Science

Hidden Stream Life as Indicators of Water Quality

The Watershed Management Division has had one of the nation’s premier stream biological monitoring programs for over 30 years. Biological monitoring, or “biomonitoring”, refers to the use of biological organisms and biological responses to assess changes in Vermont’s surface waters. The scientists in this program focus specifically on monitoring the biology of wadeable streams throughout Vermont. Each summer and fall we visit over 100 stream sites, assessing both fish and benthic macroinvertebrate communities.

This stonefly larvae is found in smaller high elevation streams, and processes autumn leaves that fall in the stream

This stonefly larvae is found in smaller high elevation streams, and processes autumn leaves that fall in the stream

Most people recognize what a fish looks like, but not everyone is familiar with the term “benthic macroinvertebrate”. These are the small creatures that live on the stream bottom, most commonly found in “riffles”, the shallow areas of streams where water flows rapidly around boulders and over cobbles (small-medium naturally rounded rocks). These macroinvertebrate communities are made up largely of insects, many of which are larvae that will eventually hatch and fly away. Other members of this community include crayfish, mussels and snails. If you wade into a stream riffle and pick up a medium sized rock, there is a very good chance that you will see some of these creatures scurrying around on it. Macroinvertebrate communities are both abundant (often greater than 1000 individuals per square meter), and very diverse. In fact, there are frequently more than ten times the number of macroinvertebrate species than fish species in a wadeable stream.

Macroinvertebrates are extremely important for protecting our water quality, and serve many essential functions in stream ecosystems. They provide food for brook trout and other fish. Some scrape and eat algae and bacteria from stream rocks. Many break down autumn leaves into smaller pieces that can be used as food or washed away. Others have evolved to filter and consume organic matter from the water.

This caddisfly larvae lives in larger streams, and constructs nets that filter organic matter from the water

This caddisfly larvae lives in larger streams, and constructs nets that filter organic matter from the water

Many macroinvertebrates are very sensitive to human stresses, such as chemical pollutants, nutrient enrichment, and stormwater runoff. As water quality or quantity changes, some species are no longer able to survive in the altered environment, while other more tolerant species move in to take their place. Some highly sensitive stream insects that fly fishermen might recognize are mayflies, stoneflies, and caddisflies. The vast quantity of historical data collected by our biomonitoring program lets us know what a healthy macroinvertebrate community in a pristine stream should look like. By collecting macroinvertebrate samples from Vermont’s streams, and identifying the organisms in the lab, our scientists can tell how far from the “natural condition” the community is, and what water quality issues might be affecting a particular stream. Assessments of these macroinvertebrate communities often form the foundation of our Division’s efforts to identify problems and improve water quality throughout the State’s rivers and streams.

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