Macroinvertebrates are the "bugs" found throughout the riparian system and are excellent indicators of the overall health of the system. These "bugs" spend the majority of their lives in the water, sediment, algae, and vegetation around the stream or pond. Some organisms are relatively resistant to pollution and/or variable stream flow, while others are very sensitive to changes in the water quality. By observing what type of species are present in the stream we can get a better understanding of the long-term health of the stream or pond.
In this activity you will learn how to recognize different macroinvertebrates and formulate conclusions regarding riparian habitat.
This activity can be performed either in the field or in the classroom. If time is limited the teacher can collect a limited amount of submerged rocks and aquatic vegetation and bring the habitat to the classroom. You will be amazed at the number of organism found under just a few rocks!!
To contact the Water Resource Educator who can set you up with the materials, call (303) 413-7365 or send an email.
1. Field collection
Divide the class up into several groups. Provide each group with a net, specimen jars, taxonomy key. Make sure each group has at least one person to record data.
Macroinvertebrates are found throughout the riparian system. The type of organism identified will depend on the flow of the stream section, the amount of gravel substrate, and the overall water quality. Many macroinvertebrates prefer water high in oxygen, and will thus be found in stream sections with plenty of ripples and a gravel substrate.
Samples can be collected in a variety of ways. A common technique is to place the net in the stream and then use a stick, your feet, or hands to stir gravel up-stream from the net. Macroinvertebrates will be dislodged and washed into the net. Empty the net into the specimen jar.
Another method is simply to collect a few submerged rocks, place them in a bucket and return to analyze the substrate back in the classroom. The bottom of the rocks can be scrubbed with a soft dishwashing brush to dislodge macroinvertebrates.
2. Classroom analysis
Specimens can be classified using a variety of taxonomy guides. The Izaak Walton League guide is attached and divides commonly found invertebrates into 3 classifications, depending upon the type of water quality they can tolerate.
For example: mayfly larvae are generally found in good quality water. Leeches may be found in all ranges of water quality, but you would not expect to find mayflies in water that has been severely polluted.
Have the students work in groups of 2-3 for classifying the bugs. Have each group write up a summary of their results, evaluating what type of water quality they think exists, the diversity of organisms, etc.
Classifying water quality based on macroinvertebrates found is simply one more tool to complete the picture regarding the health of your stream.
Measuring Diversity: The Sequential Comparison Index
The diversity of organisms is also a potential indicator of stream quality. A simple diversity index, called the Sequential Comparison Index (SCI) can be performed by placing a random sample of invertebrates in a tray and counting the different organisms. Each time a different type of organism is encountered, the student will record this as the start of a new run.
SCI = # of runs divided by # of organisms
The SCI runs from 0 to 1.0, with 1.0 representing the greatest diversity. You can use the SCI to evaluate water quality.
For example: You have collected 15 bugs. You identify a sequence of 5 mayflies, and then find a leach, then 4 mayflies, two scuds, a gilled snail, and then 2 more mayflies. Your number of runs is 6.
6/15 = 0.40
The water quality is fair!!
The advantage of the SCI is you don't have to accurately identify all of the organisms, just whether or not they are different.
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NOTE: The types of organisms present will also vary seasonally. Many of the larval stage flies (i.e. mayflies, caddisflies) are abundant in the spring but beome less plentiful in the summer and fall months as they have already hatched into their adult phase.