Introduction: Benthic macroinvertebrates are fundamental components of aquatic ecosystems and, through their roles in nutrient cycling and as a food source for higher trophic levels, influence ecosystem dynamics. Given their sensitivity to environmental changes, these organisms are used as indicator species for assessing river health. Environmental factors such as temperature, current velocity, and substrate type affect the diversity and abundance of these biological indicators. By examining the effects of environmental factors on the distribution of benthic macroinvertebrates in the Zohreh sub-basin, this research contributes to a more precise understanding of community structure and to the improvement of aquatic ecosystem management.
Materials and Methods: To study the diversity of benthic macroinvertebrates in the Zohreh sub-basin, nine stations were selected based on environmental characteristics and site accessibility. Sampling was carried out in autumn 2023 with three replicates. Six environmental factors, altitude, current velocity, depth, width, water temperature, and substrate type, were measured. To quantify diversity and dominance data, the Shannon–Wiener, Margalef, Pielou’s evenness, and Simpson indices were used. Statistical analyses, including one-way ANOVA, cluster analysis, multidimensional scaling (MDS), LINKTREE (linkage tree analysis), and BEST (best-fitting method), were performed using SPSS version 27.1 and PRIMER 6.1 software at a significance level of 0.05.
Results: The study showed that the structure and distribution of benthic macroinvertebrates in the Zohreh sub-basin are directly influenced by physical environmental variables. Among the six measured factors, only depth showed no significant differences among stations, whereas the other factors, including current velocity, temperature, elevation, width, and substrate type, exhibited marked differences. A total of 22 families were identified, with Baetidae and Lumbriculidae exhibiting the highest abundances. Despite significant differences in the abundance of benthic macroinvertebrates among stations, cluster analysis and multidimensional scaling (MDS) indicated that most stations were grouped similarly in terms of species composition, and that the overall distribution did not differ significantly. The mean values of the Shannon–Wiener diversity index, Margalef species richness, Pielou’s evenness, and Simpson index were 1.2504, 1.2847, 0.5564, and 0.5680, respectively. The highest diversity (2.107), richness (2.364), evenness (0.8215), and species dominance (0.8612) were recorded at Station nine. The BEST analysis revealed that current velocity and depth are the most important factors influencing the distribution of benthic macroinvertebrates. In addition, the LINKTREE test discriminated among stations based on combinations of environmental variables, including current velocity, width, depth, and temperature. Overall, the findings indicate that substrate conditions, salinity, temperature, and current velocity intensity play a decisive role in the presence of sensitive or tolerant species.
Discussion: The results of this study indicated that physical factors such as current velocity, temperature, elevation, width, and substrate type directly influence the composition, abundance, and species diversity of benthic macroinvertebrates. Rapid responses to changes in temperature, current velocity, and substrate quality make sensitive families like Baetidae effective biological indicators for monitoring the ecological status of rivers. In our study, natural variations in environmental conditions led to significant differences in the presence and abundance of these species. For example, at more favorable sites like Station Nine, we observed higher species diversity and richness. In contrast, stations that experienced rapid current velocities or had unsuitable substrates, such as Station Four and some intermediate stations, exhibited lower diversity. The presence of more tolerant families, such as Lumbriculidae, at sites with higher temperatures and lower dissolved oxygen indicates the dominance of resistant species under such conditions. This pattern aligns with findings from international research, indicating that species composition results from the simultaneous interaction of various environmental factors. Therefore, continuous monitoring of environmental conditions and benthic communities is crucial for effective management and conservation of riverbeds, flow regimes, and water quality.