Credits
Barb Liukkonen developed this lesson.

Goals
This activity introduces students to patterns of temperature variation during a 24-hour period in temperate lakes and builds skills in importing, managing, graphing, and interpreting data.

Introduction
As features of a local landscape, lakes moderate air temperature close to their shores during the open water season. Casual observers understand that weather influences water temperature on a daily and seasonal basis. What is less understood is how much water temperature varies during the course of a single day and to what depth the variation occurs. Abiotic ecological factors including air temperature, wind, day length, cloud cover, and lake basin structure play a role in determining daily temperature variation in lakes. Understanding the interaction of these factors helps students develop an understanding of temperature stratification and seasonal turnover in lakes.

Outcomes
Students will:

1. Use RUSS units to retrieve temperature data for a 24-hour period.
2. Use a data table to record the effects of time and depth on water temperature.
3. Graph and interpret temperature data by depth over time.
4. Hypothesize what environmental factors could influence daily temperature variations within a lake.
5. Make plausible predictions about diel temperature variation based on presented environmental conditions.

Keywords
Diel, temperature, stratification

Prerequisites
Students should have a basic understanding of water density, thermal stratification, and seasonal overturn. This activity provides a useful follow-up to lessons on convection, conduction, and radiation.

Materials/Resources/Software
Excel spreadsheet (optional)

Time Required
The time needed depends on students’ knowledge of the WOW website and their graphing abilities. The lesson requires approximately one to two hours, preferably on consecutive days. Students collect air temperature in the vicinity of the lake from the appropriate National Weather Service site (see Current Conditions for each lake), by directly measuring air temperatures as frequently as possible, or by finding weather dates on the Internet at sites such as the University of Minnesota's Climatology Working Group http://www.climate.agri.umn.edu/scripts/hradius.htm or the NOAA National Data Center http://www.nndc.noaa.gov/cgi-bin/nndc/buyOL-002.cgi. Students will retrieve and graph the RUSS data and answer questions.

Curriculum Connections
Physics - conductive cooling and heating, evaporation, convection currents, heat reflection, electromagnetic radiation, angle of incidence, water clarity

Math - coefficient of heat transfer

WOW Curriculum Links
Heat Budgets; Thermal Stratification

Procedure
Students can meet the goals for this lesson plan by completing a directed study or an inquiry lesson. Students may want the directions for their lessons printed.

The directed study lesson is found in the student section of WOW under the title: "Studying Diel Temperature Variation in Lakes."

The inquiry lesson is found in the student section of WOW under the title: "Investigating Diel Temperature Variation in Lakes."

Knowledge Base
The WOW data visualization tools can help illustrate changes in temperature during an extended period of sampling (see Figure 1). Changes in temperature could also be demonstrated by advancing the Profile Plotter through several sampling periods or by creating a graph in Excel (see Figure 2). You may want to display these 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: Ice Lake Temperatures

Figure 2. Diel Temperatures in Ice Lake on Aug. 18, 1999

Directed Study and Student Inquiry
Introduce this lesson by asking for student observations about changes in lake temperature during different times of the day. Discuss changing temperatures over a 24-hour period.

Ask students to hypothesize or brainstorm what they feel the three primary influences on lake temperature may be and attempt to reach a class consensus.

Experimental Design

Directed Study and Student Inquiry
Explain that this lesson is an activity that investigates climatic influences on lake temperature over a 24-hour period and answers the research question, "How much does a lake vary in temperature during a 24-hour period in the summer?" Students select a WOW lake and date to examine temperature data.

Directed Study

• Refer students to the data table in the "Studying Diel Temperature Variation in Lakes" lesson

Student Inquiry

• Students will need to decide which temperature measurements and depths are necessary to answer the research question.

Data Collection

Directed Study

• Assign student teams to retrieve RUSS data on water temperature at one-meter intervals every four to six hours for a 24-hour period beginning at midnight.

Student Inquiry

• Students use the WOW database to find the temperature data they need.

Data Management and Analysis
Students download RUSS data into their spreadsheets and graph and analyze the data.

Directed Study

• Students need to format a data table in Excel to receive temperature profile data. Students need to consider how depth, time, and temperature data should be organized for plotting on a graph. Ask students to explain whether a bar graph or line graph is most useful when others need to understand data. Can missing or erroneous data make the data unusable?

• Students analyze the data for errors or inconsistencies and answer worksheet question 2.
• They construct a line graph that plots temperature by selected depth over their 24-hour period of study. Surface temperature (1 m will be the shallowest) and the 2-3 meter intervals will give a reasonable number of lines to graph. They may use the graphing capabilities in the spreadsheet program or construct the graph by hand on graph paper. Remind students to label the x axis as time and the y axis as depth. Each different line also requires a label.
• Students use the Internet, newspaper, or other resources to identify and mark the time of sunrise and sunset for their sampling day on their graphs. They could also devise their own method to estimate the amount of cloud coverage for their sampling day. Hypothesize how cloud coverage affected the temperature profiles that they recorded. (Daily cloud cover is a feature in certain weather web sites.)

Student Inquiry

• Students construct a table and graph to display data and answer the research question.

Interpretation of Results
Wrap up the lesson with a discussion of how diel temperature changes may vary in different settings. Discuss the environmental factors that might affect the diel temperature changes.

Directed Study and Student Inquiry

• Students write an explanation of their findings.

Reporting Results

Directed Study

• Students should finish their work on diel temperature changes by completing and turning in their worksheet.

Student Inquiry

• Students develop a summary of their research findings. You will need to specify the final format: a written paper, oral presentation, poster, or multi-media presentation.

Evaluation
The completed data tables and graphs demonstrate students' ability to retrieve and present temperature data from a lake using RUSS units. Completion of the student worksheet or research summaries provides evidence of their level of understanding of the conceptual material contained in the lesson.

Extensions
1. If you are monitoring a nearby lake, record surface temperature on opposite shorelines during windy weather and calm weather. What do you observe?

2. Visit CoastWatch's website and view satellite images of surface temperatures in the Great Lakes (http://coastwatch.glerl.noaa.gov). How do you explain:

a) the patterns of surface temperature within a single lake?

b) the differences between lakes on a single date?

c) the presence of very cold water in Lake Superior during late June and the presence of warmer water (than June) in late October?