Karst aquifers

It is generally recognized that karst aquifers have different properties than porous media such as sand. But just what is a karst aquifer? This is not an easy question to answer, and this paper describes five contrasting definitions. Based on these different definitions, the percentage of near-surface carbonate aquifers that can be classified as karstic ranges from <1%  to >50%, as shown in the figure.

Estimated percentage of near-surface carbonate aquifers that can be classified as karstic, based on five different criteria (after Worthington et al., 2017).