Dissolved load in the Chirchik and Akhangaran river basins (Uzbekistan, Central Asia): Natural and anthropic inputs

The understanding of the sources of dissolved load influencing water chemistry is a critical step to ensure water safety and effective water management. In Central Asia, Uzbekistan experiences water scarcity and water stress, being highly dependent on external flow from the upstream water-rich neighboring countries. In this study, the major ion chemistry and trace element data were obtained on surface- and groundwater collected during a survey in October 2023, from the Chirchik-Akhangaran river basins, in the Tashkent province (Uzbekistan). These rivers are of great importance to industry, agriculture, and household water supply, and their water resources are intensively used for hydropower production, industry, and crop irrigation, causing the river flow to decrease rapidly. The aim was to investigate the geogenic and anthropogenic contributions to the dissolved load, with implications for water quality and management plans. The results indicate that the geochemistry of waters from the upstream Akhangaran-Chirchik catchments reflect silicate and carbonate rock weathering. The downstream increase in Na+, K+, SO4 2-, Cl-, and NO3 - reflects anthropogenic pressure from the use of fertilizers in crop production and manure spreading. Nevertheless, the common water quality indices (SAR, Na%, and KI) indicate that most river waters are suitable for irrigation purposes. The concentration of potentially toxic elements in most waters is lower than the thresholds set for water quality by different regulations. An exception is the water in a coal fly-ash pond related to the Angren coal-fired power plants, showing exceedingly high As, Al, B, Mo, and Sb concentrations due to leaching of contaminants from the coal fly-ash, with possible groundwater impacts associated with infiltration. Although the effects of seasonal changes and irrigation periods on water quality require further investigations, the results obtained are suitable indicators for water resource management.