Karst Hydrogeology and Human Activities: Impacts, Consequences and Implications

IAH International Contributions to Hydrogeology 20

David Drew

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351436120
• Edition: 1
• Topic: Ciencias biológicas
• Subtopic: Ciencia medioambiental

One quarter of the world's population lives in karst terrains, yet karsts are highly vulnerable to stresses caused by human activity. This book surveys human impact on karst water, showing that the increasing pollution of the environment has, to a great extent, spoiled sensitive karst ecosystems. This text examines such consequences and offers proposals for future solutions and strategies. Part One provides an overview of the functioning of karsts and of human interaction with karst environments over several millennia. Part Two consists of a systematic examination of the major areas of human activity affecting karst waters, such as agriculture, industry, mining and water exploitation. Finally, Part Three views the effects on karst groundwater within a broader societal and legislative perspective and considers possible changes of methodology and approach.

Part 1: Karst waters and human activities: An overview

CHAPTER 1

Introduction

DAVID DREW

Department of Geography, Trinity College, Dublin, Ireland

1.1 THE PURPOSE OF THE BOOK

A concern for the effects that human activities have upon the environment is now widespread, in large part of course, motivated by the adverse effects that environmental degradation may have upon the quality of human life. One particular hydrogeological environment, that commonly termed karstic, is the concern of this book for three main reasons:

1. Karstic terrains (underlain by highly soluble rocks) are highly sensitive and vulnerable to imposed stress. Karsts usually lack resilience in the face of such stresses – in this instance those generated by human processes.

2. The response of karst and karst waters to such pressures is highly distinctive and sets the karst environment apart from other terrains irrespective of location or geological type.

3. Although only some 7-12% of the Earth’s land surface is underlain by karstic rocks (depending on the definition of karst chosen) karst regions provide water supplies for up to a quarter of the world’s population (Ford 1990) including more than 100 million people in China alone and including significant proportion of the populations of many countries of Europe (Fig. 1.1). Also many karsts are areas of outstanding scenic value and are major tourist attractions thereby increasing the intensity of human impact on their geological and hydrological systems.

Therefore, an understanding of the basis for the distinctiveness of the karst system and its workings in the context of human activities is likely to be of value to a variety of professionals whose work may at times involve them in aspects of karst and karst waters. Such people would include hydrogeologists who lack specialist training in karstic hydrology and engineers, particularly geotechnical engineers operating in karst terrain. Equally, environmental planners, legislators and other policy makers and decision takers who function occasionally or frequently in a karstic milieu would benefit from a knowledge of the fundamentals of human impact on karsts. It is to these people rather than to the professional karst hydrogeologist and geomorphologist that this book is addressed.

1.2 CHARACTERISTICS OF THE KARSTIC SYSTEM

The term karst is used to describe an area of limestone or other highly soluble rock, in which the landforms are of dominantly solutional origin and in which the drainage is underground in solutionally enlarged fissures and conduits (caves). In this book the emphasis is on karst terrains developed in limestone and dolomite rocks with the exception of Chapter 6.7 which is concerned with impacts in a halite (sodium chloride) karst region of the USA. However:

‘All terrains in which carbonate, sulphate or chloride rocks crop out or are in the shallow subsurface are probably some type of karst (Johnson & Quinlan 1995).’

Another useful definition of non-evaporite karst is provided by Quinlan et al. (1995):

‘…any terrane in which carbonate bedrock (limestone and/or dolomite and/or chalk) is exposed, is present beneath soil and/or regolith, and/or may be partially or totally capped by other sedimentary rock. Sinkholes, springs, caves, integrated conduits (dissolutionally enlarged joints (fissures) and/or bedding planes) may be present in a carbonate terrane but may not be obvious. The presence at the ground surface of one, some, or all of these features is not necessary for a carbonate terrane to be defined as a karst. … Some karst terranes are more extensively developed than others. ‘

Carbonate rocks are widespread as may be seen from Figure 1.1 with Europe having the largest percentage of carbonate rock outcrop relative to its area of any continent (Fig. 1.2).

Figure 1.1. Major outcrops of carbonate rocks, most of which exhibit karstification at least to some extent (after Ford & Williams 1989).

The degree to which the rocks have been karstified varies greatly from place to place depending upon how much the fissures in the rock have been enlarged by the solutional action of acidified rainwater and the extent to which the underground drainage system has become organised and integrated into efficient conduits for the collection, transport and ultimately discharge of recharge waters. In general, pure, highly soluble carbonate rocks with well developed secondary permeability karstify best. In some areas the karstified rocks may be overlain with non-carbonate strata or unconsolidated deposits and this is termed a covered or mantled karst.

Figure 1.2. Major outcrops of karstified carbonate rocks in Europe (after Bakalowitz & Biondic in EC COST 65).

Old karstic landforms, surface and underground, which have been infilled by subsequent deposits, often have no surface expression and do not function hydrologically. They are called palaeokarsts. Palaeokarst may be reactivated to some extent if environmental conditions change.

Prohic (1989) remarks that what distinguishes karst systems from non-karst systems is the existence of solutionally enlarged underground spaces in which the groundwater is stored and moves and the occurrence of complex and deep interconnections between surface and underground which are much more apparent than in conventional hydrogeology. He also identifies the characteristics of many karsts that render its groundwater particularly liable to contamination (Fig. 1.3):

1. There is often little or no soil or cover which means poor filtration, poor pre-purification, rapid infiltration (this is not explicitly a karst water factor but an incidental aggravating factor).

Figure 1.3. Illustration of the various modes of recharge, flow and discharge in a karst area (adapted from Gunn 1985).

