Natural and anthropogenic hazards in karst areas: an introduction

Abstract

The distinctive hydrology and landforms of karst create a very special environment. Although several types of karst have been identified worldwide, a common thread is the dominantly subterranean drainage. The paucity of water flowing at the surface, a consequence of rapid infiltration underground through a network of discontinuities in the soluble rock mass, results in two important but contrasting points: the considerable value of karst water resources (representing about 25% of the drinkable supply in the world) is strongly counteracted by the ease with which human activities can negatively impact this precious resource. The same narrow discontinuities, and the larger dissolution conduits and karst caves, are the main pathways through which potential pollutants may travel swiftly to regional groundwater bodies, or directly to springs. Contaminants can be introduced by means of dispersed infiltration as well as from point sources and are frequently transmitted with minimal filtering. This example, just one of the many natural and/or anthropogenic hazards that may affect karst areas, illustrates the fragility of karst environments. Their high vulnerability is further expressed by a very simple concept that is true for many other environments but probably shows its best evidence in karst: it is very easy to damage or destroy natural resources but restoration to a pristine situation is an extremely difficult and commonly impossible, task. Where some degree of remediation is possible, the economic cost is commonly very high. Since the early 1960s there has been a great deal of progress in understanding the processes and landforms of karst areas (e.g. Ford & Williams 1989; Gillieson 1996; Klimchouk et al. 2000; Gabrovsek 2002). There have also been several initiatives designed to translate theoretical knowledge into practical application, for example work by the International Geographical Unions Karst Commission (Williams 1993; Barany-Kevei & Gunn 2000), the IUCN (1996) and the World Bank (Vermeulen & Whitten 1999). However, projects continue to fail, and resources are lost or damaged owing to a failure in understanding the peculiarities of karst (for examples see Waltham et al. 2005). Hence, there remains a strong need to develop appropriate techniques to manage karst landscapes and protect karst resources. There are many human activities that, intentionally or not, produce severe impacts in karst, often with irreparable damage. For example, in some regions land degradation has been intense with deforestation and overgrazing leading to soil erosion, destruction of the epikarst and rocky desertification. Rehabilitation of these desert lands is extremely difficult, although in some parts of the Mediterranean reduction of grazing has been followed by a return of shrubs and small trees. Legislation, and even more its practical enforcement, still appears to be extremely inadequate at facing these problems, even in well-developed countries. Lack of laws and acts specifically devoted to karst is very common, but even when legislation takes into account the complexity and peculiarity of karst the potential benefits deriving from these acts frequently remain on paper owing to a lack of enforcement and control by the authorities. The best example is probably provided by the management of aquifers in carbonate rocks, as this requires an understanding of the character and type of water circulation within the rock mass. For many years the principles developed for non-carbonate aquifers, and the resulting methodologies created for groundwater vulnerability assessment, have also been applied to karst environments. However, it has long been known that the planning and management of carbonate aquifers poses different problems to those encountered in non-carbonate groundwater. Karst groundwater watersheds often do not coincide with topographic divides, to indicate just one of the main differences between karst hydrology and those in other environments. Only in recent years have some significant efforts been produced to give due weight to the peculiarity of karst hydrology and hydrogeology (for example, the COST 65 (1995) and subsequent COST (Co-Operation in Science and Technology) programmes in Europe and the report by Eckenfelder Inc. (1996) in the United States).