Description

Target audience - This lesson is most appropriate for undergraduate students (both lower- and upperclassmen, and biology majors as well as non-science majors). No specific background knowledge is required.  

Summary of the lesson - This activity is appropriate for a 2-hour or, ideally, 3-hour lab. Depending on logistics (e.g., distance from classroom to the stream site, potential time limitations), instructors could consider giving the introductory lecture in the prior class meeting or delivering a brief streamside (rather than classroom) introduction. After a introductory lecture (10-15 min) on bioassessment and insect order ID, students conduct macroinvertebrate sampling in a stream (30-60 min), identify macroinvertebrates using the provided key (30-60 min), and calculate a stream bioindex - a quantification of ecosystem health based on organisms present - using the provided worksheet (15 min). If time allows, two different habitats in the same stream (or two different streams) can be sampled and compared. After bioindex calculation, the group discusses (10-20 min) practical applications of this technique, considerations for collecting accurate data (e.g., which habitat is best to sample), and limitations of “standardized” bioindices that are not adapted for a particular region.

Approach to engagement - This lesson engages students in the classroom and field through the hand-on exploration of concepts and practical applications related to ecological indicators. After introducing the concept, history of biological indicators, and macroinvertebrate identification and ecology, students are asked to develop hypotheses before collecting data. Teams of students can then work together to develop hypotheses and collect data. Instructors should encourage every student to be involved in collecting and identifying macroinvertebrates from the field sites. Teams will calculate biotic index scores and discuss scores with the instructor and other teams. The instructor will end the lesson by leading a discussion of the lesson using aspects from the Reflection section of this document. 

Logistics and materials needed - Instructors are strongly advised to scout the site first to determine specific hazards and concerns (site accessibility for disabled students, tripping hazards, broken glass, etc.). The stream(s) should be safely wadeable and ideally less than 30 cm deep unless students are wearing waders. Students should be instructed to wear rubber boots or, at the very least, closed-toed shoes that can get wet.

Equipment needed includes:

• kick nets and/or dip nets (whichever is easier to obtain)

• white plastic sorting pans

• plastic ice cube trays or petri dishes

• forceps,

• plastic pipets,

• laminated handouts of insect order key (available in the appendix), and

• bioassessment worksheet (also available in the appendix).

Ideally each pair of students should receive a net, sorting pan, ice cube tray or 6-8 petri dishes,
    two pairs of forceps, and two pipets. 

Further reading for the instructor – Allen and Castillo Stream Ecology textbook chapter 13.3.1
Hilsenhoff, W.L., 1987. An improved biotic index of organic stream pollution. The Great Lakes Entomologist, 20, p.7.

Learning Outcomes

1. Develop and test a prediction relating to ecosystem health of a particular stream site.

2. Evaluate stream health by sampling stream macroinvertebrates in a standardized manner in the field, identifying macroinvertebrates to order using a pictorial key, and calculating a bioindex score using a common stream bioassessment tool.

Assessment of Learning Outcomes

• Pre-lab: students predict a bioindex category based on their previous knowledge and/or visual survey of the stream OR students predict how and why bioindex values will differ between two sampled sites/habitats.

• Post-lab: students demonstrate their calculation of a bioindex score and explain whether their data supported their prediction.

Required Background Information for Students

The introductory lecture should include the following content:

• Definition of the term “bioindicator” (an organism that indicates ecosystem health/integrity); the term is relevant to both terrestrial and aquatic systems, and this lesson focuses on streams. Diatoms, fish, zooplankton, and macroinvertebrates can all be used as aquatic bioindicators; this lesson will focus on macroinvertebrates.

• Sampling techniques: note that some sampling techniques require colonization (Hester-Dendy samplers, leafbags, rock baskets) while other techniques provide “snapshot” samples (Surber samplers, dipnets/kicknets). For this lab, dipnets and/or kicknets will be used. Sampling techniques can be demonstrated using this video: https://www.youtube.com/watch?v=vHyorstx85w

• Macroinvertebrate identification: explain use of the attached key and review key characteristics of macroinvertebrate orders likely to be found at the site(s) in question (e.g., mayflies typically have three “tails” and abdominal gills). Note that different taxa have different tolerances to disturbance, as shown on the back (second page) of the key.

