Hydrochemical evolution and salinization dynamics in Lake Chaiwopu Basin (Arid NW China): Insights from multi-tracer and geochemical modeling

Terminal lakes in arid northwestern China, such as Lake Chaiwopu, are facing increasing salinization driven by climate change and intensive groundwater exploitation. This study integrates hydrochemical observations, stable isotope analysis (δD, δ¹⁸O), and pH-Redox-Equilibrium-C (PHREEQC) modeling to investigate the mechanisms of salinity accumulation from 2008 to 2023. Total dissolved solids (TDS) in lake water increased from 4,475 mg/L in 2008 to 21,500 mg/L in 2023, with notable seasonal variation (e.g., TDS increased from 8.8 to 19.1 g/L in summer 2023). Groundwater TDS also rose significantly from 262 mg/L in 2008 to 568 mg/L in 2023, alongside substantial increases in Na⁺ (from 216.1 to 498.9 mg/L) and Cl⁻ (from 122.5 to 295.5 mg/L), with variation coefficients exceeding 200%. Isotopic enrichment in lake water (δ¹⁸O up to 1.6‰) and a reduced slope of the local meteoric water line (from 6.86 to 5.83) indicate intensified evaporation. From 2018 to 2022, groundwater abstraction increased nearly fourfold, lowering the water table by ∼3 m and reducing subsurface inflows, further exacerbating salinization. Geochemical modeling reveals that evaporite dissolution (gypsum: 6.71 mmol/L; halite: 4.02 mmol/L) and cation exchange (9.83 mmol/L Na⁺ released, 4.91 mmol/L Ca²⁺ adsorbed) are key processes, contributing to the shift from Ca-HCO₃ to Na-Cl/SO₄ hydrochemical facies. These findings highlight the combined role of hydroclimatic factors and human-induced flow path modifications in accelerating lake salinization. This study provides valuable insights for the development of basin-wide water management strategies aimed at mitigating salinization and preserving terminal lake ecosystems in arid regions.