Recovery of a headwater stream from an insecticide-induced community disturbance.

Faunal assemblages, leaf litter processing rates, and seston export were followed in two streams after one was altered with an insecticide. Two years after treatment ended, the macroinvertebrate trophic structure of the treated stream community had recovered and was similar to that of the reference stream; however, major differences in taxonomic composition persisted. Some taxa which were rare or absent before treatment became locally abundant during recolonization. Other taxa, which were known to be abundant before treatment, remained absent or rare. Restoration of shredder biomass, leaf litter processing, and organic seston concentrations supports the concept that stream ecosystems are resilient to disturbance. Thus recovery of trophic function may occur in a fashion not recognizable solely by taxonomic criteria.