Aquatic respiration can have a profound effect on an ecosystem. In the laboratory portion of this lesson, you explore how aquatic respiration affects water chemistry. Dissolved oxygen (DO) and pH are used as the indicators of the complex chemical interactions which occur. In the second part of the lesson, you use RUSS data to explore the changes in pH and DO that occur in the hypolimnion during the summer.

Part I — Aquatic Respiration in a Lab

Knowledge Base
Participate in the class discussion of events such as aquaria that have been overfed or left untended for prolonged periods of time, or minnow buckets that have been left without fresh water for a prolonged period of time. Consider what happens. Why do the animals often die in these situations? What water quality measures might relate to this situation? Why might similar situations occur in lakes?

Experimental Design
You need the following equipment:

1. Hach or Lamotte water quality testing materials (for analyzing dissolved oxygen and pH.) You will perform up to 5 analyses for pH and for DO if using meters, or two analyses if using chemical reagent kits.
2. 250 ml bottle with a cap
3. One (or more) of the following three options to place in your bottle:
   1. 4 two-inch minnows (fathead minnows are readily available and tolerant of low oxygen levels)
   2. 75-100 ml of sandy sediment
   3. 75-100 ml of organic/mucky sediment
4. A copy of the Respiration in a Microcosm Worksheet

The worksheet contains additional experimental design considerations and instructions for microcosm set-up.

Data Collection
Data Management and Analysis
Interpretation of Results
Reporting Results
Refer to the worksheet for these lesson components.

Part II — Aquatic Respiration in a Lake

Knowledge Base
Consider how what you have learned from working with microcosms might apply to a lake environment. How would you interpret changes in pH and DO in the hypolimnion of a lake?

You need a copy of the Aquatic Respiration in a Lake worksheet and access to WOW water quality data from a lake.

Experimental Design, Data Collection, Data Management and Analysis, Interpretation of Results, and Reporting Results

Refer to the Aquatic Respiration in a Lake worksheet for these lesson components.