Downstream hydrochemistry and irrigation water quality of the Syr Darya, Aral Sea Basin, South Kazakhstan

Abstract

New hydrochemical measurements from the Syr Darya provide insights into factors affecting the composition and quality of one of the two major freshwater sources replenishing the Aral Sea. This river is heavily used for power and irrigation and crosses territories of four central Asia republics. It is intensely managed, draining several major tributaries, many reservoirs, and numerous irrigation distribution systems and canals. Analysis of seasonal changes in dissolved ion concentrations using geochemical diagrams, elemental ratios, statistical correlation, and equilibrium modeling allowed the characterization of mineral formation processes that control the dissolved chemical composition. Measured water hydrochemistry and composition type differs substantially from previous reports from the upper reaches of the Syr Darya in Kyrgyzstan. Element ratios, statistical correlation, and the presence of NO3- and NO2- suggest that the downstream trend of increasing total dissolved solids (TDS) from Zhetysay city to the Aral Sea in June is controlled by evaporation–crystallization processes, which contribute to the river dissolved load through soil runoff and return irrigation waters following leaching of secondary salts. Downstream sample composition during the growing season shows significant changes in magnesium-to-calcium ratios in the river water. Elevated magnesium levels in Syr Darya waters may pose a problem to sustainable uses for irrigation.

Assesment of the soil erosion & water quality state in the downstream portion of Syrdarya using the water quality index arithmetic method

“…The latest research, which focuses on assessing the concentrations of dissolved and acid-leachable trace elements concerning applicable water quality standards in the Syrdarya, Aral Sea Basin, South Kazakh-stan [19], also scrutinized the levels of metallic and non-metallic chemical compounds, along with other minerals and total dissolved solids. This analysis was conducted based on three distinct criteria: minimum, average, and maximum, as illustrated in table 2.…”

Water quality and dissolved load in the Chirchik and Akhangaran river basins (Uzbekistan, Central Asia)

“…The Akhangaran and, in particular, Chirchik rivers contribute signi cantly to the annual runoff in the upper Syrdarya, and their water quality may in uence the salinization trend. Four indexes were applied to evaluate the Chirchik and Akhangaran water quality in term of irrigation suitability, considering that the agricultural area is vulnerable to soil salinization Isaev et al, 2004): the sodium adsorption ratio (SAR), sodium percentage (Na%), Kelly's index (KI), and total hardness (TH) (Satybaldiyev et al, 2023). SAR represents the relative activity of Na + in soil exchange reactions and is used with EC to evaluate the degree of alkalization of irrigation water.…”

Relation of Hydrogeology and Contaminant Sources to Drinking Water Quality in Southern Kazakhstan

“…In the Kyzylorda region, groundwater pollution of the upper aquifer was noted within the Torangylysai field and the developed Kyzylorda field. Groundwater pollution from irrigated cropland may also contaminate shallow aquifers in this region [53,54].…”