Spatiotemporal variation in macroinvertebrate community composition along the stressor gradients in rivers of a middle‑eastern basin
The study of community structure changes in relation to environmental gradients can help assessing and predicting community response to anthropogenic disturbances; however, such types of studies are rare in semi-arid regions. This study aimed at investigating the macroinvertebrate community composition in response to environmental variables in rivers of a semi-arid mountainous region, i.e., the Zagros mountain range, southwestern Iran. Environmental variables and macroinvertebrates were sampled at 54 sites in four seasons during 2018–2019. A total of 101 families of benthic macroinvertebrates from 8 classes and 21 orders were identified. Diversity and evenness indices showed significant temporal variation (p < 0.05). Also, taxa richness and Ephemeroptera, Plecoptera, and Trichoptera taxa showed strong seasonal stability, whereas spatial variation among all metrics was significantly different (p < 0.05). Taxa richness and density weekly correlated with altitudinal gradient. Correlation analysis, cluster analysis, non-metric multidimensional scaling, and canonical correspondence analysis demonstrated associations between community composition and environment variables, including definition of site groupings according to aggregated quality estimates. The results suggest that both physico-chemical variables of water (nitrate, total dissolved solids, Escherichia coli, temperature, chemical oxygen demand, and dissolved oxygen) and habitat structure (wetted river width, altitude, and riffles presence) determined the community composition of macroinvertebrates. Seasonal variation of community indices and community composition in our region seemed to differ from those estimated from subarctic, temperate and subtropical ecosystems. Our study provides a strong basis for further research, planning, and conservation of macroinvertebrate communities in the Karun River basin and similar river systems in the region.