Project

Evaluation of hypogenic karstification focusing on the microbially mediated processes

Goal: Goals of the Project:
1. Characterization of the different hypogenic karst formation processes and evaluation of their controlling factors in regional groundwater flow system context.
2. Understanding the role and activity of microbes in the recognised special environment, as well as their relation and adaptation to the elevated radioactivity.
3. Adaptation of the understanding of recent cave forming processes to the evaluation of palaeo caves.
4. Extension and generalization of the results for similar settings worldwide.

The research hypotheses and the goals of the project display complexity involving wide range of processes, therefore multidisciplinary approach is essential and crucial to accomplish the
project’s purposes. Groundwater flow systems are responsible for the generation of hypogenic karstification, and the associated mineral precipitation in regional to local scale. Therefore hydrogeology denotes the main topic of the project complemented by diagenetic and speleogenetic studies. Iron and manganese hydroxide precipitates are key local discharge features both in the understanding of the role of microbes in hypogenic speleogenesis and in the radioactivity of springs, as well. Therefore microbiology ensures the second, while nuclear physics the third priority of the project. Examination of iron hydroxide precipitates requires special chemical analytics, namely
Mössbauer Spectroscopy. The evaluation of the processes and products connected to the microbes is only possible in micro to nano scales, and consequently requires the use of scanning electron
microscope.

This project is supported by the Hungarian Research Fund (NKFI) NK 101356.

Methods: Water Microbiology, Radium, Hypogenic Caves, Biomineralization, Fluid Inclusions, Diagenesis, Numerical Simulation, Geogenic acids, Dissolution kinetics, Mixing corrosion, Epigenic Caves, Paleocaves

Date: 1 March 2012 - 28 February 2017

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Judit Mádl-Szőnyi
added a research item
A Gram-stain-negative, aerobic, non-motile and coccus-shaped bacterium, designated strain FeSDHB5-19T, was isolated from a biofilm sample collected from a radioactive thermal spring (Budapest, Hungary), after exposure to 5 kGy gamma radiation. A polyphasic approach was used to study the taxonomic properties of strain FeSDHB5-19T, which had highest 16S rRNA gene sequence similarity to Deinococcus antarcticus G3-6-20T (96.5 %). The 16S rRNA gene sequence similarity to type strains of other Deinococcus species were 93.0 % or lower. The DNA G+C content of the draft genome sequence, consisting of 3.9 Mb, was 63.9 mol%. Strain FeSHDB5-19T was found to grow at temperatures of 10-32 °C (optimum, 28 °C) and pH 5-10 (pH 6.5-7.5) and tolerated up to 1.5 % NaCl (w/v) with optimum growth at 0-0.5 % NaCl. The predominant fatty acids (>10 %) were C16 : 0 and C16 : 1ω7c. The cell-wall peptidoglycan type was A3β l-Orn-Gly1-2. The whole-cell sugars were glucose and low amounts of galactose. Strain FeSDHB5-19T possessed MK-8 as the predominant respiratory quinone, typical of the genus Deinococcus. The polar lipid profile contained unidentified phosphoglycolipids and unidentified glycolipids. The isolate was found to be highly resistant to gamma (D10<8 kGy) and UV (D10~800 J m-2) radiation. According to its genotypic, phenotypic and chemotaxonomic characteristics, strain FeSDHB5-19T represents a novel species in the genus Deinococcus, for which the name Deinococcusfonticola sp. nov. is proposed. The type strain is FeSDHB5-19T (=NCAIM B.02639T=DSM 106917T).
