Marlene Schoeneck initiated this lesson
introduces students to the affect of winter ice cover on the temperature,
dissolved oxygen (DO), and pH content of a lake.
lakes are sealed off from terrestrial influences in the winter
by a lid of ice. The ice prevents gas exchange at the lake /
and reduces light levels as snow cover accumulates. Life processes
go on, but decreased photosynthesis, accumulated waste products,
and continued respiration reduce DO levels. In extreme cases of
shallow lakes and ponds with high amounts of organic matter, DO
can be totally depleted (anoxia) and toxic concentrations of hydrogen
sulfide (rotten eggs) gas can accumulate. The buildup of repiratory
carbon dioxide, while not harmful, leads to decreased pH
(for more details and a specific example take a look at the Ice
Lake overview). This makes survival in the self-contained environment
more difficult. Prolonged exposure to such conditions may create
problems in managed systems where maintenance of fish populations
is an important factor to consider since mitigation (e.g. aeration)
is expensive and not necessarily effective.
meet the goals for this lesson by completing either a studying or
investigating lesson. The directed study lesson guides students
through the process of experimental design and data collection.
The student inquiry lesson provides more student choice and asks
students to plan design experiments and data collection.
contains two parts. In part one, students create simulated lakes.
One is placed under a bright light (summer) and the other is kept
dark and chilled (winter). Students measure temperature, DO, and
pH readings five times over a week-long study period. They graph
these data and compare the two lakes. Part two places students in
the role of lake biologists asked to answer a question posed by
a local Sportsmen's group: should aerators be placed in a study
lake to help fish survive the winter? Using RUSS data, students
take weekly readings of DO, temperature and pH in a real lake over
one winter. They organize and interpret this data, and devise a
recommendation for the Sportsmen's Club.
are found in the appropriate student section of WOW under the title
"Sustaining Life Under the Ice."
the components of lake chemistry affected by ice cover
2. Diagram the relationships between pH, DO and temperature and
3. Explain how winter ice cover may affect lake organisms
4. Use lake data to make reasonable recommendations for wildlife
of physical, chemical, and biological processes occurring in lakes,
and experience with water testing devices will help students complete
this lesson successfully.
or other method of chilling a class set of 250 bottles
Sensors or kits
for measuring pH, DO and temperature (sensors are preferred)
Class set of
1. 2, 250ml
clear bottles or jars with essentially airtight lids
2. Pond, lake, or aged tap water
3. Organic/mucky sediment, 75 ml per jar
4. 6 sprigs of Anacharis (Elodea) or other aquatic plant
Part 1: Lake
Simulation-1 hour set up plus 15 minutes each day for five days
Part 2: Sportsmen's Club Recommendation-2 hours for data gathering
and management, at least 2 nights for preparing presentations, and
at least 1 class period for presentations.
ecology, environmental science, wildlife management
Respiration, Chemistry of
Oxygen Solubility, Data Interpretation,
Effect of pH on Aquatic Organisms,
Effect of Photosynthesis and Respiration
on Aquatic Chemistry
RUSS parameters; temperature,
Lake overviews on Ice
Lake and Lake Independence
Part I -
Winter Lake Laboratory Simulation
lab group, or as a class, discussions of the wildlife management
problems that have developed in area lakes from winter conditions.
What physical, chemical and biological factors determine the severity
of ice effects? What types of management practices may improve or
limit the negative impacts of ice cover? Reference to specific
cases of winterkill in a lake may help to engage students' interests.
Some examples include: Illinois
You will need
the following equipment:
5. 2 , 250ml clear bottles or jars with essentially airtight lids
6. Pond, lake, or aged tap water
7. Organic/mucky sediment, 75 ml per jar
8. 6 sprigs of Anacharis (Elodea) or other aquatic plant
9. A refrigerator or other method of keeping one of the microcosms
chilled. (The colder the better, without freezing the jar solid!)
You may want
to divide students into groups of 3-4. Refer groups to instructions
posted in lesson plans. Look to the studying plan for a step-by-step
example of the simulation.
