Influence of Impoundments on Mayfly Diets, Life Histories, and Production

Abstract

We investigated the influence of stream regulation on the dietary composition, life histories, and production of four mayfly species (Drunella grandis, Ephemerella infrequens, Paraleptophlebia heteronea, and Baetis tricaudatus) at three sites in the Upper Colorado River. Sites (unregulated, intensely regulated, and recovery) were selected based upon degree of regulation (i.e., upstream, 0.4 km downstream, and 4.0 km downstream from a deep-release reservoir). Although levels of food abundance (diatom density and sedimentary detritus) varied between sites, the dietary compositions of B. tricaudatus (primarily diatoms) and P. heteronea (detritus) did not change. However, D. grandis and E. infrequens consumed diatoms downstream from the reservoir whereas their diet was strictly detritivorous at the upstream site. The number of degree days and mean annual water temperatures at the downstream sites were greater than at the free-flowing unregulated site. Baetis tricaudatus responded to regulated conditions by hi...