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Aquatic Respiration
Chemistry of Oxygen Solubility
Data Interpretation
Diel Temperature Variation in Lakes
Effect of pH
Effect of Photosynthesis and Respiration on Aquatic Chemistry
Fish Stocking Decisions
Heat Budgets of Lakes
Increased Conductivity
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  Studying Diel Temperature Variation in Lakes

Student Name(s): _____________________________________________

Date: ______________________

Knowledge Base
Select a WOW lake to study for this lesson. Predict the greatest temperature change you expect to observe during a 24-hour period during the summer. Base this prediction on your knowledge and experience with lakes. Identify the lake depth where you expect that change to occur. Enter your information into Table 1.

Experimental Design
The research question to investigate is: "How much does a lake vary in temperature during a 24-hour period during the summer?" Select a date during the summer when there is temperature data available over a 24-hour period. Enter the date into Table 1.

Data Collection
Complete Data Table 1 with the data for the 24-hour period. Be sure to enter the depth of the deepest reading. (If you have access to spreadsheet software you may want to create a spreadsheet that replicates the table.)

What time was your morning data collected? ______________

What time was your afternoon data collected? ______________

What time was your evening data collected? ______________

What time was your night data collected? ______________

Data Table 1

WOW Lake:

Date studied:

Prediction of greatest temperature change:

Predicted depth of greatest temperature change (in meters):

Temperature Data

Depth in meters





Top (1 m)


4 m


7 m


10 m


Bottom = ___ m


Data Management and Analysis

  1. Create a line graph of your data (using either graph paper or spreadsheet software.) Label your X-axis as time and your Y-axis as depth.
  2. Review your data table and graph and answer the following questions.
    1. At what depths or times is there missing or incomplete data?
    2. Look for reasonable temperature values. Do the temperatures make sense for this time of year? Which temperature readings might represent some type of error? (Explain why you believe these might be erroneous readings.)

Interpretation of Results

  1. Use the Internet, a newspaper, or other resource to identify and mark the time of sunrise and sunset on your graph.
  2. Write a brief explanation of what your data shows. Relate your results to what you know about temperature changes and/or to your personal experiences with lake temperatures. Knowing that heat energy is transferred through the process of conduction, and radiation, describe the variables you believe may influence temperature changes in a lake. Which of those processes appears to lead to the greatest changes of temperature?

Reporting Results
Turn your results in to your teacher. You need to include your data table and answers to questions 1-4. Also, include answers to the following questions. (Base your answers on what you know about the transfer of heat energy and what you have observed about temperatures in your lake over a 24-hour period.)

  1. What was your initial prediction for the greatest temperature change and lake depth for that change?
  2. Describe how the following might affect surface water temperatures:
    1. rain
    2. wind
    3. lightning
    4. sunlight
    5. cloud cover
    6. water clarity
    7. human activities
    8. geothermal energy (the temperature of the earth beneath a lake)
  3. Is there a thermocline located in your lake? At what depth?
  4. Between what time periods did the surface water temperatures change most rapidly?
  5. How deep into the water column was temperature affected by surface events?
  6. What might have happened to the air temperature above the lake's surface as the surface waters cooled? Explain your thinking.
  7. How might a greater or lesser amount of wind affect the temperature changes you observed?
  8. Explain how diel temperature changes might differ in:
    1. a crystal clear lake that is long, narrow, and 30 meters deep
    2. a bog-stained lake that is over 3 kilometers in diameter and less than 3 meters deep
    3. a small creek without tree cover
    4. a spring-fed creek with full tree cover

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date last updated: Saturday March 06 2004