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# Activity: Air Supply – Graphing Dissolved Oxygen

Summary: Students graph dissolved oxygen (DO) from the surface to the bottom of Lake Erie using real data collected from the lake.

You Need:

• 100 minutes (2 class periods of 50 minutes each)
• Graph paper
• Pencils
• Ruler
• DO data from surface to the bottom for six stations in Lake Erie:

## Procedure

Create groups of six students and assign a station to each student in each group.

• The six stations are 1047, e10, 968, E42, 1003 and 1190.

### Part 1 – As a class

• Determine the minimum and maximum depth for all of the stations.
• Determine a scale for plotting profiles (minimum and maximum depths and dissolved oxygen levels necessary to fit all data onto the graphs).
• Y-axis – 0 to 35 meters
• X-axis – 0 to 8 milligrams per liter (mg/l)
• Discuss reasons for setting ‘0’ at the top of the y-axis.
• 0 is the surface, the deepest station is 33 meters deep

### Part 2 – Each student

• Using graph paper, create a graph using the agreed upon scale.
• Y-axis – 0 to 35 meters
• X-axis – 0 to 8 mg/l o Label x-axis and y-axis.
• Create a title using the station ID number.
• Label the bottom of the lake at each station.
• For example, station E42 is 22 meters deep.
• Plot dissolved oxygen (mg/l) by depth (meters).

### Part 3 – In small groups

• Answer data sheet questions.
• Compare your graph and data sheet answers with other students in your group.
• Collaboratively prepare a summary of findings to share with the rest of the class. Summaries should use evidence from graphs and data sheets and should include:
• Station(s) with the largest and smallest hypoxic zones.
• Location of station(s) with the largest and smallest hypoxic zones (on map of Lake Erie).
• Possible causes/factors related to the location of hypoxic zones.

Content source: Scavia, D., Professor of Natural Resources and Environment and Environmental Engineering, Graham Sustainability Institute Director and Special Counsel to the University of Michigan President for Sustainability. Donald Scavia has studied coastal dead zones for 25 years and led the first Gulf Dead Zone scientific assessment on behalf of the Clinton White House.