Performance of the STAR_ICMi macroinvertebrate index and implications for classification and biomonitoring of rivers

Abstract

-Although biomonitoring is the core approach adopted by the European Union's Water Framework Directive (WFD), many biotic indices still lack a thorough analysis of their performance and uncertainty. The multihabitat sampling and the application of STAR_ICMi index on macroinvertebrates are the standard methods to assess the ecological status of rivers in Italy. Ever since the Italians' implementation, dates back to 2010, few studies have tested the index performance with different sampling efforts, and even rarer are those assessing index uncertainty. However, these are worthwhile topics to investigate because all the Environmental Agencies are applying this index with both ecological and economic consequences. Aims of this study were (i) to assess the effect of subsampling on the STAR_ICMi index, (ii) to propose a standard method to calculate the index precision, and (iii) to test several less timeconsuming alternatives to census all the individuals in the sample. I showed that the index is strongly affected by subsampling, and unbiased comparisons of ecological status can only be done at the same sampling effort. The index precision, calculated by bootstrapping the observed abundance of taxa, was so low in some circumstances, to increase the risk of misclassification. Finally, I showed that to avoid counting all the individuals in a sample, it is possible to estimate the most abundant taxa using a rank-abundance model. With this less time-consuming method, the STAR_ICMi index is predicted with sufficient precision.Keywords: sampling effort / rarefaction / index uncertainty / sampling variation / Italy Résumé -Performance de l'indice macroinvertébrés STAR_ICMi et implications pour la classification et la biosurveillance des cours d'eau. Bien que le biomonitoring soit l'approche de base adoptée par la directive-cadre sur l'eau de l'Union européenne, de nombreux indices biotiques manquent encore d'une analyse approfondie de leur performance et de leur incertitude. L'échantillonnage multihabitat et l'application de l'indice STAR_ICMi sur les macroinvertebrés sont les méthodes standard pour évaluer l'état écologique des rivières en Italie. Depuis leur mise en oeuvre qui remonte à 2010, peu d'études ont testé la performance de l'indice avec différents efforts d'échantillonnage, et encore plus rares sont ceux qui évaluent l'incertitude de l'indice. Cependant, ce sont des sujets intéressants à étudier parce que toutes les agences environnementales appliquent cet indice avec des conséquences écologiques et économiques. Les objectifs de cette étude étaient les suivants : (i) évaluer l'effet du sous-échantillonnage sur l'indice STAR_ICMi, (ii) proposer une méthode standard pour calculer la précision de l'indice et (iii) tester plusieurs alternatives moins coûteuses au recensement de tous les individus dans l'échantillon. L'indice est fortement influencé par le sous-échantillonnage et des comparaisons impartiales de l'état écologique ne peuvent être faites qu'au même effort d'échantillonnage. La précision de l'ind...

Application of macroinvertebrate multimetrics as a measure of the impact of anthropogenic modification of spring habitats

“…The remaining indices were calculated using excel (Microsoft, Redmond, WA). The six metrics for the calculation of the STAR_ICMi index (Buffagni et al, ) were independently calculated and then merged in a weighted average formula (van de Bund, ; for a discussion of the STAR_ICMi index performance, see Spitale, ).…”

Response of Chironomidae (Diptera) to DDT, Mercury, and Arsenic Legacy Pollution in Sediments of the Toce River (Northern Italy)

“…Sampling of chironomids followed the Italian standard protocol for benthic macroinvertebrate community [ 21 ], employing a multihabitat proportional method. Within each site (a 50 m long river stretch), a depositional area (pool mesohabitat) and an erosional area (riffle mesohabitat) were visually identified, where possible.…”

“…Partial Redundancy Analysis (RDA) revealed that 5% of the total variance was associated with sediment contamination. Different biotic metrics were calculated, including non-stressor-specific metrics such as the Multimetric Intercalibration Index STAR_ICMi [ 21 ] and stressor-specific metrics such as Species at Risk for pesticides (SPEARpesticide [ 22 ]) and mean Sensitivity to Hg (SHg [ 23 ]), but significant differences between communities upstream and downstream of the factory were not emphasized.…”

Biotic indices of hydrological variability as tools to inform dynamic ecological status assessments in river ecosystems

“…However, even if all taxa in a dataset were included in an index's calculation, performance beyond its region of development would not reach 100% due to variation among index scores not accounted for by TR. This non-taxonomic variation may relate to differences among river types ( Verdonschot and Nijboer, 2004;Aroviita et al, 2009), taxonomic identification levels (Monaghan, 2016), and sampling strategies (Spitale, 2017). Climatic and geomorphological conditions are among the key causes of variability in macroinvertebrate distribution among different river types ( Verdonschot and Nijboer, 2004), with assemblages varying between river types due to differing taxon-specific habitat requirements.…”