On June 10, 2019, Kirby Reed and his students from Truckee High School will join us for a program around their local streams. We have an ongoing partnership with Mr. Reed and are grateful for his help and support, as well as the opportunity to investigate one of the most stunning features of the Sierra with his students: our waterways. This article features resources we have used in the Truckee High School River Ecology Program.

What are aquatic macroinvertebrates?

Stonefly larva are indicators of healthy streams

One of the most interesting facets of studying river ecology is looking at aquatic life. Meet your new friends: aquatic macroinvertebrates! According to an article by the EPA, “aquatic macro invertebrates” refers to small water-dwelling animals or aquatic insects in their larval stages. This includes dragonfly and stonefly larvae, snails, worms, and beetles. They lack a backbone, are visible without the aid of a microscope, and are found in and around water bodies during some period of their lives. Benthic macroinvertebrates are often found attached to rocks, vegetation, logs and sticks or burrowed into the bottom sand and sediments.

These “indicators” can teach us about the health of a waterway, providing clues about its biological condition. Generally, waterbodies in healthy biological condition support a wide variety and high number of macroinvertebrates, including many that are intolerant of pollution. Samples yielding only pollution–tolerant species or very little diversity or abundance may indicate a less healthy waterbody, says the EPA.

Macroinvertebrates respond to human disturbance in fairly predictable ways. In fact, because they cannot escape pollution, macroinvertebrates have the capacity to integrate the effects of the stressors to which they are exposed, in combination and over time. Biological condition is the most comprehensive indicator of waterbody health. When the biology of a waterbody is healthy, the chemical and physical components of the waterbody are also typically in good condition.

The full article can be found at: https://www.epa.gov/national-aquatic-resource-surveys/indicators-benthic-macroinvertebrates

Perform your own macroinvertebrate study:

Our full manual for this activity includes more information on aquatic macroinvertebrates, a guide to our suggested research methods, and an identification key. You can access the manual here.

Surveying macroinvertebrate health in waterways activity:

Methods: Many different types of questions beyond “how healthy is this waterway?” can be answered through a macroinvertebrate survey. Students could add measurements of water quality, habitat parameters, or compare benthic macroinvertebrate populations between different locations. Below is a basic methodology you can adapt to fit your specific research question.

  1. To conduct survey in flowing water, agitate the streambed upstream of a catching net for 60 seconds. (If there is no flowing water rake the vegetation along the riverbank upwards in a circular motion for 60 seconds to collect insects.) Be sure to agitate the streambed for the same amount of time every sample.
  2. Turn the contents of the net inside out into a sorting tub half full of water. You may need to let the water settle for a few minutes before sorting.
  3. Using an eyedropper, put similar looking macroinvertebrates into the same section of an ice cube tray.
  4. Once you have fished out as many macroinvertebrates as possible, use the ID chart in our manual to identify the order of each type. If there are more than 25 of one type of in the sorting tub, you can estimate the total number.
  5. Some groups will focus on the number of macroinvertebrates found from certain pollution tolerance groups, while others create a weighted macroinvertebrate score using the following formula:

Group 1 – Very Intolerant of Pollution number of organisms x 4 =
Group 2 – Moderately Intolerant of Pollution number of organisms x 3 =
Group 3 – Fairly Tolerant of Pollution number of organisms x 2 =
Group 4 – Very Tolerant of Pollution number of organisms x 1 =

Weighted macroinvertebrate score is the sum of each group: ___________

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