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Home > Special Topics > The Dead Zone > Activity #1

The Dead Zone: Activity #1

Profile Mapping of Dissolved Oxygen (DO) by Depth for Each Station

Individual student

Introduction/Purpose:
Scientists gather information about the dead zone at several stations. Data from each station are analyzed from the surface to the bottom, and changes in dissolved oxygen (DO) and other variables such as temperature, salinity and nutrients can be observed and hypoxic zones are identified. This activity will introduce students to the first step in analyzing oceanographic data in a water column profile by plotting and observing the changes in DO from the surface to the bottom at one station. These profiles will be used in Activities # 2, 4 and 5. The same procedure can also be used to graph profiles of temperature and salinity.

Objectives:
Each student will:

  • Work with data from one or more stations.
  • Plot DO (mg/l) by depth (meters).
  • Observe and record changes in DO with depth.

Louisiana Science Standards:

  • Grades 5-8: SI-M-A4, A-4-M, D-1-M
  • Grades 9-12: SI-H-A3, D-7-H
  • Skills: Observing, measuring communicating, formulating models, using data, interpreting data, graphing and determining scale

Materials:

Procedure:
As a class:

  1. Assign station data sheets to each student.
  2. Determine the maximum and minimum depth for the whole project area (all stations).
  3. Determine a scale for plotting profiles for all students to use.
  4. Discuss reasons for setting “0" at the top of the “y” axis (“0" is at the water surface). Note that the gulf bottom will be determined by depth.

Each Student:

  1. Set up the graph by using the agreed upon scale from the class discussion.
  2. Draw the gulf bottom on the graphs by plotting depth to bottom for his/her station.
  3. Label the upper end of the “y” axis as “0" (“0" will not be at the x, y intercept) to represent the ocean surface.
  4. Plot the water column profile by plotting DO (mg/l) by depth (meters).
  5. Determine depths where hypoxic conditions occur at each station.
  6. Observe and record changes in DO with depth.
  7. Answer questions about the profile.

Questions:
Using your data table and profile plot, answer the following questions. The answers to these questions will be used for Activity #2.

  1. How deep is your station?
  2. What was the maximum and minimum temperature in your water column?
    At what depth does each occur?
    Does the temperature increase or decrease with depth? Why?
  3. What was the maximum and minimum salinity in your water column?
    At what depth does each occur?
    Does salinity increase or decrease with depth? Why?
  4. What was the maximum and minimum density in your water column?
    At what depth does each occur?
    Does the density increase or decrease with depth? Why?
  5. What happens to the salinity and density of the water as the temperature changes?
  6. What was the maximum and minimum DO in your water column?
    At what depth does each occur?
    In your station profile does DO change consistently with depth? Why or why not?
  7. Does your station fall within the hypoxic zone (<2 mg/l)?
    Does your station have anoxic (0 mg/l) conditions?
  8. What is the maximum and minimum depth at which hypoxic conditions exist in your profile?
  9. What is the height of the dead zone at your station in meters (difference between the minimum and maximum depth of hypoxic zone).
  10. What percent of the water column is hypoxic at your station (depth of dead zone divided by total depth)?
  11. Compare your profile with other students’ profiles.

Teacher Note:
An additional graphing activity, which involves graphing the water column profile through time and observing changes through time was developed by the Virginia Institute of Marine Science on its website, www.vims.edu/bridge (go to Data Port-Data Tip Archives-Chemistry, October 1999). This exercise can be completed using online data and Microsoft Excel software to acquire the data and complete the graphing on an IBM-compatible computer. For instructions for this exercise for 1994 cruise data comparing water column profiles from March through October 1994,go to www.vims.edu.bridge/deadzoneexercise.html. An example of profiles created in this exercise is provided in a PowerPoint file (DZ visuals).

Go to Activity #2