Characterization of thermal karst aquifers in Hungary using natural tracers
2 Nucfilm GmbH, Schweiz
3 Abteilung der Atomphysik, Eötvös Loránd Universitaet
4 KIT Institut für Angewandte Geowissenschaften
P 8.2 in Isotope and tracer methods in hydrogeology
Considerable parts of the global thermal water resources are hosted in carbonate rocks (Goldscheider et al., 2010), also in Hungary, where many of these reservoirs are characterized by natural thermal water discharge, usually at the boundary of outcropping carbonates and adjacent sedimentary basins. These regional discharge areas are favourable sites for the development of hypogenic caves as well. This study summarizes the results of geochemical studies in three thermal karst areas in Hungary, focusing on natural tracers.
The Buda Thermal Karst is situated in the capital city of Hungary. The waters of the three distinct discharge areas within the city are characterized by different temperature and chemical composition: in the North only lukewarm waters (18-24°C, 570-690 mg/l TDS), in the central discharge area both lukewarm (20-35°C, 770-980 mg/l TDS) and thermal waters (40-65°C, 800-1350 mg/l TDS), in the South only thermal water discharge (33-43°C, 1450-1700 mg/l TDS) occur. Radionuclides helped to identify mixing of fluids and to infer the temperature and chemical composition of the end members for the central discharge area. For the southern discharge zone mixing components could not be identified, which suggests different cave formation (Erőss et al., 2012).
The Bükk region in the northeastern part of Hungary is one of the largest karst areas of the country. Owing to the complex geological and structural build-up, the area is largely compartmentalized. Majority of the waters is low mineralized (TDS < 600 mg/l) regardless of their temperatures (8–77 °C). This may indicate deep but relatively short flow paths which might be the consequence of the close vicinity of recharge and discharge areas and their considerable elevation difference (500–600 m). Some thermal wells are characterized by higher TDS (1000-2500 mg/l) and radium content (400-1900 mBq/l). Since these thermal wells are related to hydrocarbon exploration, the elevated radium and TDS content might be explained by the effect of hydrocarbon reservoir fluids (Erőss et al., 2015).
The Villány Thermal Karst area is situated in the southern part of Hungary. Majority of the springs is characterized by lukewarm waters (20-26°C) with 712-930 mg/l TDS. Natural thermal water discharge (52-62°C, 1100 mg/l TDS) occurred only in Harkány, as a marshland. The sulphur and CO2 content of these thermal waters may indicate the influence of the adjacent sedimentary basin.
The National Research, Development and Innovation Fund has provided financial support to the project in Villány under the grant agreement no. PD 116227. The research in the Bükk area was supported by the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TÁMOP-4.2.4.A/ 2-11/1-2012-0001 National Excellence Program. The Buda Thermal Karst research was funded by Shell International E&P and by the Hungarian Scientific Research Fund under the grant agreement no. NK 101356.
ERŐSS, A., MÁDL-SZŐNYI, J., SURBECK, H., HORVÁTH, Á., GOLDSCHEIDER, N., CSOMA, A.É. (2012): Radionuclides as natural tracers for the characterization of fluids in regional discharge areas, Buda Thermal Karst, Hungary. - J. Hydrol. 426-427:124-137.
ERŐSS, A., SURBECK, H., CSONDOR, K., HORVÁTH, Á., MÁDL-SZŐNYI, J., LÉNÁRT L. (2015): Radionuclides in the waters of the Bükk region, Hungary. - J Radioanal Nucl Ch 303(3): 2529-2533.
GOLDSCHEIDER, N., MÁDL-SZŐNYI, J., ERŐSS, A., SCHILL, E. (2010): Review: Thermal Water Resources in Carbonate Rock Aquifers. - Hydrogeol J 18(6): 1303-1318.