Credits
Barbara Liukkonen developed this lesson.
Goals
Students will investigate how much energy is stored in lake water as latent
heat,
calculate how much
latent heat
is exchanged with the atmosphere, and consider the effects of heat gain and heat loss on the surrounding environment.
Introduction
Water has unique properties that affect its ability to store and release
heat energy.
In this activity students develop an understanding of latent heat. They calculate
heat budgets
for lakes and explore the effects of lake temperatures on the surrounding environment.
Students can meet the goals for this lesson by completing either a directed study or student inquiry lesson.
The "Studying Heat Budgets of Lakes"
lesson uses a worksheet approach to prepare students for class discussions on the subject. Students need
to print the lesson to complete it as a worksheet.
The directed study lesson is found in the student section of WOW under the title: "
Studying Heat Budgets of Lakes."
The student inquiry lesson provides students with an assignment as a television
meteorologist. The end result of the television assignment is an oral
presentation, written paper, TV script, video, or multimedia presentation
about heat budgets, depending on the instructor’s requirements.
The student inquiry lesson is found in the student section of WOW under the title:
"Investigating Heat Budgets of Lakes."
Outcomes
Students will:
 Review how to estimate lake volume.
 Calculate how much latent heat is stored in lake water.
 Calculate how much energy is released to the atmosphere as a lake cools at night.
 Calculate how much energy is required to freeze the lake surface.
 Consider how latent heat stored in and released from a lake can affect local weather conditions.
Keywords
Calorie,
temperature,
conduction,
latent energy,
states of matter
Prerequisites
Students should have a basic understanding of
calories
as units of energy. It is also helpful if they have had prior experience calculating lake volumes.
Materials/Resources/Software
 A copy of the "Studying Heat Budgets of Lakes"
lesson for student groups doing the directed study lesson.
 Access to WOW temperature profile
data for Ice Lake or Independence Lake at different times during the day. (46 hour intervals of data are useful.)
Students could be told to find this data through the WOW web site, or the data could be provided as a handout.
Time Required
Two — three class periods
Curriculum Connections
Physics  calorie, temperature, radiation,
conduction, latent energy, states of matter
WOW Curriculum Links
Diel
Temperature Variation
Procedure
Knowledge Base
The "Understanding" section of the WOW website includes
information about heat budgets for some WOW lakes (see Figure
1). You may want to display information such as this for the students.
This could be done either during your initial discussions for this lesson,
or as part of the discussion and closure for the lesson.
Figure
1. Heat Budget for Ice Lake (click for full figure)
Directed Study
Discuss students’ experiences with air and water temperatures around lakes.
What have students noticed about the differences in air and water temperatures
during the day? What are air and water temperatures like at night?
Student Inquiry
Students play the role of a television meteorologist. Their television station
has asked them to develop a series about heat budgets
of lakes. Students should review daily and seasonal air and lake water temperature changes.
Ask students to write a one paragraph script that includes the following details:
Is air or water usually warmer in the early spring?
Does air or water retain heat longer in the fall?
Does air or water warm up more quickly early in the morning?
Does air or water retain heat longer as night falls?
Notes: Water temperature changes lag behind the changing seasons. For example, during
warm spring days, the water temperature is much cooler than the air
temperature. During cool, early fall days the water temperature is much
warmer than the air temperature. There is also a daily temperature lag;
air temperatures warm up during the day before the surface of the lake.
The night air also cools much more quickly than the surface temperature
of a lake.
Experimental Design
Directed Study
Review how to calculate water volumes for each one meter layer of a lake. Review
the basic concepts of calories
and energy transfer. Energy is required to raise the temperature of
water. Ask students to hypothesize about the source of energy for lakes.
Notes: Energy from the sun is the primary source of increasing temperatures in a lake.
It takes 1 calorie to raise one cubic centimeter of water one degree (at 20°C).
How many calories does it take to raise 1 cubic meter of water one degree?
When a cubic centimeter of water drops one degree, energy is released.
How many calories are given off when a cubic meter of water drops one
degree? (Have students describe and explain how they arrived at their
answers.)
Notes: 1 million calories are required to change one cubic meter of water by
one degree (Celsius), if no changes of state are involved.
Divide the class into groups of two before handing out the "
Studying Heat Budgets of Lakes"
lesson. Each member of the group should have a responsibility. If one member of the group is the "recorder"
and responsible for writing answers on the worksheet, then the other
member could be the "research technician," responsible for finding
the data to insert into the tables and doing the necessary calculations.
When students are half done with the worksheet they should switch responsibilities.
Student Inquiry
Ask students to examine the depth and area calculations for Ice Lake and Lake Independence.
Students need to develop an explanation of how to calculate heat budgets
(in calories). They should also demonstrate that the heat budget changes
in each lake throughout the day.
Data Collection
Directed Study
The worksheet format of the "Studying
Heat Budgets for Lakes" will guide students through the data
collection.
Student Inquiry
Students should collect the data they need to calculate heat budgets during
a 24 hour period from Lake Independence and Ice Lake. Students need
to develop a table or other appropriate format for recording their data.
Data Management and Analysis
Directed Study
Students are required to complete several calculations for questions 48 on
their worksheet. Encourage them to think about whether their calculations
are "reasonable".
Student Inquiry
Ask students to calculate the amount of heat lost or gained (in calories) between
the periods when the RUSS gathered temperature data in lakes. As they
complete the calculations they should consider the following questions:
What was the source of energy for heat gains?
Where did the heat go when the lake heat budget demonstrated a loss of heat energy?
How many calories were involved in the heat budget changes between each period of measurement?
Interpretation of Results
DirectedStudy
Students should complete questions 919 of the worksheet before participating
in a class discussion. Discuss how lakes might affect the temperature
of the surrounding environment. Discuss variables that the students
feel may affect the lake temperature/air temperature relationship.
Conclude with a review of how to calculate the information needed for this activity
(lake volume and changes in temperature for layers of a lake.)
Notes:The lake/air temperature relationships are primarily affected by seasons, latitude,elevation, shape of the lake
(morphometry), and wind.
Student Inquiry
Television viewers responded to initial reports on heat budgets with many questions.
Ask students to reflect on the viewers’ questions as they begin
to prepare their presentation.
Reporting Results
Directed Study
When the worksheets are done, discuss the results and how the students arrived
at their results.
Student Inquiry
Students should develop a television broadcast based on their analysis of WOW
lake data and investigation of heat budgets. The broadcast can be an
oral presentation, a TV script, video, or multimedia presentation.
Extensions
1. Compare temperature changes in a lake on different days during the same season
or different days in different seasons.
2. If students had been at the lake on the morning this data was collected, would there
have been fog above the surface of the water? Why?
3. Calculate the Birgean Heat Budget for this lake  Energy/year = E(midsummer)  E(midwinter)
4. Compare the heat budget for this lake to four lakes in other ecoregions in Minnesota.
