Investigating ecological degradation of mining-impacted small river systems: A macrozoobenthic case study from Northern Armenia

The degradation and loss of aquatic ecosystems have become environmental challenges facing the world. This study aimed to assess the ecological status of the Shnogh River and its tributaries (the Kharatadzor and Dukanadzor rivers) in the northern mining region of Armenia using macrozoobenthic parameters. Macrozoobenthic samples were collected from six sites between 2013 and 2018, with the exception of two sites that were sampled only during 2013-2015 and 2015-2018, respectively. Parameters analyzed included species’ richness, abundance, the Shannon-Wiener diversity index, and the extended biotic index (EBI). Cluster analysis, based on EBI values, and principal component analysis (PCA), based on species’ richness, were applied to identify patterns of community structure and ecological deterioration. The upper sections of the Kharatadzor and Dukanadzor rivers, designated as control sites, showed higher taxonomic richness and diversity, including pollution-sensitive taxa, indicating a good to high ecological status. However, species’ richness and diversity, total abundance, and ecological quality noticeably declined at the downstream sites of the rivers, which may have been due to mining-related contamination and habitat degradation. These influences, in turn, also extended to the Shnogh River, particularly at sites downstream of the confluences with the Dukanadzor and the Kharatadzor rivers, as bio-indicated by similar patterns of macrozoobenthic parameters. Cluster analysis grouped the sites, separating upstream control sites included in the analysis from downstream impacted sites. While PCA identified two principal components explaining 83.7% of the total variance (PC1=61.5%, PC2=22.2%), with sensitive (e.g., Ephemeroptera, Plecoptera, Trichoptera) and tolerant taxa (e.g., Odonata, Decapoda) contributing to observed patterns. Macrozoobenthic parameters, supported by cluster analysis and PCA, confirmed the noticeable hydroecological deterioration and taxonomic simplification. These findings underscore the need for stricter regulations on mining discharges to safeguard freshwater ecosystems and biodiversity.