An Improved Biotic Index of Organic Stream Pollution

Major improvements were made in using a biotic index of the arthropod fauna to evaluate organic stream pollution. All tolerance values were reevaluated, many were changed, and the scale for tolerance values was expanded to 0-10 to provide greater precision. Keys to larvae of Ceratopsyche have been developed and tolerance values for species in this important genus are provided. Sorting of samples in the laboratory instead of in the field is recommended, and directions for processing and evaluating samples are included.