Summer Research Program for Science Teachers
Jennifer Lagnado
Lawrence High School
2000
Testing Water Quality Using Vernier Labpro Probes
Part I. Students are to investigate the many environmental issues that pertain to water quality in the local area (Science Content Standard F). Environmental issues to be researched are thermal pollution, pesticide contamination, and acid rain.
Variables to be tested:
1. _______________________________
2. _______________________________
3. _______________________________
4. _______________________________
5. _______________________________
Part II. Laboratory Activity
Testing for Temperature
Temperature is an important indicator of the overall quality of a body of water. Since changes in temperature can harm aquatic organisms, it must be monitored carefully. Changes in temperature can also effect other important factors such as the solubility of gases and the photosynthetic rate of aquatic plants.
1. Using the Vernier Labpro equipment and sensors, prepare your computer or calculator for data collection (See Water Quality with Computers Manual) Science Content Standard E
2. Plug the temperature probe into the calculator and place the tip of the probe into the lake.
3. When the temperature on the screen remains stable for approximately 30 seconds, it can be recorded.
Testing for pH
Water contains both hydrogen ions, H+, and hydroxide ions, OH-. To determine the pH of a solution, the relative concentrations of both ions must be measured. Neutral water has an equal concentration of these ions, while acidic solutions have a greater amount of H+ ions and basic solutions have a greater amount of OH- ions.
1. Place the water samples into 500 mL. beakers.
2. Prepare the Vernier Labpro equipment, sensors, and calculator for data collection (See Water Quality with Computers Manual).
3. Plug the pH sensor into the Vernier interface.
4. Calibrate the sensor using the prepared buffer solutions provided in the kit (See Water Quality with Computers Manual pg. 2-3).
5. Rinse the pH sensor with sample water.
6. Place the tip of the sensor into the sample water
7. When the pH value remains stable on the calculator screen, record the value.
8. Repeat steps 5 through 7 for the remaining samples.
Testing for Turbidity
Turbidity is a measure of water’s lack of clarity. Water with high turbidity is cloudy and water with low turbidity is clear. This cloudiness is produced by a large amount of particles present that are reflecting light.
1. Prepare the Vernier Labpro equipment and calculator for data collection using the Water Quality for Computers Manual.
2. Plug the Turbidity sensor into the Vernier interface.
3. Calibrate the Turbidity sensor using the directions stated on pg. 3-3 of the Water Quality with Computers Manual.
4. Gently invert the water sample to mix any settled particles.
5. Rinse and fill the cuvette with sample water.
6. Close the lid of the cuvette and place it into the turbidity sensor.
7. When the meter reading remains stable on the calculator screen, record the value.
8. Repeat steps 4 through 7 for the remaining water samples.
Testing for Total Solids
Total Solids is a measure of all the suspended and dissolved solids in a water sample. Solids measured are dissolved sodium chloride as well as silt and plankton. If total solids are too high or too low, the health of the lake or stream can be affected. High total solids can affect the clarity of the water, while low total solids does not provide ample nutrients to living organisms.
1. Collect approximately 500 mL of sample water so that two 200 mL trials may be carried out.
2. Label two 250 mL beakers as “1” and “2”.
3. Measure and record the mass of the two empty 250 mL beakers.
4. Measure 200 mL of sample water into each beaker.
5. Place the beakers into an oven at a temperature of 100-105°C overnight.
6. On day 2, measure the mass of the beakers and solids
7. Obtain and record the mass of the total solids by subtracting the mass of the empty beaker from the mass of the beaker with the solids.
8. Repeat steps 2 through 7 for the remaining water samples.
Testing for Dissolved Oxygen
Oxygen is a key component to the survival of most aquatic organisms. It is vital in the process of cellular respiration and without sufficient dissolved oxygen, most aquatic life would not survive. Some organisms require high amounts of dissolved oxygen, while others require low amounts. Aquatic plant populations and temperature of the water both are contributing factors that influence total dissolved oxygen.
1. Prepare the Vernier Labpro equipment and calculator.
2. Plug the dissolved oxygen probe into the Vernier interface.
3. Calibrate the sensor using the instructions provided (See Water Quality with Computers Manual pg. 5-4).
4. Rinse the tip of the probe with sample water.
5. Insert the sensor into the water sample, while gently stirring.
6. Monitor the dissolved oxygen reading on the calculator screen.
7. When the reading appears stable, record the value.
8. Repeat steps 4 through 7 for the remaining water samples.
Testing for Biochemical Oxygen Demand
Biochemical Oxygen Demand (BOD) is directly related to the dissolved oxygen in a lake or stream. Plants and animals use oxygen to produce energy through cellular respiration. Healthy streams replenish oxygen faster than it is used. Aerobic bacteria may decompose organic matter at such a fast rate, that dissolved oxygen decreases causing a Biochemical Oxygen Demand.
1. Prepare the Vernier Labpro equipment and calculator (See Water Quality with Computers Manual).
2. Obtain an initial dissolved oxygen reading at the sample site.
3. Collect three water samples for the BOD test at the same location that the initial dissolved oxygen reading was taken.
4. After returning to the laboratory, the three water samples should be stored in an incubator or dark closet at a temperature of 20°C for approximately five days.
5. After five days has passed, the three water samples should be removed from the incubator or closet.
6. Prepare the Vernier Labpro and plug the dissolved oxygen probe into the Vernier interface.
7. Submerge the probe tip into the water sample while gently stirring.
8. When the meter remains stable on the calculator screen, record the value.
9. Repeat steps 7 and 8 for the other samples.
Testing for Phosphates
Phosphorus is an essential nutrient for all aquatic organisms, yet excessive amounts can become a pollutant. Excess phosphorus can lead to eutrophication, where an increase in plant and algal growth can lead to reduced levels of dissolved oxygen. It is for this reason that total phosphates must be monitored carefully.
