The influence of flow reduction on macroinvertebrate drift density and distance in three New Zealand streams

Abstract

AbstractDemand for water is increasing in many parts of the world, but removal of significant volumes of water from streams for irrigation, industry, and municipal supply has the potential to affect aquatic biota. Protecting the ecological value of streams is of increasing interest to water managers and the public. However, few experimental studies address the impacts of flow reduction on stream habitat condition and biota. We reduced discharge by 80 to 95% in 3 small, stony-bottomed streams (<4 m width), using weirs and diversion channels/pipes and quantified diel patterns of density of naturally drifting macroinvertebrates before and during a 2-mo period of continuous reduced flow. We also measured artificially induced passive invertebrate drift distance in control and impact reaches to determine the impact of flow reduction on drift distance. We measured the head capsule width of common drifting taxa to determine if larval size interacted with discharge to influence drift distance. Drift density of sev...