Isotopic, hydrochemical and hydrological methods and models to investigate the function of Ziria-Kefalari karstic system, northern Peloponnese, Greece
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Date
2025-06-16
Authors
Νάνου, Ελένη-Άννα
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Abstract
Karst aquifers constitute a critical component of global freshwater resources but are highly susceptible to contamination, over-extraction, and climate variability. Their inherent heterogeneity, characterized by complex porosity, permeability, recharge, storage, and discharge mechanisms, necessitates a multidisciplinary approach for effective assessment and management. This dissertation investigates the hydrogeological functioning of the Ziria karst groundwater system in northern Peloponnese, Greece, through an integrated framework combining isotopic, hydrochemical, and hydrological analyses with numerical modeling to evaluate groundwater dynamics, recharge processes, vulnerability, and the influence of tectonics on karstification.
An extensive hydrochemical monitoring program was implemented, incorporating time-series analyses of major ion concentrations, stable isotopes, and saturation indices from selected springs and boreholes. Results delineated two distinct hydrochemical facies (Ca-HCO₃ and Ca-Mg-HCO₃), indicative of different recharge areas and flow pathways. Cluster analysis confirmed the existence of multiple groundwater sources, with the regional geological setting exerting a significant influence on hydrochemical evolution, while stable isotope signatures (δ¹⁸O and δ²H) identified recharge elevations ranging from 1,450 to 2,000 meters. Hydrodynamic monitoring revealed that the Stymphalian Spring Front, the primary discharge outlet of the system, exhibits pronounced seasonal variability in flow rates, while its immediate response to rainfall events underscores the mature karstification state of the aquifer.
To quantify recharge, the APLIS and modified APLIS methods were applied to determine the most suitable approach for karst aquifer assessment. Although both methods produced comparable mean annual recharge estimates (42.7% and 41.4%, respectively), spatial distribution differences were evident. The modified APLIS methodology emerged as the more accurate and reliable approach due to its integration of permeability assessments, enhancing the precision of recharge estimations. Recharge rates peaked at 85% in the highly permeable bare limestone outcrops of Mount Ziria, whereas lower rates were recorded in less permeable formations. Numerical simulations using the VarKarst model, calibrated with observed discharge data, further confirmed the temporal variability of recharge zones, which ranged from 46.3 to 62.1 km² over the hydrological years 2017–2018 and 2018–2019.
A comprehensive vulnerability assessment was conducted through a comparative analysis of two widely employed vulnerability mapping methodologies, COP and PaPRIKa, to evaluate their applicability in the study area. Both methods were utilized to generate a hybrid vulnerability map through geospatial and statistical analyses. COP predominantly classified the study area as having Low to Very Low vulnerability, whereas PaPRIKa identified Moderate vulnerability as the dominant category, suggesting a higher sensitivity to karst-specific characteristics. To mitigate potential biases in PaPRIKa, a single-parameter sensitivity analysis was performed, leading to adjusted weighting factors and the development of a modified version, PaPRIKa-Mod. A quantitative comparison of all three methodologies highlighted varying degrees of concordance, with PaPRIKa and PaPRIKa-Mod demonstrating the highest consistency, reinforcing their methodological robustness. In contrast, COP exhibited lower but still notable agreement with both versions of PaPRIKa, indicating their potential for integration and complementary application in karst vulnerability assessments. The resulting hybrid vulnerability map, derived from the synthesis of overlapping classifications, significantly improved the reliability of groundwater risk evaluations.
Additionally, this dissertation adopted a dual-method approach, integrating stereoscopic aerial photograph analysis with GIS-based hill-shading to enhance the detection and mapping of lineaments within the Ziria karst system. This combined methodology identified 1,214 lineaments, revealing structural and erosional features that would have remained undetected using a single technique alone. Field validation at selected sites confirmed that many of the identified lineaments corresponded to fault or fracture systems, with a predominant NNW-SSE orientation observed across multiple datasets. To further assess structural connectivity, a Fracture Network Analysis was conducted at both regional and outcrop scales. The results demonstrated higher connectivity and complexity at the outcrop scale, characterized by a greater frequency of branching (Y) and intersection (X) nodes, compared to the more isolated features at the regional scale.
A detailed karst landform inventory identified 325 karst depressions, of which approximately 62.5% were directly associated with mapped lineaments. The remaining depressions, while not in direct contact with lineaments, were predominantly situated in areas of high lineament density, indicating an indirect structural influence on their formation. The identified lineaments were subsequently utilized to refine the boundaries of the karst aquifer through the exclusion of crystalline metamorphic bedrock, and to enhance groundwater vulnerability and recharge assessments.
The findings of this dissertation underscore the crucial role of structural controls in shaping karst hydrogeological systems and provide a robust framework for assessing key hydrological processes. The integration of advanced hydrochemical, numerical, and geospatial methodologies offers valuable insights into groundwater resource management, particularly in tectonically active karst environments. These results contribute to the development of more effective strategies for groundwater protection, sustainable management, and policy implementation in vulnerable karst aquifer systems.
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Keywords
Karst, Groundwater resources, Vulnerability assessment, Recharge estimation, Spring discharge, Tectonic analysis, Hydrochemical monitoring