Implications of streamflow variability and predictability for lotic community structure: a regional analysis of streamflow patterns

Long-term discharge records (17-81 yr) of 78 streams from across the continental USA were analyzed. Based on overall flow variability, flood regime patterns and extent of intermittency, 11 summary statistics were derived from the entire record for each stream. Using a nonhierarchical clustering technique, 9 stream types were identified: harsh intermittent, intermittent flashy, intermittent runoff, perennial flashy, perennial runoff, snowmelt, snow + rain, winter rain, and mesic groundwater. Stream groups separated primarily on combined measures of intermittency, flood frequency, flood predictability, and overall flow predictability, and they showed reasonable geographic affiliation. The positions of the streams in a continuous three-dimensional flow space illustrate the wide range of ecologically important hydrologic variability that can constrain ecological and evolutionary processes in streams.