Spatio-Temporal Controls on the Hydrochemistry of Drass River Water in the Semi-arid Region of Ladakh, India

Abstract

The progressive decline in river water quality has emerged as a critical environmental challenge, particularly in semi-arid and ecologically sensitive regions such as Ladakh. Periodic assessment of riverine water quality is therefore essential, both for safeguarding potability and sustainable water resource management. This study investigates the temporal variations in the water quality of the Drass River (DR) during 2024, evaluating the water quality and the influence of geochemical processes operating within the basin. A total of fifty-four water samples were collected from six locations along the river during three hydrological phases: Early Melting Period (EMP; April), Peak Melting Period (PMP; July), and Late Melting Period (LMP; November).  The cationic composition in the DR remained consistent across all study periods, following the order Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. In contrast, the anionic composition exhibited temporal variability: HCO₃⁻ > SO₄²⁻ > Cl⁻ > CO₃²⁻ in EMP, HCO₃⁻ > SO₄²⁻ > Cl⁻ > F⁻ in PMP, and HCO₃⁻ > SO₄²⁻ > Cl⁻ in LMP. These results indicate a Ca²⁺–Mg²⁺–HCO₃⁻ water type, with rock–water interaction as the primary geochemical process in the basin. Carbonate weathering emerges as the dominant mechanism responsible for the enrichment of Ca²⁺, Mg²⁺, and HCO₃⁻, with only minor contributions from silicate weathering. The progressive increase in SO₄²⁻ concentration from EMP to LMP suggests enhanced sulphide oxidation, likely linked to glacier retreat, which exposes sulphide-bearing lithologies to intensified weathering and water–rock interactions. Elevated levels of F⁻ were noticed during PMP, indicating the possible impact of developmental activities during the period. This research thus provides a comprehensive hydrochemical appraisal of the Drass River in Ladakh, offering methodological guidance for future hydrogeochemical investigations.