Source and control factors of main ions and dissolved inorganic carbon in the lakes of Huixian Karst Wetland

Objective In order to find out the sources and control factors of main ions and dissolved inorganic carbon(DIC) in karst wetland water. Method Groundwater and surface water samples were collected from Huixian karst wetland, and the characteristics of hydrochemistry and dissolved inorganic carbon isotope(δ¹³C_DIC) were analyzed. Results The hydrochemical type of most groundwater and surface water of Huixian karst wetland is Ca-HCO₃. Ca²⁺, Mg²⁺ and HCO₃^- are mainly from carbonate rock dissolution; NO₃^- mainly from agricultural fertilizer and nitrification of soil organic nitrogen; K⁺, Na⁺ and Cl^- mainly from fertilizer, manure and sewage; SO₄^2- mainly from acid rain and pyrite oxidation. DIC in wetland groundwater mainly comes from the dissolution of soil CO₂ and carbonate minerals. According to the isotopic mass balance, the calculation results show that about 46% comes from soil CO₂, and about 54% comes from the contribution of minerals themselves. Huixian Karst Wetland is not entirely the result of carbonate weathering under the participation of CO₂. Sulfur-containing minerals, acid rain, and human activity derived H₂SO₄ also participate in the weathering of carbonate rocks as erosion media. In addition, the nitrification of agricultural input reduced nitrogen fertilizer cannot be ignored. Wetland surface water DIC mainly comes from groundwater. Wetland surface water δ¹³C_DIC value is affected by photosynthesis of aquatic plants and CO₂ degassing, and its composition is relatively positive compared with that of groundwater. Conclusion Water Chemistry and δ¹³C_DIC can help understand the weathering and biogeochemical processes of karst wetlands, and it should also be combined with wetland hydrogeology and human activities to provide more accurate information.