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Stream Investigations Understanding Water Quality through observation and data Collection

Introduction

Below the surface of the water lives a diverse community of organisms whose composition can indicate the health of their surrounding ecosystem.

As scientists we can quantify these organisms through observation, collecting information on both the diversity and abundance of benthic macroinvertebrates in a particular stream reach. The data collected will indicate the overall water quality.

Exploration

As you explore the following photos and videos be sure to move slowly and take diligent notes on the:

  • diversity: all of the different taxa we find
  • abundance: how many of them we find

Your notes will be crucial in understanding the health of this stream.

Stonefly (Plecoptera)

The first critter we are able to identify is a Stonefly. We are sure this is a stonefly because it has six legs, each with two tarsal claws on the end that are visible upon close inspection. Other quick clues to identify this stonefly are the presence of two lengthy and stout antennae and it's two tails.

Organism 1: Pictured, is a stonefly from the family Perlidae also referred to as a Common Stonefly. This animal is an engulfer-predator and will consume most small insects it finds in the small cool streams that it inhabits. If you isolate a stonefly in still water where there is less oxygen they will move their body as if they are doing push ups to force water over their gills. They tend to be very sensitive to stressors in the form of pollution or habitat disruption.

Additional Data

In addition to the organisms you noted, a partner recorded; more than 20 Caddisflies, six Riffle Beetles, three Midges, and over 20 Black Fly Larvae.

Pollution Tolerance Index

Now, let's use our observations and data to determine the water quality of this stream reach. Remember, benthic macroinvertebrates can be used as biological indicators for water quality because they have varying levels of tolerance to pollution. Download a copy of, and use the pollution tolerance index google sheet to organize the data you have gathered from our stream study above and to determine the PTI score!

Write the number of individuals you observed next to their name. Add the number of taxa present down the column for each "PT Group." DO NOT add total individuals found, just count whether they were present or not. For example, the maximum "# of Taxa" possible for the PT Group 1 is seven. Once you have calculated the # of Taxa in each PT Group multiply by the weighting factor for that group. Add all of the final values from each group to get your total PTI rating.

Once you have a Pollution Tolerance Index rating use the table below to determine the water quality of this stream!

Conduct your own stream investigation!

Now it is time to do your own rock scrub and stream investigation. Head out and find a stream nearby you would like to assess! You can use this BMI Picture Key to help you identify the organisms you find. Maybe you would like to commit a but more time to this and make your very own homemade Kick Net!

Produced by Nate Trachte and Ashley Eaton, on behalf of Lake Champlain Sea Grant. June 2020

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