• Bioindex use: introduce the Hilsenhoff Biotic Index (HBI) as students look at the provided worksheet. This index is essentially a weighted average of macroinvertebrate tolerance to pollution. Review the calculation.

Lesson Content

• The introductory lecture (see above) introduces students to key concepts and field techniques. We have provided lecture slides that can be used and/or modified by the instructor(s). Two lecture recordings are provided to coincide with the lecture slides (Intro to aquatic macroinvertebrates, Bioassessment using macroinvertebrates)

• A brief introduction in the field demonstrates appropriate net-sampling technique.

• Students develop a prediction about water quality at their site(s), conduct standardized stream sampling, identify macroinvertebrates captured, calculate a Hilsenhoff Biotic Index (HBI) value for their site(s), and evaluate whether their prediction was supported.

Lesson Procedure

• The instructor provides a brief introductory lecture on bioindex use, common aquatic macroinvertebrates, and stream sampling techniques.

• Students work in pairs and use the HBI key on their worksheet to predict an HBI score range for their site (e.g., a stream that appears to be in excellent condition would have a predicted score of 0-3.75).

• Students continue to work in pairs and follow directions on the “Stream Sampling Instructions” sheet  to conduct sampling at one or more stream sites. Students should be warned about the possibility of tripping and/or slippery substrates and advised not to ingest streamwater. After completing their data collection and analysis, students complete the post-assessment part of the worksheet.

Data Sheet

Worksheets are provided as resources in this lesson. 

Data Analysis and Interpretation 

Students will use the worksheet to calculate a bioindex and interpret their data. For example, a stream with a bioindex of 0-4.25 would be considered a high-quality site, while a bioindex of 5.76-10 would indicate poor water quality. Students’ final values should be averaged to provide a class value for each site.

Reflection

Some reflection/discussion questions are included as post-assessment questions on the worksheet; additional topics can be introduced in a class discussion. Students should refer back to their prediction and use the class average(s) to determine whether their prediction is supported. Final reflection/discussion topics can include (1) why using class averages is better than using individual groups’ bioindex values, (2) which habitat(s) would be best to sample for accurate bioindex calculation, (3) the importance of standardizing area and/or time of sampling, (4) importance of considering regional differences and potentially using regionally specific bioindices rather than a “standardized” bioindex, and (5) how seasonality may affect data collection.

Links to Other Lessons and Concepts

• Cummins, C., Martinez, A. E. (2024). Microhabitats and macroinvertebrates: Logjam influences on stream morphology and macroinvertebrate traits.  River Field Studies Network, QUBES Educational Resources. doi:10.25334/ZVG7-2F67

• Washko, S., Waring, E. (2022). Exploring Detritus-Based Food Webs in Streams.  River Field Studies Network, QUBES Educational Resources. doi:10.25334/XG53-EK16

• Aquatic Macroinvertebrate Lesson Plans (Utah State University Extension): https://extension.usu.edu/waterquality/educator-resources/lessonplans/macro

• Benthic Macroinvertebrates Lesson Packet (Headwaters Science Institute): https://headwatersscienceinstitute.org/benthic_macroinvertebrates/

• Biological Indicators Lesson Plan (Cuyahoga Valley Environmental Education Center): https://www.nps.gov/teachers/classrooms/upload/Biological-Indicators-Lesson-Plan.docx

• Stream Ecosystem Field Activity (Cary Institute for Ecosystem Studies): https://www.caryinstitute.org/eco-inquiry/teaching-materials/water-watersheds/stream-ecology/stream-ecosystem-field-activity

Further Reading

• Allen and Castillo Stream Ecology textbook chapter 13.3.1

• (for upper-division majors students) Wellnitz, Todd, Se Yeon Kim, and Eric Merten. "Do installed stream logjams change benthic community structure?" Limnologica 49 (2014): 68-72.

Notes

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