Complexity and Fragility of Apulian Groundwater Resources

Complexity and Fragility of Apulian Groundwater Resources Isabella Serena Liso¹ and Mario Parise¹ Department of Earth and Environmental Sciences, Aldo Moro University, Italy Abstract Apulia, southern Italy, is an almost entirely carbonate peninsula, with widespread karst landforms. Lacking superficial runoff, the water stored into the subsoil represents the only resource, to be protected and pre- served. The geological and geographical characteristics of Apulia make freshwater resources very fragile and subjected to degradation via both seawater intrusion and anthropogenic pollution, especially along its coast- lines, where a high number of wells are present. The worst situation occurs in central Apulia where a high salinity area crosses the whole peninsula, linking the two sides of the region, a sort of underground connec- tion between the Adriatic and Ionian Seas. Further, anthropogenic pollution contributes to reduction of freshwater resource volume, through high rates of in- dustrial and agricultural chemical pollution (i.e., PCA, PCB, oil, pesticides, etc.), and microbiological pollution (i.e., fecal coliforms, Escherichia coli, etc.) close to wastewater treatment plants. The only efficient app- roach to protect freshwater resource, in such a fragile setting, is represented by monitoring actions. At this goal, the only two caves in Apulia reaching ground- water have become hydrogeological natural labora- tories. There, two multiparameter probes have been installed to measure temperature, electrical conduc- tivity and water level. Groundwater quality has been assessed by chemical and microbiological analyses, and through biospeleological studies to ascertain the pre- sence of species characteristics of unpolluted environ- ment. All these actions, necessary to assess the ground- water quantity and quality, should be continued and guarantee a full comprehension of available Apulian groundwater resources

Sinkholes evolution in coastal settings: some examples from Southern Italy

The southernmost sector of Apulia Region can be described as a karst peninsula surrounded by the Adriatic and the Ionian Seas. The process of seawater intrusion, together with groundwater outflow, mainly coming out at the coastline, produces a water mixing that enhances the solution of soluble carbonate rocks. The effect of these processes can be observed along the coastline, characterized by several areas interested by sinkhole development and evolution. In some cases, they have become famous touristic attraction as at Grotta della Poesia, visited every summer by thousands of tourists; in other cases they represent spectacular sites of high ecological values, since they host peculiar ecosystems, with many fauna and flora species. At several sites along the Apulian coasts, sinkhole evolution form elongated bays, completely protected from sea waves, as in the sector between Fasano and Brindisi. Along this coastal stretch, field surveys revealed different sinkholes stages that can be described as successive phases in the development of bays: from opening of individual collapse sinkholes, typically at distance lower than 20 m from the coastline, to evolution in elongated sinkholes deriving from coalescence of nearby features, eventually leading to the final stage, with formation of protected bays, which main elongation depends upon the main discontinuity systems in the rock mass, and the main direction of sea storms as well. These examples highlight the importance of sinkhole processes in predicting the future evolution of the coast, and may be of help to local authorities for the most proper management of such a fragile environment

Using cave data for improving the reliability of karst groundwater flow models

Rock masses are typically anisotropic and heterogeneous, due to presence of sin-sedimentary discontinuities as bedding planes and of post-depositional features such as joints and faults. When compared to soil mechanics, therefore, a greater complexity of the simulation models for rock masses derives, which is further increased when dealing with carbonate rock masses. Beside the aforementioned types of discontinuities, other features are produced by karst processes; these latter are able to create highly complex networks of voids and conduits, with passages of variable size, which may reach dimensions enterable by man. These features definitely represent the larger discontinuity families within carbonate rock masses, in terms of size, frequency, and pervasiveness, and significantly control the flow of water. The peculiar characteristics of karst require dedicated approaches to take into the due account the presence of its typical landforms (voids, conduit/caves of variable size, swallow holes, etc.), and their variable functionality as well. Ignoring karst features in the analysis and characterization of carbonate rock masses, any approach followed, or model implemented, will inevitably result in too great uncertainties (if not errors), and in incorrect information to the engineers. What stated above is true also as regards the study of water flow in fractured carbonate rock masses, that cannot be initiated without considering the stratigraphic and structural discontinuity families. To implement flow models scholars typically start from traditional structural-geological surveys, characterization of rock masses through the classical geomechanical approaches, and elaboration of outcrop pictures elaborated by means of image process softwares. The statistical outcomes are then used as parameters in mathematical models, where also the hydrogeological boundary conditions need to be defined. A significant step forward in this approach is the use of data directly collected underground, through surveys within the cave systems. The data so collected can be used with a two-fold goal: first, to add a view from the inside of the karst underground landscapes to what is generally observed only at the surface; second, to validate the models, when these are initially implemented only with surface data. Plan maps of explored cave systems may be useful to determine in first approximation the main direction of development of the karst processes. Reliable maps of caves are nowadays available, that can be used to extract the main direction of karstification, as well as the average size of the explored karst conduits and passages. All these informations are precious underground-truth data that are definitely worth to be included in hydrogeological models aimed at improving them and their reliability as well

