Hypoxia:
The 0₂ Blues

Lesson Overview:

National Science Education Standards:

Content Standard A: Science as Inquiry
Abilities Necessary to do Scientific Inquiry

Strand 3: Skills for Understanding and Addressing Environmental Issues
1. Skills for Analyzing and Investigating Environmental Issues

Key Concepts:

1. An understanding of phenomena associated with eutrophication, such as dead zones and overturn, requires an understanding of how water can layer due to density differences.

2. Water layers can create boundaries or zones that prevent vertical mixing of the water column.

Students will:

compare various water samples for density differences.

model a thermocline.

Cross-Curricular Connections:

Language Arts:
• Communicate student observations and results.

Mathematics:
• Plot data changes over time.

Visual Arts:
• Create color-coded models of different layers in the water columns of ocean or lakes.

Controlling Variables
Hypothesizing
Modeling
Experimenting

Materials:

Per Group
Clear plastic containers (The 1 quart containers that you get at the deli section of a grocery store are great for this. You may also use recycled plastic soft drink bottles)
Salt
Red and blue food coloring
Spoon

One 50-minute class period

Procedure:

1. Assign students into cooperative groups of 4.
   
2. Each member of the group should prepare the following in quantities suitable for the containers being used.
   a. a saturated salt solution
   b. freshwater with blue food coloring
   c. hot tap water with red food coloring
   d. cold tap water
   
3. A member of the group should fill a container one third full making a layer of freshwater.
   
4. Have each group member predict what will happen when saltwater is mixed with the freshwater and what will happen when the freshwater is mixed with the saltwater.
   
5. Have a group member slowly add the saltwater to raise the volume up another one third of the container. Pour the water slowly over a spoon to prevent turbulence.
   
6. Have each student make and record observations.
   
7. Reverse the procedure in step #5 and make and record observations.
   
8. Repeat steps 3 - 7 using cold and hot water.

Suggested Discussion Questions:

Is saltwater higher or lower in density than freshwater? Why?

Is hot water higher or lower in density than cold water? Why?

Explain your observations in light of the equation for density (D=M/V).

Where in natural ecosystems do we find saltwater and freshwater mixing or layering?

Where in natural ecosystems do we find cold water and warm water mixing or layering?

Further Investigations:

Recreate one of the setups above that formed a visible layer and let it set for an extended period of time. How long does it take for mixing to occur?

Water Quality Expert
Oceanographer
Coastal Planner

Assessment Procedures:

Using a rubric students should be assessed on:

• hypothesis development
• experimental procedures
• record keeping
• conclusions based upon evidence