Diurnal Characteristics of Zooplankton and Macroinvertebrates in the Tailwater below a Kentucky Flood Control Reservoir

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Abstract
Zooplankton and macroinvertebrate drift was sampled in the Barren River Lake tailwater in July 1980 and Jan. 1981 at 2 stations, 0.4 and 23 km downstream from the dam, to determine variations in diurnal, seasonal and spatial abundance. Zooplankton, largely from the reservoir, was densest near the reservoir outflow and was reduced downstream. Some diurnal variation in abundance was noted in Jan. but not in July. Zooplankton was about fivefold more abundant in the tailwater in Jan. than in July; this difference was related to reservoir stratification and vertical movement of these organisms in the reservoir. During both sampling perioids, macroinvertebrate drift in the immediate tailwater was dominated by Chaoboridae, which were exported from the reservoir during the night. At the downstream station, macroinvertebrates were less influenced by the reservoir, and the nocturnal increase in densities and taxa was more typical of the drift in a natural stream. Macroinvertebrates were several times more abundant in July than in Jan.