Judit Mádl-Szőnyi
added a research item
The thermal waters of Gellért Hill discharge area of the Buda Thermal Karst System (Hungary) are characterized by high (up to 1000 Bq/L) 222 Rn-activity due to the radium-accumulating biogeochemical layers. Samples were taken from these ferruginous and calcareous layers developed on spring cave walls and water surface. Accumulation of potentially toxic metals (e.g. As, Hg, Pb, Sn, Sr, Zn) in the dense extracellular polymeric substance containing bacterial cells and remains was detected by inductively coupled plasma mass spectrometry. The comparison of bacterial phylogenetic diversity of the biofilm samples was performed by high throughput next generation sequencing (NGS). The analysis showed similar sets of mainly unidentified taxa of phyla Chloroflexi, Nitrospirae, Proteobacteria, Planctomycetes; however, large differences were found in their abundance. Cultivation-based method complemented with irradiation assay was performed using 5, 10 and 15 kGy doses of gamma-rays from a 60 Co-source to reveal the extreme radiation-resistant bacteria. The phyla Actinobacteria, Firmicutes, Proteobacteria (classes Alpha-Beta-and Gammaproteobacteria), Bacteriodetes and Deinococcus-Thermus were represented among the 452 bacterial strains. The applied irradiation treatments promoted the isolation of 100 different species, involving candidate novel species, as well. The vast majority of the isolates belonged to bacterial taxa previously unknown as radiation-resistant microorganisms. Members of the genera Paracoccus, Marmoricola, Dermacoccus and Kytococcus were identified from the 15 kGy dose irradiated samples. The close relatives of several known radiation-tolerant bacteria were also detected from the biofilm samples, alongside with bacteria capable of detoxification by metal accumulation, adsorption and precipitation in the form of calcium-carbonate which possibly maintain the viability of the habitat. The results suggest the establishment of a unique, extremophilic microbiota in the studied hydrothermal spring caves.
Petra Kovács-Bodor
added a research item
Buda Thermal Karst (BTK) in Hungary is an active hypogenic karst system, characterized by various discharge features like thermal and lukewarm springs, hypogene caves, different chemical and biogeochemical precipitates. Though the physicochemical characteristics of the springs in the Southern Discharge Area of BTK are similar, the morphology and diversity of the bacteria of the biofilms are different. Biogeochemical precipitates have distinct colours (reddish brown, dark grey, brown), which is indicative of the different physical and chemical properties. The goals of the study were to identify the physical and chemical properties of the biogeochemical precipitates and whether there is a connection between the chemical composition or physical parameters (flow velocity) of the water and the characteristics of these precipitates. The precipitates were analysed by gamma spectroscopy and mass spectrometry. Parallelly the field parameters, major ions, trace elements and radionuclides were measured in spring waters It was found that the field parameters and the concentration of major ions are similar of the studied spring waters, but the trace element and radionuclide content is different. The distinct colour biogeochemical precipitates indicate different main adsorbed component (Fe in red, Mn in dark ones). The radionuclide content of the precipitates is also different and because of that, the 222Rn content of spring waters. The main differences between the studied precipitates can be the consequence of the microchemical deviations between the spring waters and the different flow kinetics. The research was supported by the European Union and the State of Hungary, co- by the European Regional Development Fund in the project of GINOP-2.3.2.-15-2016- 00009 'ICER'.
Judit Mádl-Szőnyi
added a research item
Organic and inorganic precipitates are both characteristic in the active hypogenic karst area of Buda Thermal Karst in Hungary. As an active system, it is a good natural laboratory to study ongoing precipitation processes. Because of anthropogenic influence and the complexity of spring environments, it is challenging to reveal all the governing factors in the process of precipitation. In situ experiments, i.e. artificially controlled natural systems simplify the complexity by adding, excluding or stabilizing influencing parameters during the experiment. CO2 degassing drives changes in the physicochemical parameters of spring waters from the discharge along their flow path. The rate and spatial extension of these changes depend on local hydrogeological, geological, climatic, topographical etc. factors, affecting precipitation processes. In this study, two one-day-long in situ experiments were executed to examine the physicochemical parameter changes of thermal water in a tunnel. The integration of the results with reactive transport models revealed the physicochemical processes of ingassing and degassing and predicted CaCO3 precipitation along the flow path. Small-scale roughness of the channel surface seemed to further influence pH and concentration of HCO3−. After 6 weeks of thermal water flowing, organic precipitate (biofilm) formed close to the discharge and then, with a sharp change, inorganic precipitate (calcite) dominates a bit further from the discharge. In situ experiments and connected numerical simulations revealed the role of CO2 degassing and calcite precipitation in the changes of physicochemical parameters, but organic precipitates also have to be considered near the discharge.
