Long-term evaluation of water quality parameters of the Karoun River using a regression approach and the adaptive neuro-fuzzy inference system

This paper investigates chemical water quality parameters of the Karoun, the greatest and the most important river of Iran, during a 48-year period, from 1968 to 2015. Water discharge (Q) fluctuates between 191.1 m3 s− 1 and 1758.7 m3 s− 1, with a decreasing trend over the 48-year period. Except pH, other water quality parameters increased, significantly, so that the rate of increase for EC and TDS was 25.71 μS cm− 1 y− 1 and 16.66 mg l− 1 y− 1, respectively. Moreover, SO4− 2, HCO3−, Cl−, Ca+ 2, Mg+ 2 and Na+ have increased by 0.116, 0.012, 0.151, 0.066, 0.052 and 0.168 meq l− 1 y− 1, respectively. Result indicated that water discharge can be a satisfactory predictor of chemical water quality parameters in this river. It was finally concluded when water discharge of the river decreases to less than ~ 500 m3 s− 1, the vales of water salinity (EC and TDS) and soluble salts will increase, severely.