Assessment of water quality in Iran’s Anzali Wetland, using qualitative indices from 1985, 2007, and 2014

Abstract

In the present study, the water quality of the Anzali Wetland, located southwest of the Caspian Sea in Iran, was compared for the years 1985, 2007, and 2014, using a weighted arithmetic mean function (National Sanitation Foundation Water Quality Index: NSFWQIa), a weighted geometric mean function (NSFWQIm), and the Oregon Water Quality Index (OWQI). To that end, nine water quality parameters [pH, turbidity (TURB), temperature (T), dissolved oxygen (DO), nitrate (NO3), total solids (TS), phosphate (PO4), biological oxygen demand (BOD5), and fecal coliforms (FC)] were analyzed at eight selected stations. According to the proposed classification for water quality indices (higher value (0–100), better water quality), the Wetland water quality was classified as the mean values of the three indices for the three sampled years, as follows: NSFWQIa (13.72, 12.81, 12.07); NSFWQIm (63.049, 52.388, 49.108); and OWQI (26.867, 14.477, 15.53). The values of NSFWQIa, NSFWQIm, and OWQI for the western stations were better than for the other stations in the region over the 29-year span of investigation; however, the remainders of the stations’ values were very poor. Because wastewaters discharged from industrial and agricultural areas are more concentrated in the eastern part of the Anzali Wetland, the eastern stations of the Wetland showed lower water quality compared to the central and western stations. The water of the Anzali Wetland has different quality classes according to the aggregation methods employed. It is concluded that when evaluating water quality of aquatic ecosystems, several indices should be used to obtain more comprehensive results.