What Determines Water Quality?

Grade Level: 6,7,8
Subjects: science
Duration: 45 minutes

Objectives: Students will have a better understanding of pH as a water quality parameter. Students will also begin to think about what makes a body of water healthy, and can be used as an introduction to other water quality parameters such as dissolved oxygen.

Materials:
5 beakers/glasses
Vinegar
Baking Soda
Cooking oil
Sediment-dirt or sand
pH strips
DO meter (optional)
Tap water

Procedure:
1. Before class, have 5 beakers lines up and filled with tap 600 ml water. To each beaker add one of the following and mix well:
· Sediment (1 T. - filter out any large debris)
· Distilled vinegar (75 ml)
· Baking soda (1 T.)
· Cooking oil (1 T. or enough to cover the top of the water)
· Just water

2. When students arrive, tell them that each one of the glasses represents a lake. Have the students vote as to which lake they think fish would like best to live in. Ask them how they can tell if a lake (or other body of water) is clean. Can you tell by sight alone? What other things are important to look at? [Plant growth, clarity, pH, pollutants, plant and animal diversity, etc.]

3. What you can't see might be a problem. How can you tell if a lake is healthy? What kind of tests would a limnologist (someone who studies freshwater) do to look at the health of these 5 lakes? [A limnologist is going to look at a lot of different things and mostly they want to see what has changed over time. The same way a doctor would run tests to see if you were sick and to figure out the problem so that they could prescribe a solution. For lakes, you would take the temperature- some fish survive better in colder temperatures. You would also test the pH (fish can survive in pH of 5.0-8.5, but some of the more sensitive fish, like salmon may not do well when the pH drops below 6). How much oxygen is in the water (dissolved oxygen) is also important.]

Use pH strips to look at differences in water alkalinity as part of a way to determine water quality. Acid rain plays a roll in many of the ecosystems in the Adirondacks, especially lakes. In what range do the fish like the pH to be in a lake? [6.5-8]. Which of the 5 above lakes would the fish be able to live in based on pH?

What do fish breathe? [oxygen] Do they need the oxygen to be at a certain level? [If the DO drops below 2 ppm, most aquatic organisms will not be able to survive. Most aquatic organisms will be very stressed when the DO is between 3 and 4 ppm. At 5 ppm or more, most aquatic organisms will thrive.] Measure the dissolved oxygen in each of the containers. Which would be able to support fish and other life?

Does temperature play a part in the health of a lake? Which would you say is healthier for aquatic life, warm water or cold water? What does water temperature affect? [Dissolved oxygen, growth and reproduction of fish and aquatic organisms, rate of photosynthesis in plants, stress and sensitivity of organisms to disease.] In cold water, DO levels will increase. In warm water, DO will decrease, plant photosynthesis will increase (up to 89°F) and bacteria will grow faster. The more plants and algae grow, the more other plants are blocked from sunlight and die and decompose. As things decompose, they consume oxygen.] You may want to try heating/ cooling different jars of plain tap water and then test the DO levels in each and compare the results. Does time of year affect DO? How about time of day?

4. Follow up activities: Look at water temperatures for some of the lakes with water monitoring units (http://www.ourlake.org or http://lakeaccess.org). Compare different water quality parameters on the same date for different lakes. (Lake George's RUSS unit is no longer working but data from 2002 and 2003 is still available: http://waterontheweb.org/data/george/index.html) Discuss with the students why there are differences in pH. Which lake seems to be the healthiest?