Postojna Cave Research Articles

Characterization of the vadose flow and its influence on the functioning of karst springs: Case study of the karst system near Postojna, Slovenia

In three selected drips in the Postojna cave in SWw Slovenia and in the nearby Korentan spring, which in general belongs to the same karst aquifer, the discharge and electrical conductivity were measured at 15-minute intervals. Simultaneously, the meteorological parameters in Postojna were measured and the effective infiltration was assessed. The data obtained in the period of one hydrological year, 2003–2004, was compared in order to study the influence of the vadose flow on the characteristics of groundwater flow in a karst system and on the functioning of a karst spring. The highest discharges of the Korentan spring are the result of the inflow of water through a hierarchy of fissures of various permeabilities within the vadose zone, but the contribution of stored water from low-permeability zones is especially important. One of our most significant findings is that in the conditions of high saturation of the vadose zone, the network of small fissures is hydraulically connected, which enables an integral reaction of the system to the pressure pulse induced by infiltrated precipitation. On the other hand, a detailed comparison of effective infiltration and discharge indicates that in dry periods with a lower saturation of the vadose zone, the infiltrated precipitation is mainly stored in the system and only the most permeable fissures enable a rapid transfer of the recharge impulses toward the spring. Data on measured discharge and conductivity were additionally compared in order to study the complex conditions of the actual mass flow of water through the system.Key words: karst aquifer, vadose zone, Postojna Cave, Korentan spring, Slovenia

Impact of peak period visits on the Postojna Cave (Slovenia) microclimate

Cave air temperature, carbon dioxide concentrations in the cave air and external air temperature were analysed at several locations in Postojna Cave over the course of six holiday periods in 2009–2011. The results show that a 1-day increase in visitor numbers from 200 to 3,500 raised the cave air temperature by a maximum of 0.5 °C. The air temperature increases are within the annual range of cave air temperature variations. A fivefold increase in visitor numbers resulted in a carbon dioxide concentration that was at least twice as high as normal. The carbon dioxide concentration increased from 450 to 1,750 ppm (December 2009–January 2010). After 10 days of peak period visits, both the CO2 concentration and the temperature returned almost to the pre-holiday values. The gradual increase in mean annual air temperature in the cave (2004–2010) is not related to the number of visitors but to outside climate conditions.

Comparative microbial sampling from eutrophic caves in Slovenia and Slovakia using RIDA ®COUNT test kits

RIDA®COUNT test plates were used as an easy-to-handle and rapid indicator of microbial counts in karst ecosystems of several caves in Slovakia and Slovenia. All of the caves had a high organic input from water streams, tourists, roosting bat colonies or terrestrial surroundings. We sampled swabs, water and air samples to test robustness and universality of the RIDA®COUNT test kit (R-Biopharm AG, Germany, http://www.r-biopharm.com/) for quantification of total bacteria, coliforms, yeast and mold. Using data from swabs (colony-forming units CFU per cm 2 ) we proposed a scale for description of biocontamination level or superficial microbial load of cave niches. Based on this scale, surfaces of Ardovska Cave, Drienovska Cave and Stara Brzotinska Cave (Slovakia) were moderately colonized by microbes, with total microbial counts (sum of total bacterial count and total yeast and molds count) in the range of 1,001-10,000 CFU/100 cm 2 , while some surfaces from the show cave Postojna Cave (Slovenia) can be considered highly colonized by microbes (total microbial counts ≥ 10,001 CFU/100 cm 2 ). Ardovska Cave also had a high concentration of airborne microbes, which can be explained by restricted air circulation and regular bat activity. The ratio of coliform to total counts of bacteria in the 9 km of underground Pivka River flow in Postojna Cave dropped approximately 4-fold from the entrance, indicating the high anthropogenic pollution in the most exposed site in the show cave. The RIDA®COUNT test kit was proven to be applicable for regular monitoring of eutrophication and human influence in eutrophic karst caves.

