Why monitor macroinvertebrates?
history * case studies

Most people are interested in water quality because they want to know if their water is safe for drinking and can support healthy populations of fish and other animals. In other words, we're interested in the ability of a water body to support life.

In the past, water chemistry was measured and physical habitat monitored to make sure human activity was not limiting the ability of waters to function as effective drinking water for humans or life support systems for fish and other aquatic animals. Unfortunately, water can be chemically pure and habitat can be structurally sound, but the aquatic life not diverse or healthy as expected. Perhaps periodic chemical input affected the organisms, but was promptly removed by the water's flow. Maybe, invasive species have altered food availability, eliminating native organisms. For whatever reason, the water body's chemical and physical characteristics alone do not necessarily reflect the biological condition.

Biological monitoring is sometimes thought of as a motion picture, integrating cumulative effects of human activities on aquatic systems, while chemical monitoring is better described as a still image, recording only the information at a single point in time. For these reasons and more, a comprehensive monitoring plan must include biological data with chemical and physical information, or else run the risk of missing the answer to the key question of monitoring. "Can the water support life in its many forms?" Cumulatively, the chemical, physical, and biological data will help you better understand the true impacts of various land-use practices or pollutants on the organisms in your streams.

Why macroinvertebrates instead of fish or algae?
Evaluating the biological community of a stream by assessing algae, macroinvertebrates, fish, and sometimes amphibians or even birds, provides a sensitive and cost effective means of determining the biological condition of the stream. Such evaluations are particularly effective when stream impacts are from non-point sources, sporadic events, or cumulative low-level pollution. Each group of organisms (algae, macroinvertebrates, and fish) has advantages and disadvantages for use in assessment.

For example, relatively few species of fish live in the Northwest, and many fish populations are threatened by human activity and could be irreversibly impacted by intensive study. Algae are incredibly abundant and diverse in Northwest waters, but finding people with the skills to identify samples of algae can be a challenge (though it's getting easier). Benthic macroinvertebrates (aquatic animals that lack an internal skeleton, are large enough to be seen by the unaided eye, and live on or among the substrate) are especially useful for stream monitoring because they are common in most streams, readily collected, relatively easily identified, not highly mobile, sensitive to pollution and human disturbance, and have life cycles from several days to more than 120 years.

Protocols for monitoring fish, algae and macroinvertebrates have been synthesized by the EPA's Rapid Bioassessment Protocols for Streams and Wadeable Rivers (.pdf in this Guide or online at http://www.epa.gov/owow/monitoring/rbp/), but macroinvertebrates have taken the lead as the organisms of choice for monitoring wadeable streams in the Pacific Northwest.

Studies of toxicology, chemical bioaccumulation, habitat recolonization, physical deformities, and community measures (including biotic indices, diversity indices, similarity indices, and descriptions of community structure and function) are all ways in which macroinvertebrates can be used to assess water quality. This Guide focuses on the process of monitoring community measures, which provides a simple, hands-on approach to understanding and measuring stream health.

 

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