Water: Middle School
Exercise IV. Phosphates in Your Water
Goals and Objectives
This experiment looks at how fertilizer runoff affects waterways. Students will:
- Examine the effects of detergents and fertilizers on aquatic life.
- Test for dissolved oxygen in water samples.
- Determine the relationship between pollutants and dissolved oxygen in water.
- Collect and interpret data.
- Access to a nearby pond or stream
- Dissolved oxygen test kit
- 10 jars
- Water, plants (get some with roots), and mud from a pond
- Detergent containing phosphates
- Fertilizer in powder form
- Measuring spoons
- Label jars 1 through 10. Cover the bottom of each jar with mud and plants (roots and all). Fill each jar with pond water.
- Place the appropriate amount of fertilizer or detergent in each jar using the amounts listed in the following chart.
- Following test kit directions, measure the amount of dissolved oxygen in the pond water.
- Put all the jars in a sunny location.
- Make observations daily for 2 weeks.
- Measure the amount of dissolved oxygen, according to the kit directions, on day 7 and day 14 of the experiment.
- Discuss your observations.
|Day 1||Day 7||Day 14|
|3.||1/8 tsp detergent|
|4.||1/4 tsp detergent|
|5.||3/8 tsp detergent|
|6.||1 tsp detergent|
|7.||1/8 tsp fertilizer|
|8.||1/4 tsp fertilizer|
|9.||3/8 tsp fertilizer|
|10.||1 tsp fertilizer|
At the end of the experiment, which jar had the most vigorously growing plants?
Which jar had the least dissolved oxygen?
What would happen in a stream that has an excess of phosphates, warm temperatures, and good sunlight?
How are phosphates in the water important?
Look around your home and school and list possible sources of phosphates that might be entering local streams.
Does your state have a phosphate detergent ban? What does it do? When was it implemented?