Activity: How dissolved oxygen varies with lake depth and thermal stratification

Summary: Students will be able to describe how lake thermal stratification and dissolved oxygen levels relate to a lake’s ability to support animal life.

You will need:

Procedure: This lesson and activity utilize the 5 E learning cycle, to find out more check out this factsheet

Explore

In this phase of the lesson, students are introduced to the Great Lakes FieldScope project. They will explore how it can be used to map and graph dissolved oxygen data. Take the students to a computer lab or distribute laptop computers. Direct students to the Great Lakes FieldScope website. Take a minute to read the welcome screen and become familiar with the available options. Walk students through the different options so they are comfortable navigating the site on their own.

Optional:

Assign stations to student groups.

  • Six research stations within the Great Lakes provided data for this assignment. These are labeled 1047, e10, 968, E42, 1003 and 1190. Students can work as teams or individually to analyze data from their assigned station.

Have each student read and follow these instructions:

  • On the FieldScope homepage select the Map Data tab.
  • From there, select under the Select a Map, choose the Teaching Great Lakes Science tab.
  • Choose the Exploring Great Lakes Environmental Data map. This will open up the map with the selected stations for this lesson.
  • On the map page, select Analyze Data on the bottom of the list on the left hand side of the screen. This will take you to the Graph Data section of Great Lakes FieldScope.

Lake Erie points
Figure
1: Lake Erie Bathymetry (Credit: NOAA)

Select Variables:

  • In the Variables section, highlight Depth and Dissolved Oxygen and click the green arrow between the two columns to move the desired variables to the Selected Variables
  • Figure 2. Selecting scatter plot.Once variables are selected, the Scatter Plot graph on the right side of the screen will become enabled. Click on the Scatter Plot. Then click the Next button at the bottom of the screen.

GL FieldScope screenshot
Figure 2. Selecting scatter plot.

Filter Data:

Next, apply a filter so only your station appears in the graph.

  • On the right hand side in the Filter List, deselect all stations that are not your assigned station. Once you have selected the appropriate station, click Next.

Define Axes and Labels:

  • Click the Define Axes and Labels tab. Ensure Dissolved Oxygen is selected as the Y-axis and Depth is selected as the X-axis by using the drop down menus. The X-axis is always the independent variable, while the Y-axis is the dependent variable. Delete the “Dissolved Oxygen vs Depth” in the title of the graph and change it to the assigned station name “Lake Erie Station ___”. Once complete, click Next.

View Graph:

  • Now students can view the graph they just created. Students may have to adjust the maximum value on the X- and Y-axes so the graph is centered on their points. This can be done by selecting Graph Settings on the left hand side of the graph and changing the min and max values of the X- and Y-axes. The value of each data point can be viewed by clicking directly on the point. Check the box next to Data table at the top of the graph to view all the data at once. View the legend of the graph by selecting Show Legend in the top right corner of the screen.

Note: It is important to notice that the left end of the X-axis is the shallowest water. As data points move along the X-axis to the right, they are moving down the water column.

Lake Erie Station 968
Figure 3. Example graph for station 968.

Explain

This section of the lesson and activity asks students to look at the data they have just graphed and draw conclusions. Have students work through the worksheet together with their classmates to promote a discussion.

  • Provide students with the attached data worksheet. Ask them to answer each question using the graph they just created. While students are working, display the FieldScope Map of Lake Erie station locations so they can compare graphs from each station.