LIMNOLOGY, FALL 2006

PRACTICE EXAM QUESTIONS FOR EXAM 1

ANSWERS AT THE END OF THIS FILE!

The exam has three sections:

1.      Definitions – choose 6 of 7 terms to define.  For full credit you must both define the term and explain why it is important in limnology.  This section is worth 18 of 100 points (<20%).

2.      Short answer – fill in the blanks, circle the correct answer, multiple choice.  Some of these questions will involve interpretation of graphs.  This section is worth ~40 points (40%).

3.      Short essays – these questions can be answered with short essays or bulleted lists.  Some of these questions will involve graph interpretation and applying knowledge to case studies.  This section is worth ~40 points (40%).

 

Please define the following terms and explain briefly why each term has significance in limnology (3 points each)

 

1. Neuston

 

2. Warm polymictic

 

3. Graben

 

4. Richardson's number

 

Please fill in the blanks or circle the correct answer (1 point for each correct answer)

 

1. When lake water warms in summer, aqueous carbon dioxide concentrations tend to increase / decrease / remain unchanged, and pH tends to increase / decrease / remain unchanged.

 

2. Geological and climatic activity during the earth's recent past (last 30,000 years) has tended to increase / decrease / keep unchanged the number of lakes present in North America.

 

3. If water is anoxic, then iron will exist in the Fe2+ / Fe3+ valence state and will / will not form an insoluble precipitate with OH- / CO32-

 

example redox reaction

Given the above diagrams:

 4. The reaction that might have been responsible for the change in sulfate concentration in the sediments from time 1 to time 2 is:                           .  Alkalinity should have increased / decreased between time 1 and time 2.  These sediments are most likely oxic / anoxic.

 

Please provide short but complete answers for the following questions:

 

1. During the summer the epilimnion of many lakes, like Lake Michigan, have a decrease in transparency simultaneously with formation of mineral particles in the water column.  These calcium carbonate whitings occur in part for physical reasons and in part for biological ones.  Please describe the processes and explain how the phenomenon occurs, including why transparency decreases.

 

2. Two lakes affected by the same climatic and geological conditions are quite different limnologically.  In one lake the spring turnover lasts for 1 week, while in the other lake the turnover lasts for 6 weeks.  Give two reasons why the lakes might differ.

 

3. Describe two factors that control bacterial numbers in lakes.

 

Please define the following terms and explain briefly why each term has significance in limnology

 (3 points each)

1. Neuston

2. Warm polymictic 3. Graben 4. Richardson's number


Please fill in the blanks or circle the correct answer (1 point for each correct answer)

1. When lake water warms in summer, aqueous carbon dioxide concentrations tend to increase / decrease / remain unchanged, and
        pH tends to increase / decrease / remain unchanged.
2. Geological and climatic activity during the earth's recent past (last 30,000 years) has tended to increase / decrease / keep unchanged
        the number of lakes present in North America.
3. If water is anoxic, then iron will exist in the Fe2+ / Fe3+ valence state and will / will not form an insoluble
        precipitate with OH- / CO32-
 
 

Practice Question 1
 

Given the above diagrams:
 4. The reaction that might have been responsible for the change in sulfate concentration in the sediments from
    time 1 to time 2 is:   sulfate reduction  .  Alkalinity should have increased / decreased between time 1 and time 2.
    These sediments are most likely oxic / anoxic.

Please provide short but complete answers for the following questions:

1. During the summer the epilimnia of many lakes, like Lake Michigan, have a decrease in transparency simultaneously with formation of mineral particles in the water column.  These calcium carbonate whitings occur in part for physical reasons and in part for biological ones.  Please describe the processes and explain how the phenomenon occurs, including why transparency decreases.

The key points to include are:

The transparency then decreases due to the suspension of small calcium carbonate particles in the water column that attenuate light.

2. Two lakes affected by the same climatic and geological conditions are quite different limnologically.  In one lake the spring turnover lasts for 1 week, while in the other lake the turnover lasts for 6 weeks.  Give two reasons why the lakes might differ.

Some possible differences are:

3. Describe two factors that control bacterial numbers in lakes.

Bacterial numbers are relatively constant in lakes, but there are many factors that contribute to bacterial growth and loss.

Some possible answers include:


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