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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.

Organism 2: Does this look familiar? This is another stonefly! This stonefly is from the genus Pteronarcys, also know as Giant Stonefly. Aptly named, this creature can grow to nearly two inches long in its larval stage. Despite it's armored appearance and menacingly massive size relative to the first stonefly we found, this group of stoneflies are primarily shredders meaning they feed on plant matter like decaying leaves that have entered the stream. Just like the Common Stonefly this creature is very sensitive to pollution and other forms of environmental degradation.

We are not all that surprised to find multiple variations of stoneflies here. Scientists have noted 100 species of stoneflies in the Adirondack Park alone. During our stream investigation we found more than 30 individual stoneflies.

Water Penny (Psephenidae)

Organism 3: A Water Penny! These folks are pretty easy to identify. Looks like a penny to me... They seem like they are suction cupped to the bottom of rocks and indeed they are often quite difficult to remove. They are classified as scrapers, perfectly adapted to move along the surface of rocks scraping off the film of algae to consume. We found four of them during our collection, another good sign for this stream as they are very sensitive to pollution.

Dobsonfly (Corydalinae)

Organism 4: Look at this behemoth! This is a Dobsonfly from the order Megaloptera. We found five of these engulfer-predators who crawl around their environment looking for small invertebrates to consume.

Mayfly (Ephemeroptera)

Organism 5: This is a Mayfly. They are widely know among anglers, and one of the most popular benthic macroinvertebrates. Larvae typically live in a stream for roughly six months. Once they are ready to emerge as adults massive numbers will live, breed, and die over the course of about 24 hours. Due to their short period of life as an adult, mayflies do not eat once they emerge and have no mouthparts during this life stage. During large emergence events in the Great Lakes region snowplows have been used to clear them from bridges! We found more than 40 mayfly larvae in this stream.

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!

Plattsburgh High School students conducting a benthic study on the Saranac River in NY

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

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