Interaction analysis of hydrochemical factors and dissolved heavy metals in the karst Caohai Wetland based on PHREEQC, cooccurrence network and redundancy analyses

Highlights: • Soil smelting zinc may have led to the collective input of Zn and Cd. • pH and DO promote the insoluble component of Pb in water. • SO₄²⁻ accelerates the dissolution of formation minerals. • The dissolution rate of carbonate rocks increases in dry season. In this study, to clarify the interaction between dissolved heavy metals and the coexisting chemical factors in karst wetland waters, surface water samples were collected from the Caohai Wetland during a water year, and the hydrochemistry and heavy metal pollution characteristics of the samples were analyzed. The main influencing factors of heavy metals in different water periods were identified through a cooccurrence network analysis. To further analyze the influence mechanism of these main influencing factors, the forms of heavy metals in the water were simulated with PHREEQC software, and the effects of these main influencing factors on the forms were analyzed by redundancy analysis. The results show that Ca²⁺ was the main cation in the wetland water, while the main anion was HCO₃⁻. The hydrochemical facies of the Caohai Wetland in the wet and dry seasons were Ca-Mg-SO₄-HCO₃ and Ca-HCO₃, respectively. Cd was the main pollutant in the Caohai Wetland, with Cd levels seriously exceeding the standards. The characteristics of the karst water in the Caohai Wetland are apparent. The cooccurrence network analysis shows that pH, dissolved oxygen (DO), electrical conductivity (EC), SO₄²⁻ and HCO₃⁻ are the main factors regulating heavy metals. The results of morphological simulation and analysis were used to explore the mechanism of action of these factors. These data provide geochemical information useful for water quality assessment and management plans on heavy metal pollution.