Abstract: Hydrochemical technology and environmental isotopes were used to analyze the hydrogen and oxygen isotopes and hydrochemical properties of water samples from the Yinchuan Plain. The research showed that the δD and δ¹⁸O values of stream systems in the plain were distributed below the local meteoric water line(LMWL) and the δD-δ¹⁸O relationship line of Yellow River water. Compared with other kinds of surface water, the isotopic composition of lake water was more positive, and the d-excess (negative) was far lower than that of global meteoric water line (GMWL) due to the strong evaporation. According to the isotopic characteristics, both surface water and groundwater were recharged by the Yellow River. The consistent isotopic composition of river water, canal water and groundwater indicated that the hydraulic connection between surface water and groundwater was very close. The correlation between δ¹⁷ O and δ¹⁸O followed an equation of ln(δ¹⁷ O+1)=0.524ln(δ¹⁸O+1)+0.000 94, which was similar to the global meteoric water line 〔ln(δ¹⁷O+1)=0.528ln(δ¹⁸O+1)+0.000 33〕, but the ¹⁷ O-excess was higher than that of seawater. The waters in the Yinchuan Plain are alkaline. The conductivity of lake water was the highest, then that of groundwater,and that of river water was the lowest. The chemical types of the waters included mainly HCO₃-Na and HCO₃-Ca·Mg, and the main cation and anion were Na⁺ and HCO^-₃, respectively. The Gibbs plot revealed that the chemical compositions of the water samples were mainly affected by rock weathering and evaporation. The hydrogen and oxygen isotopes and hydrochemical data indicated that the water hydraulic connection between surface water and groundwater was strong.

Key words: water body, hydrogen and oxygen isotope, hydrochemistry, Yellow River water, ¹⁷ O-excess, Yinchuan Plain