The taxonomic distinctness (Δ+) index has been recognized as a robust measure to assess human impacts on marine biodiversity. However, its applicability in freshwater ecosystems has still not been confirmed. We aimed to propose the most suitable data design for calculating the Δ+ index for application in assessing anthropogenically caused degradation in lotic environments. We calculated the values of Δ+ based on different taxa groups and taxa resolutions, in order to examine its utility as a potential metric in bioassessment programs. We found that the exclusion of non-insect taxa and selected insect orders significantly increased the index sensitivity. Thus, we believe that an appropriate data design for Δ+ calculation based on macroinvertebrate assemblages is the main prerequisite for the effective estimation of degradation in lotic environments. In addition, we argue that a decrease in taxonomic resolution up to genus level is completely acceptable, as it results in only minor information loss. Bearing this in mind would significantly facilitate its application in rapid bioassessment programs. Despite the observed correlation, the utility of Δ+ as a potential bioassessment metric is rather limited, since its fails to detect fine differences in environmental stress, and instead only roughly distinguishes between two basic classes of degradation level, unimpacted and impacted.
Keywords: Bioassessment; Macroinvertebrates; Metrics; Self-organizing map (SOM); Taxonomic resolution.
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