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| Nets are used to block off a stream reach before it is sampled. |
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| Fish are collected and then identified and wieghed before they are returned to the stream. |
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A "Dnet" is used to collect aquatic insects. These are used as indicator of a stream's health. |
Streams, even the one meandering through your backyard, are habitat for fish, aquatic insects, and other life. If nothing is living in the stream, then chances are there’s a problem. Even polluted streams are home for pollution-tolerant species like the blacknose dace, mummichog, or black fly larvae.
Biological monitoring, watching and tracking the living things in our waters, is one of the ways to determine that waterway’s health. By combining information on species living in streams with data from chemical analysis and the physical condition of the stream channel scientists determine stream health.
In the summer, teams of scientists and volunteers don their waders and head to the streams to count, weigh and categorize the fish. Pumpkinseed, stoneroller, white suckers, rosyside dace, greenside darters, brown trout and about 100 other species are catalogued during the survey.
Some fish species can tolerate a great deal of pollution and can live in conditions that other fish would not survive. During the survey, scientists record the number of different species, the types of species and the number of fish. They also weigh and measure the fish. The information that they collect is entered into a variety of mathematical formulas which provide an index, called the IBI (Index of Biological Integrity). This index allows scientists to quantify and compare for streams around the county and state.
Similar mathematical formulas are used to evaluate the insects in streams. The insects, like the fish, vary in their tolerance for pollutants. If particular species are found in a waterway, you can be relatively confident that the waterway is healthy.
Every spring insects are collected from rocky, fast flowing, shallow sections of streams. These spots are called riffles and are the part of the stream referred to when we speak of babbling brooks. The insects we’re interested in live between and beneath the rocks on the bottom of the stream and are called benthic macroinvertebrates. Benthic, because they live on the bottom, and macroinvertebrate because they are large invertebrates (without backbones). Large is a relative term: the largest of these insects is a couple of inches long and the smallest, quite small, but still visible to the naked eye. Scientists sometimes refer to these pollution-sensitive insects EPT. This is an acronym for the scientific orders Ephemeroptera, Plecoptera, and Trichoptera. Using macroinvertebrates as a measure for stream health is an easy and to effective way to track changes in water quality.
When the information on insect species is combined with a fish index and other monitoring efforts, the county gains a great deal of understanding about stream health. The IBI for insects is often referred to as the BIBI which stands for the Benthic Index of Biotic Integrity. Using these statistics, we are able to assign values to the biological health of a stream and determine if the health of the stream is improving or declining.
We look to the life in the streams to determine whether the streams are healthy, but don’t forget that it is that beauty and diversity of life that we’re working to protect. You can join our science geeks looking for insects and counting fish. Check out the Maryland Stream Waders program and get your waders on!
Dennis Genito, Natural Resource Specialist
Watershed Management and Monitoring
Phone: 410-887-4488 x243
Fax: 40-887-3510
E-mail: dgenito@baltimorecountymd.gov
Revised June 20, 2007
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