Natural and Anthropogenic Impacts on Cave Climates: Postojna and Predjama Show Caves (Slovenia)

By Stanka Sebela

Natural and Anthropogenic Impacts on Cave Climates: Postojna and Predjama Show Caves (Slovenia) presents an analysis of continuous time-series data for show caves in Slovenia and their significance in understanding global cave microclimates. The book presents detailed guidelines and procedures for conducting temperature and CO2 measurements in caves and uses Slovenian caves as a detailed case study to demonstrate their application. Critical interpretations of these temporal series provide the reader with specific indicators of the conditions for water condensation to occur and CO2 thresholds and how to apply them to different cave systems.

Direct comparisons are made between microclimate data from caves with varying levels of tourism, and the linkage between the number of visitors and microclimate changes is discussed in detail. This book is a unique reference on cave meteorology for Climate Scientists, Meteorologists, Geologists, Microbiologists, Environmental and Conservation Scientists, and Cave Managers.

• Presents and analyzes an exceptional 10-year record of hourly time-series meteorological data of karst cave systems
• Provides methods and guidelines for conducting meteorological measurements in caves with detailed case studies
• Demonstrates the impact anthropogenic influences have on cave microclimates through real-time data analysis

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 12, 2021
• ISBN: 9780128231036

Stanka Sebela

Dr. Stanka Šebela has worked at ZRC SAZU (Karst Research Institute, Postojna, Slovenia) since 1988 and is currently professor at University of Nova Gorica and University of Primorska, Faculty of Humanities. She received her PhD in geology in 1995 (University of Ljubljana). Her research interests are: karst geology, geological mapping, monitoring of active tectonic structures, micro-climatic monitoring of caves, and sustainable use of caves for tourism. In 1998, she gained a post-doctoral Fulbright grant at USGS (Reston, Virginia) and Desert Research Institute (Nevada). She has scientific experience from exchange projects with University of Nevada Las Vegas (USA), Yunnan University (Kunming, China), Institute of Rock Structures and Mechanics (Czech Republic), M. Nodia Institute of Geophysics, Ivane Javakhishvili Tbilisi State University (Georgia), and others. Recently she has been involved in EC H2020 research infrastructure projects EPOS IP (European Plate Observing System Implementation Phase) and EPOS SP (European Plate Observing System Sustainability Phase).

Book preview

Natural and Anthropogenic Impacts on Cave Climates

Postojna and Predjama Show Caves of Slovenia

Stanka Šebela

ZRC SAZU, Karst Research Institute, Postojna, Slovenia

Table of Contents

Cover image

Title page

Copyright

Acknowledgments

Chapter 1. Introduction

Chapter 2. Purpose of research

Chapter 3. Worldwide studies of cave meteorology and cave climate

Chapter 4. Methods

Chapter 5. Microclimatic monitoring in show caves

Chapter 5.1. Postojna Cave air temperature and carbon dioxide monitoring

Chapter 5.1.1. Postojna Cave entrance

Chapter 5.1.2. Biospeleološka Postaja

Air temperature monitoring

Carbon dioxide monitoring

Carbon dioxide: noon and midnight concentrations

Deposition of flowstone

Chapter 5.1.3. The most visited parts of Postojna Cave

Chapter 5.1.3.1. Pulpito

Chapter 5.1.3.2. Velika Gora

Historic air temperature measurements at Velika Gora

Chapter 5.1.3.3. Lepe Jame (Postojna 3 site)

Air temperature monitoring

Carbon dioxide monitoring

Chapter 5.1.3.4. Lepe Jame (Postojna 2 site)

Air temperature monitoring

Carbon dioxide monitoring

Chapter 5.1.3.5. Koncertna Dvorana

Chapter 5.1.3.6. Sepolcro

Chapter 5.1.4. Črna and Pivka Jama

Air temperature monitoring

Črna Jama 1

Črna Jama 2

Črna Jama 3

Črna Jama 4: Pivka Jama

Correlation coefficients

Matevžev Rov

Chapter 5.1.5. Otoška Jama

Air temperature monitoring

Chapter 5.1.6. Visitors to Postojna Cave

Chapter 5.1.7. Anthropogenic and natural impacts on Postojna Cave microclimate

Chapter 5.1.7.1. Difference between day and night air temperatures in Postojna Cave

Chapter 5.1.7.2. Extreme natural events in Postojna Cave

Floods

Drought

Earthquakes

Lightning strikes

Bora wind

Sleet

Chapter 5.2. Predjama Cave

Chapter 5.2.1. Air temperature monitoring

Chapter 5.2.2. Carbon dioxide monitoring

Chapter 5.2.3. Visitors to Predjama Cave and castle

Chapter 5.2.4. Natural impacts on the Predjama Cave microclimate

Chapter 5.2.4.1. Difference between day and night air temperatures in Predjama Cave

