Hydrochemical Signals in Urban River-Lake Systems: Insights for Stable Ice Formation

The surface freezing process is a crucial and widespread driver of water chemistry dynamics. This study investigates the hydrochemical changes during seasonal freezing in an urban river-irrigated lake system. Results demonstrate that freezing redistributes solutes, with ion concentrations in ice being significantly lower than in underlying water due to exclusion from the ice lattice. Effective segregation coefficients (Keff) and concentration factors (CF) confirm the persistent solute exclusion, which was stronger in the hydrologically quieter lake than in the river. This exclusion is primarily governed by ion-specific properties (e.g., solubility, hydration energy), while ice thickness was a secondary factor. Although the predominant Ca-Cl and Ca-HCO₃ hydrochemical facies remained unchanged, the ionic composition within ice was distinctly altered. Principal component analysis (PCA) revealed that mineral weathering and dissolution control solute dynamics in the river, while agricultural activities significantly influence the relatively enclosed lake. Our findings underscore that the freezing process acts as a key regulator of winter water chemistry, with important implications for water quality and ecological management in seasonally frozen basins globally.