Judit Mádl-Szőnyi
added 2 research items
The Buda Thermal Karst area, in central Hungary, is in the focus of research interest because of its thermal water resources and the on-going hypogenic karstification processes at the boundary of unconfined and confined carbonates. Understanding of the discharge phenomena and the karstification processes requires clarification of the groundwater flow conditions in the area. Accordingly, the aim of the present study was to present a hydraulic evaluation of the flow systems based on analyses of the archival measured hydraulic data of wells. Pressure vs. elevation profiles, tomographic fluid-potential maps and hydraulic cross sections were constructed, based on the data distribution. As a result, gravitational flow systems, hydraulic continuity, and the modifying effects of aquitard units and faults were identified in the karst area. The location of natural discharge areas could be explained and the hydraulic behavior of the Northeastern Margin Fault of the Buda Hills could be determined. The flow pattern determines the differences in the discharge distribution (one- and two-component) and related cave-forming processes between the Central System (Rózsadomb area) and Southern System (Gellért Hill area) natural discharge areas. Among the premises of hypogenic karstification, regional upward flow conditions were confirmed along the main discharge zone of the River Danube.
Judit Mádl-Szőnyi
added 2 research items
Reliability is the greatest concern in recent karst vulnerability assessments. Checking the validity of results and understanding the operation of karst systems are therefore the most promising areas for improvement. We report an application of the Slovene Approach to a test site in the Gömör-Torna Karst of Hungary and Slovakia. The resource vulnerability map provided an appropriate result and showed that the overlying sediments and thicker soil may effectively decrease the vulnerability of this unconfined area. The source vulnerability of the Kis-Tohonya Spring was evaluated for the purposes of protection zoning. The results of long-term hydrograph and recession curve analyses were helpful in understanding the functioning of the Kis-Tohonya Spring and the karst system. The importance of the different regimes contributing to the slow and fast flow of the spring under different hydrological conditions was shown. Ongoing research aims to feed these results back into the source vulnerability assessment of the spring.
The Molnár János Cave is part of the northern discharge area of the Buda Thermal Karst System, and is the largest active thermal water cave in the capital of Hungary. To compare the prokaryotic communities, reddish-brown cave wall biofilm, black biogeochemical layers, and thermal water samples from the phreatic mixing zone of the cave were subjected to three investigative approaches, scanning electron microscopy, cultivation, and molecular cloning. According to the SEM images, multilayer network structures were observed in the biofilm formed by iron-accumulating filamentous bacteria and mineral crystals. Cultivated strains belonging to Aeromonadaceae and Enterobacteriaceae were characteristic from both water and subaqueous biofilm samples. The most abundant molecular clones were representatives of the phylum Chloroflexi in the reddish-brown biofilm, the class Gammaproteobacteria in the black biogeochemical layer, and Thiobacillus (Betaproteobacteria) in the thermal water samples. The reddish-brown biofilm and black biogeochemical layer’s bacterial communities proved to be somewhat more diverse than that of the thermal water. The archaeal 16S rRNA gene clone libraries were dominated by thermophilic ammonia-oxidizer Nitrosopumilus and Nitrososphaera phylotypes in all three habitats. Considering the metabolic characteristics of known species related to the detected clones, it can be assumed that these communities may participate in the local sulfur and nitrogen cycles and may contribute to microbial mediated sulfuric acid speleogenesis. © 2017, National Speleological Society Inc. All rights reserved.
