Evaluation of a fine sediment biomonitoring tool across a wide range of temperate rivers and streams

Abstract

Elevated levels of fine sediment (suspended and deposited) are a common cause of ecological degradation in freshwater ecosystems. However, it is time-consuming and expensive to monitor these parameters to support national and international water resource legislation. The Proportion of Sediment-sensitive Invertebrates (PSI) index is a biomonitoring tool that is designed to identify the degree of sedimentation in rivers and streams. Despite having a sound biological basis, until now, the PSI index has only been tested against observed fine sediment data in two catchments; other published applications of the PSI index have relied on inferred fine sediment values. In this study, we report the results of a comprehensive analysis of the performance of the PSI index across a wide range of reference condition temperate stream and river ecosystems, including 835 sites with data on deposited sediment and 451 sites with data on suspended solids (>12 500 data points measured between 1978 and 2002). The effect of taxonomic level and taxonomic resolution on the performance of the PSI index was also examined, as was the performance of the PSI index against other non-sediment-specific indices, including Average Score Per Taxon (ASPT), Lotic-invertebrate Index for Flow Evaluation (LIFE), Ephemeroptera, Plecoptera and Trichoptera (EPT) abundance, % EPT abundance, EPT richness and % EPT richness. The results of this study show that the PSI index was more correlated with fine sediment metrics than the other biological indices tested: rs = -0.64, (P < 0.01, n = 2502) for deposited sediment and rs = -0.50 (P < 0.01, n = 1353) for suspended solids. We highlight the optimal conditions for applying the PSI index, in its current form. Given the variability in the relationship between PSI and fine sediment metrics, we propose that the use of data from more objective, quantitative methods of measuring deposited fine sediment may help to enhance the performance of the model for future applications and advance understanding of fine sediment dynamics and the pressure-response relationship.