The effect of the release of an artificial discharge of water on invertebrate drift in the R. Wye, Wales

Abstract

An artificial discharge of water (3.0 m3/sec), over a 48 h period, from an impoundment into the R. Wye did not substantially affect water temperature or concentrations of dissolved oxygen and suspended solids at a site 16 km below the impoundment. However, the load of suspended material on the second day of the release was about 10 times greater than the pre-release load. The total number of drifting macroinvertebrates on the first and second days of the release were about 7 and 3 times greater than the number on the day preceding the release. The initial increase in flow at 15.00 h resulted in an immediate increase in the number of drifting larvae of Rheotanytarsus, a tubicolous chironomid. Subsequently there was an enhanced night-time increase in the total number of drifting invertebrates, particularly the mayfly, Ephemerella ignita (Poda), and this also occurred on the second night of the release. Increases in the number of drifting Rheotanytarsus and Ephemerella, the most abundant invertebrates, resulted in increase in drift density.