Timea Havril
added 2 research items
Numerical simulations have provided new insights into the processes controlling fluid flow and heat transport within the deep and thick carbonate system of the Buda Thermal Karst, which can be considered as a pilot area to examine the importance of these driving forces. Different model scenarios of four cases were tested to represent snapshots of the fluid evolution and heat distribution of the system, from the fully confined carbonate stage in the Late Miocene through to partly and completely unconfined conditions (over the left Buda block), the latter representing the recent situation. The effect of changes in different parameters of the numerical model on the potential field and temperature distribution were examined. The conceptual evolution of groundwater flow and thermal energy transport within the Buda Thermal Karst System was simulated in the 2D vertical plane using the Heatflow-Smoker finite element model (Molson and Frind 2014) which couples groundwater flow and density-dependent heat transport. The preliminary results highlight the effects of paleo-recharge and cover formations on heat distribution and dissipation. In most cases, conditions led to strong thermal convection cells which might have played an important role in system evolution. The results should later contribute to a better understanding of hypogene karstification, and utilization of geothermal resources and hydrocarbon resources of deep carbonate systems. The research is supported by the Hungarian Research Fund NK 101356. Extended abstract is downloadable here: http://earthdoc.eage.org/publication/publicationdetails/?publication=80123
Ádám Tóth
added a research item
Carbonate regions have great economic importance for water supply, oil and gas reservoirs, geothermal fluids and also Mississippi Valley-type ore deposits. Therefore, the understanding and consequences of flow pattern in carbonates require special interest. The hypogene and epigene karst areas of carbonate sequences were distinguished and associated with different orders of groundwater flow. However, the effect of confinement on flow pattern of carbonate aquifers was not fully considered in previous studies. We demonstrated the most important prerequisites and consequences of the application of the gravity-driven regional groundwater flow concept for carbonate sequences at different degrees of confinement. The results put into a frame the distribution of different springs and caves (epigene and hypogene) of the carbonate system of the Transdanubian Range, Hungary, and provide insights for better understanding of the hydrogeology of areas with similar unconfined and confined settings. Relationship among different flow regimes, distribution and character of springs and hypogene karstification processes, in addition to natural discharge-related phenomena, such as mineral and microbial precipitates, were recognized in the area of Buda Thermal Karst. This area is a natural laboratory where the connection between groundwater flow and karstification processes can be studied.
Ádám Tóth
added a research item
The goal of the study was the evaluation of regional pressure regimes for different regions of confined carbonates and understanding the influence of pressure conditions on geothermal exploration. The confined basement carbonate region with its adjacent unconfined part and siliciclastic confining strata were examined based on the application of the hydrodynamic approach. The research could reveal different pressure regimes for the study area of the Paleogene Basin, Hungary. The location of these regimes depends on the elevation of basement carbonates, the structures and thickness, hydraulic conductivity and the heterogeneity of the covering layers. The effects of gravity-driven regional groundwater flow systems were proven down to an elevation of-500 m asl including recharge and discharge areas. Down to this elevation, both vertical and horizontal hydraulic communication exist. This area is characterized by close to hydrostatic pressure conditions. Nevertheless, a hydraulic boundary (a colinear ridge in the north and sink in the south) was delineated in the study area. This impedes horizontal hydraulic communication between the shallower unconfined-confined carbonates in the west and the deeper confined carbonates in the east. Below-500 m asl elevation southeast through-flow can be observed, terminating in a regionally underpressured zone caused by the presence of a regional aquitard in the uplifted eastern region. Both underpressured and overpressured blocks determined by faults were found to influence vertical connections between siliciclastic confining layers and carbonates in the vicinity of a significant strike-slip fault. The differently pressurized regions (underpressured, close-to hydrostatic and overpressured) influence the geothermal exploration possibilities of the basement carbonates (production and injection).