Mineralogical and chemical characteristics of black coatings in Postojna cave system

Mineralogical and chemical analyses of black coatings from two sites in Postojna cave system were studied. Scattered samples were taken from the entrance parts of the cave and from Crna Jama. Thin sections, powder X-ray diffraction (XRD) technique and scanning electron microscope coupled with energy dispersive X-ray spectrometer (SEM/EDS) were used. Microscopic investigation of thin sections of black coloured material from both locations revealed that the main material is carbonate – calcite, with evenly dispersed prevailingly minute opaque black grains. The XRD analysis on samples from both locations confirmed just a presence of calcite with minor quartz and dolomite, excluding Mn and Fe oxides or apatite-group minerals as reason for black colouring. The SEM/EDS analysis of samples from the entrance parts of Postojna cave system was consistent with XRD analysis, which did not show any Mn oxides. The high content of C measured in the black coatings from the cave entrance parts indicates organic C, which deposited on the cave walls at time of the petrol explosion during WW2. We can attribute black coatings from Crna Jama to one form of organic C as well, but it is certainly different from the one in the entrance parts of Postojna cave system. As in Crna Jama no other evidence indicates for old human inhabitation of the place: torches of first tourists are a more probable origin of charcoal. On both locations black coatings can be at least partly described by microclimate conditions at cave entrances, which caused the deposition of organic material of allogenic origin (for example soot due to the forest fires).

Inscriptions of some historically known persons in Postojnska jama

Imenski rov (Rov starih podpisov), the Old Cave (Stara jama), was the only part of Postojnska jama known for several centuries until 1818 when Luka Cec discovered the access to the inner parts of the cave. Here we documented ca. 400 inscriptions. About 100 more were also recorded in the historic part of Predjama Cave. From these signatures we correlated 19 with independently historically known persons, less than 5% of the total. The correlation is firm for 15 names, but only tentative for Bellegarde, Kotze, Mihanovic and Karl von Zur. The oldest one is that of Johann Melchior Ott(o) of 1642, a painter in the service of Johann Anton zu Eggenberg (1610–1649) the owner of the Castle of Adelsberg at the time, whose coat of arms Ott drew as well. The next oldest is the name Josef Anton Nagel 1748 who also left Latin inscriptions in Predjama cave and in Sloup Cavern, Moravia. All other inscriptions of historic persons are younger than 1800 including those of Franz Graf von Hohenwart, Joseph Petsch Ritter von Lowengreif and Alois Schaffenrath (each with several inscriptions). Noteworthy are also the signatures of Josef Franz Eggenhofner (1801 or 1809, and 1820; developer of Grotta di Padriciano), Johann Natterer (biologist, 1815, who stayed 19 years in Brazil and laid the basis of the zoological department of the Natural History Museum in Vienna), Karl Beyrich (1819, botanist who died during an expedition in Arkansas, 1834), Giuseppe de Volpi (1820, from Trieste who published first evidence of the cave bear presence in Postojnska jama), Johann Fercher, mine supervisor, and his team of miners from Idrija who signed during their survey of the cave in 1833, Johann Ritter von Hauer (1836 in Pisani rov, Vienna, Imperial Councelor of War and Palaeontologist), Ivan Andrej Perko (the later director of the cave) and several cave guides. Members of the nobility or state employees include Bellegard, Adrienne Brandis Desenffans and her brother Karl Graf Desenffans, Carl von Kotze, and Mihanovic.

Impact of chlorides, nitrates, sulfates and phosphates on increased limestone dissolution in the karst vadose zone (Postojna Cave, Slovenia)

Distinctive karst hydrology arises from a combination of high carbonate rock solubility and well developed secondary porosity (fissures). Soil CO 2 is the most important influence on solubility of carbonate rock (Ford & Williams 2007). Human activity on the karst surface results in pollution that has an important influence on water quality. Degradation of organic pollution (e.g. waste water, leachates from landfill sites) results in inorganic acids too. These acids could have an important additional influence on dissolution of carbonate rocks in the vadose zone. In the framework of more than 20 years of research on precipitation percolation and transfer of contaminants (direct outflow of waste water from a small military facility where about twenty troops were stationed) through the 100-m thick vadose zone of Postojna Cave, contaminated water was observed in drips and trickles in the cave (up to 60 mg Cl - /l, up to 180 mg NO 3- /l, up to 2.8 mg PO 43- /l, and up to 50 mg SO 42- /l). At the same time the sum of calcium and magnesium (Ca+Mg) of trickles was up to two times larger than the Ca+Mg of either the uncontaminated reference trickle or the input waste water. The amount of dissolved limestone carried by waste water to trickles and drips in the cave was directly proportional to the concentration of contaminant anions present. This demonstrates that there is an accelerated widening of fissures below source points of wastewater. Water with contaminants can penetrate faster and deeper into the vadose zone along the increasingly permeable fissures without losing its dissolving power, and thus significant dissolution occurs ever deeper in the vadose zone. This results in ever faster penetration of contaminants through the vadose zone. In the final phase of such development, which takes many decades or longer, relatively rapid transfer of contaminants through the aquifer all the way to karst springs with minimal self-cleansing effects can be expected.

