Freshwater and its good quality play an essential role in human life, environmental protection, survival and excellence of human societies and the economy. One of the best methods to assess water quality is to use rapid bioassessment indices based on tolerance value or sensitivity to disturbances caused by human activities. Rivers and streams in Iran, like many other rivers in the world, are facing increasing problems due to pollution, and so far no study has been conducted to define a local index in Iran. Since the tolerance values and bioassessment indices are specific to the geographical area and their use in the areas with different ecological features is not logical and acceptable, so the localization of a biological index seemed necessary for Iranian running waters. In this study, a local index and compatible with the ecological conditions of one of the most important water basins of Iran (Karun River basin) was defined and its efficiency was eva‎luated. This basin is one of the largest sources of freshwater in Iran with about 56 rivers, diverse climates and various habitats from upstream to downstream. Sampling was done in 54 sites of rivers in this basin (with a minimum length of 200 meters, including 10 transects and different mesohabitats) in four seasons (autumn, winter, spring and summer) from October 2018 to November 2019. Sampling of benthic macroinvertebrates was performed using Surber and D-net and identified in the laboratory up to the family level. Water samples were taken in three replications and 22 physicochemical parameters measured in the laboratory. Hydro-morphological, habitat and descriptive parameters were measured and recorded at the sampling site. In this study, 101 families of benthic macroinvertebrates belonging to eight classes and 21 orders were identified. Stressor gradient and least disturbed conditions were determined using 11 physico-chemical parameters of water and 6 physical factors of habitat using principal component analysis (PCA). The least, moderate and most disturbed categories included 14, 26 and 14 sites, respectively. Confirmation and validation of stressor gradient and reference sites were performed by studying the changes of water quality index, physical habitat index, community structure, biological indices, correlation analyses and NMDS test. Tolerance values for 95 families of benthic macroinvertebrates were defined based on the stressor gradient and using weighted average method. In order to define the local biological index called Karun benthic macroinvertebrate tolerance index (KMTI), different mathematical formulas were tested and the best formula was selected based on its discrimination efficiency (DE) in different seasons. The average DE of the KMTI index in four seasons was 84.20% and in the best season was 90%. Water quality classification table for the KMTI index was determined using different percentiles of stressor gradient scores and the best classification table was selected based on its DE. The average DE of the proposed classification table in four seasons was 86.9%. The KMTI index is a rapid bioassessment method to eva‎luate the water quality that only requires the identification of benthic macroinvertebrates at the family level. The results of this study and the KMTI index are a very good alternative to non-native indices as well as a suitable tool for eva‎luating water quality in Iran and conveying the clear and concise information to environmental managers. This study can be considered as a suitable basis not only for the inland waters of Iran, but also for other countries in Iran's neighborhood with similar climatic conditions (especially in Southwest Asia).

عيسي ابراهيمي درچه، اميد بيرقدار كشكولي

جيمز استربلينگ، اندرياس برودر

يزدان كيواني، محمود رضا همامي، مهرداد فتح اللهي