Watershed Wednesday: Macroinvertebrates as Indicators of Water Quality

When we think of a river or stream and it’s corresponding health, we often think of pristine, crystal clear water. Although this can be a good determining factor, the health of a water body cannot be determined by visual interpretation alone.

Through the Gallatin Stream Teams, a citizen science volunteer team held in partnership with the Gallatin Local Water Quality District, a variety of indicators are used to determine water quality - pH, Dissolved Oxygen (DO), Total Nitrogen, Total Phosphorus, Total Suspended Solids (TSS), amongst others.

Did you know that bugs can also be used to help determine water quality? Macroinvertebrates are organisms that are large enough (macro) to be seen with the naked eye, and also lack a backbone (invertebrate).

Some macroinvertebrates are more sensitive to pollution than others, and require less oxygen. Macros are often categorized into three categories: sensitive, facultative, and tolerant.

Stonefly nymphs are very sensitive to pollution and cannot survive in streams that have a dramatic drop in dissolved oxygen. Leeches on the other hand, thrive in murkier waters with less oxygen and can tolerate added pollutants. Therefore, if a stream that typically can support a healthy stonefly population is found to have an abundance of leeches in their place, that gives scientists a tip that the waterbody in question is suffering.

The examination of macroinvertebrates as a form of biosurveying tells us that something is wrong, but not what definitively caused the absence of sensitive species. This is where the other indicators mentioned above come into play!

To collect macroinvertebrates from a stream, one must perform the “bug dance” featured in this picture. The collector takes a dip net, and facing downstream does a small twist for about one minute to stir up any of the critters that dwell on the stream floor or under rocks to corral them into the net. Samples are sent to the lab for analysis.

Here at the Gallatin Watershed Council, we host many educational activities that include the observation of macroinvertebrates to bring awareness to their importance as indicator species. Visit our event page to stay updated on all upcoming educational events!

If you are interested in being a citizen scientist and want to help collect water quality data within the Lower Gallatin Watershed for the 2022 season, fill in an interest form here!