Ádám Tóth
added a research item
This study examines the patterns of groundwater flow and salinity in a region of confined basement carbonate aquifer along with the region's unconfined adjacent part and siliciclastic confining strata. An understanding of regional-scale flow patterns in this setting may prompt a rethinking of the traditional view. According to that view confined carbonates are bounded and isolated by impermeable confining layers from their surroundings. A basin-scale analysis of the subsurface conditions promises better to accentuate otherwise unseen signs of hydraulic communication both horizontally and vertically between different parts of the flow domain. This study reveals that various flow regimes exist, in the area of the Paleogene Basin, Hungary. The pattern and intensity of these flow regimes depend on the elevation of basement carbonates and the structures, thickness, hydraulic conductivity and heterogeneity of the covering layers. Effects of gravity-driven regional groundwater flow were identified down to an elevation of −500 m asl including recharge and discharge areas. Hydraulic communication occurs both vertically and laterally in this zone but the direction and intensity of flow are influenced by aquitards or confining layers. Nevertheless, a hydraulic boundaries (a colinear ridge in the north and a sink in the south) was recognized in the study area. This impedes horizontal hydraulic communication between the shallower unconfined-to confined carbonates in the west and the deeper confined carbonates in the east. Southeasterly through-flow can be observed below −500 m asl elevation which terminates in a regionally underpressured zone due to a regional aquitard in the zone of uplift. Both underpressured and overpressured blocks bounded by faults appear to influence vertical connections between siliciclastic confining layers and carbonates in the vicinity of significant strike-slip faults. The flow regimes thus recognized affect the subsurface salinity pattern, and hydrocarbon migration and as a result the planning of geothermal exploration. Consequently, a priori assumption of impermeability of confining layers and hydraulically isolated carbonate compartments below seems to be an oversimplification.
Petra Kovács-Bodor
added 8 research items
The Rózsadomb area is one of the three main discharge areas of the Buda Thermal Karst. Here both warm (>36,7°C) and lukewarm (20 – 36,7°C) springs arise. It is an important area from both a theoretical, and a practical point of view to understand the temporal changes of the physic–chemical parameters of lukewarm waters. The warm springs are fed by regional flow systems, while the lukewarm waters are originated from intermediate flow systems. The exact recharge area of these intermediate flow systems is not known, presumably the water infiltrates through the open karst surfaces in Pilis and Buda Hills. The effect of River Danube and precipitation are the two main influential factors of the groundwater and the springs in this area. The aim of the study was to analyze the changes of the physico-chemical parameters (temperature, volume discharge, pH, electric conductivity) of the lukewarm springs and the influence of precipitation and the River Danube. Furthermore, the effect of precipitation was analyzed in the theoretical recharge area of the lukewarm waters. Correlation-and cross correlation analyses were used to study the relationship between the two influential factors and the parameters of the lukewarm springs. The effect of precipitation on the karst water level in the theoretical recharge area was studied in six wells based on dynamic factor analysis.
Ádám Tóth
added a research item
The vulnerability of carbonate systems is basically determined by their confinement (Mádl-Sz˝ onyi and Füle 1998). Confined carbonate units are traditionally considered to be aquifer systems hydrodynamically independent of their siliciclastic cover and unconfined parts. This is due to the widely accepted view, that confining layers are generally impermeable relative to the underlying carbonate aquifers. The nature of how deep confined carbonate units are linked to unconfined gravity-driven regional groundwater flow (GDRGF) is poorly understood. The very first study of Mádl-Sz˝ onyi and Tóth (2015) examined the flow systems for unconfined and for marginal areas of confined carbonate settings and adapted the Tóthian-flow pattern for unconfined and adjoining confined cases. The modified GDRGF pattern with considering further driving forces (such as buoyancy) was used as a working hypothesis for the numerical understanding of evolution of hydrodynamics of marginal areas of unconfined and confined carbonate aquifer systems by Havril et al. (2016). In the recent study the main aim is the application of the GDRGF concepts to confined deep carbonates. Here the focal point is the handling of the karstified carbonate rock matrix and its siliciclastic cover as a whole. If we simplify the problem we can focus on to reveal the hydrodinamically interacted or insulated nature of confined carbonate systems. Beside hydrodynamic character of an area the salinity pattern can also reflect the potential connections. The interpretation of salinity in the context of GDRGF hydrodynamics therefore can assist in the determination of replenishment of formation waters with meteoric infiltration and can help to understand the flow pattern of the system. These hydrodynamic interactions also determine the vulnerability of carbonate systems not only in conventional sense but in relation to geothermal and hydrocarbon production. The study area is located in the Hungarian Paleogene Basin of the Pannonian Basin (Báldi and Báldi-Beke 1985), in which the Pre-Cenozoic aquifers are mostly covered by Paleogene and Neogene formations. The study displays the flow pattern for the region; reveals the interrelationships between siliciclastic confining layers and carbonate aquifer system and shows the salinity character of fluids. The regional fluid pattern reveals the efficient interaction of unconfined and confined carbonates, the boundaries of the communication; in addition to demonstrate the protection role of confining layers which are important to understand the vulnerability. However, the interaction between confining layers and underlying aquifers were also recognized. It reflects the geological and tectonic pattern of the area. These research are significant for the understanding of vulnerability not only for surface human activity but also for geothermal and hydrocarbon intervention.
