Simulation of the buffering process of karst soil on sulfuric acid rain and the characteristic of δ13CDIC and the carbon sink flux in Guilin City, southwest China

To clarify the buffering process and karst carbon sink effect of the karst soil with acid rain, experiments on the leaching of sulfuric acid rain were conducted at pH 3.5, 4.5, and 6.5 with different karst soil thicknesses. The buffering process of karst soil on acid rain occurred in the topsoil. During strong acid precipitation, the soil-exchangeable calcium and magnesium were predominantly exchanged with H+ in acid rain, while during weak acid precipitation, the amount of calcium and magnesium exchanged with H+ in acid rain was lower than the H+ generated via dissociation of soil CO2 dissolved in the precipitation. At pH 3.5, 4.5, and 6.5 precipitations, the δ13CDIC value in the leached liquid ranges from − 18.9 to − 14.2‰, − 19.0 to − 13.2‰, and − 12.0 to − 7.1‰, respectively, and with increasing precipitation intensity, the δ13CDIC value was increased, relatively stable, and decreased, respectively. A total of 74% of dissolved inorganic carbon (DIC) in the leached liquid was from soil CO2. In the karst soil area (soil thickness ≥ 10 cm), soil-exchangeable calcium and magnesium can buffer 33,303–336,987 mm in pH 3.5 precipitation and 145,701–371,550 mm in pH 4.5 precipitation, while the soil buffer in pH 3.5 precipitation can generate 0.22–1.04 mol m−2 carbon sink per year, and 0.39–0.64 mol m−2 carbon sink per year in pH 4.5 precipitation.