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Abstract:
The removal of limestone from the bedrock at the surface and below ground by CO2-containing aqueous solutions sculptures karst landscapes and complex karst aquifers. To understand the evolution of such karstic features requires the knowledge of dissolution rates under various hydrogeological conditions. These rates are controlled by several complex mechanisms: 1) The rate equations of Plummer et al. (1978), from which surface reaction rates can be obtained when the concentrations of reacting species at the surface are known. 2) The slow reaction of CO2 to H+ and HCO3, which provides the H+ ion for converting carbonate to bicarbonate ions. 3) Mass transport by diffusion, either in laminar or turbulent flow. 4) Inhibition of surface reaction rates by the presence of impurities in natural carbonate minerals. 5) Open- or closed-system conditions with respect to CO2, under which dissolutional removal of limestone is active. Depending on the actual conditions each of these processes can greatly effect dissolution rates. This paper addresses these problems and provides data, which can be used to obtain realistic dissolution rates, when solutions flow laminarly in narrow fractures, but also for turbulent flow in large conduits, and a variety of other different hydrogeological conditions. These data are also necessary as input for modeling the evolution of karst.