Credits
Mitch Albers developed this lesson.

Goals
Students will investigate the properties of water and develop an understanding of how water behaves in a lake environment. Wet laboratory and WOW data experiments demonstrate the unique properties of water and its importance to lakes and living things.

Introduction
Water is essential to life on earth and totally dominates the chemical composition of all organisms. The characteristics of water regulate a lake's metabolism. Its unique thermal-density properties, specific heat, and freezing point allow the formation of a stratified environment that controls the chemical and biological properties of lakes.

Students can meet the goals for this lesson by completing either a directed study or student inquiry lesson. The directed study lesson guides students through two worksheets. One worksheet corresponds to a lab experiment on temperature density stratification. Students analyze WOW data on the second worksheet. Students need to print both worksheets.

The directed study lesson can be accessed in the student section of WOW under the title "Studying the Properties of Water."

The student inquiry lesson places students as chemistry teachers. It challenges students to use WOW data and a lab experiment to teach about typical summer and winter lake profiles. The end product is a written report, poster, oral report, or multi-media presentation.

The directed study lesson can be found in the student section of WOW under the title "Investigating the Properties of Water."

Outcomes
Students will:

1. Understand the unique properties of water and apply them to a lake environment.
2. Retrieve real-time and historical data obtained from WOW lakes.
3. Explain how WOW data illustrates some properties of water.

Keywords
Polarity, hydrogen bonds, cohesion, surface tension, adhesion, capillary action, density, specific heat, neuston, heat of vaporization, universal solvent

Prerequisites
Students need a basic understanding of chemistry and basic spreadsheet and graphing skills. They should also be able to retrieve WOW data prior to completing this lesson.

Materials/Resources/Software

1. Excel spreadsheet, Internet Access, Web Browser, Netscape version 4.07, MSIE version 4.0 w/Java 1.1.1 plug-in
2. Two 5-10 gallon aquaria
3. Plastic rulers
4. Thermometers
5. Red food coloring
6. 2 gallon carboy with valve/tygon tube/U-tube assembly
7. Salt
8. Pasteur pipettes
9. 5 gallons of refrigerated tap water (4-5°C)
10. Lake Models and Temperature Density Stratification Worksheets (for students completing the directed study lesson)

Time Required
Three hours

Curriculum Connections
Chemistry - dissolving, polarity, hydrogen bonds, cohesion, surface tension, adhesion, capillary action, density, specific heat, heat of vaporization, universal solvent

WOW Curriculum Links
Thermal Stratification, Heat Budgets of Lakes

Part 1

Knowledge Base
The WOW data visualization tools can help illustrate the changes in temperature and density during a year (see Figure 1). These changes could also be demonstrated by advancing the Profile Plotter through several sampling periods or by creating graphs in Excel. The WOW website resources for teachers and students includes several movies. The movies will take awhile to download (they are 2 - 5 Mb), but are useful illustrations of lab demonstrations showing thermal stratification and mixing in water. Check out the following links to see the kinds of thermal effects your students can demonstrate using simple lab materials. You will need the Quicktime Plug-in from Apple (no support for OS X) to view these movies.

• Movie 1 - Here's what happens when warmer water (green) enters the surface of a lake in winter. The second addition shows that the warm water is buoyant (less dense) than the cold water and therefore rises.
• Movie 2 - Here's what happens when colder water enters a summer-stratified lake.
• Movie 3 - Same movie 2 without the dyed green epilimnion.
• Movie 4 - See what happens to the epilimnion (mixed layer) and thermocline during a storm. Did the lake mix?
• Movie 5 - Same as movie 4, but with increased turbulence. See what starts to happen when the class 5 tornado hits.
• Movie 6 - Shows how stream sediment entering a lake or reservoir deposits its load. Why does some material stay in the upper layer and some crash to the bottom?
• Movie 7 - An estuary is a 2-layer system with freshwater overlying salt water. Here we see how freshwater behaves when added to each layer.
• Movie 8 - Same as movie 7, but here we introduce water that is saltier than the upper freshwater layer. Example: Hurricanes can "throw" huge amounts of saltwater into coastal lakes. What happens to this water and what might its impact be?

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: Temperature Profile for Ice Lake

Figure 2. Temperature Profiles for Winter and Summer on Ice Lake

Directed Study - Lake Models
Refer students to the student reading on the unique properties of water. The reading introduces students to the unique structure of water, cohesion of water molecules, water's specific heat, evaporation and cooling, water’s liquid range, frozen lake density, density relationships of water, and water as a universal solvent.

Student Inquiry - WOW Lake Profiles
Refer students to the student reading on the unique properties of water. The reading introduces students to the unique structure of water, cohesion of water molecules, water's specific heat, evaporation and cooling, water’s liquid range, frozen lake density, density relationships of water, and water as a universal solvent.

Experimental Design

Directed Study
Students create summer and winter lake models based on density stratification (modified from R. Axler). The Lake Models Worksheet provides directions for creating the lake models. Ask students to hypothesize what will happen when hot water is added to the summer and winter lake models.

Student Inquiry
Students play the role of a chemistry instructor. They need to demonstrate typical summer and winter lake profiles to their class. Ask them to write a 1-2 paragraph lesson plan detailing how to use WOW data to teach students about how water behaves in a lake environment.

Data Collection

Directed Study
Refer students to the appropriate section on the Lake Models Worksheet. Students need to collect and record the temperature of each model at 2 cm intervals.

