TEMPORAL DYNAMICS OF GROUNDWATER AND SOIL SALINIZATION IN IRRIGATED LANDS OF THE LOWER KASHKADARYA RIVER BASIN: DRIVING FACTORS, RISKS, AND SUSTAINABLE MANAGEMENT STRATEGIES.

The reclamation condition of irrigated lands in the lower Kashkadarya River Basin is closely associated with long-term changes in groundwater levels, groundwater mineralization, and soil salinity. In this study, temporal changes in groundwater depth and dry residue content were comparatively assessed using monitoring data collected at different locations in 1951 and 2016. The results revealed substantial changes in the groundwater regime. In 1951, groundwater depth at the observation sites was generally within 5–10 m and exceeded 8 m in some areas, whereas by 2016 it had decreased to 2.5–4.5 m. At the same time, the dry residue content in groundwater increased markedly: values that were mostly within 127–1910 mg/L in 1951 reached 2900–5400 mg/L in 2016. In particular, the dry residue content increased from 430 to 3700 mg/L in the Gubalak area, from 127 to 4000 mg/L in the Isa Bai area, and from 388 to 5400 mg/L in the Ok Machit area. The obtained results indicate that the rise of groundwater toward the land surface was accompanied by an increase in groundwater mineralization, representing an important reclamation factor contributing to a higher risk of secondary soil salinization in irrigated lands. The expansion of irrigated areas, water–salt exchange processes, changes in the groundwater regime, and drainage conditions were considered among the principal factors affecting the reclamation stability of the region. The findings provide a scientific and practical basis for the effective use of the monitoring-well network, regular control of groundwater levels and mineralization, early identification of areas at high risk of salinization, and improvement of sustainable water and land management strategies in the lower Kashkadarya River Basin.