The study of aquatic macroinvertebrates and their responses, is used to determine environmental conditions. One type of biological monitoring involves collecting, processing, and analyzing aquatic organisms to determine the health of the biological community in a stream. Aquatic macroinvertebrates are good indicators of stream quality because:
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The basic principle behind the study of macroinvertebrates is that some are more sensitive to pollution than others. Therefore, if a stream site is inhabited by organisms that can tolerate pollution and the more pollution sensitive organisms are missing a pollution problem is likely. For example, stonefly nymphs aquatic insects that are very sensitive to most pollutants cannot survive if a stream's dissolved oxygen falls below a certain level. If a biosurvey shows that no stoneflies are present in a stream that used to support them, a hypothesis might be that dissolved oxygen has fallen to a point that keeps stoneflies from reproducing or has killed them outright.
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Identification of the macroinvertebrates is an essential step in conducting a stream survey. Entomologists, John Flannigan, Bob Sharp and the work of Bill Stapp collaborated to develop the dichotomous key shown below. This key is first used to identify the macroinvertebrates, then the data is entered into a spreadsheet that tallies the survey results and gives a general water quality indicator.
After students have selected and identified the different macroinvertebrates along with counts of each of the different orders or families, the counts are entered into the spreadsheet shown below.