The response of macroinvertebrates to inundation in floodplain wetlands: Apossible effect of river regulation?

A large number of permanent and temporary wetlands are associated with the lowland rivers in south-eastern Australia. Regulation of these rivers for i rrigated agriculture has probably increased the temporary nature of some we tlands because the reduced frequency of overbank flows causes them to remai n dry for longer. The responses of macroinvertebrate assemblages(species co mposition and abundance) to inundation in permanent and temporary wetlands on the floodplain of the unregulated Ovens River were examined, and these r esponses were compared with those from permanent and temporary wetlands in the Barmah-Millewa forest of the regulated River Murray. The compositions o f macroinvertebrate assemblages in permanent wetlands could not be distingu ished from those of temporary wetlands on the Ovens after inundation, altho ugh changes in abundance of some taxa (especially chironomids) meant that t he assemblages in permanent wetlands differed significantly before and afte r flooding. In contrast, after inundation permanent and temporary wetlands in the Barmah-Millewa forest differed significantly and this difference was sustained through time. This different response of macroinvertebrate assem blages on the two floodplains may be an effect of regulation, although othe r explanations, such as differences between the floodplains in the mechanis m of inundation and historical water regimes, or climatic differences betwe en years, may also be important. Further studies should include concurrent sampling on a wider range of regulated floodplains and experiments manipula ting water allocations to wetlands, to test specific hypotheses about the e ffects of water regime on biota. Copyright (C) 2000 John Wiley & Sons, Ltd.