Hydrochemical evaluation and qualitative deterioration assessment of Gorganrud River

In this study, the hydrochemical evolution and qualitative deterioration of Gorganrud River water were investigated in a distance of approximately 100 km from the northern margin of the Alborz highlands to Gorgan Gulf. For this purpose, the analyses results of elven physicochemical parameters related to four hydrometric stations over a ten-year statistical period were used. Gibbs, Stiff, Piper, Durov diagrams as well as five saturation indices for carbonate, sulfate and chloride minerals were used to study the hydrochemical evolution of the river. Water quality changes from drinking (using Schoeller Diagram), agricultural (using Wilcox Diagram), industrial and (using corrosion indices) along the Gorganrud River were also investigated. In this study, F test and hierarchical cluster analysis were used to analyze the variance of data and the number of factors affecting water hydrochemistry, respectively. The results showed that rock-water reaction, evaporation, and Gorgan Gulf saline water intrusion are the most important factors controlling the river water chemistry. Also, the dominant water type of Gorganrud River at the highlands margin is bicarbonate and as it enters the plain, it tends to reach full maturity (i.e. the type of sodium chloride). At all stations, river water is supersaturated with respect to calcite and dolomite but it is under saturated with respect to anhydrite, gypsum and halite. However, evaporite minerals saturation increases in the flow direction. The quality of water for drinking and agriculture is suitable at the margins of highlands and it decreases sharply as enters the plain and pathes into the Gorgan Gulf. According to the statistical analysis results, most of the changes are observed between the Lazoure Station at the highlands margin and the Qazaghli Station in the middle parts of the plain and after that no significant changes is observed between the quality parameters as far as Gorganroud outlet.