Student Inquiry
Ask students what data they plan to collect to develop a typical summer and winter lake. How do they plan to organize the data? Remind students that their presentation must be clear for their students. They should collect the data from WOW.

Data Management and Analysis

Directed Study
Refer students to the worksheet. They need to graph the temperature data. Remind them to label their axes and legend and title their graph.

When the graphs are completed students should fill a jar with hot water (from faucet) and add enough food coloring to make it very red. They should forcefully inject it as deep as possible into the winter lake model and observe how the water behaves. After students have recorded observations for the winter lake model, they should fill another jar with hot water and add food coloring to make it very red. They should forcefully inject it as deep as possible into the summer lake model and observe how the water behaves.

Student Inquiry
Students should create graphs and/or tables to display the WOW data. Remind them to label axes and legends and title graphs and tables. Students should consider how to explain the graphs and tables to their class.

Interpretation of Results

Directed Study
Refer students to the appropriate section on the Lake Models Worksheet. Students need to explain how each of the models responded to the injection of hot water and provide a reason for that response. As time permits, students can make up several jars of different temperature water (ice water, 10-15 degrees C, hot, and hot plus a tablespoon of salt), and inject each at different depths and observe the behavior of the water.

Student Inquiry
Students should reflect on conclusions that their class might draw from the data. How can they help their students reconsider any possible misunderstandings about lake profiles? What other data might help their students understand typical lake profiles?

Reporting Results

Directed Study
Ask students to share their results with the class. Were there discrepancies among results? Can students provide an explanation for the discrepancies? Students should turn in their worksheet.

Student Inquiry
After students complete Part 2, they should create a lesson about typical lake profiles. It can be a written paper, poster, oral report, or multi-media presentation. They should prepare to answer any questions their class might have.

Part 2

Knowledge Base

Directed Study - Temperature Density Stratification in WOW Lakes
Ask students to consider how to use WOW data to replicate what they learned from the student reading and the laboratory exercise. What WOW data might demonstrate temperature density stratification?

Student Inquiry - Lake Models
Students need to consider the following scenario - some students in the class are still a bit confused about typical summer and winter lake profiles. How can a teacher demonstrate the profiles in a laboratory? What questions can guide students’ thought processes?

Experimental Design

Directed Study
Refer students to the appropriate worksheet section. They need to use WOW temperature data and the Profile Plotter to determine if the results from the lake models apply in an actual lake environment. Ask students to consider what data might verify their results.

Student Inquiry
Provide students the following materials to create summer and winter lake models.

1. two 5-10 gallon aquaria
2. plastic ruler
3. thermometer
4. red food coloring
5. 2 gallon carboy with valve/tygon tube/U-tube assembly
6. salt
7. Pasteur pipettes
8. 5 gallons of refrigerated tap water (4-5 °C)

Students need to write a lesson plan detailing how to use these materials to demonstrate typical summer and winter lake profiles to their class.

Data Collection

Directed Study
Refer students to the appropriate worksheet section. Students collect temperature data for Ice Lake on January 2, 1999 and July 2, 1999.

Student Inquiry
What do students expect to see in their lake profiles? How do they plan to organize the data? Remind them that their presentation must be clear for students. They should create their lake profiles.

Data Management and Analysis

Directed Study
Refer students to the appropriate worksheet section. Students graph the temperature data. Remind them to label axes and legends and title their graphs.

Student Inquiry
Students should create graphs and/or tables to display their results. Remind them to label their axes and legends and title their graphs and tables. Did the results replicate the WOW data?

Interpretation of Results

Directed Study
Refer students to the appropriate worksheet section. Students determine when Ice Lake became isothermic and provide environmental conditions that contributed to making the lake isothermic. They consider whether or not the analysis of Ice Lake verifies the lab results and what additional data might confirm the earlier results.

Student Inquiry
Ask students to reflect on what conclusions their students might draw from the experiment. Does the experiment confirm the WOW data? If not, why? How can they help their students reconsider any possible misunderstandings about the lake profiles? What other data might help students understand typical lake profiles?

Reporting Results

Directed Study
Students should present their results to the class and explain any problems with the data. Are results consistent among the class? If not, why? Students should turn in their worksheet.

Student Inquiry
Students should use the data, tables, and graphs to create a lesson about typical lake profiles. It can be a written paper, poster, oral report, or multi-media presentation. They should prepare to answer any questions the class might have.

Extensions and Links

1. Lessons for teaching biology to prospective K-12 teachers can be found at http://www.biologylessons.sdsu.edu/classes/lab1/lab1.html
2. The Universities Water Information Network disseminates information of interest to the water resources community and all concerned with water resources. Access at http://www2.uwin.siu.edu/WaterSites/index.html
3. The Minnesota Water Resources Research Institute is another helpful site. Its address is http://wrc.coafes.umn.edu/wrri/

Resources

• Campbell, Neil, (1996) Biology, (Fourth Edition). Benjamin Cummings Publishing.
• Cole, G.C. (1988) Textbook of Limnology. Waveland Press: Prospect Heights, IL
• Dorsey, Ernst N. (1968) Properties of Ordinary Water. New York, Hafner Publishing.
• Monson, Bruce A. (1992) A Primer on Limnology (Second Edition). Public Report Series #6. Water Resources Research Center: St. Paul, MN.
• Wetzel, R.G. Limnology, (1983) W.B. Saunders Publishing.