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

Abstract

AbstractAfter acid rain has settled onto the surface and has been buffered by karst soil, the capacity of acid rain to participate in carbonate rock erosion and its impact on the karst carbon sink are still unclear. To clarify the buffering process and karst carbon sink effect of karst soil with acid rain, experiments on leaching of sulfuric acid rain were conducted with pH 3.5, 4.5, and 6.5 with different karst soil thicknesses. Results have shown that the karst soil buffer to acid rain predominantly occurs in the surface soil layer. The loss of Ca2+and Mg2+due to acid rain H+accounted for a small proportion of the Ca2+and Mg2+in the leached liquid. Soil water-soluble Ca2+, Mg2+, and soil exchangeable calcium and magnesium are the main Ca2+and Mg2+components in the leached liquid. They were exchanged by the H+generated by the dissociation of soil CO2dissolved in the soil water. A total of 74% of dissolved inorganic carbon (DIC) in the leached liquid came from soil CO2. Differences in the rainfall pH value had little effect on the sources of DIC in the leached liquid. In the karst soil area, the carbon migration process caused by rainfall is mainly dominated and driven by the soil carbon pool. Under strong acid (pH 3.5) precipitation conditions, the surface soil carbon sink was significantly higher than the deep soil carbon sink. Meanwhile, under weak acid (pH 4.5) precipitation conditions, the difference in soil carbon sink capacity of different soil thicknesses was relatively low. The capacity of the soil carbon sink had no pronounced relationship with soil depth.