2. Flow is turbulent and conduit dominated and there are no fine grained aquifers and so only limited self-purification.

3. High flow velocities allow transit times that may be too short for microorganisms to die off, particularly in shallow groundwater systems.

4. Large numbers of interconnected fissures mean that pollution inputs are possible from the surface almost anywhere.

Prohic (1989) also observes that it is unfortunate that enclosed depressions such as dolines are such a common landform in most karst areas because they are at one and the same time, tempting sites for waste disposal (and for leachates etc. to flow down into) and also the major recharge input zones to ground water.

For many people a karst region is visualised as a spectacularly rocky and barren terrain with disappearing rivers and many caves (Photos 1.1, 1.2). This is a true picture of some exceptionally well developed karst regions but many degrees of karstification can exist from slight to extreme. The absence of obvious karst features such as those mentioned above does not necessarily mean that karst processes are not operative in an area.

Photo 1.1. Karst landscape in the Yorkshire Dales, England, with limestone pavement and impressive karren formations (photo: Drew 1972).

Photo 1.2. The ‘small natural bridge’ of Rakov Skocjan, Slovenia, forming a collapsed part of the underground connection from the Cerkniško Polje to the Planinsko Polje (photo: Hötzl 1982).

All of the above statements concerning karst hydrogeology are generalisations but the extent to which they apply to any given area is much more difficult to ascertain. It is often said that the only predicable thing about karsts are their unpredictability, and indeed the site specific nature of karsts is a major problem as is apparent from the examples presented in this book.

Much fuller descriptions of the character of karst landforms and hydrology may be found in Ford & Williams (1989) in White (1988) and in LaMoreaux et al. (1984). A good summary of the nature of karst groundwater systems with particular emphasis on their vulnerability is also given in the pan-European project report COST action 65 (EC-COST 65 1995).

1.3 HUMAN IMPACT ON KARST

As remarked in Section 1.1, in recent decades there has been a shift from an attitude towards the environment that centred upon exploitation of its resources and containment of those aspects of the environment that threaten human beings, to a more holistic approach towards living in and intelligently managing the resources of our planet. Environmental impact assessments for proposed projects are now the norm and concern over possible long term environmental impacts caused by human activity such as changes in climate is increasingly a part of the political agenda.

This changed perspective has been reflected in attitudes towards karstic environments. For example, a symposium focused on karst water resources is held in Turkey every five years and the papers delivered are an indication of priorities in karst investigation. At the 1985 meeting (Günay & Johnson 1985) only one of 46 papers was concerned with human impacts. At the 1990 symposium (Günay et al. 1990) some 5% of presentations were oriented towards human impacts but at the 1995 meeting, which was explicitly entitled Karst Waters and Environmental Impacts (Günay & Johnson 1997) 15% of contributions dealt with human-environmental problems in karsts.

A similar change of emphasis may be seen in the series of symposia held by the Sinkholes Institute in the USA at approximately two year intervals and concerned with sinkholes in karst terrains Beck (1984, 1989, 1993, 1995), Beck & Wilson (1987), Beck & Stephenson (1997). The thrust of the contributions to these symposia has altered from the hazards posed by karst terrains to investigations of anthropogenic processes in karsts.

In recent years a series of publications have dealt with human impacts on karsts although in many cases the focus has been upon changes caused to soils, vegetation, landscapes and caves rather than to water in karst regions. Examples of these studies include the publications of the International Geographical Union study group on Human-Karst Interaction: Mans Impact on Karst (International Geographical Union 1987), Resource Management in Limestone Landscapes (Gillieson & Smith 1989), Environmental Changes in Karst Areas (Sauro et al. 1991). A special supplement of the journal Catena entitled Karst Terrains: Environmental Changes and Human Impact (Williams 1993) contains a number of case studies of degradation of karst areas together with a summary of the character of karst aquifers and their susceptibility to pollution (Smith 1993). Similarly an issue of Environmental Geology (Ford 1993) had as its theme Environmental Change in Karst Areas. Environmental Effects on Karst Terrains was the theme of an issue of Acta Geographica Szegediensis (Barany-Kevei 1995) with an eastern European perspective. Similarly a special issue of the journal Acta Carsologica dealt with the topic: Man on Karst (Kranjc 1995) as did the symposium held in Poland in 1996 Karst-Fractured Aquifers – Vulnerability and Sustainability (Rozkowski et al. 1996). Although concerned largely with caves, the Australian book: Caves: Processes Development, Management (Gillieson 1996) also explicitly addresses more general problems of conservation of karsts.

Although comparatively few of the publications mentioned above are primarily concerned with impacts on karst waters they do illustrate the complexity of chains of cause and effect in karst terrains.

Figure 1.4 is adapted from Williams (1993a) and summarises the consequences of various human activities on the karst system. The impacts upon karst waters have been emphasised. As Williams notes, modifications to vegetation can provoke soil erosion, but unlike non-karstic areas, the eroded soil does not accumulate in river valleys but rather in the numerous enclosed depressions (for example dolines) that characterise many karst regions. Dolines are points at which concentrated recharge of a karst aquifer takes place and therefore modifications to dolines alter the groundwater hydrology of the area. Even if dolines are not apparent in...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• PREFACE
• LIST OF AUTHORS
• PART 1: KARST WATERS AND HUMAN ACTIVITIES: AN OVERVIEW
• PART 2: THE NATURE OF HUMAN IMPACTS ON KARST WATERS
• PART 3: IMPLICATIONS AND CONCLUSIONS
• REFERENCES
• SUBJECT INDEX
• LOCATION INDEX