Background Information

The world’s supply of water appears tremendous (326 million cubic miles of water). About 70 % of the earth’s surface is covered with water. Saltwater makes up 97 % of all the water on earth and is therefore undrinkable by man and not suitable for most of man’s needs. About 2 % of all the freshwater on earth is frozen in glaciers and ice caps leaving less than 1% of all water on earth useable by man. The water in aquifers and the soil (ground water) is also very small making up only 0.5 % of all water. The water in lakes and the water flowing in streams and creeks (surface water) make up about 0.009 %. Atmospheric water makes up 0.001 % of all water. We estimate that less than 0.0001 % of all the water on earth is flowing in rivers.

Water on Earth

If the total world supply of water, including the oceans, was considered as in a 55-gallon drum, freshwater lakes would be equivalent to a 5 oz. glass of water and the water in rivers would be equivalent to a single drop of water.

Approximately 90 % of the miles of rivers in the USA are small streams and creeks that flow through our schoolyards, neighborhoods, forests and farms. These are the streams most effected by land-uses that occur next to them and are highly susceptible to point and non-point source pollution. These small streams make excellent field laboratories because they are found almost everywhere, are shallow enough to safely wade and are very sensitive to pollution.

In this exercise you will be using a technique called bioassessment to determine water quality in a small stream or creek. Bioassessment is the use of living organisms as a measure of water quality.  The small animals that we will use for bioassessment live on the stream bottoms (benthos). They are called benthic macroinvertebrates and are excellent indicators of water quality.
Benthic Macroinvertebrates are animals you can see without a microscope (macro) and they do not have backbones (invertebrates). Benthic means that they live on stream bottoms. Examples of benthic macroinvertebrates are crayfish, snails and aquatic insects like mayflies, caddisflies and dragonflies. Benthic macroinvertebrates do not have the mobility of fish so they cannot swim in and out of areas with polluted water. When they are eliminated from a section of a stream because of some pollutant, they will not return for at least one generation. When you sample a stream you are collecting only those benthic macroinvertebrates that have endured natural selection and the affects of pollutants. Research has taught us that some organisms are very sensitive to pollutants and that others can tolerate very polluted conditions. For example, mayflies which are very sensitive to pollutants, do not show-up in benthic samples collected from polluted waters. Aquatic worms and midges tolerate high levels of organic pollution and are very abundant in soft organic deposits found on stream bottoms located downstream of ineffective animal waste treatment facilities. The organisms you collect will tell the history of that stream.

Terms
Detritus: Fragments of leaves, wood and bottom substrate.

Benthic macroinvertebrates: Animals you can see without a microscope (macro) and they do not have backbones (invertebrates).

Bioassessment: The use of living organisms as a measure of water quality.

Biotic index value: Numerical value that comes from multiplying an organism’s pollution sensitivity value times it’s abundance. Here, higher numbers indicate better water quality.

Nonpoint source pollution: Pollution that cannot be traced to a single point. It comes from many different sources or a widespread area. (e.g., agricultural or urban runoff).

Point source pollution: pollution from a single source (e.g., outlet pipe).

Riffle: area of the stream that is shallow and fast moving. Usually the surface is broken with small waves that pass over rocks.

Taxa: A general classification name given to a category of organisms.

Procedure

I.  Setting the Stage

1. Before the field trip review water safety.

2. Review bioassessment techniques.

3. Hand out Bioassessment Data Sheet and review Macroinvertebrate Picture Key.

4. Organize sampling teams and assign duties to each member.
   Team member duties:
   a. hold collection net.
   b. disturb bottom so animals drift into net.
   c. pick animals from organic material and bottom sediments (detritus).
   d. identify macroinvertebrates.
   e. conduct calculations and make a bioassessment of the water quality.

II.  Field Activity

1. Each team will select a section of a riffle, shallow area or rooted plant-bed to sample. For a “real-world” education, sample upstream and down stream of a suspected source of pollution.
   1. Approach the area to be sampled from the down stream side to avoid disturbing organisms.
   2. Use a screen, kicknet or homemade sampler to collect benthic macroinvertebrates. Do the “benthos waltz” up-stream of the collection device. See Procedures for Collecting Macroinvertebrates.

2. Samples may be collected at other stream habitat types such as on pools, around the roots of trees located next to the stream or at other stable structures.

3. Sample for ½ hour (or measured time that works for your outing).

4. Sampled material should be placed in pans so that the macroinvertebrates can be picked from the organic material and sediment (detritus) in which they live and feed.

5. Place look-a-like organisms together and identify them using the Macroinvertebrate Picture Key.

6. Record data on the Bioassessment Data Sheet and conduct calculations to make a stream quality assessment of the sample site.

III.  Follow-Up and Extensions

1. Have each group graph the results using biotic index values and total numbers of organisms.

2. Have groups compare graphs and
   1. Discuss results.
   2. Make a composite graph of the results from all teams.

3. Answer these questions.
   1. What is the water quality of this stream?
   2. What are the reasons for the water quality in this stream?
   3. Which organisms are most sensitive to pollution and which can tolerant pollution?
   4. What natural environmental factors might cause the stream to appear polluted and why?
   5. How would you set up a sampling program to determine if your city impacts a stream that flows through it?

4. Write a report on the stream water quality at your sample site including the graphs developed. Include the typical report sections:
   1. Methods
   2. Results
   3. Discussion

Background Information

(Please include the Background Information from the Field Activity as well)

This exercise was developed for classes that cannot get to the stream but want some training on how land-use practices affect the organisms that live on the bottom of streams (benthos). The classroom exercise may also be used to prepare students to conduct a field bioassessment of water quality in a stream. The pictures of benthic macroinvertebrates on the cards are the same as those used in the Benthic Macroinvertebrate Picture Key. On the back of the cards is the organism name, water quality group (1,2 or 3) and water quality conditions where they are found (e.g. fair to poor water quality). The cards are shuffled and randomly selected. This is similar to the field sampling that occurs in the stream. The cards or organisms most abundant will occur most frequently in your sample. This is the principle behind sampling. It is impossible to collect all of the organism in a section of a stream so we take a sample and assume that this represents the distribution of animals in the stream. We sample the cards as we sample the stream and assume that the cards drawn are a good representation of the cards in the deck.

Procedure

I.  Setting the Stage

1. Examine the map to see the different sample sites (blue, grey of tan)

2. Assign students to one of three different bioassessment teams.
   1. Each team will be assigned one of the sites (blue, grey of tan) and given a corresponding colored deck of cards.
   2. The organisms on the same colored cards are typical of those that might be found at these different sites.

3. Spend some time examining the cards and try to learn the common names and how sensitive these organisms are to pollution.

II.  Simulation Activity

Each team will: