Karstification and the global carbon cycle are closely related. Understanding the features of dissolution variations in carbonate rocks and the variables influencing carbonate dissolution is crucial for producing reliable estimates of karst carbon sinks. The seasonal variations in carbonate dissolution rates and the primary factors affecting carbonate dissolution in the Maocun watershed, Guilin, are examined under external source water (Xiaolongbei), karst water (Beidiping), and the mixed external source water and karst water (Bianyan) conditions. In this work, the characteristics of carbonate dissolution rates in several water bodies are investigated using field sampling and indoor experimental measurements. A correlation analysis is performed to analyze the key environmental factors impacting carbonate dissolution. The findings demonstrate that there is a clear seasonal and regional variation in the rate of the dissolution of carbonate rocks. The seasonal characteristics of the carbonate dissolution rate are summer > autumn > spring > winter. The carbonate dissolution rate ranges from −0.023 to 0.258 mg/cm²/d, with a mean value of 0.068 mg/cm²/d. The variation in carbonate dissolution rates on a spatial scale is characterized by exogenous water (Xiaolongbei) > exogenous water mixed with karst water (Bianyan) > karst water (Beidiping). As the rate of carbonate erosion in the Maocun basin is influenced by many factors, the correlation analysis shows that the main controlling factors for the rate of carbonate erosion in the Maocun basin are flow, the saturation index, pH, and pCO₂. Seasonal variations in carbonate dissolution rates are mainly influenced by pCO₂ and the flow rate, and the spatial variations are mainly influenced by pH and the saturation index. The results of this study are important for the scientific assessment of karst development in the study area and the accurate estimation of karst carbon sinks.

Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H₂SO₄ is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H₂SO₄ on different lithological carbonate weathering and the related carbon sink budget, karst spring water in the typical limestone and mixed limestone–dolomite catchments in Yaji and Beidiping affected by acid precipitation in southwest China were sampled monthly for the analysis of hydrochemical and δ¹³C_DIC characteristics. Results show for the period of sampling (August 2013 to December 2014) that the average contribution rates of atmospheric inputs and carbonate weathering to total dissolved cations are 2.24% and 97.8%, and 3.09% and 96.9% in Yaji and Beidiping, respectively. The δ¹³C_DIC values (−17.0% to −14.7‰) and the [Ca²⁺ + Mg²⁺]/[HCO₃⁻] (0.98 to 1.25) and [Ca²⁺ + Mg²⁺]/[HCO₃⁻ + SO₄²⁻] (approximately 1) equivalent ratios of samples prove that H₂CO₃ and H₂SO₄ simultaneously participate in carbonate weathering. The contribution rates of H₂SO₄ to [Ca²⁺ + Mg²⁺] and [HCO₃⁻] produced by carbonate weathering in Yaji and Beidiping are 0–30% and 0–18%, and 0–37% and 0–23%, with average values of 14% and 7%, and 19% and 11%, respectively, suggesting that the influence of H₂SO₄ on different lithological carbonate weathering is different. H₂SO₄ precipitation participating in carbonate weathering increases the weathering rate by 14–19%, whereas it decreases the flux of karst carbon sink by 7–11% in Southwest China. Therefore, anthropogenic acids have influenced the global carbon cycle and climate change by carbonate weathering due to the large karst areas in the world, and their influences on different lithological carbonate weathering should not be ignored in the regional and global carbon cycles in future studies.