We used simple empirical relationships between flow, water quality and benthic macroinvertebrate community structure and function to establish an evidence-base for decision making in environmental water provision. The resulting response curves are readily communicated to a non-scientific audience and provide an objective measure of the environmental risk associated with a given level of extraction.

Under South Australian legislation, resource managers are required to incorporate environmental needs within water allocation frameworks. The Mount Lofty Ranges, located near to Adelaide, are drained by a network of small streams. Prevailing Mediterranean climates interact with spatially unpredictable but reliable groundwater discharge to produce flow regimes spanning a gradient of permanence. Environmental water determination has previously utilised a maximum permissible deviation in hydrological measures, assessed on the basis of modelled ‘current’ and ‘no-development’ scenarios. Such approaches are ecologically defensible, but remain somewhat opaque to the ecological processes they seek to support. Articulating the likely environmental consequence or benefit of a given scenario is not straightforward and as a result the environmental success of water allocation plans is difficult to determine.

We used both functional and biodiversity-based measures of macroinvertebrate communities to demonstrate within-catchment responses to variation in antecedent flow and electrical conductivity. Biological measures declined in a linear manner above a threshold value of electrical conductivity, with flow responses similar in shape but opposite in orientation owing to covariance. Such threshold responses are widely sought in environmental policy making, as they provide an intuitive means to establish a meaningful level of risk to competing scenarios. They remain however, generally elusive. The specifics of the approach have not to our knowledge been attempted in other climatic zones although they are readily transferable. Where applicable, these provide a means to incorporate macroinvertebrate community condition in water allocation decisions, based on ecologically relevant and readily quantified responses.