Petra Kovács-Bodor
added an update
Project goal
Goals of the Project:
1. Characterization of the different hypogenic karst formation processes and evaluation of their controlling factors in regional groundwater flow system context.
2. Understanding the role and activity of microbes in the recognised special environment, as well as their relation and adaptation to the elevated radioactivity.
3. Adaptation of the understanding of recent cave forming processes to the evaluation of palaeo caves.
4. Extension and generalization of the results for similar settings worldwide.
The research hypotheses and the goals of the project display complexity involving wide range of processes, therefore multidisciplinary approach is essential and crucial to accomplish the
project’s purposes. Groundwater flow systems are responsible for the generation of hypogenic karstification, and the associated mineral precipitation in regional to local scale. Therefore hydrogeology denotes the main topic of the project complemented by diagenetic and speleogenetic studies. Iron and manganese hydroxide precipitates are key local discharge features both in the understanding of the role of microbes in hypogenic speleogenesis and in the radioactivity of springs, as well. Therefore microbiology ensures the second, while nuclear physics the third priority of the project. Examination of iron hydroxide precipitates requires special chemical analytics, namely
Mössbauer Spectroscopy. The evaluation of the processes and products connected to the microbes is only possible in micro to nano scales, and consequently requires the use of scanning electron
microscope.
This project is supported by the Hungarian Research Fund (NKFI) NK 101356.
Background and motivation
The research hypotheses and the goals of the project display complexity involving wide range of processes, therefore multidisciplinary approach is essential and crucial to accomplish the project’s purposes. Groundwater flow systems are responsible for the generation of hypogenic karstification, and the associated mineral precipitation in regional to local scale. Therefore hydrogeology denotes the main topic of the project complemented by diagenetic and speleogenetic studies. Iron and manganese hydroxide precipitates are key local discharge features both in the understanding of the role of microbes in hypogenic speleogenesis and in the radioactivity of springs, as well. Therefore microbiology ensures the second, while nuclear physics the third priority of the project. Examination of iron hydroxide precipitates requires special chemical analytics, namely Mössbauer Spectroscopy. The evaluation of the processes and products connected to the microbes is only possible in micro to nano scales, and consequently requires the use of scanning electron microscope.
 
Dóra Anda
added 2 research items
The Buda Thermal Karst System is an active hypogenic karst area that offers possibility for the analysis of biogenic cave formation. The aim of the present study was to gain information about morphological structure and genetic diversity of bacterial communities inhabiting the Diana-Hygieia Thermal Spring (DHTS). Using scanning electron microscopy, metal accumulating and unusual reticulated filaments were detected in large numbers in the DHTS biofilm samples. The phyla Actinobacteria, Firmicutes and Proteobacteria were represented by both bacterial strains and molecular clones but phyla Acidobacteria, Chlorobi, Chlorofexi, Gemmatimonadetes, Nitrospirae and Thermotogae only by molecular clones which showed the highest similarity to uncultured clone sequences originating from different environmental sources. The biofilm bacterial community proved to be somewhat more diverse than that of the water sample and the distribution of the dominant bacterial clones was different between biofilm and water samples. The majority of biofilm clones was affiliated with Deltaproteobacteria and Nitrospirae while the largest group of water clones was related to Betaproteobacteria. Considering the metabolic properties of known species related to the strains and molecular clones from DHTS, it can be assumed that these bacterial communities may participate in the local sulphur and iron cycles, and contribute to biogenic cave formation.
