Yakima WATERS Mini Lesson
Lake Washington’s Algae Problem Case Study
Targets and Assessment
WA Science Standards Addressed:
9-12
SYSB
Systems thinking can be especially useful in
analyzing complex situations. To be useful, a
system needs to be specified as clearly as
possible.
Feedback is a process in which the output of a
system provides information used to regulate
the operation of the system. Positive feedback
increases the disturbance to a system. Negative
feedback reduces the disturbance to a system.
9-12
Scientists generate and evaluate questions to
INQA investigate the natural world.
9-12
Scientific progress requires the use of various
INQB
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
Conclusions must be logical, based on
INQC
evidence, and consistent with prior established
knowledge.
9-12
The essence of scientific investigation involves
INQE
the development of a theory or conceptual
model that can generate testable predictions.
Assessments:
 The student worksheets
Lesson Parameters
Content Area: Chemistry
Overview: In this lesson student will learn about pollution
and nutrient enrichment that causes blue-green algae
blooms in the early stages of pollutant degradation.
Grade Level: 11th&12th grader
9-12
SYSA
Suggested Time: 45 to 55 minutes
Special Materials:

Learning Outcomes:
Knowledge: Upon completion of this lesson students will be able to describe how pollution cause
enrichment of nutrients like phosphates and nitrates which result in blue-green algae blooms
Skill: students will be able to determine the main question of the case study, determine the importance
of the study, use observations to generate null and alternative hypotheses, design simple experiments
to test hypotheses’, predict result of experiments for each hypothesis and use research data to accept
or reject a hypothesis.
Science Concept Background:
For a sufficient background please read chapter 1&2 of W.T. Edmondson’s Book entitled The Use of
ecology; Lake Washington and beyond.
Materials:
- One copy of the case study for every four students.
- A computer lab or word accesiblity
Procedure:
1) Instruct groups to get on a computer as they will be typing up their answers in Microsoft Word.
2) Have student get into groups of no more than four students. Each group will need one person to
record answers, one to mediate discussion, one to report back to the class and one runner to
gather and return papers to you (the teacher).
3) Have each group’s runner get part 1. Read the introduction aloud to the class and have students
work in their groups to answer questions. If you haven’t already now would be a good time to
introduce and explain how to generate null and alternative hypotheses. When students are finished
have the groups reporters share their groups answers with the class.
4) Have the runners return part 1 and get part 2. Have groups work together on part 2. When
students are finished have the groups reporters share their groups answers with the class.
5) Repeat step 3 of the procedure until part 4 is completed.
6) Have student submit their case study answers via email attachments.
Extension(s):
Lake Washington’s recovery case study.
Teaching Tips:
Before this lesson teach students how to write questions and alternative and null hypotheses. Be sure
to explain the difference between prediction and hypotheses and any vocabulary students are unfairly
with.
Scientific thinking is difficult so I like to make comment and suggestions via the track changes function
in Word. I allow students a week to make revisions a resubmit their case study questions.
Supplements:
Author: Sara Rosario, Yakima WATERS Project, CWU, Fall 2010
Lake Washington’s Algae Problem (Part 1)
This case study is based on Edmondson, Anderson and Peterson’s Artificial Eutrophication of Lake
Washington.
Introduction :
In 1955 Dr. George C. Anderson (an ecologist whom studied plankton many local lakes including Lake
Washington) noticed that Lakes Washington looked different. The lake appeared murky and rust colored. He
collected a sample of the Lake Washington’s water. This sample sent it to an algae expert for analysis, the most
abundant organism in that sample was found to be a type of myxophyceae plankton called Oscillatoria
rubescens. Oscillatoria rubescens is fresh water blue green alga that normally does not appear as the most
abundant microorganism in lakes. These same blue - green algae appeared in a lake in Switzerland called
Zürichsee; shortly after the appearance of these algae the lake became too polluted to support trout and other
fish. Trout are freshwater fish that require lots of oxygen to survive. Anderson and his colleagues became
interested in the changes in Lake Washington that resulted in Oscillatoria rubescens blooms.
Other Observations:
In 1883 the city of Seattle started construction on a primitive sewage system; this sewage system was a net
work of pipes that moved raw sewage from Seattle and into two bodies of water, the Puget Sound and Lake
Washington. By 1922 the primitive sewage system had expanded a great deal, with 50 “outfalls” into the Puget
Sound and 30 “outfalls” into lake Washington. At this point in Seattle’s history many of its citizens still used
lake Washington as a source of drinking water. Consequently the city became concerned that lake Washington
was being polluted by sewage and made plans to construct a new sewage system. This new system was
completed in 1936; it diverted all 30 outfalls into lake Washington (that’s about 70 million gallons of raw
sewage per day) to new outfalls along the Puget Sound.
In the 1933 two researchers did a detailed study of chemical, physical and biological characteristics of lake
Washington. They found lake Washington had a relatively low concentrations of the nutrients phosphate and
nitrates and average concentrations of dissolved oxygen. At this point in time lake Washington contained only
one species of blue-green algae known as Oscillatoria Sp.
In 1941 the city completed construction on the first two of eleven sewage treatment plants, which put secondary
or treated sewage into Lake Washington. These sewage treatment plants were state of the art and consisted of
primary and secondary sewage treatment. It is important to note that raw and secondary sewage contain high
levels of nutrients (phosphates in particular) that microorganisms like bacteria and algae consume.
Questions:
Make a list of observation s (between 5 and 7) that are important to this case study.
What is the basic question of Anderson’s study? And why is this interesting?
Develop a hypothesis that explains the observations and answers the main question of this study.
What predictions can you make about the algae blooms that would support your hypothesis?
Lake Washington’s Algae Problem (Part 2)
Hypotheses:
Anderson and his colleagues noticed a connection between increased nutrients loads as a result of sewage
pollution and the blue-green algae blooms that immediately precede pollution degradation of lakes. They
hypothesized that if nutrient load increased in lake Washington, it must result in Blue-green algae blooms.
Questions:
State the null and alternative hypothesis of this study.
Design a set of experiments to differentiate between the null and alternative hypotheses.
What type of control should you use in your experiments?
Lake Washington’s Algae Problem (Part 3)
Experiments:
The authors of this study used research data from 1933, 1950 and 1955 and designed some simple experiments
to test their hypothesis.
In the field the researchers collected water samples at ten or more locations and at depths greater than twenty
meters for analysis in the lab for their chemical and biological characteristics. In the lab the samples were
analyzed for dissolved oxygen, phosphate and nitrate concentrations. These samples were analyzed for bluegreen algae species such as Oscillatoria rubescens and oscillatoria agardhi.
Questions:
Given the observations make predictions of the results if the null hypothesis is supported?
Given the observations make predictions of the results if the null hypothesis is supported?
Lake Washington’s Algae Problem (Part 4)
Results:
Chemical Characteristics
Chemical Characteristic
Dissolved Oxygen
(mg/L)
Phosphates (mg/L)
Nitrates (mg/L)
1933
11.08
1950
11.00
1955
7.00
0.007
0.04
0.013
0.04
1.5
1.0
Biological Characteristics
Mycophyceae (blue- green algae)
1933
1950
1955
type
Oscillatoria sp.
>1%
NA
NA
Oscillatoria agardhi
NA
34%
>1%
Oscillatoria rubescens
NA
NA
96%
Data are represented as percent abundance of total microorganisms in lake Washington.
Questions:
How do your predictions fit with the results?
Do the data support accepting or rejecting the hypothesis?
Can the results of this study be used to make broader generalizations about blue-green algae blooms?
References: