HS8.2.4

Karst groundwater dependent ecosystems (KGDEs) represent an important asset worldwide due to their ecological and socioeconomic values. Although they are increasingly recognized as such, they have not been adequately documented and studied. The present contribution aims at characterizing the main KGDEs of the Dinaric karst in Slovenia. Their classification is based on their position within the hydrological system, geomorphology and ecological settings The main hydrological processes (i.e., extent, duration and frequency of groundwater inflow), the main biota and indicator communities, and the factors limiting the evolution of species (e.g., darkness) were identified. An overview of rare, endemic and charismatic species was also shown including Proteus anguinus, Marifugia cavatica, Monolistra racovitzae racovitzae and others. Due to its location in an area of very high geographical diversity and between different climate types, the Slovenian Dinaric karst is one of the hotspots of subterranean biodiversity on a global scale. The interaction between orographic, climatic, hydrological and edaphic conditions, as well as the fact that the area served as a hub for different species and as a refuge during the ice ages, are crucial for the very high biodiversity in this area. Due to deforestation in prehistoric times, man has even contributed to the diversification of the flora by creating space for the appearance or spread of habitats that are now considered natural (e.g., dry grasslands). An important factor in maintaining a particularly rich diversity of karst flora and fauna is also the low human impact and the very well preserved landscape in its natural state. KGDE sites in Slovenia with the greatest known species diversity are the Postojna-Planina and Škocjanske Jame cave systems, Cerkniško and Planinsko Polje, and the intermittent lakes of Pivka. Characterization of KGDEs is a prerequisite for a better understanding of the processes that control them, their biological function, and their vulnerability. Based on knowledge of how they will change and adapt under current pressures and global challenges from climate, land use, and societal changes, appropriate protection can be built. The ecohydrological characterization of KGDEs of Slovenian Dinaric karst presented here can serve as a pilot study for other karst regions with high biodiversity.

How to cite: Ravbar, N. and Pipan, T.: Ecohydrological characterization of the karst groundwater dependent ecosystems of the Dinaric karst in Slovenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3675, https://doi.org/10.5194/egusphere-egu22-3675, 2022.

Groundwater recharge of mountain aquifer requires detailed knowledge of the hydrologic system and adequate monitoring and modeling methods to determine water amount and water quality evolution. Mountain aquifers are well known of their highly complex lithologic structure and surface morphology. These become more significant in dry climate regions (<300 mm rainfall/year) which are characterized by erratic rain pattern and extreme deep thickness unsaturated zone.

In this study we monitor the isotopic and geo-chemical evolution affecting the composition of the unsaturated porewater during deep infiltration, from surface to depth that is not affected from evaporation. The geo-chemical processes were characterized related to land surface morphology and climate conditions.

The research setup includes instrumentation of first-order stream which is characterized by two main typical geomorphologic setting: rocky terrain and deep soil along the stream channel. Each plot was instrumented with a monitoring setup that include a meteorological station and Vadose Zone Monitoring System (VMS) that enables continuous water content measurement and collection of unsaturated porewater from the vadose zone.

Fast increases in water content and arrival of depleted δ¹⁸O (VSMOW) reveal quick and deep infiltration of rainwater during storm events, while enriched δ¹⁸O arrival indicates slower infiltration of water that is exposed to evaporation. In addition, the geo-chemical processes exhibited depletion in δ¹³C (PDB) of rainwater during the infiltration (-19 to -11 ‰) which indicates on dominant of biogenic activities and relatively low rock-water interactions. Major elements correlation network expresses the contribution of dust and rain to the rock evolution across the water flow path.

The study results clearly exhibited different infiltration rates in each site. Fast infiltration at the rocky terrain due to rock outcrops on the surface create funnels for collecting the local runoff and delivering it into high permeability fractured zones where the water penetrates directly to the deep sections. In contrast, the bare soil areas such as hilltops or man-made terraces in streams with highly developed soil cross-section, reveal limited infiltration. Also, the annual rainfall pattern impacts the geochemical process and finally impacts the groundwater quantity and quality.

How to cite: Letz, O., Siebner, H., Avrahamov, N., Egozi, R., and Dahan, O.: Isotopic and geochemical evolution of rainwater percolating through the rocky outcrops: Judaea mountain case study.  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3926, https://doi.org/10.5194/egusphere-egu22-3926, 2022.

A hydrological model is a simplified representation of the water cycle. A model helps people to understand, predict, and manage water resources. The scope and complexity of the model depend on the modelling goal, availability of required inputs, and computational resources. A wide variety of different hydrologic models exist, which are from simplistic to complex.  Complex models are often computationally very expensive, hampering robust calibration, sensitivity evaluation, and uncertainty analysis. The purpose of this study was to develop a parsimonious distributed land surface-subsurface hydrological model.

The parsimonious model we are developing is a combination of the land surface model V2Karst and a groundwater model that adopts a two-dimensional representation of groundwater flow. V2Karst is a large-scale model for simulating land surface hydrological processes. . The coupled hydrological model can make the simulation steps clearer and meet the simplifying assumptions in some specific demand situations. The model will be useful for robust model calibration, sensitivity tests, and uncertainty analysis.

How to cite: Liu, H. and Rahman, M.: Developing a parsimonious distributed land surface-subsurface hydrological model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5759, https://doi.org/10.5194/egusphere-egu22-5759, 2022.

Starting from previous experiences in karst settings of southern Italy, and following the same procedure for the identification of dolines and endorheic basins (Zumpano et al., 2019; Pisano et al., 2020), we focus here our attention on several dolines characterizing the landscape of the Salento peninsula, in the southernmost part of Apulia. This region shows a typical low-topography karst, with elevations reaching maximum values of about 120 m a.s.l.. Thus, very often the main karst landforms, such as dolines and endorheic basins, are not clear to identify and present subdue connections with the adjoining land. Only at those sites where the doline was produced by collapse of the carbonate bedrock, or of the overburden above it, and where an active swallow hole is present, recognition appear more direct and straightforward.

Nevertheless, it is exactly this difficulty in identification of the karst landforms which makes particularly intriguing the research in the central sector of Salento. Further, in this area one of the two Apulian caves where speleologists are able to directly reach the water table, at depth of -60 m below the ground surface, is located: Vora Bosco opens within a narrow, W-E oriented, fissure in the topographic surface, and develops through the overall stratigraphic succession of Salento, from Quaternary deposits, to Plio-Pleistocene and Miocene calcarenites, down to the Cretaceous limestones, with these latter hosting the water table.

In a 240km²-wide area around Vora Bosco, a systematic survey was carried out aimed at identifying all dolines. The work started from analysis of historical sources, integrated by periodic field surveys, and by detailed analysis of multi-temporal sets of aerial photographs. Several tens of dolines and endorheic basins of variable size were mapped, and distinguished on the basis of the mechanism at the origin of their formation, according to the most widespread international classification (Gutierrez et al., 2014).

In addition to the genetic and morphometric characterization of the identified dolines and endorheic basins, these were also discriminated as concerns the role they play for hydraulic functioning: based upon the local situation, with particular regard to presence and thickness of residual deposits, and to the discontinuity networks in the rock mass, these sites may act as absorption point to recharge the karst aquifer, or as impervious areas which retard the downward infiltration of water.

References

Gutierrez F., Parise M., De Waele J. & Jourde H., 2014, A review on natural and human-induced geohazards and impacts in karst. Earth Science Reviews, vol. 138, p. 61-88.

Parise M., 2019, Sinkholes. In: White W.B., Culver D.C. & Pipan T. (Eds.), Encyclopedia of Caves. Academic Press, Elsevier, 3^rd edition, ISBN 978-0-12-814124-3, p. 934-942.

Pisano L., Zumpano V., Liso I.S. & Parise M., 2020, Geomorphological and structural characterization of the “Canale di Pirro” polje, Apulia (Southern Italy). Journal of Maps, vol. 16 (2), p. 479-487.

Zumpano V., Pisano L. & Parise M., 2019, An integrated framework to identify and analyze karst sinkholes. Geomorphology, vol. 332, p. 213-225.

How to cite: Pisano, L., Francesca, L., Liso, I. S., and Parise, M.: Geomorphological analysis of dolines in a low-topography karst, and considerations about their hydraulic functioning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2372, https://doi.org/10.5194/egusphere-egu22-2372, 2022.

Spatial characterization of the hydraulic properties in the subsurface is an extensively studied problematic. Inverse problems allow to image those properties by interpreting the information from a dataset of field measurements with a chosen physical formulation of fluxes in a numerical distributed model. However, karst media characterization remains a complex task, due to the fact that the matrix and conduits entities generate a highly contrasted distribution of property values. Furthermore the matrix and conduits compartments respond to different flow physics that can be approached by considering Darcy flow and pipe flow, respectively. Thus, one needs to employ a multi-physics model, an inversion method able to capture the properties contrast, and also to use data providing information on the localization of the conduits network and its connectivity.

