Hydrogen and oxygen stable isotopes and hydrochemical characteristics of the Kaidu River

To investigate the recharge sources and major ion origins of the Kaidu River, twelve river water samples were collected. By analyzing ion ratios and isotopic characteristics of the water, combined with Piper trilinear diagrams and Gibbs diagrams, we examined the hydrochemical and hydrogen-oxygen isotopic features to explore water recharge relationships. The results indicate that: 1) The river water is weakly alkaline, with the main cation concentration order being Ca ²⁺ > Mg ²⁺ > Na ⁺ > K ⁺ , and the primary anion content sequence as HCO ₃ ^- > SO ₄ ^2- > Cl ^- > NO ₃ ^- . In the upper reaches of the Kaidu River, ion concentrations show significant variations, while changes are smaller in the lower reaches. All water samples exhibit a HCO ₃ -Ca hydrochemical type. 2) Rock weathering is the primary factor influencing ion concentrations in river water. Based on Gaillardet diagrams and ion ratios, the main sources of riverine ions are the dissolution of carbonate and silicate minerals. 3) The hydrogen and oxygen isotopic characteristics indicate that atmospheric precipitation is the major source of the river, with some degree of evaporation occurring along its course. The δD and δ ¹⁸ O values of the Kaidu River water exhibit a strong negative correlation with elevation, decreasing as elevation increases. For every 100 m rise in elevation, δD decreases by 1.29‰ and δ ¹⁸ O by 0.21‰. The δD and δ ¹⁸ O values of the Kaidu River water show a notable continental effect, decreasing with increasing latitude.