During the experiments,
you should expect that DO will decrease steadily, the rate dependent
on the biochemical oxygen demand of the water (including macro and
microorganisms) and the amount of sediment oxygen demand (a function
of the rate of bacterial and invertebrate respiration occurring
in the sediments and the amount of sediment contact with overlying
water; essentially the area of sediment to water volume ratio).
pH will typically decrease under the ice, as it does in most of
the hypolimnion over the course of the summer in thermally stratified
lakes. This is caused by a buildup of CO2 from respiration. The
magnitude of the observable change in pH is controlled by the rate
of respiration as well as the buffering capacity of the water (as
measured by its alkalinity which is also called its acid neutralizing
capacity or ANC).
to questions 1 and 2. Have students in groups split the tasks of
Follow the same
directions as studying plan; however be sure to have students explain
their experimental design before proceeding with data collection.
There should be at least two groups that choose to measure pH,
Data Management and Analysis
refer to directions. They will create one graph for each factor
measured (temperature, DO, pH), which compares data collected from
each of the simulated "lakes" (date on x-axis; temperature,
DO, or on y-axis). They may graph data by hand or use the excel
spreadsheet, following instructions for the template on the WOW
to instructions. They should graph their data by hand or use an
Excel spreadsheet--follow instructions for the template on the
site. Ask them to explain their rationale for data presentation.
Interpretation of Results
answer the questions posted under the lesson plans. These are the
same for both studying and investigating lessons.
1. What changes
occurred in your "lakes" during the course of the study?
2. How do you
account for the changes in your "lakes"? (Think about
the content and covering of your "lakes".)
3. How are these
changes related to conditions in an actual lake in winter? What
ramifications do they have for lake life?
4. What aspects
of this simulation are not realistic? Suggest some revisions that
would more accurately simulate winter lake conditions?
keep results to turn in with part 2.
Part II. - Changes in a Winter Lake
or class discussion of the results of the winter lake simulations.
What lake chemistry changes might they expect to see in an actual
lake? Recall the discussion of the physical, chemical, and biological
components of lakes, considering their influence on a specific
and its winter dynamics.
Guide the students
in imagining that their local Sportsmen's Club has asked to purchase
aerators for the local lake to reduce winter fish kills. The Club
first would like to be sure that winter conditions in the lake
the installation of these units. Since your science class has been
monitoring the lake for several years, the club has come to your
school in search of needed evidence.
students to use the DVT Toolkit, located in the data section of
the WOW site under launch new DVT Toolkit, to look at weekly Ice
Lake profiles for the winter of 1998-1999. The data plotter tool
allows them to create a graphic representation of each sample (see
example below). Students use these graphs to compare changes in
temperature, DO and pH and over time.
See the WOW
DVTools Index for example. Check the Ice Lake box, and then
click on Get this Data. Click Profile Plotter. Try plotting a few
different dates. Winter data sets alos exist for Lake Independence
and Lake Minnetonka.
RUSS data on the WOW site to determine a study lake with relevant
data. Ask them to consider how they will determine ice formation
and ice out on their lake. Typically water is densest at 4 degrees
Celsius. Lakes that are frozen would be expected to have bottom
temperatures of 4 degrees Celsius, with water temperature decreasing
toward the surface to 0 degrees Celsius (freezing) at the top.
temperatures warm above 0 at ice out. Keep in mind that the RUSS
units are pulled off the lakes shortly before ice-over, and again
at ice-out. There will be "holes" (missing data) at these
points, but you will still have an indication of when each event
also explain the reasoning behind their experimental design.
Data Management and Analysis
to directions. They will use the data visualization tools or an
Excel spreadsheet on WOW to graph and interpret their data.
the following questions:
1. What changes
did you observe in the parameters you measured over the winter at
2. What physical
characteristics of your lake might have had an influence on the
results that you observed in your data? How?
3. What knowledge
do you have of the biological characteristics and trophic state
of your lake? How might these have affected the life sustaining
ability of your lake?
4. Based on
the above research, what recommendations would you have for the
Sportsmen's Club in regards to installing (or not installing) aerators
on the lake?
5. What other
management practices might help prevent fish kills in the lake besides
students to prepare posters or graphs for an oral presentation to
the class. This is a good opportunity to engage students in comparative
debate. Did each group get similar results? Did they make the same
recommendation to the Sportsmen's Club? However, you probably want
to limit presentations to 10-12 minutes each.