2. Water Analysis

Summary

Students conduct 3 tests of water quality in the classroom that can then be applied to their terraqua columns and to the outdoors: pH, dissolved oxygen, and temperature. They make comparisons between different types of water and draw conclusions about how "healthy" each water source is for fish and other organisms. Through this process, students practice their observational and data analysis skills. Water quality monitoring data is routinely used in the "real world" to determine the effects of habitat restoration, development, pollution, and wastewater treatment. It is often the initial step in describing the health of an ecosystem. There are hundreds of ways to extend this simple activity and make connections to the real world - from monitoring water quality in a local creek to making comparisons between different bodies of water in your area.

Objectives

Can make comparisons between different water samples.
Can conduct tests of water quality.
Can interpret tests of water quality.
Can record data in a science lab notebook.

Vocabulary

pH
acid
base
dissolved oxygen

Attachment Size
2water_analysis.doc 56.5 KB
water_stations.doc 26 KB

2. Water Analysis - Logistics

Time
5 min introduction to water quality 20-25 min conduct water quality tests 20-30 min discussion of class results

Grouping
2-3 students

Materials
For whole class to share:

  • 1 package removable dot labels or rolls of masking tape
  • pH test strips
  • dissolved oxygen test kit - Kits cost between $10-60 depending on the type of test. Usually, each kit can perform 50-100 tests. They are widely available at pet stores (for testing fish tanks) and at science supply stores. See the Sources section for a selection of distributors.
  • 4 pool or aquarium thermometers
  • a stack of disposable paper cups (the 5 ox Dixie cups available for $3 at supermarkets and pharmacies work well)
  • various water sources to compare against room temperature tap water
    • for the temperature test try water in the sun, ice water, water on black asphalt, water in the shade, etc.
    • for the pH test try rainwater, vinegar, muddy water, stream water, bottled water, soda, diluted detergent, fertilizer, fish tank water, salt water, etc.
    • for the dissolved oxygen test try water left in the refrigerator overnight, boiled water, water bubbled with an aquarium pump, fish tank water, etc.

Setting
Classroom, although some tests such as water left out on black asphalt might require access to the outdoors.

2. Water Analysis - Background

Teacher Background
This activity, like the Soil Analysis activity are fabulous springboards for future independent investigations and real world connections. Water quality is one of the first things analyzed by environmentalists, government agencies, aquarium owners, gardeners, and business men and women when asked about the health of an ecosystem. It is a question you can ask about the water that comes out of your tap and that goes down the drain. This lesson gives students experience with 3 very simple water quality measures although there are many many more tests available to try (salinity, phosphates, chlorine, nitrates, fecal coliform, and others).

The first test is temperature which simply measures how hot or cold something is. Water temperature significantly affects the type of life that can survive. High temperatures reduce the amount of dissolved oxygen. The rate of photosynthesis gradually increases as water temperature rises, although beyond 32 degrees Celcius, the rate of photosynthesis falls again. Similarly the metabolic rate of plankton, insects, and other water life varies according to the temperature of the water. Human impacts that can affect water temperature include thermal pollution from industry, deforestation resulting in fewer trees to shade water, and soil erosion adds sediments to the water increasing the absorption of solar heat.

The second test measures pH. pH is a measure of the hydrogen ion concentration in liquids and other substances. Acids such as vinegar and lemon juice have high concentrations of hydrogen ions and register below 7 on the pH scale. Bases such as soap and milk have low concentrations of hydrogen ions and register above 7 on the pH scale. Pure deionized water has a neutral value of 7. Pure rainwater has a pH closer to 5.6 although natural freshwater sources such as creeks, ponds, and lakes fall between 6.5 and 8.5. Some water sources such as bogs (with a pH as low as 4.2) have naturally low pH. Human impacts such as acid rain, pollution, and chemical spills can affect pH values.

The final test, dissolved oxygen, measures the presence of oxygen in the water, an essential ingredient for animal life. Dissolved oxygen is measured in parts per million or ppm. Although some organisms can survive at very low dissolved oxygen levels, 7-14 ppm is generally considered healthy for most fish and other aquatic life. Levels of 3-5 ppm are considered stressful and 0 is termed anoxic. Oxygen is introduced into water from the atmosphere (running water and wind increases the amount of oxygen) and from aquatic plants. A reduction in dissolved oxygen often is the result of increased temperature, changes in stream flow such as damming a river, the build up of organic wastes from pesticides and fertilizers, and eutrophication (if too much algae and plant life grows, as the plants die the bacteria population explodes, virtually eliminating all dissolved oxygen from the area).

