This paper is the result of hydrogeological survey engineering.

Objective In order to determine the sources and control factors of main ions and dissolved inorganic carbon (DIC) in water of the Huixian karst wetland,

Methods groundwater and surface water samples were collected from the Huixian karst wetland to analyze the hydrochemical ions and dissolved inorganic carbon isotope(δ¹³C_DIC).

Results The Ca−HCO₃ water was identified as a main hydrochemical type in most water samples of the Huixian karst wetland. The dissolution of carbonate rock was primary contributor to Ca²⁺, Mg²⁺ and HCO₃⁻, while NO₃⁻ was mainly derived from synthetic fertilizers and soil organic nitrogen. Moreover, K⁺, Na⁺, and Cl⁻ were driven by the mixed inputs of synthetic fertilizer, manure, and sewage, and the acid rain and pyrite oxidation contributed more to karst water SO₄²⁻. Further, karst water DIC was respectively derived from the soil CO₂ with the contribution rate of 46% and from the carbonate minerals with the contribution rate of 54% according to the obtained result from isotopic mass balance. In addition to the H₂CO₃ produced from CO₂ and H₂O, the H₂SO₄ derived from sulfur−containing minerals, acid rain, and anthropogenic emissions was involved in carbonate weathering in the Huixian karst wetland. Additionally, microbial nitrification processes of the reduced nitrogen fertilizers could be also ignored in the study area. For the surface water, the DIC was mainly derived from groundwater recharges, and the value of δ¹³C_DIC was affected by the photosynthesis of aquatic plants and CO₂ degassing, thereby resulting in the more enrichment of δ¹³C_DIC compared with that in groundwater.

Conclusions The obtained results provided insights into the understanding of minerals weathering and biogeochemical processes, and also highlighted the control factors of hydrogeological conditions and human activities in precisely determining hydrochemical mechanisms in the karst wetland.