Hydrodynamic and Geochemical Features of Metamorphic Carbonate Aquifers and Implications for Water Management: The Apuan Alps (NW Tuscany, Italy) Case Study

Carbonate rocks may be considered among the most important and strategic aquifers, given their widespread and the general high quality of groundwater flowing through them. Nevertheless, the karst systems developed within such aquifers promote conditions of high vulnerability to contamination and a high variability of groundwater flow rate, thus making the management of these water resources difficult. These critical features can be accentuated in metamorphosed carbonates, because of the massive structure of the rock that favours a low density of the karst network, and a preferential flow pattern throughout well-developed karst conduits. Furthermore, these rocks are often subject to quarrying and associated risk of pollution, mainly due to the fine slurry produced during marble cutting. This chapter presents the case of the Apuan Alps (NW Tuscany, Italy), where the main hydrogeological units are represented by metamorphosed dolostones and limestones (“Grezzoni” and marble, respectively), the latter being widely quarried to produce ornamental stones, as the famous Carrara marble. High-pressure ductile deformations and the consequent metamorphism have reduced the hydraulic conductivity of bedding surface, whereas the tectonic exhumation due to low-angle extensional faults has limited the development of diffuse fracture joints. For these reasons, an important subterranean storage of water is represented by epikarst porosity (unloading fissures and solution pockets) and vadose seepage, whereas in the epiphreatic and phreatic zones, the karst conduits have a high hydraulic conductivity but a low storage capability. Large flow rates and physical-chemical and isotopic variations, both in space and time, are observed at the springs as a consequence of differentiation of groundwater flow paths and hydrodynamic conditions. The main results derived from several years of study in the region are discussed in order to underline the high complexity of aquifer systems hosted in metamorphic carbonate rocks and to emphasize that multidisciplinary studies can provide knowledge useful for managing water resources in these very complex contexts.