Quality trend of Kura River in Azerbaijan by major ion concentration

Abstract The analysis of water samples taken from 14 points along the Kura River, the principal waterway in the South Caucasus, including Azerbaijan, allowed for the determination of fluctuations in the amount of mineralization, especially in the concentration of the major ions during the monitoring conducted between 2020 and 2022 by the Central Laboratory of “Azersu” OJSC (now Azerbaijan State Water Resources Agency), starting from the Georgian border to the river mouth. The findings discovered a consistent increase in mineralization towards the river mouth. Sample points in Kura River are selected to reflect the water quality before and after major interference into the river-reservoir, tributary sewage, etc. Seasonal variations and anthropogenic influences, particularly agricultural runoff and tributaries flow, contribute to significant changes in ion concentrations. The results provide a robust background for future research and policymaking to enhance the region’s water quality monitoring and management strategies. Significantly, the mineralization value experiences a 2.5-fold increase shortly after merging with the Aras River, with the concentration at the Neftchala station surpassing 3000 mg/l. This represents an 8.8-fold increase compared to the value observed at the I Shikhli station. Alongside natural factors, anthropogenic activities contribute to the elevated concentration of major ions. The sulfate ion concentration, for instance, demonstrates a 1.8 to 2.1-fold increase, while the chloride ion concentration escalates by 3 to 10 times. Additionally, the combined sum of sodium and potassium experiences a 2 to 2.5-fold increase. The concentration of magnesium ions remains constant throughout the river, constituting approximately 4 to 5% of the major ions. Conversely, there is a notable decrease in the concentration of bicarbonate ions by 2.3 to 8.5 times and a decrease in the concentration of calcium ions by 1.3 to 2 times. Consequently, the chemical composition of the river water transitions from calcium-bicarbonate waters to sodium-sulfate waters downstream of the Kura River, since in the chemical composition of the river water from Zardab to the estuary, sulfate ion prevails over bicarbonate, and the sum of sodium–potassium surpasses calcium.