Credits
Marlene
Schoeneck initiated this lesson.
Most
northern lakes are sealed off from terrestrial influences in the
winter by a lid of ice. The ice limits gas exchange at the lake/air
interface, and reduces light levels as snow cover accumulates. Life
processes go on, but decreased photosynthesis, accumulated waste
products, and continued respiration make 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.
Part
I - Winter Lake Laboratory Simulation
Knowledge
Base
Discuss in your lab group, or as a class, problems that have
developed in area lakes from winter conditions. What physical and
biological
factors determine the severity of ice effects? What types of management
practices may improve or limit the negative impacts of ice cover?
Experimental
Design
You will need the following equipment:
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
5. A refrigerator or other method of keeping one of the microcosms
chilled. (The colder the better, without freezing the jar solid!)
Set
up 2 identical jars as simulated "lakes" using the materials listed
above. Begin by placing 75 ml of organic sediment in the bottom
of each jar. Add 3 equal-sized sprigs of your aquatic plant to each
jar and fill to the brim with the water. Cap the jars and place
one jar under a plant light in room temperature. Label this jar
"Summer." Put the second jar in the refrigerator or other means
you have selected to keep it cold. This jar represents a lake in
winter. Label it "Winter." Take care not to allow the jar to freeze
solid! You may need to do some experimenting with temperature settings
previous to the start of your experiment.
Data
Collection
1.
Measure dissolved oxygen (DO), pH and CO2 levels in each of your
jars. Sensors, rather than kits, are preferable for testing. (If
using a test kit, slowly replenish the water taken from each bottle
with water from the same source so as not to introduce more oxygen
to the sample.
2.
Take readings once or twice a day over a 5-day period. Enter your
values for each reading in the chart below.
Lake
Chemistry Readings
|
dissolved
oxygen
|
pH
|
temperature
|
Day
|
winter
|
summer
|
winter
|
summer
|
winter
|
summer
|
1
|
a
|
a
|
a
|
a
|
a
|
a
|
2
|
a
|
a
|
a
|
a
|
a
|
a
|
3
|
a
|
a
|
a
|
a
|
a
|
a
|
4
|
a
|
a
|
a
|
a
|
a
|
a
|
5
|
a
|
a
|
a
|
a
|
a
|
a
|
Data
Management and Analysis
Create
one graph for each factor that you measured (DO, pH, Temp), which
compares data collected from each of your "lakes". Graph your data
by hand or use an Excel spreadsheet. Follow instructions for the
template on the WOW site. Be sure all parts of the graph are properly
labeled.

Interpretation
of Results
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 might these changes relate 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?
Reporting Results
Keep your results to turn in with part 2.
Part
II. - Changes in a Winter Lake
Knowledge
Base
Consider
the results of your winter lake simulation. What lake chemistry
changes might you expect to see in an actual lake? Recall your
discussion
of the physical and biological components of lakes as you consider
their influence on a specific lake and its winter dynamics.
Experimental
Design
Imagine
your local Sportsmen's Club has been asked to purchase aerators
for Ice Lake to reduce winter fish kills. They first would like
to be sure that winter conditions in the lake justify 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 the needed evidence. Use the DVT Toolkit, located in the data
section of the WOW site, to look at Ice Lake profiles for the winter
of 1998-1999. Assume that ice formation occurred around 12/27/98
and ice out occurred around 3/21/99. Use the "plotter" function
to display your data.
Data Collection
Collect Ice Lake RUSS data weekly for the period
spanning Sept. 1, 1998 to May 1, 1999. Create a table and record
temperature, pH,
and dissolved oxygen values at depths 2-4m and 8-10m during this
period of time.
Data
Management and Analysis
Use an Excel spreadsheet to graph the data
you have collected.
Interpretation
1.
What changes did you observe in the parameters you measured over
the winter at your lake?
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? What else would you like to know
to increase your confidence in your recommendations?
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 installing aerators?
Reporting
Results
Plan an oral presentation of your results. Create graphs
or posters to illustrate your discussion. How do your results and
recommendations
to the Sportsmen's Club compare with other groups? Turn in your
graphs and responses from part 1 and 2 to your teacher.
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