What’s living in our water? Probably more than you think.
Lakes, rivers and wetlands are full of life of all sizes. We see the big animals — the fish, turtles, crayfish and frogs that call these waters home. But what about the smaller animals?
Most water monitoring is chemistry based, testing for oxygen levels, sediment, and nutrients such as phosphorus and nitrogen. Bio-monitoring is a method that measures what is living in the water, typically using insects. There is a whole underwater world of aquatic insects we don’t see. And these insects can tell us a lot about the health of water.
The type of insects collected during bio-monitoring are called macro-invertebrates. Macro-invertebrates are small bugs, without a backbone, that you can see without need of a microscope. You probably know some of them already: snails, leeches, water beetles.
Others you may not be as familiar with: scuds, water scorpions and caddisflies. And many insects we know and see on land spend the earlier part of their lives underwater as larvae or pupae. These include dragonflies, mayflies, and mosquitoes.
The types of macro-invertebrates we collect in a sample tell us about health of the water, streambanks and habitat. Some of these aquatic insects are very sensitive to water pollution. Others are tolerant to water pollutants and low oxygen levels.
In a sample, if the only insects present are those tolerant of poor water quality conditions, that tells us the water quality of that area might be poor. Healthier streams support a wide diversity of macroinvertebrates, while impaired streams support fewer, pollution-tolerant species.
Macro-invertebrates also have very specific living conditions. Some of them only live in the gravel parts of a stream, others on woody plants in the stream, others find shelter in the plant leaves that hangover from the side into the stream. The types of aquatic insects in a sample tell us what habitats are present, and over time how habitats change, or if there is habitat loss due to human activity.
Carver County Water Management Organization staff began bio-monitoring again in 2019. They collected samples of aquatic insects from West Chaska Creek, East Chaska Creek and Silver Creek.
Staff evaluated each sample, counting how many different types of aquatic insects were present, and how many types of aquatic insects with pollution sensitivities were present.
All creeks received good scores for diversity, having many types of macro-invertebrates. However, the creeks all received low scores for the number of pollution-sensitive species. So, our creeks have a good diversity of species, but are not supporting sensitive species, meaning the water quality could stand to improve.
Macro-invertebrates are really fun to capture live and study. You can watch how they swim, learn how they feed, and more. Staff will be offering an outdoor program with macro-invertebrates this summer at different places around the county. The program is targeted towards ages 7 years old and up, but younger children can join. Families can sign up and will stay with their family unit.
Check out www.co.carver.mn.us/water for more details.