Chapter 5.2.4.2. Extreme natural events in Predjama Cave

Chapter 6. Sustainable use of show caves

Chapter 7. Conclusions

Appendix

References

Index

Copyright

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Acknowledgments

Research data used for this manuscript were collected and analyzed within the research program Karst Research (P6-0119) and infrastructure program Natural and Cultural Heritage (I0-0031) financed by the Slovenian Research Agency. Writing of this manuscript was part of the research project Karst Research for Sustainable Use of Škocjan Caves as World Heritage (L7-8268) co-financed by the Slovenian Research Agency and Park Škocjanske Jame, and research project Methodology for monitoring the sustainable use of karst show caves with automatic measurements—role model—Postojna cave (L6-9397) co-financed by the Slovenian Research Agency, Postojnska jama d.d. and REODOM d.o.o.

Field work and the use of research infrastructure used for this monograph were performed within the project operations Development of Research Infrastructure for the International Competitiveness of the Slovenian RRI Space—RI–SI–EPOS and RI–SI–LifeWatch co-financed by the Republic of Slovenia, the Ministry of Education, Science and Sport, and the European Union from the European Regional Development Fund. Microclimatic monitoring in show caves was also part of EC Horizon2020 project EPOS SP.

I am grateful to the management of Postojnska Jama d.d. Company, Škocjan Caves Regional Park, and the management of Županova Jama and Kostanjeviška Jama for allowing me and my colleagues to perform microclimatic monitoring in their show caves. Thanks are also due to my co-workers at Karst Research Institute ZRC SAZU in Postojna where I have worked since 1988. This research was also part of the study programme at University of Nova Gorica (Karstology (third level) graduate school).

I thank also Allison Hill, Editorial Project Manager at Elsevier, and Peter W. Adamson, PhD Editor at Elsevier, who invited me to write this book.

I am grateful also to my family, especially my daughter Sara, for support during the writing of this book.

Chapter 1: Introduction

Abstract

In Slovenia, karst covers 43% of the country. We have 13,660 registered caves in Slovenia (Cave Register, November 2020), what means that the cave density is 1.56 caves per 1 km² on average. Slovenia is also the home of Classical Karst from where the international scientific term   karst is adopted. This monograph primarily addresses microclimate research in two show caves in Slovenia (Postojna and Predjama Caves) because these are the caves with the longest air temperature data sets, as air temperature monitoring started at hourly intervals in 2009. Additionally, some other show caves (Škocjan Caves, Županova Jama, and Kostanjeviška Jama) are discussed more briefly.

Keywords

Cave microclimate; Postojna Cave; Predjama Cave; Slovenia

Slovenia is the home of Classical Karst, which is an area that extends across the border between southwest Slovenia (Figs. 1.1 and 1.2) and northeast Italy (Gams, 2004; Jurkovšek et al., 2016). The Classical Karst Region lies in the northwestern part of the External Dinarides, which stretch in a northwest–southeast direction (Jurkovšek et al., 2016). The international scientific term karst was adopted from the name of Classical Karst (Gams, 2003, 2004). Classical Karst is part of Dinaric Karst, which is the largest continuous karst surface in Europe and one of the largest karst surfaces in the world (https://whc.unesco.org/en/tentativelists/6072/).

In Slovenia, karst areas represent 43% of the country (see Fig. 5.1 in Chapter 5, Microclimatic monitoring in show caves). There are 13,660 registered caves in Slovenia (Cave Register, November 2020), what means that the cave density is 1.56 caves per 1   km² on average. A bare karst landscape was typical in the past but in the last 150 years vegetation has covered the karst areas and the expression   green karst is becoming commonly used (Fig. 1.2). Nevertheless, there are still typical bare karst areas in southwest Slovenia with a strong northern wind called the   burja   or bora wind (Fig. 1.3).

Figure 1.1 Karst landscape in the area of Škocjan Caves with Vremščica mountain (1027   m) in the background. 

Photo: S. Šebela.

Figure 1.2 Karst landscape in the area of Škocjan Caves. 

Photo: S. Šebela.

Figure 1.3 Karst landscape illustrating the bora wind on the high plateau of Nanos Mountain (1313   m at the highest peak). 

Photo: S. Šebela.

This monograph primarily addresses microclimate research in two show caves in Slovenia (Postojna and Predjama Caves, Fig. 1.4). Those are also the caves with the longest air temperature data sets, as air temperature monitoring started at hourly intervals in 2009. Additionally, some other show caves (Škocjan Caves, Županova Jama, and Kostanjeviška Jama) in Slovenia are discussed more briefly (see Chapter 5, Microclimatic monitoring in show caves).

