Seasonal Correction Factors for the Biotic Index

Abstract

For evaluating streams using the biotic index (BI), samples of arthropods should be collected in the spring before degree day (DD) accumulations of mean air temperatures above 4.5°C reach 440° in warm-water streams, and before they reach 1050° in cold-water streams that remain below 20°C. Sampling in the autumn may be resumed 60 days after the 440 DD accumulation in warm-water streams and 45 days after the 1050 DD accumulation in cold-water streams. In studies of Wisconsin streams, stream temperature had no effect on the BI, except as it affected seasonal difference. Current had less effect on the BI than anticipated, but currents of 0.3 m/sec should be avoided.