The ecology of two intermittent streams in Victoria, Australia. I. Multivariate analyses of physicochemical features

SUMMARY. 1. Amplitudes in physicochemical features in intermittent streams exceed those in nearby permanent streams and strongly influence macroinvertebrate community structure. Hitherto, seasonal variation in the physicochemistry of intermittent streams has been described only anecdotally; there has been no objective attempt to describe phases of flow that could subsequently be compared with patterns in biotic composition.
2. Multivariate techniques of ordination and classification were applied to environmental data collected from pools and riffles at four sites on two intermittent streams in central Victoria during a drought year followed by a wetter year. A cyclical sequence of How phases was usually evident in poo and riffle habitats at all sites over both years: pre-flow, early flow, main flow, diminishing flow and post-flow. Several spates that occurred during the sampling period only briefly distorted the cyclical pattern.
3. No single variable characterized these phases at each site; instead, the phases represented complex combinations of discharge, current velocity, dissolved oxygen, conductivity, water temperature and time-related variables. This highlights the advantages of an integrative, multivariate approach to seek patterns in environmental data, especially since physicochemical features are often highly inter-correlated.