1. Label two erlenmeyer flasks as “A” and “B”
2. Measure 25 mL of sample water into each flask
3. Digest the water samples by adding one Potassium Persulfate/Sulfate Powder Pillow to each flask.
4. Add 2.0 mL of 2.63 M H2SO4 to each flask.
5. Boil the samples for 30 minutes. Add distilled water periodically to keep the volume at 25 mL.
6. After heating, allow the flasks to cool.
7. Label as third erlenmeyer flask as “S” for the standard solution and add 25 mL of 10.0 mg/L Phosphate Standard.
8. Add a PhosVer 3 Phosphate Powder Pillow to the flask and swirl.
9. Prepare the Vernier Labpro equipment and plug in the Colorimeter into the Vernier interface.
10. Calibrate the Colorimeter using the instructions provided (See the Water Quality with Computers Manual).
11. Add one PhosVer 3 Phosphate Powder Pillow to each sample flask.
12. Rinse the cuvette twice with solution from Flask A and fill it approximately ¾ full. Place the cuvette inside the Colorimeter and close the lid.
13. When the absorbance reading has stabilized on the calculator screen, record the value.
14. Repeat steps 11 through 13 for the remaining samples.
Testing for Nitrates
Nitrogen is an important nutrient for plants and animals to synthesize amino acids and proteins. If excessive amounts are introduced into lakes or streams, eutrophication may occur leading to excessive growth of aquatic plants and algal blooms.
1. Collect approximately 100 mL of sample water and stored in the refrigerator.
2. Prepare the Vernier Labpro equipment and calculator
3. Soak the Nitrate Ion-Selective Electrode in High Standard.
4. Plug the electrode into the Vernier interface and calibrate the sensor using the instructions provided in the Water Quality with Computers Manual.
5. Rinse the Nitrate Ion-Selective Electrode with distilled water and blot it dry.
6. Place the tip of the probe into the water sample and stir gently
7. Hold the probe still and wait approximately 30 seconds.
8. When the meter reading remains stable on the calculator screen and record the value.
9. Repeat steps 5 through 8 for the remaining water samples.
Testing for Fecal Coliform
The concentration of fecal coliform must be monitored in order to determine the likelihood of contamination by microbiological organisms. A common source of coliforms and pathogenic bacteria is raw sewage. Coliform bacteria tests are used to monitor recreational areas, stormwater out-falls, and drinking water supplies.
1. Label a Whirlpak bag with the site and time collection.
2. Pull open the Whirlpak bag using the yellow tabs. Make sure to not touch the inside of the bag in order to maintain sterilization.
3. Collect water in the Whirlpak facing into the current.
4. When the collection is finished, close the Whirlpak using twist ties.
5. To begin filtration of the sample, obtain eight petri dishes.
6. Two petri dishes will be used for two 10 mL water blanks, two petri dishes will be used for 1 mL samples, two for 10 mL samples, and two for 30 mL samples.
7. Pour 1 ampoule of mFC/Rosolic Acid Broth into each petri dish.
8. Remove the top of the filtration unit and use sterilized forceps to place a filter into the filter holder and pour a small amount of distilled water onto the filter.
9. Filter the samples as listed in step 6. Place the lids on each lid and incubate them upside down for 24 hours at 44.5°C.
10. Repeat steps 5 through 9 for the remaining water samples.
11. After incubation, count and record the fecal coliform colonies that are bluish colored spots.
12. Calculate the Colony Forming Units (CFU) per 100 mL using the formula:
average colony counts x 100 = CFU/100 mL
mL filtered
Calculating the Water Quality Index
1. The results for the tests listed above should be recorded and listed on a data sheet.
2. Using the graphs provided in the Water Quality with Computers Manual, record the Q-value for each test.
3. Multiply the Q-value by the weighting factor by the following numbers listed below:
Temperature 0.11
pH 0.11
Turbidity 0.08
Total Solids 0.07
Dissolved Oxygen 0.17
5-Day BOD 0.11
Total Phosphates 0.10
Nitrates 0.10
Fecal Coliform 0.16
4. Calculate the sum of the tests and record the final result. Use the table below to find the Water Quality Index Ratings.
90 - 100 Excellent
70 - 80 Good
50 - 70 Medium
25 - 50 Poor
0 - 25 Very Poor
Conclusion Questions
1. Why is it important to monitor temperature of a lake or stream?
2. What factors may affect water temperature of a body of water?
3. What effect does an increase in temperature have on solubility of dissolved oxygen?
4. pH measures the relative concentration of what two ions?
5. The pH scale ranges from ______ to _______, with _______ being the most acidic and _______ being the most basic.
6. What factors can cause changes in pH?
7. What are sources of turbidity?
8. What effects does high turbidity have on water clarity and water temperature?
9. How does high total solids affect water clarity and water temperature?
10. What are sources of dissolved oxygen in a lake or stream?
11. As aquatic plant populations increase what effect does this have on the biochemical oxygen demand and on the dissolved oxygen available to other aquatic organisms?
12. If heavy rainfall produces large amounts of agricultural runoff, what effect does this have on the amount of phosphates and nitrates in a lake or stream?
13. If total phosphates and nitrates increases, what effect does this have on the aquatic plant population?
14. What is meant by the term eutrophication?
15. What are common sources of fecal coliform? Why is it important to monitor this concentration?
16. How do the drainage patterns of the local areas contribute to the results of these tests on each body of water tested?
17. How may the quality of these bodies of water contribute to the quality of the local drinking water?
References
Johnson, R.L, Holman, S, and Holmquist, D.D. “Water Quality with Computers”.
Vernier Software & Technology, Beaverton, OR. 2000.