Testing Dissolved Oxygen Content of Local Stream Water
A Yakima WATERS “5-E” Inquiry Lesson
Overview
This experiment is helpful for high school students to practice their techniques of writing
hypotheses, constructing data tables and analyzing results. Keeping accurate lab notes and
working with lab partners on research projects are the skills which they will be building.
This lesson is targeted to 11th and 12th grade students and is expected to take two full class
periods and a small amount of discussion time the class days directly following both
experiments.
Excess nitrogen will be added to local stream water filled containers and the changes in
dissolved oxygen content will be recorded. Students will be testing dissolved oxygen and
recording data. They will also manipulate the experiment during this lesson.
Standards
9-12 INQA Question Scientists generate and evaluate questions to investigate the natural world
9-12 INQB Investigate Scientific progress requires the use of various methods appropriate for
answering different kinds of research questions, a thoughtful plan for gathering data needed to
answer the question, and care in collecting, analyzing, and displaying the data
9-12 INQC Explain Conclusions must be logical, based on evidence, and consistent with prior
established knowledge
9-12 INQE The essence of scientific investigation involves the development of a theory or
conceptual model that can generate testable predictions.
9-12 SYSC In complex system, entirely new and unpredictable properties may emerge.
Consequently, modeling a complex system in sufficient detail to make reliable predictions may
not be possible.
9-12 APPD The ability to solve problems is greatly enhanced by use of mathematics and
information technologies.
9-12 APPA Science affects society and cultures by influencing the way many people think about
themselves, others, and the environment. Society also affects science by its prevailing views
about what is important to study and by deciding what research will be funded.
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9-11 LS1A Carbon-containing compounds are the building blocks of life. Photosynthesis is the
process that plant cells use to combine the energy of sunlight with molecules of carbon dioxide
and water to produce energy-rich compounds that contain carbon (food) and release oxygen.
Outcomes
Knowledge:*Students should be able to: explain how nitrogen or sugar affect dissolved oxygen,
and use a dissolved oxygen probe.
Skill:* Students should be able to: produce a hypothesis that will be tested by the experiment,
accept or reject their hypothesis and revise their hypothesis based on their observations, and
design a data table.
Materials and Equipment (for one class period of approximately 20 students)
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Dissolved Oxygen probe
Nitrogen fertilizer
Eight clean plastic bottles with lids (any size as long as all bottles are the same)
Water from an outdoor body of water
Markers and tape for labeling
Sugar (any amount of sugar, as long as it is kept consistent)
measuring cup
Prior Knowledge
What the students know: Students should have an introduction to the nitrogen cycle and the
process of eutrophication. It is necessary to understand the role of fixed nitrogen in the
nitrogen cycle as a nutrient as well as the adverse influences of nitrogen saturation on
ecosystems.
What the students need to know: Students should understand that through human influence,
the amount of nitrogen in the biosphere has doubled from the Earth’s natural amount.
Safety
No food or drinks should be out at the time of this lab. Also, safety goggles should be worn
when boiling water.
Engage (10 min)
Ask the students:
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Where are some local streams that you are familiar with?
What do you think is in this local stream water?
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Luckily for us, there are several ways to measure what is in our water. These scientific tools
are very important for humans to maintain clean neighborhoods, wildlife, and drinking
water. The water that I collected is from the stream on Central Washington University’s
campus. Today we will begin an experiment to measure the dissolved oxygen in this water.
That means the amount of oxygen that is carried in the water.
Explore (30 min)
The goal of this lesson is for the students to accurately construct a data table and a
hypothesis.
Begin with showing the students four bottles of the stream water. You should tell them when
and where you collected the water. The students will record this information. It is helpful to
explain that when doing an experiment, accuracy and attention to detail is highly important, so
you must collect the water the same day and from the same location for all the bottles.
Then show the students the Dissolved Oxygen probe. Test the water using the probe in
front of the students prior to adding anything to it. (This part could be a demonstration or
you can let the students try taking the DO reading depending on the amount of time).
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It is important to note that the probe must be turned on at least twenty minutes prior to
using it. Also, the membrane in the probe must be kept moist, and batteries should be
removed from the probe once the experiment is done. This probe can be borrowed
from the biology department of CWU.
The students will record the percent of dissolved oxygen and the temperature of this water as it
is naturally. (Chart showing the DO numbers needed to sustain life is available at the end of
this lesson plan under the Resources section).
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It is important here to remind them of the significance of oxygen for life in ecosystems
as a reason why someone would want to measure the dissolved oxygen of water.
Too little oxygen could suppress life. This is called hypoxia. Too much bacteria grows and
not enough aerobic life forms.
Next, explain to the students what you are putting in each of the four bottles in detail. (They
will record all of this information to build their data table. You should label each bottle with the
date, amount of dissolved oxygen and temperature prior to adding anything, then what you
added and how much was added to the bottle. (You can add any amount of each fertilizer and
sugar, as long as you keep in consistent throughout the experiment.) This part could also be a
demonstration or you can let the students put the additives in the water depending on the
amount of time).
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One bottle has fertilizer
One bottle has sugar
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One bottle has both fertilizer and sugar
One bottle will be our control. This bottle of water will not have anything added to
it.
The students will formulate a hypothesis on what think will happen to the water in the
twenty four hours until the next day’s class. They should rank the bottles from which will
have the least oxygen at the end of the experiment to which will have the most, and explain
why.
(There is no correct prediction. The results will depend on what is in your water.)
Explain (25 min)
The following day after beginning the experiment they will see the results.
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Before testing the Dissolved Oxygen content, they should share their thoughts on what
they think will happen.
Then, ask for student volunteers to come up and help testing each of the bottles.
Have the student volunteers test each bottle in the same order that you presented the bottles
on the first day. In between testing the water, rinse the probe with distilled water.
