Most of us have experienced temperature variation in lakes. In the same lake, a chilling morning swim becomes comfortable in the afternoon and then cool again in the evening. The physics principles of energy transferred as heat by conduction, convection, and/or radiation apply to lakes. In this lesson you will explore temperature changes in a lake over a 24-hour period. You will explore temperature change at different lake depths and hypothesize about factors that account for the changing daily temperature of lakes.

Knowledge Base
The research question to investigate is: "How much does a lake vary in temperature during a 24-hour period during the summer?" Based on your knowledge and experiences, predict the depth where you would expect to find the greatest change in temperature during a 24-hour period? How much change in temperature would you expect to find at that depth?

Experimental Design
Choose one of the WOW lakes for your investigation. As a scientist familiar with lakes you know that lake temperatures vary throughout the day and at different depths. The RUSS instrument is collecting temperature data at about 1 meter intervals through the depth of the lake. In trying to answer your research question, you need to make several decisions.

1. For what date will you collect your measurements? (Check the WOW data to make sure data are available for that date.) Why did you choose this date to collect your data?
2. Will you collect temperature measurements for all depths, or only selected depths?
3. What range of temperature measurements would you identify as "reasonable" for the date you selected? How will you handle measurements that do not fall in this range - measurements that might represent errors?
4. What do you think would be a reasonable maximum change in temperature at any depth of a lake during a 24-hour period in the summer? How will you handle measurements that exceed this?

Data Collection
Use the WOW web site to find the temperature data you need for your lake.

Data Management and Analysis
Create a table(s) and record your results. If you have access to computer spreadsheets you may want to create the table(s) on the computer to make it easier to graph your final results.

Graph the results of your table to show if there are any changes in temperature at different depths during a 24-hour period.

Interpretation of Results
Write a brief explanation of what your data shows. Relate your results what you know about temperature changes and/or to your personal experiences with lake temperatures. Refer to your predictions. Knowing that heat energy is transferred through the process of conduction, convection, 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
You need to present a research summary of your investigation. Your teacher will specify the format: a written paper, an oral presentation (like a presentation for a scientific conference), a poster format (these are also often done at conferences), or a multi-media presentation. Finish your research summary by describing how you would like to extend or expand your collection of lake data to more fully answer the research question.