Karst solution: a global model for groundwater solute concentrations.

The equilibrium concentration of ions in a groundwater in any regional carbonate aquifer can be simply modelled as the end point of either an open or a closed system evolution from an initial partial pressure of carbon dioxide (PCO2) that is determined by the response of soil activity to annual mean temperature. Open system conditions, leading to higher ionic concentrations, apply when either there is carbonate material in the overburden (due to natural factors such as glaciation, or to human activities such as soil liming), or the carbonate bedrock is very porous and near the surface. Closed system conditions apply either where a non- carbonate unit intervenes between the soil and the carbonate rock, or where a carbonate-free regolith is considerably deeper than the soil CO2 producing zone.-Authors