Seasonal Water Chemistry and Reclamation Status of Irrigated Lands in the Syr Darya Basin

This article addresses the deterioration of reclamation conditions and the decline in soil fertility in the middle and lower reaches of the Syr Darya River Basin, where the major irrigated agricultural lands of Kazakhstan are located. The paper presents the results of comprehensive studies conducted during 2023–2025 and summarizes seasonal changes in the chemical indicators of water resources within the Syr Darya River Basin, as well as assesses the impact of water quality on the reclamation status of irrigated lands. The quality of irrigation water primarily affects the “soil solution–soil adsorption complex” system and, through this mechanism, influences nearly all components of the soil reclamation regime. The study revealed that most water quality indicators in the Syr Darya River Basin do not exceed maximum permissible concentrations and generally remain within acceptable limits. However, in some cases, irrigation water is characterized by high mineralization (up to 1.5 g/L and higher), the predominance of toxic ions (Na⁺, Mg²⁺), and unfavorable magnesium cation concentrations, which contribute to soil magnesium sodification. Collector-drainage and wastewater discharges were identified as the main sources of irrigation water contamination in the basin. Analysis of the calculated data made it possible to assess changes in soil chemical properties at the beginning and end of the growing season. The results demonstrated the influence of irrigation water quality on the degree of soil salinization and sodification. Furthermore, irrigation with highly mineralized water leads to the accumulation of toxic salts in agricultural lands and contributes to the degradation of irrigated soils.