Hydrogeological and geochemical overview of the karst aquifers in the Apuan Alps (Northwestern Tuscany, Italy)

Abstract

Apuan Alps, in north-western Tuscany (Italy), have a very complex geological structure. For this reason karst springs show very different behaviours according to the geological setting of aquifer systems. More than 80 springs are fed by carbonate aquifers; flow rates (Q) range from 10 to 1600 L/s, in average, temperatures range from 8 to 15 °C. Deep and very slow groundwater flow feed some low-thermal springs (20-30 °C). Major karst springs (Q > 100 L/s) are concentrated in two altimetry ranges, one from 200 to 300 m a.s.l. in the seaward side (SW-NW) and a second one from 500 to 600 m a.s.l. on the inner (NE-SE) side of the mountain range. Most of the springs are the final destination of large karst systems developed in meta-dolomite and marbles characterized by a very rapid flow. Some springs have a regular regime and are fed by bathyphreatic systems in metamorphic rocks or by carbonate aquifers with a major contribution of fissured drainage in non-metamorphic rocks. Large physical-chemical variations, both in space and time, are observed as a consequence of lithological heterogeneity, mixing processes and hydrodynamic conditions. Most waters are of the Ca-HCO3 type, but Ca-SO4 and Na-Cl facies are also present. A wide range of electrical conductivity is recorded, with values between 0.1 μS/cm and 10 μS/cm. Significant differences in the average isotopic signature (e.g. δ18O from -5.5 to -8.5‰) of the “base-flow” are registered due to the variability of hydrogeological basins dimension and their distribution in terms of altitude range and side. In some cases, springs with similar chemical features and located close to each other, point out very different isotopes signature, thus highlighting complicated flow path of groundwater. Furthermore, different seasonal evolutions of isotopic signatures are registered.

Hydrodynamics of karst aquifers in metamorphic carbonate rocks: results from spring monitoring in the Apuan Alps (Tuscany, Italy)

“…The main Apuan metamorphosed karst systems consist of marble and metadolostone that display high infiltration rates and the development of Piccini et al 1999 for further details about the regional hydrogeology of the Apuan Alps). The red squares show the two investigated systems: 1 Equi, 2 Renara extensive underground conduit networks (Piccini 2002;Menichini et al 2016;Doveri et al 2017). Marbles and metadolostone aquifers have a low storage capacity due to low matrix porosity and to reduced fracturing at depth.…”

Modelling tools for quantitative evaluations on the Versilia coastal aquifer system (Tuscany, Italy) in terms of groundwater components and possible effects of climate extreme events

“…The knowledge related to this aquifer is based on numerous hydrogeological works of literature (Giardi et al 1983, Duchi andFerrari 1984;Musetti 1985;Ferrari et al 1987;Salvatori 1994;Salvatori 1997;Tabbì 1999;Giuntini 1999;Tessitore 2002;Doveri 2004;Pranzini 2004, Regione Toscana 2008Da Prato et al 2011;Menichini 2012;Da Prato et al 2015;Menichini et al 2018). In the foothill sector, the deposits of coastal aquifer are locally related to fractured hydrogeologic structures of the Apuan Alps (Menichini et al 2016;Doveri et al 2019). In particular, the aquifer of the plain could be in connection with carbonate hydrogeological complexes characterized by high permeability due to fracturing and karst phenomena (e.g.…”

“…Among Ca-HCO 3 waters some samples have a higher sulphate content that could be indicative of a feeding component by water flowing in the cavernous limestone (Figs. 4a and 4b), whose local springs are characterized by Ca-SO 4 facies (Menichini et al 2016). In the coastal area, there are also waters belonging to the chemical facies Na-Cl-HCO 3 , mix-Cl-HCO 3 , mix-HCO 3 and Na-HCO 3 attributable to relatively prolonged interaction with rocks or ion exchange.…”

Groundwater and potentially toxic elements in a dismissed mining area: Thallium contamination of drinking spring water in the Apuan Alps (Tuscany, Italy)

“…Superficial fracturing, linked to unloading and physical-chemical processes, is responsible for high rates of rainfall infiltration (Doveri et al, 2018). Metamorphic dolostone, dolomitic marble, marble and cherty limestone host prominent groundwater resources mainly drained by karst springs, whose total discharge amounts to about 5.6 m 3 /s (Menichini et al, 2016).…”