Characteristics of Seasonal Changes in Surface Water Hydrochemistry and Controlling Factors in the Kaidu River Basin

<p indent="0mm"> With the intensification of climate warming and the impact of human activities, the water quality of the Kaidu River has been affected to a certain extent, and the hydrochemical characteristics of the watershed can reflect the water quality status of the watershed, which can effectively indicate the environmental changes of the water quality of the watershed. This study took the Kaidu River in inland Northwest China as the object of study, and collected surface water from the Kaidu River basin in summer (June) and autumn (October) in 2024, and used Piper′s trilinear diagram, Gibbs′ model, and correlation analysis to explore the characteristics of different water bodies in the Kaidu River basin and to analyse the causes of their formation and their environmental significance. The results showed that the mean pH values of Kaidu River water in summer and autumn were 8.70 and 8.01, respectively, which were both weakly alkaline; cations in Kaidu River water in summer and autumn were dominated by Mg²⁺ and Ca²⁺, anions in summer were dominated by HCO₃^–, and anions in autumn were dominated by HCO₃^– and SO₄^2–. The hydrochemical types in summer and autumn are HCO₃‒Ca·Mg and HCO₃·SO₄‒Mg·Ca, respectively. Hydrogeochemical processes are weakly affected by human activities in summer and strongly affected by human activities in autumn, and both summer and autumn are mainly controlled by rock weathering, but the main ions in summer originate from the weathering and dissolution of carbonate and silicate rocks, and the main ions in autumn originate from the weathering and dissolution of carbonate rocks.