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Benthic Bugs and Bioassessment Lab

Last updated over 3 years ago
11 questions
Background Info & Pre-Lab Assignment

“The most direct and effective measure of the integrity of a water body is the status of its living systems” (Karr, 1998). One important way to determine the status of water’s living systems is through biological assessment (bioassessment), which is the use of biological surveys and other direct measurements of living systems within a watershed. Aquatic macroinvertebrates (animals without backbones that live in aquatic environments and are large enough to be seen without the aid of a microscope or other magnification) are commonly monitored and are the basis of this activity.

Macroinvertebrates are valuable indicators of the health of aquatic environments in part because they are benthic, meaning they are typically found on the bottom of a stream or lake and do not move over large distances. Therefore, they cannot easily or quickly migrate away from pollution or environmental stress. Because different species of macroinvertebrates react differently to environmental stressors like pollution, sediment loading, and habitat changes, quantifying the diversity and density of different macroinvertebrates at a given site can create a picture of the environmental conditions of that body of water.

If exposed to an environmental stressor (e.g., pollution, warming due to low flows, low dissolved oxygen due to algal blooms, etc.), those macroinvertebrates that are intolerant to that stress may perish. Tolerant macroinvertebrates often inhabit the spaces left by the intolerant organisms, creating an entirely different population of organisms. For example, an unimpacted body of water will typically contain a majority of macroinvertebrates that are intolerant of environmental stressors, such as mayflies (Ephemeroptera), stoneflies (Plecoptera), and Caddisflies (Trichoptera). A body of water that had undergone environmental stress may contain a majority of macroinvertebrates that are tolerant of these conditions such as leeches (Hirudinea), Tubifex worms (Tubifex sp.), and Pouch Snails (Gastropoda).

Bioassessment of macroinvertebrates are particularly helpful to biologists and others trying to determine the health of a river or stream. Bioassessment of macroinvertebrates is a procedure that uses inexpensive equipment, is scientifically valid if done correctly, and can be conducted by students. Bioassessments can provide benchmarks to which other waters may be compared and can also be used to define rehabilitation goals and to monitor trends. Trend monitoring is a common application of bioassessment by student groups and others involved in water quality monitoring.

Collecting, identifying, and quantifying macroinvertebrates are the initial steps in a bioassessment. The next step involves using formulas to calculate the relative water quality based on the diversity and quantity of the sampled organisms. These formulas, called metrics, relate the numerical diversity and density of organisms to a water quality rating. The most common metrics are the EPT/Midge Ratio and the Pollution Tolerance Index.

The EPT/Midge Ratio metric compares the total number of intolerant organisms, specifically the E.P.T – Ephemeropterans (mayflies), Plecopterans (stoneflies), and Trichopterans (caddisflies) – with the total number of tolerant organisms, specifically Chironomids (midges). Typically the higher the number of intolerant organisms, the better the water quality.

The Pollution Tolerance Index assigns a numerical value to each macroinvertebrate order, with the higher numbers assigned to pollution intolerant organisms, and decreasing numbers assigned to increasingly pollution tolerant organisms. The scores are totaled and compared with a water quality assessment scale to yield a relative water quality rating for the sample.

To gather the best quality and most usable data, the Environmental Protection Agency (EPA) recommends that biological sampling of macroinvertebrates be conducted in ways that minimize year-to-year variability. To accomplish this, biologists tend to sample for at least one week during the same season(s) each year. Additionally, sampling is conducted when sites are easily accessible and the number of organisms is high. This usually occurs in the spring after the ice has broken and late-stage larvae are present, or in the late fall when organisms are more mature.
While bioassessments are extremely important in and of themselves, they are most useful when combined with chemical and habitat assessments. “Biodiversity techniques, such as the Rapid Bioassessment Protocols, are best used for detecting aquatic life impairments and assessing their relative severity. Once an impairment is detected, however, additional ecological data, such as chemical and biological (toxicity) testing is helpful to identify the causative agents, its source and to implement appropriate mitigation” (EPA, 1991).
Objective: Students investigate the relative water quality of a stream by conducting a simulated bioassessment by sampling aquatic macroinvertebrates (represented by ordinary materials)

Materials:
  • Calculators
  • Student Lab Sheet w/ questions (1 per person)
  • Macroinvertebrate Data Sheets (1 per group)
  • Simulated Streams 1, 2, 3 w/ simulated aquatic macroinvertebrates (prepare 2 of each to allow for 6 groups total)
  • Tubs (stream) – 6
  • Colored Water (4+ inches at least)
  • Simulated aquatic macroinvertebrates
  • Collection bowls – 6
  • Aquarium nets, small – 6
  • Sorting trays – 6
Pre-Lab Assignment: READ the background information on benthic bugs and bioassessments. Answer the pre-lab questions and complete the Macroinvertebrate Identification Chart. (Instructions are below)
1

Define aquatic macroinvertebrate.

1

List at least 4 examples of aquatic macroinvertebrates and their role in the food web of a stream.

1

Have one group member download this document and share it with the group and me. Complete the chart with your lab group by adding an image of each in the appropriate area and writing in the corresponding item we will be using to represent that organism during the simulation (see chart above). When you have finished filling out the chart take a screen shot of it (or parts of it) and place it in the "show your work" area below.

Procedure:
  1. You will be simulating a bioassessment of a stream using ordinary objects to represent macroinvertebrates
  2. There will be three streams (stations). (Note: there will be two set-ups of the lab. One along the front tables and one along the back tables). Each group will be in charge of ONE stream.
  3. Once you are divided into groups, assign tasks to each group member. You will all work together on everything!
  4. Stream sampling
  5. Sorting out the collection bucket
  6. Counting/recording on Macroinvertebrate Data Sheet I
  7. Calculating/evaluating on Macroinvertebrate Data Sheet II
  8. Calculating/evaluating on Macroinvertebrate Data Sheet III
  9. Simulate a rapid bioassessment at your stream sampling site:
  10. Using an aquarium net, you will have 20 seconds to collect as many macroinvertebrates from the stream as possible and place them in the collection bucket.
  11. Collection Bucket – Sort the collected macroinvertebrates into like categories on the sorting tray based on the Macroinvertebrate Identification Chart
  12. Using the Macroinvertebrate Data Sheet I tabulate the sorting results onto the data sheet and calculate the percent composition of each macroinvertebrate in the stream site.
  13. Using the Macroinvertebrate Data Sheet II take the data from Data Sheet I to calculate the EPT/Midge ratio.
  14. Using the Macroinvertebrate Data Sheet III take the data from Data Sheet I to complete the Pollution Tolerance index to determine your Water Quality Assessment score for your stream sample.
  15. RECORD your FINAL results on the front white board.
  16. Macroinvertebrate Data Sheet I – Total # of organisms & Top 2 organisms with %
  17. Macroinvertebrate Data Sheet II – EPT/Midge Ratio
  18. Macroinvertebrate Data Sheet III – Water Quality Assessment Score
1

Analysis Questions

1

What were the similarities and differences between each stream site?

1

Which stream had the highest level of water quality?

1

Which stream had the lowest level of water quality?

1

Write a paragraph describing your stream based on the macroinvertebrate sample you collected. Describe habitat, address possible pollution sources, give other pertinent details (be creative, but accurate.)

1

What did you think of the rapid bioassessment scientific sampling process? Did it work? Is it accurate? Is the sampling biased? Positives and negatives? Explain.

1

Brainstorm how this process could be modified to increase accuracy. List some ideas…

1

Do you think you could use this same process to perform a bioassessment in an actual stream? Why or why not?