Have the students record the new results of dissolved oxygen content and temperature of each
bottle.
The data will support or not support their hypothesis. Students will form a conclusion
statement based on what they saw. This is an excellent time for the students to ask any
questions they still have.
Ask them what they think made the oxygen content go up or down in each bottle. Ask to hear
some of their reasons for a class discussion. Good topics here are life and chemical reactions.
During this discussion, tell the students that the class is going to redo the experiment, but alter
one part. Have them brain storm, but if they need direction some ideas are
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Set bottles in the sun
Boil the water
Extend/Elaborate (30 min)
The next day you will collect stream water from the same place as you did the first time. Four
new bottles will be used at this time. You will need all of the same supplies for this lab, as the
last one.
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This time, tell the students it is their turn to set up the lab. Briefly review what happened last
time and ask the students to bring out their notes from it. Assign each table a job. It is good to
have approximately four groups. It is also helpful for each group to write their results on the
board.
 They should write down how they think this lab will differ from the last lab and why.
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Group 1: add the sugar and label the bottle
Group 2: add the fertilizer and label the bottle
Group 3: add both sugar and fertilizer and label the bottle
Group 4: measure the Dissolved Oxygen and temperature of water of the control and
label the bottle.
Once the lab is set up, the class should decide how they will alter the experiment. If they
choose to boil the water, safety goggles and precaution should be taken for handling hot water.
Once the water has cooled it can be put back into its respective bottle. Setting the bottles in the
sun is self explanatory.
Now, they can finish their new data table and new hypothesis. They will apply the techniques
they practiced the first time. Since the students are running the lab, they will be teaching each
other and practicing good communication.
The fourth and final day of this lab should be concluded with information about what occurred
during the course of the experiment. The latest hypotheses will be accepted or rejected based
on the results from testing the water for the oxygen content once again. Evaluation and
explanation will be done simultaneously.
Evaluate (25 min)
The student’s data tables and hypotheses that they have been recording throughout this
experiment should be collected so the instructor can read them.
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Performance Rubric
Element
Hypothesis
Data table
Excellent
(4 pts)
Shows all approaches.
Demonstrates thinking with a
clear, sequential explanation.
Work is clearly organized.
Explains how nitrogen or sugar
affect dissolved oxygen.
Clearly organized data table.
Shows and explains. Excellent
understanding.
good (3 pts)
Explanation is basic,
but lacks elaboration.
Some incorrect.
Demonstrates some
organization.
Does not finish or
leaves out important
parts in data table.
In development
(2 pts)
Explanation is
unclear or
incomplete, but
includes the
basics. Some
correct.
Disorganized
approach.
Minimal
understanding.
Fails to complete.
Needs rethinking
(1 pt)
Shows no evidence
of understanding.
Explanation is
confusing or
nonexistent. Lacks
organization
Attempts, but
generates no
understanding of
problem.
Teacher Background Info
Reviewing the students hypotheses and data tables is a good way to see where your students
are at in terms of writing a quality scientific statement and keeping accurate data. It is helpful
to do this experiment before beginning a large scientific research project because it gives the
students a chance to practice using scientific equipment, setting up a lab, and thinking of
satisfactory questions to ask. This allows the instructor to see how each student understands
the concept and score progress based on what they have been able to accomplish during the
assignment. Pointers can be given on what they need to improve on for the next scientific
experiment they do. Some helpful definitions:
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Hypoxia- Deficiency of oxygen
Aerobic- requiring oxygen
Eutrophication- Excessive richness of nutrients in a lake or other body of water,
frequently due to runoff from the land, which causes a dense growth of plant life and
death of animal life from lack of oxygen
What is the significance of dissolved oxygen?
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Dissolved oxygen levels provide information about the biological, biochemical, and
inorganic chemical reactions occurring in aquatic environments. Most aquatic organisms
are highly dependent upon dissolved oxygen and will experience stress, or perhaps even
be eliminated from a system, when dissolved oxygen levels fall below about 3.0 ppm
(parts per million). Trout species normally require an oxygen concentration greater than
10 ppm (10 mgL) whereas carp can live in water containing as little as 1-2 ppm (1-2 mgL)
oxygen.
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Poor water quality is also indicated by low percent saturation readings. Levels below
60% may happen with rapid biological processes such as decomposition or high
temperatures. Supersaturation can be a problem for organisms in that blood oxygen
levels can increase resulting in gas bubbles in the blood.
Guideline for Interpretation of Dissolved Oxygen Readings
For mg/L:
0-2 mg/L:
not enough oxygen to support life
2-4 mg/L:
only a few kinds of fish and insects can survive
4-7 mg/L:
acceptable for warm water fish
7-11 mg/L:
very good for most stream fish including cold water fish
For percent saturation:
Below 60%:
poor; water too warm or bacteria using up DO
60-79%:
acceptable for most aquatic organisms
80-125%:
excellent for most aquatic organisms
112% or more: too high, may be dangerous to fish
Resources
Washington State Science Standards:
https://courses.cwu.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_4_1&url=%2Fweba
pps%2Fblackboard%2Fexecute%2Flauncher%3Ftype%3DCourse%26id%3D_83181_1%26url%3D
%252Fwebapps%252Fblackboard%252Fexecute%252FdisplayIndividualContent%253Fmode%2
53Dview%2526content_id%253D_1294584_1%2526course_id%253D_83181_1
Textbook for environmental science: Miller, G.T. & Spoolman, S.E. (2009) Living in the
Environment. Belmont: Brooks/Cole.
Guideline for interpretation of D.O. readings: http://www.gvsu.edu/wri/education/instructor-smanual-dissolved-oxygen-30.htm
By: Jessica Giblin, Fall 2011, for Davis High School
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