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DATASHEET FOR IN-TEXT LAB
Eutrophication: Too Much of a Good Thing?
Plants depend on nutrients such as phosphates and nitrates to survive. However,
when people release large amounts of these nutrients into rivers and lakes,
artificial eutrophication can occur. In artificial eutrophication, nutrients cause
algae and plant life to grow rapidly and then die off and decay. When microorganisms decompose the algae and plant matter, they use up oxygen in the water,
which causes the death of fish and other animals that depend on oxygen for survival. Eutrophication is commonly caused by phosphates, which are often found
in detergents, and by nitrates, which are found in animal wastes and fertilizers.
In this lab, you will observe artificial eutrophication in an aquatic ecosystem.
OBJECTIVES
Observe the effects of nitrates and phosphates on an aquatic ecosystem.
Compare the growth of organisms in different levels of nutrients.
Predict possible effects nitrates and phosphates would have on an aquatic
ecosystem in your area.
MATERIALS
•
•
•
•
•
•
•
•
•
•
•
distilled water
eyedropper
fertilizer, household use
fluorescent lamp
graduated cylinder
microscope
microscope slides with coverslips
plastic wrap
pond water that contains viable
organisms
• stirring rod
• wax pencil
guide to pond life identification
jars, 1 qt (3)
Procedure
1. Working with your team, use a wax pencil to label one jar “Control,” a second
jar “Fertilizer,” and a third jar “Excess fertilizer.”
2. Put 750 mL of distilled water in each of the three jars. Read the label on
the fertilizer container to determine the recommended dilution of fertilizer
for watering plants. To the “Fertilizer” jar, add the amount of fertilizer
recommended for a quart of water. To the “Excess fertilizer” jar, add 10 times
this amount of fertilizer. Stir the contents of each jar thoroughly to dissolve
the fertilizer.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
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Aquatic Ecosystems
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Eutrophication: Too Much of a Good Thing? continued
3. Obtain a sample of pond water. Stir it gently but thoroughly to ensure that the
organisms in it are evenly distributed. Measure 100 mL of pond water into
each of the three jars.
4. Cover each jar loosely with plastic wrap. Place all three jars about 20 cm from
a fluorescent lamp. (Do not place the jars in direct sunlight, as this may cause
them to heat up too much.)
5. Observe a drop of pond water from your sample, under the microscope. In the
space below, draw at least four different organisms that you see. Determine
whether the organisms are algae (usually green) or consumers (usually able
to move). Describe the total number and type of organisms that you see.
6. Based on what you have learned about eutrophication, make a prediction
about how the pond organisms will grow in each of the three jars.
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Eutrophication: Too Much of a Good Thing? continued
7. Observe the jars when you first set them up and at least once every three days
for the next 3 weeks. Make a data table to record the date, color, odor, and
any other observations you make for each jar.
8. When life-forms begin to be visible in the jars (probably after a week), use an
eyedropper to remove a sample of organisms from each jar and observe the
sample under the microscope. Record your observations.
9. At the end of your 3-week observation period, again remove a sample from
each jar and observe it under the microscope. Draw at least four of the most
abundant organisms that you see, and describe how the number and type of
organisms have changed.
Analysis
1. Describing Events After three weeks, which jar shows the most abundant
growth of algae? What may have caused this growth?
2. Analyzing Data Did you observe any effects on organisms other than algae in
the jar that had the most abundant algae growth? Explain.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
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Eutrophication: Too Much of a Good Thing? continued
Conclusions
3. Applying Conclusions Did your observations match your predictions?
Explain.
4. Drawing Conclusions How can artificial eutrophication be prevented in
natural water bodies?
Extension
1. Designing Experiments Modify the experiment by using household dishwashing detergent instead of household fertilizer. Are the results different?
