1. The power of selected biological invertebrate traits for discriminating different types of human impact (heavy metal pollution and cargo-ship traffic) were tested using ecological reasoning and linear Discriminant Function Analysis (DFA).
2. Frequency distributions of individual traits and categories of traits from 68 least impacted river reaches (LIRRs) and 304 impacted river reaches were used to define simple assessment rules based on ecological reasoning for specific impairments in large European rivers. In calibration, a maximum of three variables with a priori predictions and two different impairment threshold levels were used. Similarly, DFA was performed on the same variables included in the ecological reasoning approach, but also on all available traits or trait categories.
3. Validation with an independent data set (40 LIRRs, 291 variously impacted river reaches) and using the ecological reasoning approach showed that 75–78% of the reaches were correctly assign with rules on all impact types, 35–57% with rules on heavy metal pollution and 78–93% with rules on cargo-ship traffic. By comparison, validation showed that DFA performed globally poorer than the ecological reasoning approach. In addition, the performance of the rules based on ecological reasoning remained stable, whereas DFA performance changed between calibration and validation.
4. Although not defined for this purpose, our study provided alarming evidence regarding the impact of cargo-ship traffic on invertebrate communities in river reaches. Reaches with cargo-ship traffic were found to have more genera with long life cycles that reproduce repeatedly by ovoviviparity and have a sessile life.
5. The performance of our trait-based approach to correctly assign reaches to either least impacted or impacted conditions should promote further research on the topic across larger geographic areas (without regionalization) and across smaller stream types to provide a powerful biomonitoring tool that fulfils current European Union directives.
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