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Springs have an important role both in groundwater flow system understanding and in maintaining groundwater-related ecosystems. The aim of the research of the lukewarm karst springs in Kistapolca is to understand the origin of the elevated temperature (22–24 °C), i.e., whether it is the result of mixing of cold and thermal waters or it represents the terminal area of intermediate flow systems. This question has also an important relevance to the evaluation of recent cave formation in the area. In case of mixing of different waters dissolution by mixing corrosion could take place. This scenario was proposed for the formation of the Beremend Cave, which is situated in the close vicinity of the springs, and which is the only known cave of the area, where the passages are partly filled by water. Therefore, several methods, including geophysical, geochemical and stable isotope measurements, evaluation of continuous-time series of water level change, temperature, and electrical conductivity data and hydraulic evaluation of vertical flow conditions by pressure–elevation profiles were combined in order to acquire information about the hydrogeological environment and flow conditions in the area. The results show that a higher order flow system derived from the Villány Hills feeds the springs in Kistapolca without significant local influence. In addition, the results related to the Beremend Cave indicate that cave formation by mixing corrosion is not an active process today in the area, the cave is rather influenced by local processes.

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.

Summary Groundwater flow, driven, controlled and determined by topography, geology and climate, is responsible for several natural surface manifestations and affected by anthropogenic processes. Therefore, flowing groundwater can be regarded as an environmental agent. Numerical simulation of groundwater flow could reveal the flow pattern and explain the observed features. In complex geologic framework, where the geologic–hydrogeologic knowledge is limited, the groundwater flow model could not be constructed based solely on borehole data, but geophysical information could aid the model building. The integrated model construction was presented via the case study of the Tihany Peninsula, Hungary, with the aims of understanding the background and occurrence of groundwater-related environmental phenomena, such as wetlands, surface water–groundwater interaction, slope instability, and revealing the potential effect of anthropogenic activity and climate change. The hydrogeologic model was prepared on the basis of the compiled archive geophysical database and the results of recently performed geophysical measurements complemented with geologic–hydrogeologic data. Derivation of different electrostratigraphic units, revealing fracturing and detecting tectonic elements was achieved by systematically combined electromagnetic geophysical methods. The deduced information can be used as model input for groundwater flow simulation concerning hydrostratigraphy, geometry and boundary conditions. The results of numerical modelling were interpreted on the basis of gravity-driven regional groundwater flow concept and validated by field mapping of groundwater-related phenomena. The 3D model clarified the hydraulic behaviour of the formations, revealed the subsurface hydraulic connection between groundwater and wetlands and displayed the groundwater discharge pattern, as well. The position of wetlands, their vegetation type, discharge features and induced landslides were explained as environmental imprints of groundwater. The highly vulnerable wetlands and groundwater-dependent ecosystems have to be in the focus of water management and natural conservation policy.

The Duna-Tisza Interfluve, Hungary, is characterized by patchy surface salinization. However, in the Duna Valley, salinized wetlands appear in a N–S trending continuous zone (Lake Kelemenszek area). The source of the salts is reported to be the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. This “basement and basin origin of salts” concept is based on the strong correlation between the regional distribution of surface salinization and the basinal flow pattern. This study, applying integrated methods, presents hydrogeological evidence for this theory and creates a conceptual model for the salinization. The model reflects that the basement water rises near to the surface through conductive faults crosscutting an extensive aquitard and aquifer. These faults ensure “shortcut”-type water exchange between the basement and the uppermost aquifer. This hydraulic setting generates chemical anomalies in this aquifer up to the surface, producing Na–HCO3–Cl-type water. This water causes extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. Where a freshwater lens is located above the ascending saline water, this fresh gravity-driven flow controls the surface distribution of salts, which results in saline patches.

In the Danube Valley, a chain of saline lakes and a salinized area are situated in the discharge zone of two different waters. The two watertype were followed till the near surface by regional chemical and hydraulic investigations (Madlne Szőnyi and Toth 2009). The goals of this study were to prove the presence of these different waters in the near surface zone around the Lake Kelemenszek, and allocate their connection to the lake and to the salinized ground surface. Near-surface geophysical measurements (VES, RMT) supported the regional hydraulic and chemical results. The sediments are saturated by saline water down to 110 m beneath the lake, and to the east the fresh water is prevalent. The local chemical investigations strengthened this distribution. Highly saline water with Na-HCO3-Cl-type discharges into and around the lake. To the east there is a continuous change towards a (Ca,Mg)-(HCO3)2-type fresh water discharge. The interface between the two water types is a 2–3 km wide transition zone...

Radio frequency geophysical methods are known for being very versatile tools in ground- and groundwater investigation at shallow depths. They are fast and easy to use and allow a high density of information over large surfaces, which makes them very suitable for geological mapping sensu lato (faults, lithological contacts, groundwater-bearing structures, vulnerability maps, and contaminant plumes) and for selecting borehole locations. Significant improvement concerning 2D and 3D modelling of the data has occurred in recent decades. However, field surveys are very seldom performed in "ideal conditions"aEuro"the lack of necessary transmitters, in the convenient direction, in order to catch the structures in E- and H-pol for modelling purposes, is not an unusual situation. The present paper shows how the use of RMT and RF-EM is nevertheless of great help and suggests different ways to explore qualitative data in different geological settings.

