A Macroinvertebrate‐Based Flow Index Elucidates Responses to Environmental Water in a Highly Regulated River

ABSTRACT

Macroinvertebrate‐based flow indices have potential application to guiding environmental flow allocations and monitoring their effectiveness, but their sensitivity to such flows has seldom been tested. We examined the response of the Australian Macroinvertebrate Flow Index (AMFI), calculated from family‐level data, to three stages of increasing environmental flow in a river whose flow regime has been heavily altered by impoundment and diversion. We hypothesised that increasing flow would cause AMFI values to rise in both riffles and pools, converging toward values in unregulated reference rivers. Although AMFI values in both habitats rose as environmental flows increased, values in riffles were already high before the onset of environmental flows, whereas values for pools did not rise enough to match values at reference sites. AMFI thereby revealed aspects of the macroinvertebrate assemblage response to environmental flows that were not evident from a previous multivariate analysis of taxonomic composition. However, the sensitivity of family‐level AMFI to environmental flow provision may have been constrained by substantial variation in velocity preferences among genera within some numerically dominant families. We conclude that AMFI has potential value in monitoring the effectiveness of environmental flows and in setting recovery targets, but further testing in various types of rivers where environmental flows are provided is needed to assess possible context dependence of its performance. Comparable indices developed in other parts of the world are likely to share AMFI's potential for environmental flow applications.