Diel variations in the effect of spates on mayflies (Ephemeroptera: Baetis)

Abstract

Short-term spates were created in experimental streamside channels by pumping filtered creek water into selected channels at various times of day, resulting in three- or four-fold increases in discharge. Drift rates of Baetis from channels in spate were higher than controls at all times of day. Natural increases in drift were observed in all channels after sunset, and drift rates from channels in spate were highest at this time. The susceptibility of nymphs to drift from channels were calculated as the ratio of drift densities in spate and control channels. Baetis appeared to be more vulnerable to spates after sunset than at dawn or midday. In unmanipulated flow, large nymphs occurred most f..