Water quality index as a simple indicator of watersheds pollution in southwestern part of Iran A. Dadolahi-Sohrab 1 , F. Arjomand 1 & M. Fadaei-Nasab 2 1 Department of Environment, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran; and 2 Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Keywords Iran; Karun River; Khuzestan and Khorramshahr; Persian Gulf; water quality. Correspondence A. Dadolahi-Sohrab, Department of Environment, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, 669 Khorramshahr, Iran. Email: p_dadolahi@yahoo.com doi:10.1111/j.1747-6593.2011.00303.x Abstract The Karun River is the most important watershed in the southwestern region of Iran. Water quality parameters were sampled from October 2006 through July 2007 at three sites along a 4 km gradient, covering both the wet and the dry season. Surface water was collected at three different stations per site (close to the banks and in the middle of the river) and analysed for 14 parameters and heavy metals. The values of 1300, 196.8 and 4042.9 ppm for chemical oxygen demand, biochemical oxygen demand and chloride, respec- tively, were higher than the standards limits. water quality index (WQI) values were very useful for the classification of the waters monitored. The averaged WQI was low (47%), and quality declined significantly during the dry season [analysis of variance (ANOVA, P < 0.05)]. The annual WQI values of 54.60, 40.29 and 45.71 from sites 1, 2 and 3 correspond to medium, bad and bad water qualities, respectively. Introduction Several regions of the world today are faced with differ- ent types of problems associated with the occurrence, use and control of water resources, which may endanger the sustainable development of these resources. The Karun River is the most important watershed in the southwest- ern region of Iran because it is a crucial source of water for irrigation, as well as for heavy and light industries, aquaculture, animal farming, municipal supply and wastewater dilution. The quality of surface waters is a sensitive issue. Surface waters are degraded by a combi- nation of human activities and natural processes that impair their use for drinking, industry, agriculture, rec- reation and other purposes (Carpenter et al. 1998; Sime- onov et al. 2003). Because of the spatial and temporal variations in water chemistry, a monitoring program and a representative and reliable estimation of the quality of surface waters are necessary (Bollinger et al. 1999). The current outstanding issues for present quality management in many developing countries are deterio- ration of water quality and shortage of pollution control. Increases in population, industry and agricultural activi- ties have caused the water quality to deteriorate signifi- cantly. This situation has been exacerbated by insufficient budgets and a lack of awareness on the part of some stakeholders. To assess the water quality of aquatic systems, some countries have introduced a plan to monitor and evaluate the effects of pollution (Pesce & Wunderlin, 2002; Zampella et al. 2006; Fabiano et al. 2008). The water quality index (WQI) has been devel- oped to classify surface waters based on standard param- eters for water specification (Couillard & Lefebvre 1985; Nives 1999; Swamee & Tyagi 2000; Hernandez-Romero et al. 2004; Sanchez et al. 2007). The WQI is a mathemati- cal tool that transforms large quantities of water charac- terisation data into a single number that expresses the level of water quality. Fundamentally, the WQI provides a mechanism for expressing cumulatively derived numerical expressions that define a certain level of water quality (Miller et al. 1986). The WQI provides a quanti- tative and standard method to inform regulatory agencies about the quality of the Karun River. In this way, the WQI makes it easier for a support system to make suitable decisions about a watershed. One of the main problems with the WQI, however, is synthesising all the natural influences on water quality into a single number. In reality, many environmental parameters influence the quality of water, making it hard to assign the water quality a single term such as excellent, good, medium, bad and poor (very bad). The WQI was first established in the United States by Horton (1965) and was then imple- Water and Environment Journal. Print ISSN 1747-6585 Water and Environment Journal •• (2012) ••–•• © 2012 The Authors. Water and Environment Journal © 2012 CIWEM. 1