The influence of hydrological variability on the benthic invertebrate habitat of an intermittent upland stream in south-east Queensland Australia.

F.J. Balcombe and S.E. Bunn. Centre for Catchment and In-Stream Research, Griffith University, Brisbane, Australia 4111

In headwater streams, gravel beds may be subjected to frequent disturbance by discharge, however, the nature of change in the physical characteristics of sediment composition is not usually known at a scale relevant to the ecology of interstitial invertebrates. The aim of this study was to quantify the temporal variability in sediment characteristics in relation to catchment and in-stream hydrology in order to define the changes to invertebrate habitat. An intermittently flowing sub-tropical stream in eastern Australia was sampled over a four year period with contrasting hydrological conditions, characterised by a drought and a one in hundred year flood. The physical aspects of benthic habitat were investigated via temporal changes to fine mineral sediment texture. Invertebrate assemblages obtained from these samples were also assessed. The outcome of sediment transportation could be discriminated for low and high-energy events. Discharge regime and sediment grain size were primary determinants of localised variability in particulate organic mater retention and hydraulic filtration. The sediment fauna reflected temporal hydrological variability in terms of habitat disturbance to substrate structure and discharge intermittency. At times of drought and flood the faunal assemblage was similar, being dominated by meiofauna.