Dependence of radon levels in Postojna Cave on outside air temperature

Abstract. Postojna Cave is the largest of 21 show caves in Slovenia. The radon concentration there was measured continuously in the Great Mountain hall from July 2005 to October 2009 and ranged from about 200 Bq m−3 in winter to about 3 kBq m−3 in summer. The observed seasonal pattern of radon concentration is governed by air movement due to the difference in external and internal air densities, controlled mainly by air temperature. The cave behaves as a large chimney and in the cold period, the warmer cave air is released vertically through cracks and fissures to the colder outside atmosphere, enabling the inflow of fresh air with low radon levels. In summer the ventilation is minimal or reversed and the air flows from the higher to the lower openings of the cave. Our calculations have shown that the effect of the difference between outside and cave air temperatures on radon concentration is delayed for four days, presumably because of the distance of the measurement point from the lower entrance (ca. 2 km). A model developed for predicting radon concentration on the basis of outside air temperature has been checked and found to be successful.

Local characteristics of Postojna Cave climate, air temperature, and pressure monitoring

In Postojna Cave, air temperature and pressure monitoring has been conducted since July 21, 2008. Air pressure in the cave at three monitoring sites fluctuates synchronically with outside air pressure. Temperature data for Postojna 1 and 3 show good correlation with outside climate conditions for the period 2009–2010. The temperature at Postojna 1 was increasing constantly from March to May 2009, while at Postojna 2, it was decreasing. Postojna 1 has a seasonal trend in accordance with outer trend, while seasonal trend at Postojna 2 is just contrary to outside trend. Microclimate studies at Postojna 2 show local variability, especially in winter, and exhibit special microclimate conditions that may be due to ventilation of unknown passages in the back.

Effects of earthquakes in Postojna cave system

Regarding the studied historic references there are sufficient proofs that during the 1st January 1926 earthquake (M=5.6) in Postojna cave system (Sala del Candore or Pralnica) a stalag­mite column of 1 meter in diameter collapsed. This is a not so common event in karst caves and took place due to the close vicinity of the epicentre located at the SE end of Idrija Fault or at the Javorniki Mountain. During earthquakes in karst caves brontides are generally heard, but ground movement is rarely felt. Only strong and close earthquakes can be felt as ground shaking or waving inside the caves also, withsome possible collapses as well.

Diversity of bryophytes in show caves in Slovenia and relation to light intensities

In subterranean environments phototrophic organisms can grow only in the proximity of light sources. In a study from eight Slovenian show caves: Črna jama, Kostanjeviška jama, Krška jama, Pekel pri Zalogu, Pivka jama, Postojnska jama, Škocjanske jame, Županova jama and two mines, Idrija mer­cury mine and Mežica lead and zinc mine, equipped for tourist visits, 37 taxa of Bryophyta and Pteridophyta were identified. The most frequent organisms were mosses Amblystegium ser­pens, Brachythecium sp., Eucladium verticillatum and Fissidens taxifolius. The highest diversity of bryophytes was recorded in Mežica mine with16 identified taxa where lamps are on con­tinuously. Bryophytes were collected at wide range of photo­synthetic photon flux densities (PPFD) from 0.2 to 530.0 μmol photons/m2/s. Eucladium verticillatum had the highest span of PPFDs, ranging from 1.4 to 530.0 μmol photons/m2/s. Bryo­phytes compensate for low PPFD withlonger exposure to light irradiance. Cratoneuron filicinum identified in Mežica mine de­veloped sporophytes at 2.1 and 2.4 μmol photons/m2/s, in Post­ojnska jama Brachythecium salebrosum developed sporophytes at 4.7 μmol photons/m2/s. Recolonization of lampenflora in show caves where bleachis applied to prevent its growthis still successful at sites that are exposed to long periods of irradiance and highPPFDs.

Nano aerosols in the Postojnska jama

At the lowest point in the Postojnska Jama (jama = cave), concentration and size distribution of non-radioactive aerosols in the size range of 10–1,000 nm were measured and their concentrations are compared with those of radioactive aerosols carrying radon short-lived decay products (218Po, 214Pb and 214Bi) obtained previously. Concentration of non-radioactive aerosols during morning hours was in the range 600–2,750 cm–3, with about 90% of particles smaller than 50 nm. On the other hand, concentration of radioactive aerosols smaller than 50 nm was several radionuclide atoms per 1 cm3 and the bigger ones, less than 1 atom per 1 cm3.

