Use of Macroinvertebrates in Stream Biomonitoring


What is stream biomonitoring?

    Stream biomonitoring is the study of what biological organisms are present in a stream.  Based on what organisms are present, you can get an idea of what the stream water quality is like.

What are macroinvertebrates?

    Macroinvertebrates are organisms which are large enough to be seen with the naked eye, yet are generally small.  They lack a backbone and inhabit all types of water habitats.  Most aquatic macroinvertebrates are insects, but others include worms, crayfish, snails, and freshwater clams.

How do macroinvertebrates indicate stream quality?

    1) They are affected by the conditions of the stream, including pollution.

    2) They are fairly sedentary, and therefore cannot escape pollution events.

    3) Specific species are more or less tolerant of pollution.  Presence or absence of  certain species indicates good or poor water quality.

    4) They are fairly simple to sample and identify.

What are the drawbacks to using macroinvertebrates to indicate stream quality?

    1) They do not respond to all types of pollutants.

    2) Their presence or absence may be due to other factors than pollution (water current, substrate of stream, drought conditions).

    3) Their abundance and distribution may vary seasonally.

    4) They may disperse into and out of areas where they normally do or do not occur.

Do the benefits of using macroinvertebrates for monitoring stream quality outweigh the drawbacks?

    Yes.  Keeping in mind the limitations listed in the drawback section, a properly designed stream biomonitoring survey will give you a very good idea of the water quality of a stream.

Are there different types of stream biomonitoring?

    There are 2 major types.  (1) Surveys before and after a known pollution event.  (2) Sampling at regular intervals throughout a specific time period.

Are there different sampling designs?

    There are many different sampling designs, but they fall into 2 main categories:

 (1) qualitative- a general assessment of organisms present. 

(2) quantitative- an actual numerical count of different organisms present in order that statistics can be used more accurately.

The Ackerly Creek Subwatershed biomonitoring was done at regular intervals over two years, and was a quantitative study.  Click on the Ackerly Creek Subwatershed link to learn more about our particular study.