6.2 Classroom activity
In this classroom activity, students will be provided with photos of macroinvertebrates from Upper Mud Creek, Lower Mud Creek, and Mud Tributary. The students will then use a simple dichotomous key to identify the macroinvertebrates at each site and will calculate one or more measures of stream health based on the data that they gather.
Divide the class into three research teams. Each team will be responsible for using macroinvertebrates to assess stream health at one of the three Mud Creek study sites (Upper Mud Creek, Lower Mud Creek, and Mud Tributary). You may choose to divide the three teams into smaller groups and divide up the work within each team.
Explain the background information above to each team, and make sure students know how to use a dichotomous key. Provide each team with an envelope of photos from their site, a dichotomous key, and a data sheet. If you want to divide the teams into smaller groups, you can give each small group a dichotomous key, a data sheet, and a portion of the photos to identify.
Each team should identify their assigned macroinvertebrates using the dichotomous key and record all types of macroinvertebrates found on their data sheet. The key provided goes down to the taxonomic level of family (or sometimes order), but some macroinvertebrate families are represented by more than one species at a given site. For this reason, students may find that two different photos with two somewhat different looking organisms may key out to the same group. For example, students may find more than one kind of mayfly at a given site. This is an important part of their data and should be recorded. Students do not need to know the name of each kind of mayfly, just the number of different types of mayflies found at the site. Although a sample of macroinvertebrates collected in the field is likely to include multiple individuals of each species, the photos provided include only one example of each species. This means that each photo should provide an example of a new kind of macroinvertebrate — either it will key out to an entirely new group (e.g., the only crane fly larva) or it will provide an example of a new species for a group already found (e.g., a second or third kind of mayfly). Thus, each photo should result in new data to be added to the student data sheet.
Once students have gathered their data they should calculate at least one or two biotic metrics of stream health. One metric is simply the total number of taxa (total number of different kinds of organisms). This is similar to the idea of number of species, but it is very difficult to key out macroinvertebrates to the species level, so we simply count the total number of taxonomic groups represented. If students found three different kinds of mayflies at their site, they should report these as three different kinds of taxa. A second metric is the total number of EPT taxa. EPT taxa are taxa belonging to one of three major groups of macroinvertebrates that are particularly intolerant of pollution and demanding of oxygen: Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies). To determine the total number of EPT taxa, simply count the total number of different kinds of mayflies, stoneflies, and caddisflies found.
Once the three student research teams have finished identifying their macroinvertebrates and calculating their biotic metric(s), ask each team to present their findings to the class. Compare the results for the three sites and ask the class what these results tell us about the ability of Mud Creek to recover from the effects of urbanization.