Relationship between Biological and Qualitative Indices in Surface Waters Receiving the Effluent of Fish Farms in the Northwest of Iran

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Abstract
Background: Water quality is usually measured using various indicators based on physical, chemical and biological parameters. By using the biological index that is based on the identification of the arthropod families, it is possible to make a logical judgment about the ecosystem condition. The aim of this study was measuring correlation coefficients between qualitative and biological Indices. Methods: Water samples were collected 27 samples in northwest of Iran and aquatic insects’ samples 54 in 2019. The NSFWQI and IRWQISC as the most important indices of physical and chemical quality of water ranged from 54.45–76.21 and from 41.32 to 77.40, respectively. Results: A total of 2,953 aquatic insects were collected, and biological Index ranged from 6.26 to 3.38. It can be stated that increasing in the concentration of pollutants in the source and end of the river could lead to a sharp decrease in bio­logical index. IRWQISC index, the effluent stations of fish farms can fit into ‘fairly bad quality’ and ‘moderate quality’ categories. Conclusion: The linear regression analysis revealed a significant relationship between the Hilsenhoff biological Index and the physiochemical parameters of pH, DO (Dissolved Oxygen) and total dissolved solids. The activity of fish farms and discharging their effluents into water sources, can change the physical, chemical and biological parameters of re­ceiving waters, therefore it is recommended that the location of these units be reviewed and also the appropriate treat­ment for such effluents should be considered, so that the health risks caused by them can be effectively reduced.

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