Craig Goch Report No. 12 The production of two species of Ephemeropters (Ephemerella ignita PODA and Rhithrogena semicolorata CURTIS) in the upper reaches of the R. Wye, Wales

As part of a base-line ecological study of the R. Wye related to the construction of an enlarged Craig Goch, a proposed major regulating reservoir in the upper catchment which will be filled from a variety of sources, two sites (W2 and W3) in the headwaters were intensively studied during the period March 1975 – April 1976 and estimates of production made for two species of Ephemeroptera. Both study sites are typical salmon nursery areas with a substrate of cobbles and coarse gravel forming a ‘riffle’ habitat. The water, similar at both sides, is soft (mean calcium concentration = 4.1 mg/l) and low in inorganic nutrients. Samples, taken weekly during the summer and less frequently at other times, were collected from each riffle on a stratified random basis using a cylinder sampler (area, 0.05m2 ) modified after Neill (1938). Seven replicate samples were taken with weekly sampling and 14 at other sampling frequencies. The wetted area of each site was measured frequently throughout the study