OBJECTIVES:

• Learn what pH is and how to test it.
• Learn the importance of experimental controls.
• Learn the importance of repeating experiments to validate results.
• Students investigate how plants can affect the quality of water.
• Use line graphs to show data and interpret results.

VOCABULARY:

pH
data
control
base
acid
pollution (point pollution and non-point pollution)
wetlands
tule plant
bioremediation

MATERIALS:

Three fish tanks (10-gallon)
Tule plugs
Ammonia
Vinegar
Tap water
Digital pH monitor
Waterproof thermometer
pH data worksheet
Tule Ponds Temperature/pH worksheet
Plotting data blank and example

 
BACKGROUND:

Wetlands are ecosystems where the land is inundated or saturated with water. Wetlands were once destroyed because they were perceived as worthless land and their ecological value was not understood. Half of the wetland acreage existing in 1770 in the contiguous United States had been destroyed by 1970. We have since learned that wetland areas are very valuable, providing flood protection, water quality improvement, erosion control and habitats for thousands of species of plants and animals.

Wetlands can remove pollutants in a variety of ways. Some pollutants in water runoff that are toxic to humans may be taken up by the aquatic plants, bacteria and protozoa of the wetlands as part of their normal photosynthetic or respiration processes. Other pollutants, like heavy metals, can bind to clay particles that are common components of soils and sink to the bottom. These processes result in cleaner, healthier water in the wetland and for downstream areas.

Although there are now restrictions on filling in or polluting wetlands throughout the United States, pollutants from surrounding areas threaten the health of some wetlands. Sometimes wetlands are polluted by a single source, such as industrial or municipal waste (“point source pollution”). Sometimes they are polluted from a multitude of sources (“non-point pollution”), such as car emissions or motor oil, that eventually wash into the wetlands and accumulate over time to toxic levels. Whatever the source, too much pollution can cause significant damage. Our watersheds reflect the health of our environment.

 PROCEDURES:

The fifth grade has two projects and a final presentation. The first project is a long-term experiment at school and the second is a one-day field trip to take readings at a wetlands research area.

PROJECT ONE involves long-term pH monitoring of tanks “polluted” by acids and bases. Students will test to see if tule plants help to correct the pH in the tanks over time. This experiment will be repeated during the school year so students can validate their results. The experiment should take place once before Winter Break and once after Winter Break.

1. TANK PREPARATION – The Project One experiment will need three 10-gallon tanks and two smaller tanks (2- to 5-gallons).

Tule plugs (tule and a mass of their underwater roots) of similar sizes will be added to the large tanks. Each will be filled with tap water and placed in a sunny area or one with natural lighting. One tank will be polluted with vinegar to a pH of approximately 5 and one tank will be polluted with ammonia to a pH of 10. The third tank with tule should be left with only tap water and will be the control.

The two smaller tanks should be filled with tap water and similarly polluted, one with vinegar to a pH of approximately 5 and one with ammonia to a pH of 10. The polluted tanks without tule help to determine whether any pH changes are due to tule rather than exposure to air or other factors. 

As you pollute the tanks, be sure to stir them and then let them rest for a while and add more pollutant until you get the desired pH. If you add too much pollutant (i.e., it is below 5 or above 10), just take out some polluted water and add tap water until you reach the desired pH. 

2. STUDENT GROUPS – Students should be divided into groups of three to take daily readings. Each day, one team will be responsible for readings and observations. Team members take turns using the thermometer, taking pH readings and filling in the lab sheet.   

3. TAKING TEMPERATURE READINGS – The thermometer should be held with the lower part of the thermometer in the water for 30 seconds. Students can count or look at a clock for the timing. Repeat for all the tanks and enter temperature on the data sheet. 

4. TAKING pH READINGS – Use instructions provided to know how to use the pH meter. Repeat for all the tanks and enter pH on the data sheet. 

5. OBSERVATIONS – Students should be instructed to write down any observations they note when looking at the various tanks. Does one look different? If so, how? Do they smell the same, etc.? Qualitative observations are an important part of the experiment. All data and observations should be entered in the class data sheet next to the tanks.   

It is highly recommended to take daily or weekly photos of the tanks to support the final presentation.

6. READINGS AND OBSERVATIONS should be taken daily for 6 to 8 weeks. If after 6 weeks the pH of all the tanks with tule has equalized and the tanks look about the same, you can end the experiment. If not, continue the experiment for another few weeks.   

7. GRAPHING – Students should each graph the results using the graph template and following the example provided. The dates will need to be filled in. If you did not take readings due to holidays or weekends, just leave those days blank.

8. REVIEW RESULTS – Students should review their results and graphs and look for patterns. Did the tanks equalize in pH? Did the tanks without tule equalize at the same rate? Based on results, do students think tule made a difference? How did any other organisms in the water do? Is the water in each tank clear? Were there changes in clarity during the experiment?

9. REPEAT THE EXPERIMENT – The experiment should be repeated with fresh water and tule. It should be explained to students that we repeat experiments to validate the results and make sure there wasn’t an error the first time. 

PROJECT TWO is a field trip to Tule Ponds to observe living wetlands and the plants, animals and soil of wetlands in their natural setting. They take temperature and pH readings of water in the various ponds and enter the data in data booklets. They then compare readings with historical data to determine the current health of the water in the various ponds. 

PRESENTATION – After repeating the experimental project twice and completing the visit to Tule Ponds, students should prepare a summary PowerPoint presentation of their findings for both projects. How did the project experiment help them understand what is happening at Tule Ponds? How do the docent lessons help their understanding?