Stream Benthic Macroinvertebrates - Water Quality Assessment
One method to monitor the water quality in streams is to survey the benthic macroinvertebrates living in the stream. Benthic macroinvertebrates are creatures without backbones that live at the bottom. Common creatures are crayfish, snails, clams, and a large variety of insect (and non-insect) larvae. This means that if you find sensitive creatures living in the water, you can conclude that the water quality must be good. On the other hand if you only find creatures that are very tolerant of poor water quality, you can conclude that the water quality is poor.
One of the advantages of using benthic macroinvertebrates for stream water quality monitoring is that the creatures are relatively non-mobile and generally live in the water a fairly long period of time. This means that if you find a sensitive creature alive in the stream, the water quality most have been good throughout its life. As a result, a single sample of macroinvertebrates provides far more longer term information than a single water quality sample used for chemical analysis. However, the lack of sensitive creatures just says that the water quality is not good but it does not provide any indication of what is the cause.
Additional Resources
There are a large number of organizations that use various methods for benthic macroinvertebrate sampling for water quality monitoring. Many are happy to involve volunteers in this type of monitoring.
Benthic Macroinvertebrate Identification
Introductory - high taxonomic level
- Stream Macroinvertebrates, Maryland Department of Natural Resources two sided single page guide showing identifying sensitive, moderately sensitive, and tolerant organisms. Overall a good basic publication.
- Stream Insects and Crustaceans ID Card another reference sheet emphasizing identification characteristics. It is based on Voshell's work (see books below) and available from multiple Internet sources. The link here is to the University of Virginia. -->
- Key to Macroinvertebrate Life in a River a set of step-by-step steps for identification from the University of Wisconsin Extension Citizen Water Monitoring program. Their publications page has additional resources.
- MD DNR, Chesapeake & Coastal Bay Life - Insects interactive web pages
Advanced - Family taxonomic level
- Family-Level Key to the Stream Invertebrates of Maryland and Surrounding Areas A very detailed key from the Maryland Department of Natural Resources. Family-level identification often requires a microscope to compare antenna segment lengths, the shape and lenght of leg joints, and other less challenging features. guide
- The Audubon Naturalist Society offers inexpensive courses in family-level macroinvertebrate identification in Chevy Chase, Maryland. They also have a stream monitoring program in Montgomery County.
- University of Minnesota Insect Interactive Verification Program
- New York Key to Aquatic Macroinvertebrates web reference
- Macroinvertebrate photos with links to many other photo sources on the Rivanna Conservation Alliance (merged with StreamWatch)
- Digital Key to Aquatic Insects of North Dakota from the Valley City State University. The link is to their glossary which has many annotated photographs of basic and more advanced terminology.
Educational Materials
- Creek Connections Aquatic Macroinvertebrate Module Allegheny College program for middle and high school students with lessons, reference materials, links for more extensive information.
- Creek Connections Specific Aquatic Insect Fact Sheets include life cycle, habitat, diet, and water quality information.
Benthic Macroinvertebrate Monitoring Programs
- Maryland Stream Waders is a Maryland Department of Natural Resources program for annual monitoring of water quality across Maryland. The program has a strong scientific design basis and has been shown to collect data equal in quality to their professional Maryland Biologic Stream Survey. Volunteers collect the sample and turn it in to DNR for professional identification.
- Web searching for macro invertebrates or water quality monitoring will provide an abundance of additional resources.
Benthic Macroinvertebrate Reference Books
- Voshell, J. Reese Jr, A Guide to Common Freshwater Invertebrates of North America, The McDonald & Woodward Publishing Company, Blacksburg, Virginia, (2002). This is my favorite. In addition to detailed illustrations, there are extensive descriptions.