Student Prerequisites
none

2. Water Analysis - Getting Ready

Getting Ready

  1. Prepare 3 stations around the classroom with the materials needed to conduct that test and a printout of the student instructions (see attachment at bottom of summary page).
    1. Temperature: thermometers, water samples
    2. pH: pH paper, labels, small cups, water samples
    3. dissolved oxygen: dissolved oxygen kit (the student instructions are written for the tablet based test from Acorn Naturalist), labels, water samples

2. Water Analysis - Lesson Plan

Lesson Plan

  1. Introduce students to the idea of water quality testing. Water testing allows students to get a snapshot of the health of a body of water. Today's lesson is an opportunity to learn how to conduct these tests and interpret their results. These skills will be used later on in the course to examine water samples from terraqua columns and/or local water sources.
  2. Introduce each of the 3 tests and give a description of what each test measures and how each test is performed. You may want to quickly demonstrate each test using tap water as an example as you explain the procedure. Ask students for predictions of what differences one might expect between water samples?
  3. Specify the organization of the student's lab notebook and decide how data should be recorded at each station.
  4. Divide the students into groups and specify the rotation strategy. Rotate through the 3 stations, giving students 5-10 minutes per station. Allow time for a thorough clean up at the end of each station.
  5. Engage the students in a discussion of the differences between the water samples at each station. One way to do this would be to create a summary of all the students' results from each test on the board or on an overhead. Students can offer observations and comparisons for each test to add to the summarized results at the front of the room. Some examples of questions to ask:
    1. Were you surprised by any of the results?
    2. What do differences in temperature mean?
    3. What natural and man-made events might cause differences in temperature at a creek or lake? (depth, shade, velocity, altitude)
    4. What do differences in pH mean?
    5. What might cause pH differences?
    6. How should we interpret differences in dissolved oxygen?
    7. What conditions would increase or decrease dissolved oxygen?
    8. Would plant life increase or decrease dissolved oxygen? How about rotting plant life?
    9. How would differences in temperature/pH/dissolved oxygen affect the types of plants or animals that could survive in that water?
    10. How do different variables affect one another? For instance, how does temperature relate to dissolved oxygen?
    11. Did everyone get the same results? Why or why not?
  6. Armed with a thorough analysis of these water samples, begin a discussion of what makes water "healthy". Challenge students to decide what ranges of values for the various tests would be "healthiest"? and what range of values would be "unhealthy"?. This question is very open-ended and does not have a right or wrong answer but is an excellent way to generate discussion and delve deeply into the issue of water quality. One way to conduct this discussion is to allow students time to speak with their group about the question first, then share the group's conclusion with the rest of the class. A key factor to bring up is whether "healthy"? water is the same regardless of its location or use (such as a creek, pond, lake, bay or ocean).
  7. An alternative to the discussion of healthy water is to discuss the human activities that can affect water quality, both in good and bad ways. Challenge students to come up with a human impact (for example, pollution) and think about how that impact would change temperature, pH, and dissolved oxygen. Some possible impacts to consider include:
    • Pollution
    • Acid rain
    • Deforestation
    • Invasive species such as elodea (commonly found in fish tanks but which can rapidly cover the entire surface of a pond)
    • Dams
    • Wastewater treatment
    • Planting trees
    • Fishing and recreation

2. Water Analysis - Assessments

Assessment

  1. Describe one thing that humans do that changes water quality - either making it worse or better. How would it affect each of the 3 tests we conducted during class?
  2. Research another water quality test. What does that test measure? How do you perform that test? What are the natural readings and what are unnatural readings? Describe 2 natural reasons why readings would vary. Describe 2 human impacts that could affect the test.

Going Further

  1. Conduct water quality analysis on the reservoir part of the terraqua column. See Terraqua Column lesson.
  2. Conduct water quality analysis at the creek restoration site before and after restoration.See Habitat Survey lesson
  3. Conduct an independent investigation using terraqua columns that monitors water quality. See Terraqua Column Experiment lesson.

2. Water Analysis - Sources and Standards

Sources
Distributors of water quality test kits:

  • Red Sea makes the least expensive dissolved oxygen test kit I have found with 60 tests for $10. It is available at many pet stores or you can order it online at A Fishy Business. Some of the ingredients are toxic so use all available safety precautions with kids - gloves, aprons, eye protection, etc.
  • In my own classes I used a test kit from Acorn Naturalists 100 tests for $25. It is very simple for students to use - just add 2 pellets, shake and wait for a color change - however it only gives 3 readout levels: anoxic, poor and good. In fact, I could not get water bubbled overnight with an aquarium pump bubbler to give me a good readout.
  • I'm tempted to try Chemetrics next year to obtain more accurate readings. It is more expensive at 30 tests for $40.
  • Other sources of water quality test kits include:
    • Proaquatica
    • LaMotte Company
    • Hach Company
    • Carolina Biological

This activity was adapted from Monitoring Creek Health a 6-8th grade curriculum written by the Point Reyes National Seashore Association. Save the Bay also developed a superb curriculum which includes many ideas for mapping, monitoring, and restoring local watersheds. This lesson is in many ways modeled after Save the Bay's lesson plan “Keeping an Eye on Our Creeks". Kids in Creeks is a curriculum guide produced by the Watershed Project and is available to teachers who take their superb workshops. They provide extensive resources for teachers interested in adopting a local creek. Included in their curriculum are many water quality monitoring activites, including conducting an insect survey and a plant life survey as indicators of creek health. North Carolina State University has an excellent set of additional activities to further investigate the effects of water quality factors.

Standards
Grade 6 Ecology (Life Science)
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.

Grade 8
Reactions
5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:
e. Students know how to determine whether a solution is acidic, basic, or neutral.

All grades Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.