Control of soil mantle thickness and land cover types on groundwater recharge of karst aquifers in Mediterranean areas

Karst aquifers represent the fundamental groundwater resources in Italy and in many other countries because supplying urban areas of drinking water and sustaining industrial and agricultural activities. Accordingly, advancing the assessment of groundwater recharge of these aquifers is a major scientific challenge, specifically if considering the hydrological role exerted by soil covering and the related land cover types. In such a framework, the soil water balance model is an effective tool for providing accurate estimates of groundwater recharge depending on precise field and laboratory characterizations of the soil covering. Considering the features of karst aquifers of southern Italy and the ubiquitous occurrence of a soil mantle, mainly of ash-fall pyroclastic origin, a methodology based on field and laboratory characterizations, as well as modeling approaches, is proposed in this work to advance the knowledge on groundwater recharge processes. The experimental approach was applied to the Soprano-Vesole-Chianello Mts. karst aquifer (Campania region, southern Italy) which is considered representative of karst aquifers of southern Italy and Mediterranean areas as well. A comprehensive characterization of the soil mantle was developed, considering different land cover classes, measurements and stochastic spatial modeling of soil thickness. The unsaturated hydraulic properties of undisturbed soil samples were analyzed by laboratory tests resulting in the determination of Soil Water Retention Curves (SWRCs). Moreover, a field monitoring of soil water content was carried out by multi-profile soil moisture sensors, allowing the assessment of the hydrological response of the soil covering and of the regime of groundwater recharge process as well. Among the principal outcomes is the recognition, for each land cover class, of different values of the depth to which the evapotranspiration effect is extended. Based on a consistent spatial modeling of soil thickness and soil hydrologic properties, the Soil Water Balance code (SWB 1.2) was applied to evaluate the spatial and temporal variability of the groundwater recharge of the karst aquifer. As a principal outcome, groundwater recharge rates were found to be dependent on land cover class and soil thickness as well, showing lower values for wooded areas and higher for denudated ones, respectively due to the higher and lower evapotranspiration rates.