Biomonitoring, simulation, and evaluation of anthropogenic pollution in Disam River, Iran: use of macroinvertebrate-based biotic indices and Qual2kw model

Water quality and self-purification capacity of the Disam River (Iran) was studied using macroinvertebrate-based indices and Qual2kw mathematical modeling tools. We evaluated the water quality and self-purification status of the Disam River through biotic indices of macroinvertebrates and mathematical modeling (Qual2kw). A total of 10,370 macroinvertebrate specimens were collected monthly using a Surber sampler (30 x 30 cm) at five sampling sites from 2019 through 2020. The Hilsenhoff Family Biotic Index (HFBI) and Average Score Per Taxon (ASPT) indexes categorized the sampling sites 2 and 3 in "Moderate " and "Very poor " water quality classes. The Ephemeroptera, Plecoptera, Trichoptera (EPT) index categorized the river at "Good", and the Biological Monitoring Working Party (BMWP) at "acceptable " classes of water quality. We used Canonical correspondence analysis (CCA) to explain the relationships between biotic indices and physicochemical parameters. The EPT index showed a positive correlation (axis1 = 1/43, axis2 = 0.065) with most physicochemical factors of the Qual2kw. Analyses of the Qual2kw output and macroinvertebrate occurrence showed that the family Chironomidae was dominant (S2 = 37.66% and S3 = 47.33%) in all seasons except summer. Family Baetidae was dominant in S2 (79%) and S3 (78%) with a weak positive correlation with increasing stream temperature (r = 0.21) and slightly negative correlation with increasing stream velocity (r = -0.053). Analyses of BOD and DO fluctuations confirmed the ongoing flushing of pollutants along the Disam River. Our findings highlight the importance of simultaneous study of biotic indices and mathematical modeling in assessment of "ecological integrity" and flexibility of aquatic ecosystems subjected to anthropogenic impacts.