Quality Classification of Karaj River Using Macrobenthic Biotic Indices

The ASPT index is one of the most valid bio-indices for assessing river water quality. In this study, sampling which was done in the period of autumn 2017 to summer 2018, was done seasonally from nine stations along the Karaj River. Macrobenthos were sampled with sorbents and after fixation with 5% formalin and staining, the samples were identified and isolated. In the obtained results, the total number of people collected and the average annual density (SD ±) in the study area of Karaj River were 38454 units and (147 ±) 2907 units / m2, respectively, the highest number of which is equal to 15313 units in autumn. And the lowest in the summer is equal to 3806 numbers. The results showed that Arthropods as the main group of macrobenthos made up 83% of the samples. Also, ringed worms were included in 14%, flatworms in 1% and mollusks in 2% of the samples. The average of total ASPT indices in Karaj River is 3.95. The range of changes of ASPT index based on station is (0.8-0.1), respectively. The highest annual average value of ASPT index (4.64) was observed in Varangeh_ Rood station and the lowest value (3.08) was observed in Bilaqan station. The trend of ASPT index changes from upstream to downstream be decreasing. Therefore, the downstream part of the river has a worse quality than the upstream. Also the ASPT seems to be more appropriate for assessing rivers than the BMWP index.