Karst Brackish Springs of Albania

The territory of Albania presents wide outcrops of soluble rocks, with typical karst landforms and the presence of remarkable carbonate aquifers. Many karst areas are located near the coasts, which results in a variety of environmental problems, mostly related to marine intrusion. This paper focuses on the brackish springs of Albania, which exhibit temperatures approximately equal to the yearly air temperature at their location. Total dissolved solids of the springs are higher than 1000 mg/L, their waters are not drinkable, and they are rarely used for other purposes. The groundwater of the alluvial aquifers of Albania, particularly those of Pre-Adriatic Lowland, are often brackish too, but these will not be addressed here. Brackish springs of Albania are mainly of karst origin and can be classified into two groups: springs in evaporitic rock, mainly gypsum, and springs in carbonate rock. The hydro-chemical facies of the first group are usually Ca-SO4, locally with increased concentrations of Na-Cl, whereas springs belonging to the second group usually exhibit Na-Cl facies. The largest brackish springs of Albania are described in detail, including their hydro-chemical correlations

Hydrogeological Characteristics of the Makaresh Carbonate Karst Massif (Central Albania)

Carbonate rocks cover about 23% of Albania, with exploitable karst water resources estimated at 2.84 × 109 m3/year (about 65% of the total exploitable groundwater resources in the country). The Kruja tectonic zone is characterized by the presence of SE–NW-oriented carbonate structures, rich in fresh and thermal groundwaters. More than 80% of the thermal springs in Albania are present in this tectonic zone. One of its most interesting carbonate structures, with the presence of both cold and thermal waters, is the small karst structure of Makaresh, with a surface of 22 km2. The purpose of this article is to describe the hydrogeological characteristics of this massif; based on the physico-chemical characteristics, groundwaters of the study area are classified as cold waters (belonging to the local flow system) and thermal waters (originating in intermediate/deep flow systems). The former are mainly of HCO3-Ca or HCO3-Ca-Mg type (electrical conductivity 580–650 μS/cm, Temperature 13.9–16.6 °C). Thermal waters are mainly of the Cl-Na-Ca type (EC 7200–7800 μS/cm, T 18.5–22.5 °C); they are further characterized by high hydrogen sulfide concentration, up to about 350 mg/L. The presence of two groundwater types in the Makaresh massif is connected to the presence of two groundwater circulation systems. The main factors of the groundwater physico-chemical quality are the dissolution of rocks and minerals contained therein, the presence of hypogenic speleogenesis, and the mixing of the groundwater of the two systems. The hydrogeological studies proved that karst rocks contain considerable freshwater resources, partly used for water supply. Thermal waters are not currently exploited due to their temperature, but they are potentially suitable for thermal uses by drilling boreholes to a depth of about 1000 m

Karst Brackish Springs of Albania

The territory of Albania presents wide outcrops of soluble rocks, with typical karst land-forms and the presence of remarkable carbonate aquifers. Many karst areas are located near the coasts, which results in a variety of environmental problems, mostly related to marine intrusion. This paper focuses on the brackish springs of Albania, which exhibit temperatures approximately equal to the yearly air temperature at their location. Total dissolved solids of the springs are higher than 1000 mg/L, their waters are not drinkable, and they are rarely used for other purposes. The groundwater of the alluvial aquifers of Albania, particularly those of Pre-Adriatic Lowland, are often brackish too, but these will not be addressed here. Brackish springs of Albania are mainly of karst origin and can be classified into two groups: springs in evaporitic rock, mainly gypsum, and springs in carbonate rock. The hydro-chemical facies of the first group are usually Ca-SO4, locally with increased concentrations of Na-Cl, whereas springs belonging to the second group usually exhibit Na-Cl facies. The largest brackish springs of Albania are described in detail, including their hydro-chemical correlations

