Water quality assessment based on biological monitoring of the Karaj River (Alborz province) using benthic macroinvertebrates

Investigating the ecological and biological conditions of the rivers can indicate potential pressures on them. Different orders of benthic macroinvertebrates have different tolerance for contamination, which are used as indicators of water quality in many cases. This study has examined the structure and assemblage of benthic macroinvertebrates in Karaj river. Considering the factors that cause environmental disturbance, the classification and assessment of water quality of Karaj River  at the stations were done. From winter until the end of autumn (2017), 4 sites through Karaj River were sampled for macrobenthos. Based on the results, totally the samples were identified, belonging to 5 class, 10 orders and 23 families. The most abundant groups in Karaj river were Ephemeroptera ,Plecoptera and Diptera. In general, the results show that the river water has a moderate pollution based on the Shannon index and has a suitable quality according to the Hilsenhof index in the upper stations (Sierra and Polekhab) and has less quality at the lower stations of the Dam (Aderan and Pourkan). Also, based on Simpson index, dominance is high at Sierra and Polehwab stations, and based on Hill index Aderan and Puorkan have more uniform populations. Finally, the results show that biological index can present the quality of water.