A comparison of macroinvertebrate-based indices for biological assessment of river health: A case example from the sub-tropical Richmond River Catchment in northeast New South Wales, Australia

Globally, river health is deteriorating due to increased anthropogenic pressures. Accurately assessing river health is crucial for the management of river resources with macroinvertebrates commonly used as biological indicators of ecological integrity. Complex biological data is made more straightforward using indices as they offer the ability to rapidly communicate complex science in a simple form. Management decisions are often based on the results of biological river health assessments, making the identification of the most appropriate, robust and sensitive macroinvertebrate-based index vital when undertaking catchment specific assessments. Selection of a macroinvertebrate-based index should rely on a scientific method rather than arbitrary selection criteria. This study aimed to compare the performance of several macroinvertebrate-based indices to identify the index or indices most appropriate to the Richmond River Catchment (RRC) in northern New South Wales, Australia. River health within the RRC is poor with a clear pollution gradient from upper to lower catchment sites. Six commonly used indices were calculated using family-level identification. The biological assessment supported the physicochemical results with a gradient in river health from upper to lower catchment. Family Richness and Family Richness Percent were assessed as the most usable indices. In studies that have restricted time, budget and expertise they will provide accurate but limited information on river health. SIGNAL2 was identified as the most valid index for assessing river health due to its overall sensitivity to changes in river health, and level of detail on anthropogenic impacts. The poor performance of the AUSRIVAS, EPT and BCI limits or precludes their use for river health assessment in the RRC. While this model for identification and selection of an appropriate macroinvertebrate-based index for catchment scale river health assessments was useful in this context, it needs to be improved with a larger dataset and a greater environmental gradient of river health to make a less subjective evaluation.