A years' study of the drifting organisms in a brown-water stream of Alberta, Canada

Ten 24-h drift samples were taken from a brown-water stream of Alberta, Canada over a 1-year period with drift nets having a mesh size of 320 μ. Cladocerans, cyclopoids, and ostracods, collectively called entomostracans, made up a large part of the drift by numbers and contributed substantially to the total biomass of the drift. Drift densities of entomostracans tended to increase as the ice-free season progressed, but drift densities of immature insects remained relatively constant throughout the ice-free season. Total daily drift of both the entomostracans and non-entomostracan fractions tended to decrease as the ice-free season progressed, being dependent on water volume. Drift densities, total daily drift, and number of taxa in the drift were very low in winter. Most of the species exhibited nighttime behavioral drift. At the sampling site, the entomostracans and immature aquatic insects were found to be essentially evenly distributed throughout the water column. For part of the study period, drift de...