A method for quantifying the role of carbonic acid, sulfuric acid, and nitric acid in carbonate weathering after accounting for the effects of evaporites in the Qingjiang karst catchment

The Qingjiang River is the second largest tributary of the Yangtze River in Hubei Province and is also a typical karst catchment. Eighty-two important groundwater samples were collected during the high and low water periods of 2019. The results show the following. (1) The major hydrochemical types are Ca + Mg-HCO 3 and Ca-HCO 3 , indicating that carbonate weathering is the main factor controlling the groundwater chemistry. (2) The results of inverse hydrochemical modeling reveal two kinds of groundwater–carbonate rock interactions. One is the codissolution of calcite and dolomite, and the other is dedolomitization, which is widespread in the dolomite aquifers. Furthermore, gypsum has a tendency to dissolve in each aquifer, and the common ion effect of Ca 2+ caused by gypsum dissolution promotes dedolomitization. The modeling results suggest that major elements can be effectively used to trace the material source of the groundwater. (3) The chemical weathering of carbonate rock is mainly affected by carbonic acid, sulfuric acid, and nitric acid. After accounting for the impacts of evaporites and atmospheric input, the calculations show that the contribution of carbonic acid involved in carbonate weathering is 70.9% in the high water period and 70.0% in the low water period. Statistical analysis of karst spring discharge and the contributions of the acids involved in carbonate weathering reveals that the two are positively related. This result reflects the behaviors of sulfuric acid and nitric acid under the hydrodynamic conditions in different seasons. Therefore, carbonate weathering should be carefully evaluated in karst areas with abundant groundwater, and the role of groundwater in carbonate weathering is worthy of further study.