Research on the hydrochemical characteristics of groundwater and dynamic changes in water level depth in Jinchang City

Jinyu Shang^1,2Shengwen Liu³Qiaona Guo^3*Yajun Jiang⁴

• ¹Gansu Key Laboratory of Groundwater Engineering and Geothermal Resources, Lanzhou, China
• ²Gansu Geological Environment Monitoring Institute, Lanzhou, China
• ³Hohai University School of Earth Sciences and Engineering, Nanjing, China
• ⁴Gansu Hydrological and Water Resources Survey Center, Wuwei, China

Jinchang City, an arid inland city in Northwest China and one of the country’s 110 most water-stressed cities (per capita water resources: 1173 m³, far below provincial and national averages), faces continuous groundwater level decline due to rapid agricultural land expansion and large-scale groundwater exploitation—threatening regional ecology, production, and livelihoods. This study aims to utilize hydrochemical data (13 national monitoring wells, September 2023) and monthly groundwater level data (2017-2023), combined with statistical analysis (SPSS 20.0), hydrochemical graphs (Origin 2021), spatial interpolation (Surfer), and random forest (R, optimized ntree = 50, mtry = 2); Using methods such as R2 = 0.83 and RMSE = 0.19 m, elucidate the impact of groundwater dynamics on hydrochemistry and determine the driving factors behind water level decline. Results showed: (1) Groundwater is slightly alkaline (pH 7.50–7.90, avg.7.73); total hardness (TH: 229–1720 mg/L, avg.569.62 mg/L) and TDS (334–2420 mg/L, avg.905.92 mg/L); dominant ions: Ca2+ > Na+ > Mg2+ > K+ (cations), SO42- > HCO3- > Cl- > NO3- (anions); main hydrochemical type: Ca-SO4. (2) Hydrochemistry is controlled by combined silicate weathering, carbonate dissolution, and evaporite dissolution: Ca²⁺ and Mg2+ from carbonates and silicates dissolution; Na+ mainly from halite dissolution (minor silicate contribution); SO42- and Cl- mainly from carbonates (supplemented by evaporites). (3) 2017–2023 groundwater level dropped 2.26 m (avg.0.38 m/a); random forest identified over-exploitation (importance index=1.2) and reduced runoff (0.67) as main drivers. (4) Level decline increased ion concentrations ( SO42- / NO3- exceeding standards), exacerbated pollution accumulation, and destabilized hydrochemical types. Practically, these findings provide a scientific basis for groundwater management in Jinchang City: for regional water resource managers, they support targeted measures such as strengthening the control of overexploitation in central agricultural areas, optimizing upstream water diversion (to alleviate the reduction of runoff from dams such as Hanjiaxia), and promoting water-saving irrigation. For local communities, these results help raise awareness of groundwater scarcity and provide a basis for rational water use in agriculture and daily life, thereby promoting the sustainable development of regional water resources.