We propose a large-scale 2-D application of characterization of the Lez aquifer in southern France, covering a surface of about 250 km². We take advantages of long-terms measurements within the framework of the MEDYCYSS observation site, part of the Karst observatory network (www.snokarst.org) initiated by the French institute INSU/CNRS. Drawdown signals measured in 11 wells and incorporating a periodic response due to a daily pumping at the aquifers spring were thus considered to identify the location of the conduit network. The periodic responses can provide connectivity information between wells in the inversion process, while non-periodic responses permit to better assess the large-scale property values of the whole aquifer. A Cellular Automata-based Deterministic Inversion (CADI) is used to generate a contrasted property field able to reproduce the measured signals in the 2-D distributed numerical model solving Darcy flows. However, pressure data alone remain limited to characterize the fast flows that can occur in the conduits network. Thus, the flow velocities in the preferential flow paths located with the pressure data are then reconstituted by inverting a set of different tracer tests responses at the Lez spring, considering this time a pipe flow physics in the model.

How to cite: Fischer, P., Jourde, H., and Leonardi, V.: Large-scale spatial reconstitution of pressure and tracer tests responses in a karst aquifer (Lez aquifer, France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2628, https://doi.org/10.5194/egusphere-egu22-2628, 2022.

Poljes are flat closed depressions in karst terrains that are prone to regular flooding. The strongest floods can be several meters high and persist for months, making significant damages in infrastructures. To predict how climate change might affect the occurrence, amplitude and duration of the flood, a better understanding of the flooding dynamics is necessary. Among others, the computation of the water balance is a prerequisite. This method allows assessing when the polje will begin to flood, and gives information on the maximum water level potentially reached. However, this technique encounters the difficulty that a notable part of the inflow entering in poljes is generally ungauged, while it is challenging to quantify the outflow. This is because numerous springs and ponors activate only temporary with the rise of the water level. Moreover, many poljes are generally poorly monitored due to financial reasons. This work aims to see whether these drawbacks can be overcome. To this end, a typical Dinaric polje recharged by a combination of allogenic inflow and a rise of the regional groundwater level is equipped with a network of several measuring stations installed over its surface and in the nearby water-active caves. Combining an accurate Lidar of the surface with recorded water levels and inflow of the main two springs made possible to evaluate the polje flooding dynamics and to characterize its water balance. The method is able to quantify the polje total inflow, while an estimation of the outflow is presented. Then, the main ungauged signals affecting flooding are identified and separated. These values are used as input and calibration data in a numerical model aiming to reproduce the flood dynamics of the polje and its surrounding aquifer. Modelling results validate both water balance and conceptual hydrogeological model, and justify the significance of installing a network of several hydrological stations to monitor the poljes. The method can be applied to other poljes flooding in a complex way of superimposed input and output signals.

How to cite: Mayaud, C., Kogovšek, B., Gabrovšek, F., Blatnik, M., Petrič, M., and Ravbar, N.: Assessment of the water balance of a Dinaric karst polje (Planinsko Polje, Slovenia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4866, https://doi.org/10.5194/egusphere-egu22-4866, 2022.

The Nadìa spring is the second largest tapped spring in the Emilia Romagna Region (northern Italy), representing a strategic local source of drinking water, also in the perspective of future global changes. The spring flowrate ranges between 65 l/s in the recharge season and 45 l/s at the end of the low-flow season, when most of the other tapped springs in the region have flowrates lower than 5 l/s. Geological, geomorphological, hydrological and geochemical investigations were carried out in the spring watershed to unravel the factors causing this peculiarly high discharge. The spring arises at the base of a calcarenitic fractured aquifer (Pantano Formation, upper Burdigalian-lower Langhian) underlain by lower permeability units. Karst dissolution along structural discontinuities in the Pantano Formation has been suggested in the past as a possibility to account for the aquifer high permeability resulting in the high spring discharge. A continuous monitoring of the spring flowrate, temperature, electric conductivity and pH was conducted during the 2020-2021 hydrologic year. Hydrographs and chemographs indicated atypical karst flow dynamics. The time to halve the peak-discharge of the spring is between 20 and 50 days, lower than that of most springs of the Northern Apennines (> 50 days). This implies a higher average aquifer flow rate (around 10 m/day) compared to that typical of arenitic or turbiditic aquifers (around 1 m/day). Spring water samples collected once to twice a year since 2011 for the analysis of major ions revealed an obvious calcium-bicarbonate hydrochemistry that is consistent with the hypothesis of karst dissolution. However, the chemical variability over time expected in a karst system due to the drainage of different groundwater fractions (newly infiltrated vs. older groundwater) was not observed. Instead, the water chemical composition was exceptionally constant over time, suggesting that drainage occurs from a large, homogeneous reservoir. Water stable isotopes have been analyzed in 2021 revealing a composition close to that of the local winter precipitations and suggesting exceptional stability of the spring water composition over different seasons. An 80 m deep borehole has been drilled in the Pantano Formation 7 km away from the spring, documenting the occurrence of fractures with decimetric apertures as deep as 60-70 m below ground surface, which may be interpreted as the result of karst dissolution. In addition to the debatable karst aquifer hypothesis, geomorphological observations indicate the occurrence of depressed areas, of likely tectonic origin, in the aquifer overlying the spring, which may provide a favorable setting for concentrated infiltration and groundwater recharge. However, the hypothesis of concentrated recharge is in apparent contrast to the abovementioned stability of spring water chemical composition over time. A volume of the aquifer representing a reasonable reservoir for the spring has been identified based on spring flow recession analysis and a geo-structural model of the Pantano outcrop up-gradient to the spring. The structural-stratigraphic setting of the hypothesized reservoir includes the occurrence of fault-related fractures that cross-cut the low-dipping bedding of the calcarenites, possibly enhancing the local permeability and the drainage towards the Nadìa spring.