Figure 1.4 Geographic position of Postojna and Predjama Caves in southwest Slovenia (lidar relief from ARSO, 2020). On the small map of Europe Slovenia is marked with black, and the area of the Postojna and Predjama Caves is marked with a red dot.

Postojna Cave represents the southwest part of the Postojna-Planina Cave system (Fig. 1.4), because the underground water connection between both caves has been known since the explorations of Gruber (1781). There still remain about 800 m of unknown passages between Postojna and Planina Cave (6656   km long and 65 m deep) (Šebela, 2012, 2019). Postojna Cave is the second-longest cave in Slovenia (24,340 m long and 115   m deep). The cave was visited in prehistoric periods because cultural layers from Postojna Cave belong to the last half of the Middle Paleolithic (the end of the Mousterian) (Šebela, 2019). In the beginning of the Würm glacial period, the presence of Paleolithic man in the cave can be proved reliably (Brodar, 1966). Small portions of Postojna Cave were known in the 13th century (Gams, 2003; Čuk, 2008; Kranjc et al., 2007) (see Fig. 5.1.6.1 in Section 5.1.6, Visitors in Postojna Cave). However, the beginning of modern tourism started in the 19th century when the native Luka Čeč discovered new parts of the cave. The year 1818 is the official year of discovery of the most extensive section of the Postojna Cave and 1819 saw the beginning of modern tourism in Postojna Cave.

In a geological sense, Postojna Cave is developed in Cretaceous limestones (Šebela, 1998). Surface River Pivka sinks to 511   m at the contact of Eocene flysch rocks with limestone karst rocks (Fig. 1.5) and continues underground forming passages of Postojna Cave toward Planina Cave. The oldest cave sediments from Postojna Cave, that point to the age of cave passages, are dated to >2.58 and   <   3.58   Ma (Zupan Hajna et al., 2020).

Postojna and Planina Caves are type localities for ∼90 species of invertebrates. With more than 100 currently known aquatic and terrestrial troglobiotic species and a large number of troglophile and trogloxene aquatic and terrestrial species, the Postojna-Planina cave system is one of the richest cave systems in the world in terms of fauna. Postojna Cave is described as the birthplace of speleobiology, where the first specimens of cave animals were described (Culver and Pipan, 2014).

Figure 1.5 Ponor or sinking point of the River Pivka to Postojna Cave. 

Photo: S. Šebela.

Predjama Cave is, according to the Cave Register, the third longest cave in Slovenia (16,755   m long and 168   m deep). Extensive speleological research in 2020, which has not been completed yet, indicates extension of the cave passages to ∼17   km (Fidel, 2020), showing the complexity of incompletely discovered the cave system. Only an ∼700   m long entrance part of Predjama Cave is accessible to tourists, with a vertical range of 50.74   m (Šebela and Turk, 2014a, b). The rest of the cave is suitable for trained speleologists only. In a geological sense, Predjama Cave is interesting because the passages run through Upper Cretaceous limestone, Upper Triassic dolomite, and Jurassic limestones and dolomites (Čar and Šebela, 2001), providing a unique example in Slovene caves. The main cave entrances are formed at the tectonic contact between Eocene flysch rocks and Upper Cretaceous limestones (Čar and Šebela, 2001) at the sinking point of the River Lokva at 464   m (confirmed with GNSS receiver). Predjama Cave is developed at more levels with a medieval castle in front of the cave shelter (Fig. 1.6).

The main aim of this monograph is to present and analyze the results of microclimatic data sets from show caves in Slovenia, mostly from Postojna and Predjama Caves, and to define significant changes and their causes during the 10-year monitoring period. Understanding cave climates and cave biology in show caves is between top priorities for realization of sustainable use of the caves for tourism.

In Slovenia, we have a law protecting underground caves (Zakon o varstvu podzemnih jam—ZVPJ), which came into effect in 2004 (http://www.pisrs.si/Pis.web/pregledPredpisa?id=ZAKO2068). The 12th article of the ZVPJ law determines monitoring of the state of the caves, and includes the observation and monitoring of the known caves in the Republic of Slovenia, their living world and cave inventory, ecological conditions in caves, pollution in caves, and the number of visitors. The 13th article of the ZVPJ law prescribes that suggestions of measures needed for preservation and remediation of caves, especially operational program for cleaning of polluted caves, must be included in the regular reports on the state of caves.

Figure 1.6 Predjama Castle is located in a limestone wall in front of the cave shelter of the upper Predjama Cave. 

Photo: S. Šebela.

Show caves in Slovenia need a cave guardian (26th article of ZVPJ law). All karst caves in Slovenia are natural treasures of national importance and are natural public goods that belong to the State. Also, cave infrastructure is a property of the State (5th article of ZVPJ law). Postojna Cave, which is the most visited show cave in Slovenia, is managed by a private company with a concession contract. Predjama Cave is also managed by the same company.

