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  Increased Conductivity – Worksheet 4
 

Conductivity in Ice Lake

Group Names: ________________________________________________

Date: _______________________

Knowledge Base

  1. What four main factors affect conductivity in lakes?

    1.

    2.

    3.

    4.

 

Experimental Design

  1. Use the "Data" section of the Web site to find the following information. Select "Ice Lake" and "Current Profiles." Select the data for the week of Jan. 3, for the 2:00 p.m. sampling period. What changes occur in RUSS parameters as the probe drops from the surface to the depths of the lake? Circle the correct answer for your January profile.

    With increasing depth, temperature increases decreases stays the same

    With increasing depth, pH increases decreases stays the same

    With increasing depth, conductivity increases decreases stays the same

    With increasing depth, dissolved oxygen increases decreases stays the same

    With increasing depth, DO % saturation increases decreases stays the same

    With increasing depth, turbidity increases decreases stays the same

  2. Now select the data for Ice Lake for the week of July 12, 1998. What changes occur in this profile as the RUSS probe drops in the lake?

    With increasing depth, temperature increases decreases stays the same

    With increasing depth, pH increases decreases stays the same

    With increasing depth, conductivity increases decreases stays the same

    With increasing depth, dissolved oxygen increases decreases stays the same

    With increasing depth, DO % saturation increases decreases stays the same

    With increasing depth, turbidity increases decreases stays the same

  3. Compare the water quality parameters for July to those in January. In what ways are they similar or different?

  4. Using the method described in the WOW lesson on the heat budgets of lakes (http://wow.nrri.umn.edu/wow/student/heat/study.html), find the volume of Ice Lake.

    V= _______________________

  5. In early July1998, a strange pattern in conductivity measurements was recorded in Ice Lake. Download the data and then graph conductivity at 1 m, 5 m, and 10 m depths in the lake for each of the dates indicated in the table below.
Date

1 m Depth

5 m Depth

10 m Depth

6/28/98

6/29/98

6/30/98

7/1/98

7/2/98

7/3/98

7/4/98

7/5/98

7/6/98

7/7/98

7/8/98

7/9/98

7/10/98

7/11/98

7/12/98

 

Data Management and Analysis

  1. Graph conductivity vs. depth, creating a separate line for each day and use the color plotter feature online to observe changes in conductivity during the two week period. On what day did the conductivity values peak? ___________________

  2. Were there major changes in other water quality parameters during the two week period beginning June 28, 1998? If so, what might these changes tell you about the possibility of sensor error or data transmission problems?

  3. Determine the actual increase in conductivity for each of the following depths for the two week period beginning June 28.

    at 1 m = __________ at 5 m = __________ at 10 m = _________

  4. What is the average increase in conductivity during the two week period beginning June 28, 1998? (Average the three values in #9.)

Interpretation of Results

  1. What factors might explain why the conductivity increases with depth in summer and not in winter?

  2. List some factors that might explain the jump in conductivity during the two-week period beginning June 28, 1998.

  3. What further lab or field research might help explain the increase in conductivity? What other data could you download from WOW or other sources to help identify the source of this conductivity increase?

  4. An increase in conductivity of 100 uS is equivalent to an increase in salt (sodium chloride) concentration of 0.05 g/liter. Using that correlation and the volume of the lake, determine how much salt would be required to produce the observed increase in conductivity. (Choose an appropriate unit for the mass of salt.)

  5. Develop a hypothesis for why conductivity increased in early July of 1998. Explain and back up your theory with logical reasoning and evidence if possible.

Reporting Results

  1. What are some of the strengths and limitations of your team’s theory on the cause of the conductivity increase during early July 1998 in Ice Lake?

 

 

 


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date last updated: Saturday March 06 2004