Costa Rica Rainforest Experiment:
"Salinity in Soil"

- Equipment
- Data Collection Procedure
- Data Analysis
- Conclusions and Extensions

PASPORT Conductivity Sensor
(PS-2116)

Purpose

To level the conductivity of water before and after being mixed with soil samples and determine if the soil changes the level of conductivity.

Overview

In this activity, students will measure the conductivity of distilled water. Students will then filter the runoff from two different soil samples into the water and take the conductivity a second time.

Background Information

Conductivity is a measure of the ability of water to pass an electrical current.  Conductivity in water is affected by the presence of inorganic dissolved solids, such as chloride, nitrate, magnesium and calcium ions.  Organic compounds like oil, phenol, and alcohol do not conduct electrical current well and therefore have a low conductivity in water.  Conductivity is also affected by temperature.  Warmer water has a higher conductivity.

Depending upon the level of salt in soil, plant growth may also be impacted.  Salinity is a natural attribute of both soil and water.  River waters show a wide range of salinities due to the different soils, geological structures, and extent to which they are influenced by inflows of saline groundwater.  Problems arise when the natural balance of salinity in the landscape changes and can cause a major threat to surface and groundwater resources.

High levels of salinity in rivers may limit water use for irrigation and agriculture, stock watering, and domestic water supplies.  It can also affect freshwater aquatic flora, fauna, and riparian vegetation.  In urban areas, salinity reduces the lifespan of domestic and industrial equipment, leading to higher maintenance costs and greater use of cleaning products.

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Equipment

Data Collection Procedure

GLX Setup:

  1. Connect the probe to the PASPORT Conductivity Sensor.
  2. Connect the Conductivity Sensor to the port on the top of the Xplorer GLX.
  3. Calibrate the Conductivity Sensor.  Press I to access the Sensors screen and again to access the sensors menu.  Select calibrate.
  4. Use the arrow keys to scroll down to Pt 2 (microS/cm).  Place check to set the measurement for the standard solution. 


Soil GLX Screen


  1. Place the sensor into the standard solution and press I when the reading stabilizes.
  2. The Conductivity Sensor should now be calibrated. Press OK.
  3. Press h to return to the Home screen. Use the arrows to navigate to the Digits display and press c.

Equipment Setup and Recording Data:

1. Pour 250 mL of distilled water into one 500-mL beaker.

2. Place the Conductivity Sensor into the beaker and measure the conductivity of the distilled water. Wait for the reading to stabilize, and then record the value.

3. Fill a beaker with soil to the 50-mL mark. Add 250-mL of distilled water, stir, and let the mixture sit for approximately two minutes.

4. Repeat for the second soil sample.

5. Place a coffee pot filter over an empty 500-mL beaker, and slowly pour the soil and water mixture through the filter.

6. Repeat for the second soil sample.

7. Place the Conductivity Sensor into the first beaker containing water and soil. Wait for the conductivity reading to stabilize, and then record the value.

8. Remove the Conductivity Sensor from the beaker and thoroughly rinse it with distilled water before measuring the next solution.

9. Repeat for the second soil sample.


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Data

 

Sample Conductivity
Distilled Water  
Soil sample 1  
Soil sample 2  

 

Conclusions and Extensions

1. Which of the three test solutions had the highest conductivity?  The lowest?

2. What factors may have caused the different conductivity readings for the test solutions?

3. If the water and soil mixtures had been allowed to stand for a longer period of time, what kind of conductivity measurements might you expect?  Why?

4. If the same volume of water had been added to a larger amount of soil, what kind of conductivity measurements might you expect?  Why?

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Back to Costa Rica Summary -- October 2002