In this study, scanning electron microscopy (SEM) and 16S rRNA gene-based phylogenetic approach were applied to reveal the morphological structure and genetic diversity of thermophilic prokaryotic communities of a thermal karst well located in Budapest (Hungary). Bacterial and archaeal diversity of the well water (73.7 °C) and the biofilm developed on the inner surface of an outflow pipeline of the well were studied by molecular cloning method. According to the SEM images calcium carbonate minerals serve as a surface for colonization of bacterial aggregates. The vast majority of the bacterial and archaeal clones showed the highest sequence similarities to chemolithoautotrophic species. The bacterial clone libraries were dominated by sulfur oxidizer Thiobacillus (Betaproteobacteria) in the water and Sulfurihydrogenibium (Aquificae) in the biofilm. A relatively high proportion of molecular clones represented genera Thermus and Bellilinea in the biofilm library. The most abundant phylotypes both in water and biofilm archaeal clone libraries were closely related to thermophilic ammonia oxidizer Nitrosocaldus and Nitrososphaera but phylotypes belonging to methanogens were also detected. The results show that in addition to the bacterial sulfur and hydrogen oxidation, mainly archaeal ammonia oxidation may play a decisive role in the studied thermal karst system.
Judit Mádl-Szőnyi
added 2 research items
Hungary has a remarkable geothermal potential, and there are ongoing projects investigating the possibilities of thermal water utilization. The regional hydrodynamic assessment of one of the most promising geothermal sites of Hungary, the Go¨do¨ll}o Hills Region, could provide valuable additional information to them. The aim of this research was not only to carry out a regional study but also to demonstrate the relevance of the hydrodynamic approach in the reconnaissance phase of exploration. Regional evaluation was carried out based on the created database of preproduction wells’ hydraulic, temperature, and geochemical data. Based on the dataset from the depth extending to -2300 m asl, it could be shown that the temperature field (up to 120 �C) and the reservoir conditions are favorable: structurally influenced Triassic Main Dolomite and Dachstein Limestone, Miocene, and Upper Pannonian formations, and fluid flow is basically topography induced. The recharge and discharge zones of the gravity-driven system, the basement elevation, and the temperature distribution show good correlation. The vertical connections between Pannonian and Eocene-Triassic basement reservoirs could be followed through the changes of pressure regimes and by the interaction of ‘‘fresh’’ and ‘‘basinal’’ fluids of the region. It has been revealed that, due to the differentiated uplifting of the region in the Pliocene and the Quaternary, the pore pressures in the aquitards and in the basement reservoir have been shifted toward subhydrostatic, indicating geologically transient pore pressures. The detected subhydrostatic pressure gradients cause downward vertical groundwater flow in the Hills characterized by restricted recharge across low permeability strata. Upward vertical flow appears from the basement carbonate reservoir toward the highest negative pressure increment values in the aquitards. The underpressure in the basement carbonate reservoir causes an uncertainty factor in the exploration of a potential geothermal site. The area was differentiated based on flow and pressure conditions for geothermal exploitation.
