Downstream effect of impoundments on stoneflies: Case study of an epipotamal reach of the Jihlava river, Czech Republic

Different habitat types were sampled monthly at a sampling site ca. 12 km downstream from the Dalešice dam on the Jihlava River beginning before impoundment (1976–1978), prior to the addition of heated wastewaters to the reservoir (1984–1985) and from 1987 to 1989. Plecoptera was one of the model groups of macrozoobenthos that significantly responded to changed conditions of flow, temperature and chemistry of river water. There was an increase in species richness (from five to 14 species), species diversity (about double), density and biomass (about 18 to 40 times greater). The study area was originally an epipotamal (barbel) zone with a typical Plecoptera species composition— Perla burmersteriana, Isoperla grammatica, Nemoura cinerea, Leuctra digitata and L. fusca. After river impoundments the investigated reach is a typical metarhithral (grayling) zone. Production of the Plecoptera community in the river reaches affected by the dams increased (riffle, from 1.37 to 23.53; pool, from 0.26 to 6.98 gm −2 y −1 ). It was similar to production in a rhithral (trout or grayling) zone with a typical species composition of rheophilic and cold‐water species (e.g. Perlodes microcephala, Isoperla difformis, I. oxylepis, Siphonoperla torrentium, Amphinemura borealis ). The authors thank Professor František Kubiaček from our department, Professor Richard J. Strange, Tennessee University, Knoxville USA, Professor James V. Ward, Colorado State University, Fort Colins USA and an anonymous reviewer for revising the manuscript and numerous helpful suggestions. This final research was supported by grant No. 204/93/2051 from Grant Agency of Czech Republic.