
their roots which take the atmospheric oxygen and convert it into a form of nitrogen that the
plants can use. The rainfall is similar to Farmer A’s area. The lake near him is and remains a
major recreation area. The water is clear and there is good fishing. There is no algae floating
in the late summer and there are no fish kills.
Answer the following questions on a separate sheet of paper.
1. What is the most probable cause of the algae growing in the lake near farmer A’s farm?
2. Why would increased nitrogen cause the algae to grow?
3. What would cause the fish to die?
4. Why did the algae not increase in the lake near farmer B?
Extended Questions
1. If fossil fuels contain nitrogen what happens to the nitrogen oxide gas (NO) that is
produced when they are burned?
2.
As human populations increase, more food is needed. To meet the increasing demand
crops are grown using fertilizer to increase their yield. What happens to the excess
fertilizer?
3.
What would happen to the coastal marine fisheries when nitrogen fertilizer follows the
rivers to the ocean?
4.
Farmers raise cattle, hogs and chickens in large numbers. Their waste contains large
amounts of nitrogen. What takes place when that waste enters a water system such as a
creek, lake or river?
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Attachment D
Farm Scenario Key
The following key provides idealized answers, but other answers from students may be
equally valid. When reviewing student responses, assess them for evidence of understanding.
1.
What is the most probable cause of the algae growing in the lake near farmer A’s farm?
The fertilizer the farmer puts on his crops run into the creek and from there into the lake.
2.
Why would the increased nitrogen cause the algae to grow?
Fertilizers stimulate growth in plants so it affects corn and algae.
3.
What would cause the fish to die?
The amount of light that algae are exposed to in the fall is reduced which causes the
algae to die and decompose which decreases the amount of oxygen in the water resulting
in fish kills.
4.
Why did the algae not increase in the lake near farmer B?
The lake was not effected by excess fertilizer so it remained the same.
Extended Questions
1. If fossil fuels contain nitrogen what happens to the nitrogen oxide gas (NO) that is
produced when they are burned?
Nitrogen goes into the atmosphere and continues through the nitrogen cycle, eventually
returning to the Earth through rainfall.
2.
As human populations increase, more food is needed. To meet the increasing demand
crops are grown using fertilizer to increase their yield. What happens to the excess
fertilizer?
Fertilizer leeches into places where it is not desired such as streams, rivers, lakes,
oceans, and ground water.
3.
What would happen to the coastal marine fisheries when nitrogen fertilizer follows the
rivers to the ocean?
Algae growth may increase significantly. Animals that eat the algae may increase. This
fluctuation will alter the ecosystem.
4.
Farmers raise cattle, hogs and chickens in large numbers. Their waste contains large
amounts of nitrogen. What takes place when that waste enters a water system such as a
creek, lake or river?
The waste contains nitrogen and acts as a fertilizer which increases algae growth. When
the algae die, it decomposes and uses oxygen that is required by other organisms.
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Attachment E
Salmon - Tree - Bear Scenario
In the Pacific Northwest there have been studies of the forests, bears and salmon but rarely
were they studied together. Forests were logged for timber. Bears were hunted or eliminated
because they competed with man for farm animals or crops. Salmon were harvested and
were an important source of food for man and bears. But was that all? Recent research has
shown a link between the Pacific Ocean, salmon, bears and the forest trees. That link is the
common element nitrogen. Salmon reproduce in the small streams sometimes a thousand
miles from the ocean. After spawning they die and their bodies decompose along the banks
of the small streams.
Trees living along the streams use the nutrients from the dead fish (nitrogen). What happens
to the tress a greater distance from the stream? Recent research has identified isotopes of
nitrogen that are found in the trees near the stream, in trees several hundred meters from the
streams but not in trees a great distance from the streams. This isotope is also found in deep
water of the Pacific Ocean. How does this isotope from the ocean get on land? Bears now
enter the picture. Observations of bears and other predators show that when they catch
salmon they may drag the fish hundreds of meters from the stream to find a safe place to
feed. The predators rarely eat all the fish and the rest is left to decompose. Also, as nutrients
pass through the predators, plants away from the stream can benefit from the nutrients.
Answer the following questions on a separate sheet of paper.
1. For years, bears have been killed. What may be the long term affect on the forest if
there would be no bears or major predators?
2.
For years dams have been placed across the rivers and the salmon population had
dropped to the point where today all of the salmon species in the Pacific Northwest are
either threatened or endangered. What could be the long term affect on the forest if the
salmon population goes extinct or does not recover?
3.
If the forest near the streams is cut down and the water in the streams warms or gets
filled with silt (bad for salmon eggs) what could be the result on the bear and salmon
population?
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Nitrogen, Farms, Fish, Bears and Salmon – Grade Ten
Attachment F
Salmon - Tree – Bear Scenario Key
The following key provides idealized answers, but other answers from students may be
equally valid. When reviewing student responses, assess them for evidence of understanding.
1.
For years bears have been killed. What may be the long term affect on the forest if there
would be no bears or major predators?
The trees that are away from the water that use to get nitrogen from the dead fish or
bear droppings would not grow as well due to the lack of nitrogen.
2.
For years dams have been placed across the rivers and the salmon population had
dropped to the point where today all of the salmon species in the Pacific Northwest are
either threatened or endangered. What could be the long term affect on the forest if the
salmon population goes extinct or does not recover?
If there are no salmon, then none of the trees would get the nitrogen from the ocean and
would not grow or grow as well.
3.
If the forest near the streams is cut down and the water in the streams warms or gets
filled with silt (bad for salmon eggs) what could be the result on the bear and salmon
population?
If the salmon eggs do not hatch the population will become extinct and a major source of
food for bears and the source of nitrogen for the trees will be lost.
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