The term “null array” is introduced for those electrode configurations where the measured potential difference is zero above a homogeneous half‐space when using a measuring dipole M0N0. Different types of null arrays (three‐electrode, Schlumberger, and dipole axial/equatorial null arrays) and their corresponding traditional arrays are studied. It was shown in a field study carried out in a karstified limestone area covered by thin sediments that it is possible to obtain geologically meaningful results with null‐array techniques. The main features of the null‐array data are as follows. (1) Null‐array data appear to be more spatially variable than the classical data. The spatial variability provides information about the presence of karstic fractures in the subsurface; (2) The null‐array anomalies caused by nearly vertical karstic fractures in the limestone basement do not decay with depth as quickly as the classical array anomalies. (3) The strike direction of the fractures is much less ambiguous than that found by using classical arrays. Nevertheless, the depth variation of the basement is more reliably observed in geoelectric anomalies obtained using traditional arrays. Therefore a joint use of classical arrays and their corresponding null methods is recommended, because the combined methods provide more information about the subsurface structure.

The Centre of Hydrogeology Neuch‚tel (CHYN) investigates and monitors karst aquifers, which are highly vulnerable to contamination. One of our particular research tasks within this scope is the characterization and localization of the 'epikarstic zone' (0-20 m depth) (Mangin 1975; Kiraly 1995). Density, size and aperture of fractures that connect the water reservoir with the surface, are features which characterize the vulnerability of karst aquifers. Very local scale mapping of these types of high-permeability fracture zone over extensive areas is therefore of interest for karst hydrogeology. In order to investigate this zone the very low frequency (VLF, 15-30 kHz) method has been adapted at CHYN for investigation at shallow depths with high lateral resolution. Geophysical surveying using VLF radio signals began in the 1960s as a tool for prospecting conductive minerals (McNeill & Labson 1991; Paal 1965). The CHYN equipment uses VLF and low frequency (LF, 30-300 kHz) radio transmitters, which are located at several positions around the world and are used principally for navigation and submarine communication. Consequently the CHYN has developed a radio frequency-resistivity device (RF-R), also called radio magnetotelluric (RMT, 12-240 kHz), and a continuously measuring radio frequency-electromagnetic (RF-EM, 15-300 kHz) device (Turberg et al. 1994; Turberg & Barker 1996; Stiefelhagen 1998). In fissured limestone with a resistivity of several hundreds of Wm, the penetration depth for these frequencies is about 10-100 m. However, when investigating small structures at very shallow depths (0-10 m) in the epikarstic zone, these devices have limited use due to their excessive penetration depths and their poor horizontal resolution. In this paper we introduce a method that is based on measuring the vertical gradient of the horizontal magnetic field component of VLF radio signals (VLF-EM-vGRAD(Hy)). According to our knowledge, such a technique has not been previously published.

Until now no systematical field studies have been carried out by using geoelectrical arrays, having zero potential difference over a homogeneous halfspace. We call hereafter such configurations as null-arrays. In this paper we present field results obtained over near-surface fissures in limestone by using three different null-arrays. The null-arrays were selected according to three possible types of the current distribution around the current electrodes. In the first type of the current distribution the current is propagating radially. In the second one the current lines are more or less parallel with each other. In the last one the current flow is considered as it would be of a dipole origin. The first type of null-arrays was realized by a three-electrode geometry. The second type was realized by the so called Schlumberger null-array and in the last case both dipole equatorial and dipole axial configurations were transformed into null-array geometries. The connecting line of the potential electrodes in the null-arrays are always perpendicular to that in the classical arrays. This feature made it possible to obtain a very quick joint application of these two array types and also to compare the results between the traditionally used arrays and the null-arrays. All geoelectric profiles were evaluated in a close vicinity of a quarry, where the fissures were directly seen. As we found, the null-arrays located the fissures with a higher accuracy and provided a more significant anomaly than the classical configurations did, especially in case of a thicker overburden. Since the null-arrays and classical arrays give complementary information we recommend their combined use in such near-surface studies. Besides the theoretical aspects, these field test measurements have been found to be very useful in hydrogeological applications, since fractures and fissures are the most important geological features for determining groundwater vulnerability.

Bacteriophages are increasingly used as tracers for quantitative analysis in both hydrology and hydrogeology. The biological particles are neither toxic nor pathogenic for other living organisms as they penetrate only a specific bacterial host. They have many advantages over classical fluorescent tracers and offer the additional possibility of multi-point injection for tracer tests. Several years of research make them suitable for quantitative transport analysis and flow boundary delineation in both surface and ground waters, including karst, fractured and porous media aquifers. This article presents the effective application of bacteriophages based on their use in differing Swiss hydrological environments and compares their behaviour to conventional coloured dye or salt-type tracers. In surface water and karst aquifers, bacteriophages travel at about the same speed as the typically referenced fluorescent tracers (uranine, sulphurhodamine G extra). In aquifers of interstitial porosity, however, they appear to migrate more rapidly than fluorescent tracers, albeit with a significant reduction in their numbers within the porous media. This faster travel time implies that a modified rationale is needed for defining some ground water protection area boundaries. Further developments of other bacteriophages and their documentation as tracer methods should result in an accurate and efficient tracer tool that will be a proven alternative to conventional fluorescent dyes.

To “Geoelectric mapping of near-surface karstic fractures by using null arrays” (S. Szalai, L. Szarka, E. Pracser, F. Bosch, I. Muller, and P. Turberg, GEOPHYSICS, 67, 1769–1778).