Tectonic control on groundwater flow in a karst polje of southern Italy

In the last decades, climate changes are affecting the freshwater resources quality and quantity around the globe, reducing their availability. On Earth, glaciers and ice cap occupy 68,7%, but they are not easily usable for human purposes; groundwater stands for 30,1%, while surface waters represent the remaining 1,2%. Therefore, groundwater resource is by far the most important natural tank to be preserved. In karst, scientists are still working on developing new methods to understand the true groundwater hydrological behavior, due to subsoil anisotropy in both space and time. This requires a deep knowledge about discontinuity systems in the carbonates, and to improve our comprehension of karst processes, as basic elements for modelling. The possibility to collect data directly from the subsoil, thanks to speleological explorations, is a precious chance for hydrogeology, and in general, for the environmental sciences. In this contribution we take advantage from a variety of speleological data, plus traditional geological surveys, to study groundwater flow in the karst of Apulia. Many karst processes, indeed, affect the Cretaceous limestones belonging to the Apulia carbonate platform, where the deepest cave in the region opens in the Canale di Pirro polje (altitude 300m a.s.l.). This latter is a W-E elongated tectonic-karst valley, representing one of the most significant karst landforms in this sector of Apulia. The cave reaches groundwater at a depth of -260m from the ground surface, whilst additional 60m below the water table have been explored by diving the flooded channels (total depth of the cave 320m). We deal here with characterization of water flow direction into the fractured and karst aquifer, using a combined approach consisting of analysis of: i) primary and secondary discontinuities, ii) shape, size and orientation of karst conduits, and iii) geometry of the intersections between fractures and karst features. The discontinuities have been analyzed with classical geological survey at the surface, and a semi-automatic extraction of their statistical properties, using the FracPaQ software. To characterize the water flow into the karst channels, we started from collection of available speleological maps of caves in the study area, in order to assess their main directions of development . From this analysis, some preliminary links were summarized: on the polje ridges, the prevailing discontinuity systems were well correlated with cave development, and, in turn, with the main regional tectonic directions (respectively, the SW-NE anti-Apennine, and the NW-SE Apennine systems). At the polje bottom, on the other hand, direction of cave segments and discontinuities are about similar, following the Canale di Pirro polje main elongation (W-E). This first comparison among data from different sources eventually points out that water flows underground following the main structural lineations. These data, together with results of the groundwater flow model, confirm the key role of geo-structural control on karst development, and the possibility of variations at the local scale, as observed at the polje bottom. In karst, the integrated approach of geo-structural discontinuities and karst features and geometry is therefore a fundamental tool to gain insights into the understanding of the main groundwater flow directions

Understanding of reservoirs in karst: the case of Vora Bosco cave (Salento, Italy)

Vora Bosco Cave is located in the Salento karst peninsula (Apulia, S Italy), surrounded by the Ionian and Adriatic Seas. In this part of Apulia, due to climate change, the typical Mediterranean climate is moving towards arid and semi-arid, with scarce or absent surface runoff. The Salento groundwater is a freshwater lens fluctuating on seawater, entering inland because of intrusion phenomena. The freshwater volume stored in the lens is subjected to both sea level rise and an increasing pressure caused by the high water demand, especially in summer time, for touristic purposes. Therefore, developing an understanding of the hydrogeological dynamics of the karst aquifer can be a useful tool for planning better protection and management actions on Apulian groundwater resources. Vora Bosco cave was instrumented with a multi-parameter probe for groundwater level measurements from November 2017 to July 2018. Thereby, the system behaviour within the cave recharge area can be explored. To characterise and quantify the natural recharge and discharge behaviour of the system, a simple reservoir model was developed and calibrated with the measured data. The model consists of 4 reservoirs, which are filled and emptied using simple discharge equations. The model considers evapotranspiration from the soil, slow flow in the unsaturated and saturated zone, as well as fast flow in the karstic conduits. Daily data of precipitation and potential evapotranspiration are used as model inputs. The model simulates the water level at Vora Bosco and is calibrated by comparison of simulated and measured water level, using the Kling-Gupta-Efficiency as an objective function. Our results reveal that the model simulations show acceptable performance in reflecting the dynamics of the observed water level data. The calibration achieves reasonable results for the model parameters. In addition to the water level simulations, quantifying predictions uncertainty by Monte Carlo approach, it is shown that there is still potential to produce more reliable estimates of future groundwater dynamics, in order to better manage the precious regional groundwater resources