Measuring river health: The uncertainty associated with impact assessment using a single sample biological assessment technique

The AUSRIVAS modelling package is the most sophisticated rapid biological assessment technique available for assessing the health of Australian rivers. Macroinvertebrate samples are collected, and the observed taxa are compared to those expected to be present if the site was in pristine condition. However, the method relies on only a single sample collected from each site to be assessed. Multiple macroinvertebrate samples were collected from sites upstream and downstream of four wastewater treatment plants in the lower Hunter Valley, New South Wales, Australia, to assess the impacts of effluent discharge on creek health, and to investigate the implications of the within-site variability of AUSRIVAS outputs for impact assessment. Preliminary data demonstrate that the AUSRIVAS model can produce a range of outputs for a single site, and that this variability is then amplified creating greater uncertainty when sites are compared to quantify the actual ecological; impact of each wastewater treatment plant.