How to cite: Filippini, M., Segadelli, S., Failoni, M., Stendardi, F., Vignaroli, G., Viola, G., Stumpp, C., Dinelli, E., and Gargini, A.: Hydrogeological, geochemical and structural features of the aquifer feeding the Nadìa spring: an "oasis in the desert" of the Northern Apennines (Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2297, https://doi.org/10.5194/egusphere-egu22-2297, 2022.

In karst catchments, groundwater is generally drained from recharge zones towards main outlets (springs). Karst systems develop mainly in limestone and have three different porosities which are the result of sedimentation, diagenesis, tectonics but also dissolution that generate the conduits.  Continuous monitoring at high temporal resolutions is largely used to characterize the hydrodynamic behavior and variability of karst systems hydrological functioning Hydrologic models are used in order to better asses the functioning of karst systems but can also help identifying the impact of global change on water resources. Though these models require an adequate representation of main heterogeneities and processes, the heterogeneity of karst systems is often poorly characterized by available data. For these reasons, most of hydrological models considered for the understanding of karst systems hydrodynamic are lumped parameters models. In this study, we simulate precipitation-discharge relationship as a function of different karst geometries and topologies using two dimensional distributed models. We then investigate the relationship between the hydrodynamic response (e.g. flow rate at discharge point) and topology of the karst conduit network. Lumped approaches are later on compared to distributed models in term of predicting hydrodynamic response to precipitation.

How to cite: Aliouache, M., Jiang, C., and Jourde, H.: Relationship between the hydrodynamic response and the geometrical and topological properties of the karst conduit network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2785, https://doi.org/10.5194/egusphere-egu22-2785, 2022.

The Mediterranean coastline presents a high number of marine caves of different types. Marine caves are protected by the EU Habitats Directive (92/43/EEC - code 8330). Semi-dark and dark cave communities have been included in two Action Plans by UNEP-MAP-RAC/SPA (2008 and 2015 respectively) and are considered as sensitive reservoirs of biodiversity requiring protection. However, the scientific community still has scarce information about these important habitats, that are listed as Data Deficient.

The main reason for the lack of knowledge about marine caves is that they are very difficult to access and study. Lack of a breathable source, lack of light and a physical ceiling are the hazards characterising any underwater cave; specific locations can force cave divers to deal with limited visibility, restricted passages or high water flow. The number of individuals with the skills required to safely navigate such caves while carrying out research or scientific work is extremely limited.  

Our project aims at closing this information gap, by providing a methodology for surveying underwater caves. Our main study area is the Gulf of Orosei, Sardinia Italy. We count essentially on two important elements: 

• citizen science - over the years, we gained a lot of experience in coordinating groups of volunteers, working with professional scientists to achieve common goals. All our projects and missions are carried out with the precious involvement of skilled individuals that perform specific tasks.
• advanced technology - technology is essential to gather information about underwater environments in general, and caves in particular. Photogrammetry is the most detailed methodology to create a multidimensional cave model. Thanks to the precision and the very realistic representation of the environment, these models are ideal for both scientific and dissemination purposes. Photogrammetry relies on the connection between polygon line survey and photographic data. We can split the procedure in three parts: data collection (survey and media), software processing and model refinement. Once the model is finished, there are many useful applications that can be considered. For scientific purpose, the model can be geo-referenced and can be scaled and calibrated by a variety of methods to allow measurements and further analysis of the cave environment and surrounding landscape. For publication purposes to the wider public, the model can be exported to graphical design or ‘animated’ with VR and gaming softwares. Annotating the model and any artifact inside it with information can entertain and educate the visitors in virtual reality.

Possibilities are endless and to fully master the flow from data capture inside the cave down to an interactive virtual representation or a scientific survey, a lot of expertise and knowledge is required and a strong cooperation between cave divers and researchers.