Effect of hydropower peaking flow fluctuations on community structure and feeding guilds of invertebrates colonizing artificial substrates in a large impounded river

Abstract

Artificial substrates were used to monitor the invertebrate communities below a power peaking impoundment and a flow re-regulating impoundment on the Missouri River on northeastern Nebraska, USA. Invertebrate communities on shallow samplers subjected to exposure from diel fluctuations in flow averaged 3 taxa per sampler and 91 organisms per square meter. In the absence of diel fluctuations, number of taxa per sampler increased to 12 and mean densities increased to 743 per square meter. Fluctuating discharges had no significant effect on numbers of taxa or densities on continually submerged artificial substrates. However, greater numbers of taxa and total densities were observed on deep (107 cm) versus shallow (30 cm) samplers below both impoundments. Polycentropodidae (Trichoptera), Chironomidae (Diptera) and Oligochaeta were observed to tolerate diel fluctuations and exposure below Fort Randall Dam while Hydropsychidae (Trichoptera) and Heptageniidae (Ephemeroptera) were extremely intolerant. Collector-gatherers and predator-engulfers were the predominant functional groups colonizing samplers below both impoundments. Higher numbers of collector-gatherers, collector-filterers and scrapers were observed from samplers in the absence of diel flow fluctuations. This study corroborates results from a number of other investigations, separated in space and time. Examined collectively, these studies provide the framework for understanding power peaking as a stress to benthic stream communities.