This monographic work provides extensive analysis of the microclimate data obtained from field measurements in the period 2009–20, and is especially oriented to the reciprocity between natural and anthropogenic impacts on cave climates in the show caves in Slovenia. The aim of the research was for examples from microclimate studies from Slovene show caves to provide information that would be valuable for similar show caves worldwide to strengthen international scientific cooperation and understand new scientific challenges.

This book is written on the occasions of:

2021—International Year of Caves and Karst;

1991—2021—30 years of the Republic of Slovenia;

1818—2021—203rd anniversary of the discovery of the most extensive section of Postojna Cave;

1819—2021—202nd anniversary of modern tourism in Postojna Cave;

1819—2021—202nd anniversary of modern tourism in Škocjan Caves;

1947—2021—74th anniversary of the Karst Research Institute ZRC SAZU;

1981—2021—40th anniversary of the ZRC SAZU.

Chapter 2: Purpose of research

Abstract

The purpose of research described in this monograph is to present the complexity of microclimatic research in Postojna and Predjama Caves, especially regarding cave air temperatures and carbon dioxide concentrations. Microclimatic monitoring in show caves is organized as part of environmental protection monitoring, which started in 2009 within expert control for the sustainable use of the Postojna and Predjama Caves for tourism. The goal was to see the relationship between natural and anthropogenic reasons for changes in cave climates in show caves. The fact is that both causes interact, and it is not easy to distinguish between them. In this sense, the microclimate of heavily visited Postojna Cave was compared with the less visited Predjama Cave where the anthropogenic impact due to visitors was eliminated.

Keywords

Carbon dioxide; Cave air temperature; Microclimate monitoring; Postojna Cave; Predjama Cave; Slovenia

Microclimatic monitoring presented in this monograph started in 2009 within expert control for the sustainable use of the Postojna and Predjama Caves for tourism. Some scientific issues related to this subject have already been published (Šebela and Turk, 2011a, b, Šebela et al., 2013, Šebela and Turk 2014a, Gregorič et al., 2014, Šebela et al., 2015a, b, Šebela and Turk 2018, Prelovšek et al., 2018, Pipan et al., 2019), however a lot of unprocessed data remain, which have not been fully analyzed yet and it is hoped that with this monograph the gap will narrow. In additionally to Postojna and Predjama Caves, some preliminary microclimatic results for other Slovene show caves such as Škocjan Caves (inscribed in UNESCO natural heritage), Županova Jama, and Kostanjeviška Jama are included also.

The purpose of the research described in this monograph is to present the complexity of the microclimatic research in selected show caves in Slovenia, especially regarding cave air temperatures and carbon dioxide concentrations. The cave CO2 levels and CO2 exchange take part in processes such as calcite speleothem growth (Faimon et al., 2020). Exchange of CO2 between the underground caves and the exterior is a significant part of the carbon cycle and should be involved in carbon balances (Faimon et al., 2020).

Maximum perturbation cave temperature depends on the number of visitors and the duration of their stay in the cave: the higher the number of visitors and the smaller the cave, the greater is the temperature increase (Rakovec, 2020). When visitors leave the cave, only the exchange with walls remains and the temperature starts to recover toward natural conditions.

Essential increases happen in smaller caves with many visitors. Recovery back to natural conditions is quicker in smaller caves, and slower in larger ones (Rakovec, 2020).

Show caves in Slovenia are important for economic income, tourist experiences, employment, recreation, and also for scientific research. Microclimatic monitoring in show caves is organized as part of environmental protection monitoring. There are caves that have been show caves for 200   years (Šebela et al., 2015a, b) and we are asking ourselves what the impact of long-term visits to a fragile cave environment is and what can be improved to preserve sustainable use of show caves for tourism in the future.

In this work we use the terms   cave meteorology and cave climate (or   cave microclimate   when we speak of smaller portions of the cave system). Badino (2010) used both terms, where climatic was used to indicate average values of a condition, while meteorological referred to fluctuations around it and transient phenomena. In our caves, 10-year air temperature time series with mean annual temperature values are treated as   the cave climate, while   cave meteorology is related to shorter, selected periods with descriptions of interactions between different meteorological parameters such as cave air temperature, carbon dioxide concentrations, direction of air circulation, precipitation, and external air temperature.

The first impressions gained about cave air temperatures can be very disappointing, because air temperature oscillations over 1   year can be less than 1°C, which when compared to outside air temperature can be described as   constant temperature,   pointing to a very stable underground environment. However, in 1965 (Cropley, 1965) it was confirmed that cave temperatures are not necessarily constant but may vary widely. This was confirmed also in our caves with continuous