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  Studying Thermal Stratification

Knowledge Base
Consider your knowledge of thermal stratification. What does stratification look like in a lake? What evidence supports thermal stratification? Why does stratification occur? What factors might relate to thermal stratification?

A Demonstration of Thermal Stratification
You will need:

  • Two clear cups or glasses
  • One colored ice cube (add food coloring to the water before freezing)
  • One gallon of cold (the colder the better) colored water (use food coloring in the water)
  1. What do you think will happen when warm water is poured gently into a glass with cold colored water? Carefully pour a 1/4 cup of warm, clear water into the glass. (It is best if the warm water is poured slowly in from the side of a tilted glass to avoid mixing.) Try to ctreate a glass of water that has two distinctly separate layers.
  2. What do you think will happen when a colored ice cube is placed in a glass of warm water?Fill a glass with warm water. Place a colored ice cube in the glass. Observe and record what happens for 5 minutes. Empty the glass and fill it halfway with cold colored water.
You should be prepared to answer the following questions for class discussion:
  1. Why did the colored water sink?
  2. What are convection currents?
  3. Could you see convection currents in the glass? Explain.
  4. Why do you think convection currents might/might not be found in lakes?
  5. What similarities and differences exist between the layered water and what you might find in regional lakes during the summer?
  6. Why might layering occur in lakes?
Experimental Design
  1. You will be investigating temperature data from a WOW lake to determine if there is evidence of thermal stratification. Does your lake appear to act the same way as the glasses of water in the demonstration?

Data Collection
Your teacher will assign a lake and six dates to collect data for temperature profile graphs. After data are collected and analyzed the class will examine all of the temperature profile graphs in chronological order.

Data Management and Analysis

  1. Using the WOW data for your lake, create temperature profile graphs. If stratification is evident, label each of the layers (epilimnion, thermocline, hypolimnion).

Interpretation of Results
Consider the folowing questions as you prepare for your final report:

  1. Does the lake remain stratified throughout the summer?
  2. What variables might affect whether or not the lake remains stratified throughout the summer?
  3. How might temperature profiles of other lakes in the region compare to the lake monitored by RUSS?
  4. Why is this type of information important to people who monitor and manage or use our lakes?

Reporting Results
Turn your temperature profile graphs and any written responses to questions in to your teacher.

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date last updated: Tuesday September 21 2004