EXTRACTING ADDITIONAL INFORMATION FROM BIOTIC INDEX SAMPLES

Macroinvertebrates were collected from a small midwestern stream over a 3-year period as part of a non-point source pollution study. Tempora l and spatial variability in standard biotic index values (BIs) were c omputed and compared with variability expressed by a series of additio nal community measurements, including the mean tolerance value of all taxa present in a sample, irrespective of the numerical abundance of i ndividual taxa. The mean tolerance value exhibited lower spatial and t emporal variability than the standard BI; therefore, mean tolerance va lues may be useful in estimating a stream's long-term ambient water qu ality and its recovery potential. Computations of additional BI metric s are easily accomplished with no additional lab work required, and co mparisons of mean tolerance values with standard BIs should aid invest igators in interpreting changes in water quality.