Response of the aquatic macroinvertebrate communities to dam construction on the Thomson river,Southeastern Australia

Aquatic macroinvertebrates were sampled above and below the site of the Thomson Dam, Victoria, Australia, over a two-year period during dam construction. Total number of species and the number of species and individuals per sample were all lower for 33 km below the dam site, compared with sites upstream. Ordination analysis showed that the major differences between the study sites were related to longitudinal position in the river. The second ordination axis could be related to seasonal changes in the fauna. Variations in the pattern of axis 2 scores at sites downstream of the damsite suggested continuing changes in the community at these sites during the study, possibly due to increases in the density of species favoured by sediment deposition (e.g. Cheumatopsyche sp. 2: Trichoptera, Hydropsychidae). Classification analysis separated the faunal communities at sites above and below the construction zone. Inverse classifications indicated species with disjunct distributions on either side of the dam site. By comparison with preconstruction data and surrounding undisturbed rivers, species likely to have been disadvantaged by increased sedimentation were identified. These included Atalophlebioides sp. 1 (Ephemeroptera, Leptophlebiidae), Stenoperla australis (Plecoptera, Eustheniidae) and Scirtidae (Coleoptera).