Abstract

Stream water quality of a part of the four western mountainous regions of Iran:Lorastan, Kordestan, Hamadan and Kearmanshah, with a total area of 101.102´10³km² was investigated. The chemistry of major elements such as Ca, K, Na, Mg, Cl, HCO₃, SO₄ and alkalinity from hydrological basins of the regions was examined based upon samples from the relatively important basins. The difference in these chemical elements of streams was verified on a region-by-region basis. Temporal changes of water quality in the stream water were examined using a seasonal classification of data. The results showed that the dissolved load of about 70% of all water samples (at all basins during all seasons) was less than 500 mg/l. The same result can be concluded for seasonal variability of EC for the entire area. It was less than 0.550 ds/m for 68% of samples. The pH variation was from 5.5 to 9 with an average of 8.2. The highest and lowest values are from autumn and summer samples, respectively. In summer, thesodium adsorption ratio (SAR) value was maximal, and the agricultural activities cause an increasing on its normal (average annual) rate in the rivers. The results also indicated a very good relationship between the total anions and total cations, during all of seasons.There were no significant relationships between the area of the basin and the chemicalelement concentrations. These results have been used for the water resources management of the mountainous regions of Iran and the modelling of water quality predication.

Key words: Surface water chemical quality, western regions of Iran, seasonal andspatial water quality variation.

Abbreviation

EC, Electrical conductivity; TDS, total dissolved solid; and SAR, sodium absorption ratio.