Direct measurement of present-day tectonic movement and associated radon flux in Postojna Cave, Slovenia

Micro-tectonic deformations have been monitored continuously in 3D in Postojna Cave, Slovenia with TM 71 extensometers since 2004. Two instruments, 260 m apart, were installed on the Dinaric oriented (NW-SE) fault zone that is situated about 1,000 m north of the inner zone of the regionally important Predjama Fault. Monitoring on both instruments has shown small tectonic movements (i.e., a general dextral horizontal movement of 0.05 mm in four years [Postojna 1] and extension of 0.03 mm in four years [Postojna 2]). Between the longer or shorter calm periods, eleven extremes have been recorded regarding characteristic changes in displacement. The largest short-term movement was a compression of 0.04 mm in seven days, detected in March 2005, which coincided with the 25 km distant Ilirska Bistrica earthquake (ML 5 3.9). About two months before the earthquake an extension of 0.05 mm occurred and one month before the earthquake the strain changed into a compression of 0.05 mm. The largest permanent peak was detected at the end of 2004. Along the y-axis (Postojna 1) there was a dextral horizontal movement of 0.075 mm in one month (November 10 to December 15, 2004). After the sinistral horizontal movement of 0.02 mm (December 15–27, 2004), the y-axis retained its permanent position on 0.05 mm, where it remained for more than a year. Regarding the extremes, ten earthquakes were selected that coincided with tectonic micro-displacements. In terms of speleogenesis, the monitored fault zone represents a stable cave environment. Because radon flux is known to change significantly during tectonic and seismic activities, radon air concentrations were monitored in parallel since 2006. During horizontal movements, either dextral or sinistral, radon pathways underground were partly closed, thus hindering radon migration and reducing its concentration in the cave air. Extension movements do not appear to have affected radon transport. Alternatively, the compression process (Postojna 2, February–August 2007) appears to have opened some new routes for radon transport, facilitating radon migration and increasing its concentration in air.

Broken Speleothems as Indicators of Tectonic Movements

In karst caves broken and non-ideal speleothems are very wide­spread. Mostly they develop because of the instability of the ground due to its composition (loose sand or loam). The pres­ence of recent cryoturbation in some caves in higher altitudes suggests that some ancient breaks of the speleotheme can be caused by ice in the cave. And we also have some good proofs for recent and past tectonic activity in karst caves. In many cases it is very difficult to determine the real reason for broken speleothems, because several reasons could be interacting. In Postojna Cave some examples related to tectonics were stud­ied.

Cave Sediments from Postojnska–Planinska Cave System (Slovenia): Evidence of Multi-Phase Evolution in Epiphreatic Zone

The Postojnska jama–Planinska jama cave system and number of smaller adjacent caves are developed in the Postojnski kras. These caves are located between two dextral strike-slip fault zones oriented in the Dinaric direction. The caves contain lith­ologically diversified cave fill, ranging from speleothems to allo­genic fluvial sediments. The allogenic clastic material is derived from a single source, Eocene siliciclastics of the Pivka Basin. Small differences in mineral/petrologic composition between the sediments can be attributed to different degrees of weather­ing in the catchment area and homogenization of source sedi­ments. Thick sequences of fine-grained laminated sediments, deposited from suspension are common. The depositional en­vironment was mostly calm, but not completely stagnant. Sucha sedimentary environment can be described as cave lacustrine, withdeposition from pulsed flow. The homogeneity of the pa­laeomagnetic data suggests rapid deposition by a number of short-lived single-flood events over a few thousand years. This depositional style was favourable for recording of short-lived excursions in the palaeomagnetic field. The sediments were originally not expected to be older than Middle Quaternary in age (i.e. about 0.4 Ma). Later numerical dating (Th/U and ESR) indicated ages older than 0.53 ka. New palaeomagnetic data from selected sedimentary profiles within the cave system detected normal polarization in muchof the profiles studied. Reverse polarized magnetozones, interpreted mostly as short-lived excursions of magnetic field, were detected in only a few places. Therefore, we interpreted most of the sediments as be­ing younger than 0.78 Ma, belonging to different depositional phases within the Brunhes chron. Palaeomagnetic properties of two profiles in caves intersected by the artificial tunnel be­tween Postojnska jama and Črna jama had reverse polarized magnetozones and of sediments in Zguba jama, may indicate an age muchgreater than 0.78 Ma. The cave system has evolved over a long period of time, governed by the functioning of Pla­ninsko polje in the relation to the evolution of the resurgence area in Ljubljana Moor further to the east. General stabilization of the hydrological system withlow hydraulic head led to the evolution of caves in epiphreatic and paragenetic conditions over a long time-span. Individual cave segments or passages were completely filled and exhumed several times during the evolution of the cave. Alternation of depositional and erosional phases may be connected withchanging conditions within the cave system, the functioning of the resurgence area, collapse, climatic change, tectonic movement and the intrinsic mecha­nisms of contact karst.

