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Aquatic biomonitoring is best defined as the systematic use of biological information to assess or evaluate changes in aquatic environments. Information provided by biomonitoring programs is used to indicate current water quality or to describe effects of pollution or habitat alteration on aquatic communities, both past and present. The most common use of biomonitoring is to ensure compliance with clean water regulations established by Congress in 1972. Protocols have been established to assess impairment of aquatic communities using various groups of organisms including diatoms, benthic macroinvertebrates, and fish. This includes both running water such as rivers, streams, springs and seeps, and standing water such as reservoirs, lakes, wetlands and ponds. Most often aquatic benthic macroinvertebrates, more specifically aquatic insects, are used as indicators of ecological health. Benthic macroinvertebrates are defined as those invertebrates that inhabit the bottom substrate, debris, logs and plants of frehwater habitats for some part of their life cycle, and can be captured using a net with 500-micron openings. These organisms play an essential role in the function of aquatic ecosystems by processing organic material and are crucial food items for many aquatic organisms, such as fish. Common groups include the mayflies, stoneflies, true bugs (water boatman, backswimmers, etc), caddisflies, true flies (midges, black flies, etc.) and water beetles.

The most common type of biomonitoring using benthic macroinvertebrates is surveillance. This approach usually includes sampling of benthic macroinvertebrate communities before and after a project is completed or a pollution event has occurred. Surveillance is an important component of water resource management, indicating if measures taken are working. For example, after a spill of a chemical toxicant into a stream, did cleanup efforts restore the benthic macroinvertebrates to prespill levels? The second major type of biomonitoring using benthic macroinvertebrates is to ensure that there is compliance with previously established requirements of long-term water quality. For example, benthic macroinvertebrates can be used to insure that standards are maintained during and after a specific construction project.

The advantages of using benthic macroinvertebrates is that they are wide spread and common both in different types and abundances, therefore affected by pollution and habitat alterations in many types of aquatic systems from local to regional scales. Also, their long life cycles and sedentary nature allows for good analysis of both intermittent and regular inputs of pollutants or habitat alterations. Macroinvertebrates are choice organisms for sampling for the following reasons: 1) they are easily collected, 2) the taxonomy of most groups is well known, 3) presence or absence of certain groups can indicate quality of water, and 4) they are affected by various types of disturbances local to regional scales.

There are numerous excellent resources that can be consulted such as D. M Rosenberg and V. H. Resh. 1993. Freshwater Biomonitoring and Benthic Macroinvertebrates. Chapman and Hall, New York, New York, J. R. Karr and E. W. Chu. 199. Restoring Life in Running Waters. Island Press, Washington, D.C. and M. T. Barbour, J. Gerritsen, B. D. Synder and J. B. Stribling. 1999. Rapid bioassessment protocols for use in streams and wadeable rivers: Periphyton, benthic macroinvertebrates and Fish, Second Edition. EPA 841-B-99-002. U. S. Environmental Protection Agency; Office of Water Quality; Washington, D.C.