Credits
Marlene Schoeneck initiated this lesson.

Most northern lakes are sealed off from terrestrial influences in the winter by a lid of ice. The ice limits gas exchange at the lake/air interface, and reduces light levels as snow cover accumulates. Life processes go on, but decreased photosynthesis, accumulated waste products, and continued respiration make survival in the self-contained environment more difficult. Prolonged exposure to such conditions may create problems in managed systems where maintenance of fish populations is an important factor to consider.

Part I - Winter Lake Laboratory Simulation

Knowledge Base
Discuss in your lab group, or as a class, problems that have developed in area lakes from winter conditions. What physical and biological factors determine the severity of ice effects? What types of management practices may improve or limit the negative impacts of ice cover?

Experimental Design
You will need the following equipment:

1. 2 , 250ml clear bottles or jars with essentially airtight lids
2. Pond, lake, or aged tap water
3. Organic/mucky sediment, 75 ml per jar
4. 6 sprigs of Anacharis (Elodea) or other aquatic plant
5. A refrigerator or other method of keeping one of the microcosms chilled. (The colder the better, without freezing the jar solid!)

Set up 2 identical jars as simulated "lakes" using the materials listed above. Begin by placing 75 ml of organic sediment in the bottom of each jar. Add 3 equal-sized sprigs of your aquatic plant to each jar and fill to the brim with the water. Cap the jars and place one jar under a plant light in room temperature. Label this jar "Summer." Put the second jar in the refrigerator or other means you have selected to keep it cold. This jar represents a lake in winter. Label it "Winter." Take care not to allow the jar to freeze solid! You may need to do some experimenting with temperature settings previous to the start of your experiment.

Data Collection
1. Measure dissolved oxygen (DO), pH and CO2 levels in each of your jars. Sensors, rather than kits, are preferable for testing. (If using a test kit, slowly replenish the water taken from each bottle with water from the same source so as not to introduce more oxygen to the sample.

2. Take readings once or twice a day over a 5-day period. Enter your values for each reading in the chart below.

Lake Chemistry Readings

Data Management and Analysis
Create one graph for each factor that you measured (DO, pH, Temp), which compares data collected from each of your "lakes". Graph your data by hand or use an Excel spreadsheet. Follow instructions for the template on the WOW site. Be sure all parts of the graph are properly labeled.

Interpretation of Results

1. What changes occurred in your "lakes" during the course of the study?

2. How do you account for the changes in your "lakes"? (Think about the content and covering of your "lakes".)

3. How might these changes relate to conditions in an actual lake in winter? What ramifications do they have for lake life?

4. What aspects of this simulation are not realistic? Suggest some revisions that would more accurately simulate winter lake conditions?

Reporting Results
Keep your results to turn in with part 2.

Part II. - Changes in a Winter Lake

Knowledge Base
Consider the results of your winter lake simulation. What lake chemistry changes might you expect to see in an actual lake? Recall your discussion of the physical and biological components of lakes as you consider their influence on a specific lake and its winter dynamics.

Experimental Design
Imagine your local Sportsmen's Club has been asked to purchase aerators for Ice Lake to reduce winter fish kills. They first would like to be sure that winter conditions in the lake justify the installation of these units. Since your science class has been monitoring the lake for several years, the club has come to your school in search of the needed evidence. Use the DVT Toolkit, located in the data section of the WOW site, to look at Ice Lake profiles for the winter of 1998-1999. Assume that ice formation occurred around 12/27/98 and ice out occurred around 3/21/99. Use the "plotter" function to display your data.

Data Collection
Collect Ice Lake RUSS data weekly for the period spanning Sept. 1, 1998 to May 1, 1999. Create a table and record temperature, pH, and dissolved oxygen values at depths 2-4m and 8-10m during this period of time.

Data Management and Analysis
Use an Excel spreadsheet to graph the data you have collected.

Interpretation
1. What changes did you observe in the parameters you measured over the winter at your lake?

2. What physical characteristics of your lake might have had an influence on the results that you observed in your data? How?

3. What knowledge do you have of the biological characteristics and trophic state of your lake? How might these have affected the life sustaining ability of your lake? What else would you like to know to increase your confidence in your recommendations?

4. Based on the above research, what recommendations would you have for the Sportsmen's Club in regards to installing (or not installing) aerators on the lake?

5. What other management practices might help prevent fish kills in the lake besides installing aerators?

Reporting Results
Plan an oral presentation of your results. Create graphs or posters to illustrate your discussion. How do your results and recommendations to the Sportsmen's Club compare with other groups? Turn in your graphs and responses from part 1 and 2 to your teacher.