Today, the application of ecological indicators based on organisms has replaced traditional saprobic approaches for assessment of the quality of rivers impaired due to organic pollution and some other environmental disturbances. This study aimed to weigh the quality of the Ojarud River in Ardabil, Iran, applying biological and physiological indices of macro-invertebrates. A total of 12,524 samplings were fulfilled at four stations (S1, S2, S3, S4) from the headstream to downstream by a Surber sampler (30 × 30 cm2) from June/2020 to April/2021. All year round, the highest frequent families were Chironomidae (2658), Simuliidae (1025) from Diptera and Caenidae (1855), and Baetidae (724) from Ephemeroptera. The diversity pattern was analyzed by PAST software, and Primer 7 (BIO-ENV analysis) was utilized to understand what factor has the most impact on the distribution of macro-invertebrates. The least similarity of S4 to other stations was recognized by Cluster analysis. As per the ANOSIM (analysis of similarities), a statistically significant difference in the macroinvertebrates' frequency was established between S3 and other stations (p = .0001, r = .63). Moreover, the relationship between heavy metals and macro-invertebrate showed that the three families of Simuliidae, Gomphidae, and Caenidae had a positive correlation with the concentrations of heavy metals in the sediment. As per the Ephemeroptera, Plecoptera and Trichoptera index, the water quality was placed in the "excellent" class, but the Biological Monitoring Working Party and Hilsenhoff Family Biotic Index indices scored the water quality "good" class at S1 and the "poor" class at S3. Based on the results of this study, the use of physicochemical and hydro-morphological indicators can support the biological indicators but cannot replace them. In addition, careful evaluation of biological indicators is required to develop conservation strategies.
Keywords: Ojarud River; biotic indices; heavy metal; macro‐invertebrates.
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