What’s wrong with the Australian River Assessment System (AUSRIVAS)?

Bruce C. Chessman

doi:10.1071/mf20361

Abstract

The Australian River Assessment System (AUSRIVAS or AusRivAS) is a national biomonitoring scheme that supposedly assesses the ‘biological health’ of rivers. AUSRIVAS outputs observed-over-expected (O/E) indices derived from macroinvertebrate survey data obtained both at a site to be assessed and at designated reference sites. However, AUSRIVAS reference sites lack any consistent or quantified status, and, therefore, AUSRIVAS O/E indices have no particular meaning. Moreover, many studies have found AUSRIVAS O/E to be a weak or inconsistent indicator of exposure to anthropogenic or human-influenced stressors. Poor performance by AUSRIVAS may relate to numerous factors including the following: (1) variable reference-site status, (2) inappropriate model predictors, (3) limitations of O/E indices, (4) inconstant sampling methods, and (5) neglect of non-seasonal temporal variability. The indices Ephemeroptera–Plecoptera–Trichoptera (EPT) and stream invertebrate grade number – average level (SIGNAL) provide alternatives that have often outperformed AUSRIVAS O/E in comparative tests. In addition, bioassessment of Australian rivers might be advanced by the development of diagnostic methods to identify the stressors causing ecological impact rather than merely to infer impact intensity and assign quality ratings to assessment sites.

Highlights

The Australian River Assessment System (AUSRIVAS or AusRivAS) is a national biomonitoring scheme adapted from the British River Prediction and Classification System (RIVPACS: Clarke et al 2003)
The probabilities of occurrence are derived by a predictive statistical model from macroinvertebrate survey data that were collected at designated reference sites, weighted according to their physical, biophysical and chemical similarities to the assessment site for which an O/E value is to be generated
Publications on AUSRIVAS, and articles describing the application of RIVPACS-type methods to biota other than macroinvertebrates and outside of Australia, were consulted for information on factors that might limit the performance of AUSRIVAS

Summary

Introduction

The Australian River Assessment System (AUSRIVAS or AusRivAS) is a national biomonitoring scheme adapted from the British River Prediction and Classification System (RIVPACS: Clarke et al 2003). AUSRIVAS was developed and tested as part of Australia’s former National River Health Program during the 1990s (Davies 2000), and has changed little since that time. It is currently promoted by way of a website and biannual training courses. In the calculation of this index, E is the sum of probabilities of occurrence in a macroinvertebrate sample of those taxa with a predicted probability above a specified value (commonly 0.5), and O is the number of those taxa that were recorded in the sample (Nichols and Dyer 2013). AUSRIVAS O/E values are used to assign sites to quality bands, variously labelled ‘more biologically diverse than reference’, ‘similar to reference’, ‘significantly impaired’, ‘severely impaired’ and ‘extremely impaired’ (Nichols and Dyer 2013)

Methods

Results

Conclusion