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Rapid Field Assessment of Organic Pollution with a Family-Level Biotic Index

Tolerance values for families of arthropods are presented to enable calculation of a family-level biotic index (FBI) in the field. In six streams differing in substrates and degree of organic pollution, an average of 23 min, 35 s was needed to assess the condition of a stream in the field using the FBI; this period was at least an hour less than is normally required to evaluate a stream with the generic- and species-level biotic index (BI). Comparison of the FBI and BI of replicated samples from these six streams and from 120 random samples from other Wisconsin streams showed that some accuracy is lost by using the FBI, with the FBI usually indicating greater pollution than the BI in unpolluted or slightly polluted streams and less pollution in polluted streams. The purpose of the FBI is to provide a rapid, but less critical, evaluation of streams in the field by biologists who can recognize arthropod families by sight. It is not intended as a substitute for the BI.