Budapest is famous for its thermal springs and spas and outstanding thermal water resources. In the 21st century renewable energy utilization - including the use of geothermal energy - became the focus of interest. Improving the use of the different forms of geothermal energy requires the assessment of their possibilities. The potential for deep geothermal doublet systems for direct heating in Budapest was evaluated based on the temperature conditions, the depth and reconnaissance of the carbonate reservoir. NW Buda is not appropriate for thermal water exploration. SW and SE Budapest have better temperature conditions but the lithology of the reservoir is uncertain. Beneath Pest the thermal water is well exploitable. It is obvious from the map of the region that the area is promising; however, due to the hydraulic continuity of the system, reinjection is desirable. Considering the reliability of the employed data the geothermal potential map is suitable only for general orientation and guidance. The geothermal potential map for Groundwater-sourced Heat Pump Systems (GHPS; scale = 1:40,000) was assembled by evaluating the thickness and appearance of the gravel strata and water table, complemented by the sulfate content as an aggressive component of groundwater. The original geothermal potential map series can be used for the evaluation of potential sites in Budapest. It can be concluded that the Buda side of the Danube River is almost entirely unsuitable for shallow groundwater-based heat pump installations. The only areas under consideration are Óbuda and the riverbanks. On the Pest side, there is no gravel in the central part; the largest areas close to the river and in the immediate surroundings are uncertain, with patches of suitable and possible categories. The southern and eastern area of Pest is the most prospective for GHPS installation. The potential maps only consider natural parameters; however, installation may be strongly influenced by the urbanization and the city environment.
Ádám Tóth
added a research item
The main focus of the study was to help in the application of the gravity-driven regional groundwater flow (GDRGF) concept for the evaluation of groundwater flow circulation in unconfined and confined sub-basins of carbonates. The concerns of the applicability of GDRGF could be released with focusing not on an individual aquifer but on a carbonate basin and interpret its heterogeneities based on the principle of hydraulic continuity. The approach and the application were demonstrated on the example of the Buda Thermal Karst (BTK), Transdanubian Range (TR), Hungary. The hydraulic connectivity of the system was proved based on the experiences of a long-term “pumping test” for the NE part of the TR. The intense connectivity of thick carbonates could be explained by the higher hydraulic diffusivity compared to siliciclastic regions. The original (before intense water production) spring data of the BTK were grouped based on the results of statistical analysis, and their critical parameters (chloride content, temperature and volume discharge) were displayed in the function of the discharge elevation and grouping of springs. In addition, a 2D flow and heat transport simulation were carried out by EPM approach based on topographic, hydrostratigraphic and structural settings of the BTK (Southern system). Based on the results, the location and chemical and temperature character of one-component thermal springs of the Southern system of BTK could be explained. The thermal springs receive water from regional flow system with additional basinal fluid contribution from the confining Paleogene and Neogene siliciclastic sediments of Pest side. In addition, heat accumulation under the Pest side of BTK also could be revealed. This approach can be used for the understanding of GDRGF of carbonate regions on all over the world.
Judit Mádl-Szőnyi
added a project goal
Goals of the Project:
1. Characterization of the different hypogenic karst formation processes and evaluation of their controlling factors in regional groundwater flow system context.
2. Understanding the role and activity of microbes in the recognised special environment, as well as their relation and adaptation to the elevated radioactivity.
3. Adaptation of the understanding of recent cave forming processes to the evaluation of palaeo caves.
4. Extension and generalization of the results for similar settings worldwide.
The research hypotheses and the goals of the project display complexity involving wide range of processes, therefore multidisciplinary approach is essential and crucial to accomplish the
project’s purposes. Groundwater flow systems are responsible for the generation of hypogenic karstification, and the associated mineral precipitation in regional to local scale. Therefore hydrogeology denotes the main topic of the project complemented by diagenetic and speleogenetic studies. Iron and manganese hydroxide precipitates are key local discharge features both in the understanding of the role of microbes in hypogenic speleogenesis and in the radioactivity of springs, as well. Therefore microbiology ensures the second, while nuclear physics the third priority of the project. Examination of iron hydroxide precipitates requires special chemical analytics, namely
Mössbauer Spectroscopy. The evaluation of the processes and products connected to the microbes is only possible in micro to nano scales, and consequently requires the use of scanning electron
microscope.
This project is supported by the Hungarian Research Fund (NKFI) NK 101356.