Nanosize radon short-lived decay products in the air of the Postojna Cave

At two points in the Postojna Cave, short-term monitoring in summer and in winter of air concentrations of radon and radon decay products, equilibrium factor, unattached fraction of radon decay products ( f un), barometric pressure, relative air humidity in the cave and air temperature in the cave and outdoor has been carried out, with the emphasis on f un. Dose conversion factors, calculated on the basis of f un values obtained (ranging from 0.09 to 0.65) exceed 5 mSv WLM − 1 , by a factor of 11.5–14.0 in summer and of 3.0–4.0 in winter for mouth breathing, and 3.1–3.5 in summer and 1.5–1.7 in winter for nasal breathing.

Estimation of percolating water dynamics through the vadose zone of the Postojna cave on the basis of isotope composition

Within the scope of monitoring water percolation through the 100-m thick vadose zone in the area of Postojnska jama continuous measurements of precipitation were carried out on the surface, and continuous measurements of water flow and physical and chemical parameters of selected water trickles were performed under the surface. Occasional samples of percolating waters were taken for the analysis of water oxygen isotope composition. An exponential model of groundwater flow was elaborated, by means of which the retention time of water in individual trickles was estimated. Modelled retention times of groundwater range from 2.5 months to over one year.

Biodiversity and Ecology of Fauna in Percolating Water in Selected Slovenian and Romanian Caves

Biodiversity and ecology of fauna in percolating water from Slovenian and Romanian caves was studied. Research focused on unravelling the community structure of epikarst fauna, which is carried away by the trickles of percolating water from the epikarst and vadose zones. The major part of the fauna found in percolating water is represented by copepods. This fauna, originating in the epikarst, was analysed and by means of the systematic sampling and observation the same groups of animals were found in Slovenian and Romanian caves. Differences among caves and sampling points indicate that epikarst is a heterogenous habitat. Relationship between faunal richness and the physical characteristics of the water was found. Correlation between surface geomorphology and fauna in percolating water was statistically significant in the Postojna cave system.

Subterranean Waters Described in Carniolan Letters Mailed to A. Kircher (* 1601; †1680)

Kircher’s letters connected with the area of today’s Slovenia were analyzed. His Jesuit informer Wilpenhoffer’s reports on the Cerknica Lake and Idrija Mine were put forward. He also helped distribution of Kircher’s books among Auerspergs and other Ljubljana nobles. Janez Vajkard Auersperg’s letters as an example of high nobility correspondent patronage were put at the limelight in connection with Janez and his admirer Valvasor’s own research of the Postojna Cave flora and fauna.

Books about Karst and Subterranean in Auersperg’s »Prince’s« Library of Ljubljana

For the first time the karst research books at the former Ljubljanian Auersperg “Prince’s” library were put at the limelight by using the recently found manuscript catalogue 1668 (transcribed in 1762) and sales catalogues of 1982 and 1983. During the baroque times of Volf Engelbert Auersperg the science of karst was not born yet. The researchers had to wait for another century until the most fundamental facts about karst were proved by Carniolan scientists Hacquet, Gruber, and others. Nonetheless Volf collected several important books about karst with famous authors Aldrovandi, Ferrante Imperato, Johann Joachim Becher, Tommasso Buoni, Jakob Joannes Wenceslaus Dobrzensky de Nigro Ponte, and Athanasius Kircher. The special concern was put on the Count Volf Engelbert and his brother Prince Janez Vajkard interests in karst phenomena and their mutual influence on the younger visitors of their Ljublanian palace, especially Schönleben and Valvasor. Volf and Janez owned several manors at now Slovenian and Croatian karst. Janez Vajkard personally managed the first systematic research of subterranean animals in Postojna cave as a part of his Postojna Manor.

Postojnska Jama in Slovenia, the Südbahn and the Visit of John Charles Molteno: Their Influence on the Development of Railways in South Africa

In November 1871 a successful businessman and politician from South Africa toured Europe with his daughters. They arrived at Postojnska jama by train from Vienna. He wrote to the governor that it would be very desirable that the engineers should visit the Sudbahn which crosses a rugged terrain comparable to that of the Cape mountains where technical problems and increased construction costs slowed the advance. The discovery of diamonds inland was eventually responsible for the extension of the railway to Beaufort West and beyond.