H.E.L.P.
Benthic Macroinvertebrate Study
Concept/Topic to Teach: The presence or absence of benthic macroinvertebrates can be used to indicate water quality.
Standards:
Discipline: Science and Technology
Strand: Life Science (Biology)
Topic: Living Things and Their Environment 13, 14, and 15. Changes in Ecosystems over Time 17
Grade Level: 5 - 6 Time Required: 45 minutes
General Goal: Students will examine benthic macroinvertebrates to see how they can be an indicator of water
qual-ity and habitat health. Sites for collection may be chosen that show how habitat condition can vary depending on water depth and velocity, presence of shade, riffles, etc. By using macroinvertebrate identification/record sheets students will be exposed to the concept that some creatures can only live in relatively clean or completely unpolluted water.
Specific Objectives:
• Students will examine mud/water samples and find a selection of the organisms that are present.
• Using identification/record sheets the students will identify some of the organisms and assign a “water quality rating” to each of the specimens.
• Using the above information, the students will make a tentative evaluation of the health of the body of water from which the mud/water sample was taken, at least for that specific site.
Vocabulary: benthic, larva, macroinvertebrate, nymph, pollution tolerant, pollution intolerant, riffles.
Required Materials:
Materials for Collecting: • 1-2 buckets
• A kitchen strainer if sampling from a pond, or a sturdy net if from a river • A container for scooping water
Materials for Classroom Observations:
• Mud, leaves and water collected from your pond or stream • White ice cube trays or egg cartons, 1-2 per group
• Magnifiers, one per child
• “Macroinvertebrate Key,” one for every 1-2 children • “Data Collection Sheet,” one per group
• Plastic containers (food storage containers work well), several per group • Plastic spoons (white), one per child
Anticipatory Set: Ask the students how animals living in a body of water might be used to determine the water quality
H.E.L.P.
Benthic Macroinvertebrate Study
continued.
Step-by Step Procedure:
Collect samples from the habitat to be tested, either using a net in a stream or a kitchen strainer in a pond (this may be done by the lesson presenter before the class). In a pond, many organisms may be found among the vegetation, fallen leaves and/or the mucky bottom, whereas in a stream the organisms attach themselves to the rocks in riffles and can be removed with gentle rubbing. Be sure to return organisms to their original location after the lesson.
Introduce the terms macroinvertebrate and benthic (see glossary). Explain that macroinvertebrates can be an indicator of water quality because the different species have varying pollution tolerance levels. Some macroin-vertebrates are sensitive to pollution and therefore won’t be found in a polluted water body. Macroinmacroin-vertebrates that are pollution tolerant are the ONLY species found in a polluted water body. It is important for students to realize that pollution tolerant species are found in ALL water qualities, but sensitive species are only found in higher water quality environments.
Explain briefly to the students what is expected of them using the directions below. Pass out equipment to work-ing groups of 3 or 4 students: one “Data Collection Sheet,” several “Macroinvertebrate Keys,” and the various plastic containers, spoons, etc.
Locate and sort organisms: If the students were not there for the collection of the sample, describe the place and type of habitat where the samples were collected. Provide each group a sample of the collected mud, leaves and water. Have the students look for movement and locate animals in the sample. The students should use a plastic spoon to gently sort similar organisms into the compartments of an ice cube tray or egg carton. Be sure to place stream/pond water into each compartment before sorting. Allow the students to examine the sample and sort macroinvertebrates as long as time allows.
Identify organisms and record data: After sorting, each group needs to identify the macroinvertebrates found using the “Macroinvertebrate Key” and the “Data Collection Sheet.” If the identified macroinvertebrate is on the data collection sheet, it should be circled. Students should continue to identify their macroinvertebrates and circle those that are on the data collection sheet.
Calculate Index Values: Each group now must calculate the index values for each pollution tolerance category on their data collection sheet (Sensitive, Somewhat Sensitive, and Tolerant). For example, if they found three kinds of organisms in the sensitive category, the index value will be 12 (3 species x 4 points = 12). Each kind of macroinvertebrate found and circled will count toward the index value, NOT every individual organism found, unless it represents a different species. For example, if the students find five mayflies (and no other sensitive organisms), the mayflies count as only one kind of organism, and so 1 circled organism x 4 points = an index value of 4 points from the Sensitive category.
Record class results: Make a chart on the board of the three pollution tolerance categories: Sensitive, Some-what Sensitive and Tolerant. Ask each group to record the index values they calculated for each category. (Again, be sure they counted the number of circled kinds of organisms and not the number of individual organ-isms found.) Add up the groups’ results and calculate a class average for each pollution tolerance category. If any of the groups’ numbers vary widely, throw out the “outliers” or obviously incorrect samples.
To determine the water quality rating for that site, add up the averages obtained from each pollution tolerance category to get a total index value. Refer to the chart at the bottom of the data collection sheet to determine whether the water quality of the sample is Excellent, Good, Fair, or Poor.
Ask students to return the samples to the collection bucket. Explain to the students that all the samples of water, mud, and animals will be returned to the site of collection. Collect and clean all equipment.
Return the samples to the place of collection.
22 Water Quality & Watersheds
Closure: Review the class results and determine the water quality of the body of water. Compare their macroinverte-brate study results with their own personal knowledge of the stream, river, pond or lake.
Follow Up: Conduct an evaluation of the same body of water testing for chemical and physical properties (refer to
the lesson “Water Quality Monitoring”).
Resources:
Masterbug Theater: A slide show showing some of the common macroinvertebrates: http://www.epa.gov/owow_keep/NPS/kids/masterbugtheater.html
Online Aquatic Macroinvertebrate Identification Key:
http://people.virginia.edu/~sos-iwla/Stream-Study/Key/MacroKeyIntro.HTML “Key to Macroinvertebrate Life in the River”, The University of Wisconsin, Extension:
http://clean-water.uwex.edu/pubs/pdf/wav.riverkey.pdf, Aquatic Macroinvertebrates & Water Quality Resources:
http://www.bgsd.k12.wa.us/hml/jr_cam/macros/resources.html#sorting.
H.E.L.P.
Benthic Macroinvertebrate Study
- Data Collection Sheet
H.E.L.P.
24 Water Quality & Watersheds
