Rapid assessment of Australian rivers using macroinvertebrates: cost and efficiency of 6 methods of sample processing

Murray-Darling Freshwater Research Centre

MDFRC item.

The cost and efficiency of different techniques for processing rapid-assessment samples of lotic macroinvertebrates were evaluated. Subsamples of 50, 100, and 150 selectively picked individuals were compared to determine the optimal subsample size for selective picks. Selective subsampling of a set number of animals was then compared with subsampling by picking for a set time (30 min), exhaustive picking of a sample, and randomly subsampling 100 animals. Identification was to family level. Efficiency was assessed by comparing the ability of data generated by each technique to discriminate between unpolluted reference sites and sites with mild to severe pollution by municipal effluent and urban stormwater runoff. This discrimination was tested using both univariate metrics (SIGNAL biotic index, family richness, and EPT [Ephemeroptera, Plecoptera, Trichoptera] family richness) and multivariate tests (analysis of similarity--ANOSIM). Cost was assessed as the amount of time each method required for picking and identification. The selective 100-animal subsample is recommended as the most cost-effective method for assessing sites affected by municipal sewage-treatment-plant discharges and urban stormwater runoff. SIGNAL was the best of the 3 metrics, having the most highly significant differences between reference and polluted sites and being most robust to variations in processing method. ANOSIM could distinguish between the reference and polluted sites using any of the sample processing methods, but the degree of the distinction varied with sample processing method.