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, 250 ml clear bottles or jars with essentially airtight lids
2. Pond, lake, or aged tap water
3. Organic/mucky sediment
4. Several 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!)

Your goal is to develop an experiment that will model what might happen in a lake in the summer compared to the same lake in the winter. Set up 2 jars as simulated "lakes" using the materials listed above. Determine amounts of materials to use in each jar. Remember you want to generate data that will allow you to make a fair comparison of the results in each "lake." Cap each jar. Place one jar under a plant light in room temperature. Put the second jar in the refrigerator or other means you have selected to keep it cold. 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. Record the procedures you have developed so other scientists could replicate your experiment.

Data Collection
1. Decide what factors you would like to measure that you feel would be relevant to an ice-covered lake. Sensors, rather than test kits, are preferable for data collection. (If using a test kit, slowly replenish the water taken from each bottle with water from the original source, so as not to significantly change the sample. Write a brief rationale explaining why you chose to measure these factors.

2. Take readings once or twice a day over a 5-day period. Formulate a chart to enter your values for each reading.

Data Management and Analysis
1. 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" over the course of the study?

2. How do you account for changes in your lake?

3. How are these changes related 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 to more accurately simulate winter lake conditions?

Reporting Results
1. Keep 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 one of the lakes monitored by WOW in order 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 lakes for several years, the club has come to your school in search of the needed evidence.

Use RUSS data on the WOW site to determine a study lake with relevant data (many lakes have gaps in winter data sets). Consider how you will determine ice formation and ice out on your lake. What factors will you need to monitor in order determine the need for aerators on the lake? Over how long of a period of time will you need to look at data? Be prepared to explain the reasoning behind your experimental design.

Data Collection
Collect enough RUSS data for your lake to make a recommendation to the Sportsmen's Club for or against the purchase of aerators. You must make the determination of how much data is "enough" to provide clear direction, as well as what type of data is needed. Write a brief rationale for your decision (imagine justifying your plan to the club).

Data Management and Analysis
Use the data visualization tools or an Excel spreadsheet on WOW to organize and interpret the data you have collected.

Interpretation
Consider the following questions as you prepare for your presentation for the class on your winter lake:

1. What changes did you observe in the factors 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 aerators on the lake?

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

Reporting Results
Develop a presentation using graphs and other visual aids for your class, pretending they represent the "Sportsmen's Club". Explain your recommendations for installing (or not installing) aerators on your local lake. Be sure to back up your reasoning with data and explanations based on general lake processes and the characteristics of your particular lake. Compare your results to other members of the class. Turn in your presentation materials and question responses from parts 1 and 2 to your teacher.