Exploring the interplay between water quality parameters and aquatic fauna in a human-dominated stream network in Iran

Abstract

Rivers and streams are dynamic linear features that undergo numerous disturbances from nearby human activities. This is particularly evident in Iranian arid regions, where agricultural activities are concentrated along these water bodies to harness their freshwater resources. This study utilized 12 stations in the Maharlu stream network to assess the impact of human activities on its water quality and aquatic fauna. Results indicated that severe nutrient pollution attributed to a high mean nitrate concentration (67.77 ± 79.72 mg/L). By employing PCA analysis, three main principal components were extracted, explaining a variance of 82.61%. PC1 exhibited high positive loadings for dissolved oxygen (DO), while PC2 showed an elevated salt concentration. Midges and non-biting mosquitoes, predominantly from the Chironomidae family, emerged as the dominant taxon, contributing to over 98% of the total species abundance. Furthermore, integrated PCA–CCA analysis revealed downstream shifts in species composition toward more tolerant species, driven by decreasing DO levels and increasing salt concentrations. These shifts in trends found in water quality parameters and species composition were linked to agricultural runoff carrying substantial amounts of fertilizers, pesticides, and organic matter from livestock farming. Consequently, there is an urgent need to implement conservation measures to mitigate their adverse effects.