2. Research and Communications Research the watersheds that are located
close to your area. How might activities such as farming and building affect
watersheds?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Environmental Science
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Aquatic Ecosystems
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TEACHER RESOURCE PAGE
Skills Practice Lab
DATASHEET FOR IN-TEXT LAB
Eutrophication: Too Much of a Good Thing?
Teacher Notes
TIME REQUIRED One 45-minute period for set-up,
plus follow-up observations over a 3-week period
Denise Sandefur
Nucla
High School
Nucla, Colorado
SKILLS ACQUIRED
Predicting
Designing experiments
Experimenting
Collecting data
Interpreting
Organizing and Analyzing Data
RATING
Teacher Prep–2
Student Set-Up–2
Concept Level–3
Clean Up–2
Easy
1
2
3
4
Hard
THE SCIENTIFIC METHOD
Form a Hypothesis Students predict how pond organisms will grow in
Procedure step 6.
Analyze Results Analysis question 2 asks student to analyze data to determine
whether organisms other than algae were affected by abundant algae growth.
Draw Conclusions Conclusions question 4 requires students to draw
conclusions about preventing eutrophication.
MATERIALS
You may substitute plastic soda bottles for the empty jars.
Collect a 5 L water sample from a local, natural, open watershed. When collecting pond water, plankton nets are helpful for concentrating microorganisms
in the sample. Make sure the sample includes some algae and a small amount of
mud. Preview the sample to be sure that all desired organisms are identifiable.
As an alternative to collecting pond samples, you might leave tap water in a
container for 24 hours to allow any chlorine to dissipate or use a chlorine
neutralizer for aquariums. Add a stock algae culture such as Spirogyra or
Chlorella to the water. The stock culture will not provide the natural diversity
that natural pond water would provide, but it will enable students to observe
algae growth and will model the results of eutrophication.
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Eutrophication: Too Much of a Good Thing? continued
SAFETY CAUTIONS
Encourage students to wear comfortable, seasonal clothing. Old clothes and
waterproof shoes or boots are advisable when working in aquatic habitats.
Students should wear goggles, gloves, and protective clothing while handling
chemicals such as fertilizer and unknown pond organisms. Be sure to review the
safety cautions on the container of household fertilizer. Students should wash
their hands carefully after handling the pond water samples. Clean the work area
with disinfectant after completing the investigation.
DISPOSAL
Pond water samples that have not been contaminated with chemicals could be
returned to the original collection site. However, you do not want to pollute the
aquatic ecosystem with the fertilizer and detergents used in the experimental
portion of this investigation. Small quantities may be safely flushed down the drain.
TECHNIQUES TO DEMONSTRATE
Depending on your students’ level of experience with microscope techniques, you
may wish to demonstrate how to make a wet mount. Place a drop of pond water
in the well of the slide with the dropper. Pick up a coverslip and place one edge
on the slide. Slowly lower the other edge so that the water spreads out under it.
Be careful not to trap bubbles of air beneath the coverslip.
TIPS AND TRICKS
You may wish to prepare the containers on the appropriate number of days ahead
of time so students can complete this investigation during one class period.
An alternative method for this lab would be to conduct the experiment using
gradually larger concentrations of fertilizer, such as 1X, 2X, 3X, 4X and so on. This
method would better illustrate the cycle of growth that leads to eutrophication.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
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TEACHER RESOURCE PAGE
Name
Class
Skills Practice Lab
Date
DATASHEET FOR IN-TEXT LAB
Eutrophication: Too Much of a Good Thing?
Plants depend on nutrients such as phosphates and nitrates to survive. However,
when people release large amounts of these nutrients into rivers and lakes,
artificial eutrophication can occur. In artificial eutrophication, nutrients cause
algae and plant life to grow rapidly and then die off and decay. When microorganisms decompose the algae and plant matter, they use up oxygen in the water,
which causes the death of fish and other animals that depend on oxygen for survival. Eutrophication is commonly caused by phosphates, which are often found
in detergents, and by nitrates, which are found in animal wastes and fertilizers.
