Water quality assessment in the main tributaries of the Tajan River using large benthic invertebrates

To investigate the community indices of benthic macroinvertebrates and water quality assessment, sampling was carried out using surber sampler (30.5×30.5 cm with 360μ mesh size) monthly with 3 replications in the Tajan River and its main branches during July 2013 to June 2014. 6 stations were selected at Shirinrood, Korcha, Sorkhvalick, Golourd, Zaremrood (Alavicola) region and the main canal of the Tajan River (Daroupay) respectively. During this period, 39420 individuals of benthic macroinvertebrates were collected, identified and enumerated, which were blonged to 4 phyla, 4 classes, 13 orders, 43 families and 46 genera. Assessment of water physicochemical parameters among stations showed that all parameters, exept pH, had statistically significant differences among stations (p<0.05). Results of benthic macroinvertebrates community indices (Shanon-wiener diversity, Simpson diversity, Margalef richness, EPT richness, EPT/CHIR ratio and Pielou eveness index) showed stations 1 and 4 had the highest and the lowest diversity and richness indices, respectively. The Minimum (3.16) and the maximum values of Hilsenhoff biotc index (5.47) as well as the highest (6.36) and the lowest values of ASPT index (3.81) were calcuted in stations 1and 4 respectively. According to ASPT Biotic Index staion 1 (Shirinroud Branch) was classified in clean class, stations 3, 5 and 6 (Chardangeh, Zaremroud and main channel of Tajan River respectively) were classified in moderate pollution class and staions 2 and 4 (Korcha and Golvard Regions respectively) were classifieds in exterem pollution calss. The results showed that the most important factors influencing the quality of the Tajan River are bed material, uncontrolled water abstraction, the entry of agricultural, husbandry and aquaculture effluents into the river.