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

Abstract

During the last 40 years, extensive research has characterized the hydrogeology of many karst aquifers, as they are important water resources. Despite that, a systematic investigation on metamorphic karst aquifers is still lacking. The present study investigates the functioning of marble karst aquifers by means of spring hydrological monitoring, coupled with storm-hydrograph, thermograph, and chemograph (HTC) analysis and lag time analysis. Renara and Equi springs (Apuan Alps, Italy) were selected for this investigation. These springs drain catchments that have different degrees of structural complexity. Piston flow is the common hydrodynamic response of Renara spring to infiltration. Strong dilution effects were observed only during the heaviest rainfall events. Prolonged dry conditions after a sustained recharge phase showed the delayed arrival of infiltration water about a month later. Equi spring has a more complex behaviour due to its wider and more hydrologically heterogeneous catchment but the comparison of HTC graphs during the winter dry phase helped to recognize the differential contributions of proximal and distal sectors. Both springs show a rapid discharge increase in response to impulse infiltrative events. Conversely, water temperature and specific electrical conductivity increase only slightly during floods, indicating limited chemical and thermal exchanges between the rock and the water stored in these aquifers. The hydrodynamic behaviour of these karst springs suggests that the Apuan metamorphic aquifers are characterized by the predominance of conduit porosity over fissure and matrix porosities. This is explained by a reduced interstitial porosity and fracturing of the metamorphic carbonate rocks.

Mixed Recharge and Epikarst Role in a Complex Metamorphic Karst Aquifer: The Pollaccia System, Apuan Alps (Tuscany, Italy)

“…Similar lags were found only for karst springs that drain smaller catchments, otherwise the lags were longer [17,18,44,45]. However, other Apuan karst springs showed similar lags; therefore, the local setting plays a fundamental role in the functioning of these karst systems [46].…”

Hydrogeochemistry and Isotopic Composition of Waters in the Renella Cave (Central Italy): New Insights into Groundwater Dynamics

“…During precipitation events, the EC showed a significant variation (up to −100 µS/cm when the system was very dry), quickly decreasing when the water level peaks occurred, whereas the T did not always show the same pattern. Such behavior is unusual, since the temperature normally decreases due to the infiltration of meteoric and stream waters, which also normally results in a marked lowering of the EC [52]. The δ 18 O patterns of the cave sump and Regolo Creek waters were very similar, characterized by an enrichment in heavy isotopes due to the seasonal and amount effect during spring 2021.…”

Arsenic Contamination in Groundwater, Soil and the Food-Chain: Risk Management in a Densely Populated Area (Versilia Plain, Italy)

“…and Tuscan Nappe (mainly Calcare Cavernoso and polygenic breccias Fm., and cataclasites) host the two most important aquifer systems of the mountainous area. The medium-high permeability of these rocks and the annual rainfall of more than 2000 mm/year determine a significant groundwater flow that feeds several springs, with an average flow rate up to some tens L/s [39]. Some of these springs also feed the Baccatoio stream.…”