In this lab, you will observe artificial eutrophication in an aquatic ecosystem.
OBJECTIVES
Observe the effects of nitrates and phosphates on an aquatic ecosystem.
Compare the growth of organisms in different levels of nutrients.
Predict possible effects nitrates and phosphates would have on an aquatic
ecosystem in your area.
MATERIALS
•
•
•
•
•
•
•
•
•
•
•
distilled water
eyedropper
fertilizer, household use
fluorescent lamp
graduated cylinder
microscope
microscope slides with coverslips
plastic wrap
pond water that contains viable
organisms
• stirring rod
• wax pencil
guide to pond life identification
jars, 1 qt (3)
Procedure
1. Working with your team, use a wax pencil to label one jar “Control,” a second
jar “Fertilizer,” and a third jar “Excess fertilizer.”
2. Put 750 mL of distilled water in each of the three jars. Read the label on
the fertilizer container to determine the recommended dilution of fertilizer
for watering plants. To the “Fertilizer” jar, add the amount of fertilizer
recommended for a quart of water. To the “Excess fertilizer” jar, add 10 times
this amount of fertilizer. Stir the contents of each jar thoroughly to dissolve
the fertilizer.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Environmental Science
20
54
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TEACHER RESOURCE PAGE
Name
Class
Date
Eutrophication: Too Much of a Good Thing? continued
3. Obtain a sample of pond water. Stir it gently but thoroughly to ensure that the
organisms in it are evenly distributed. Measure 100 mL of pond water into
each of the three jars.
4. Cover each jar loosely with plastic wrap. Place all three jars about 20 cm from
a fluorescent lamp. (Do not place the jars in direct sunlight, as this may cause
them to heat up too much.)
5. Observe a drop of pond water from your sample, under the microscope. In the
space below, draw at least four different organisms that you see. Determine
whether the organisms are algae (usually green) or consumers (usually able
to move). Describe the total number and type of organisms that you see.
Answers may vary.
6. Based on what you have learned about eutrophication, make a prediction
about how the pond organisms will grow in each of the three jars.
Answers may vary.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
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Name
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Date
Eutrophication: Too Much of a Good Thing? continued
7. Observe the jars when you first set them up and at least once every three days
for the next 3 weeks. Make a data table to record the date, color, odor, and
any other observations you make for each jar.
8. When life-forms begin to be visible in the jars (probably after a week), use an
eyedropper to remove a sample of organisms from each jar and observe the
sample under the microscope. Record your observations.
Answers may vary.
9. At the end of your 3-week observation period, again remove a sample from
each jar and observe it under the microscope. Draw at least four of the most
abundant organisms that you see, and describe how the number and type of
organisms have changed.
Answers may vary.
Analysis
1. Describing Events After three weeks, which jar shows the most abundant
growth of algae? What may have caused this growth?
Answers may vary. The jar with excess fertilizer should show the most
growth. The extra fertilizer stimulated additional plant growth.
2. Analyzing Data Did you observe any effects on organisms other than algae in
the jar that had the most abundant algae growth? Explain.
Answers may vary. The jar with the most growth should have the fewest
number of microorganisms.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
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Date
Eutrophication: Too Much of a Good Thing? continued
Conclusions
3. Applying Conclusions Did your observations match your predictions?
Explain.
Answers may vary.
4. Drawing Conclusions How can artificial eutrophication be prevented in
natural water bodies?
Artificial eutrophication can be prevented by controlling the application of
fertilizers in areas where runoff is common.
Extension
1. Designing Experiments Modify the experiment by using household dishwashing detergent instead of household fertilizer. Are the results different?
Answers may vary. The samples with dishwashing detergent and excess
dishwashing detergent should both show no additional growth.
2. Research and Communications Research the watersheds that are located
close to your area. How might activities such as farming and building affect
watersheds?
Answers may vary.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Environmental Science
57
Aquatic Ecosystems