Technical NoteAnalysis of human induced changes in a karst landscape — the filling of dolines in the Kras plateau, Slovenia
Highlights
► In the study areas, one quarter of dolines have disappeared in the past 40 years and more are endangered. ► Dolines are filled up with construction material resulting in landscape deterioration. ► Excessive human encroachment may have a great effect on karst hydrology or ecology. ► The current standards for karst protection are loose.
Introduction
Karst landscapes most commonly formed in carbonate rocks (e.g. limestone, dolomite) that are water-soluble. Due to chemical weathering, distinctive surface and underground geomorphological features develop with particular hydrological functions (Bonacci, 1999, White, 2002, Ford and Williams, 2007). The most significant landforms for exposed karst landscapes are karrenfields, dolines (sinkholes), and swallow holes. These features on the land surface usually, but not necessarily, develop along fissured and fractured zones. The karst surface is very permeable and enables the immediate infiltration of water into the underground system, where the karstification (solutional enlarging of fissures) creates cavities and organizes a flow net in a hierarchical manner. The interior of the karst is thus characterized by a three dimensional network of underground conduits and voids (Gunn, 1981, Bakalowicz et al., 1994, Drew, 1999, Gabrovšek, 2000, Klimchouk and Ford, 2000, Király, 2002, Worthington, 2009).
Due to the described peculiarities of karst processes, these landscapes are among the most vulnerable environments and the destruction of dolines is among the topical issues in karst environments worldwide (Parise and Pascali, 2003, De Waele, 2009, North et al., 2009). Excessive human activities such as land-use modifications, alteration of surface drainage, opening or blocking of cave entrances make karst areas additionally susceptible to exceptional natural processes, such as the change of recharge conditions and corrosion, which may have a great effect on karst hydrology or ecology. It may for example cause pollution and depletion of water resources, changes of the natural morphology and hydrology, the decline of animal species, etc.
Carbonate rocks cover a non-negligible part of the world's surface (about 12–15%), and in Europe alone around 35%, of which a large part is karstified (COST Action 65, 1995). Karst areas are becoming economically more and more important: many karst massifs contain large amounts of high-quality groundwater resources and only in Europe a significant portion (between 30 and 40%) of drinking water is abstracted from karst aquifers (Bakalowicz, 2005). In some countries (e.g. in Slovenia, Austria) karst water contributes more than half of the supply of drinking water, and in many regions it is the only available source of fresh water. Karst areas that support unique ecosystems very rich in biodiversity (Culver et al., 2009) are abundant also in other resources such as stone, minerals, oil, and natural gas. Due to the environment's high diversity, these landscapes are very fascinating, and represent attractions for tourists to the numerous caves and beautiful scenic areas (Williams, 2008b).
In recent years, due to a variety of activities resulting from comprehensive economic and urban development, an increased pressure on karst landscapes, i.e. by intensive and unsustainable spread of settlement, infrastructure and industry, the development of tourism, and intensive agrarian land use has occurred. The exhaustive reshaping and degradation of the landscape have expanded beyond control largely as a result of technological development and mechanization. The excessive modern filling of dolines, as one of the most distinctive karst geomorphological features, has become a major encroachment on the environment for leveling purposes. Many dolines are filled with construction waste, which threatens the existence of unique habitats as well as the quality of groundwater and consequently the water supply. Some examples of long-term human degradation of karst surface in Slovenia (e.g. Breg, 2007, Cernatič-Gregorič and Zega, 2010) and around the world have already been highlighted (e.g. Drew and Hötzl, 1999, Parise and Pascali, 2003, Calò and Parise, 2006, Ford and Williams, 2007, De Waele, 2009, North et al., 2009).
In Slovenia valuable natural features are protected by the Nature Conservation Act (1999) and are included in the list of the Rules on the designation and protection of valuable natural features (2004). Unfortunately, dolines as “diagnostic landforms” for karst landscapes are not all recognized as valuable natural features and thus are not protected. Consequently, filling, leveling and building up of dolines are allowed without limitations. Only the most exceptional dolines (those largest which are by the rule of collapse origin), have the status of valuable geomorphological natural features of national or local importance.
In this respect the present contribution aims at assessing the filling of dolines and a detailed analysis of human induced changes in the karst landscape. It focuses on particular cases of inappropriate landscape management in the cradle of karst science, the Kras plateau in SW Slovenia where these actions expanded locally beyond control.
Section snippets
Methodology
In two selected areas, changes in land use in the past 40 years and their deleterious effects on karst landscape have been analyzed and evaluated. Special emphasis has been put on the filling of dolines and their destruction.
The study is similar to the multi-temporal analysis of dolines made by Festa et al. (2012) based upon the mapping of dolines from the 1:5000 topographic maps from different periods, i.e. originally published in 1972 and later modified in 1994, and geo-referenced aerial
Description of case studies
The study focuses on the expansion of human activities at two settlements of the Kras plateau (Hrpelje-Kozina and Divača) and on the destruction of the nearby karst landscape. The Kras is a region extending in southwestern Slovenia. It is an area regarded as the cradle of the scientific discipline of karstology due to its typical karst geomorphology. It stretches about over 440 km2 and lies between the Vipava Valley, Brkini Hills, northern Istria, and the Gulf of Trieste (Italy). It is an
Results
The Kras plateau used to be a vast rocky, dry and bare land with no surface running waters, which is today overgrown by forest. Only in dolines was the soil coverage thick enough to be cultivated (Kranjc et al., 1999, Mihevc, 2005). Inhabitants have always considered dolines a significant part of traditional agricultural land use and have transformed them in order to gain as much arable land as possible (Cernatič-Gregorič and Zega, 2010). Clearing of stones from the doline's bottoms and
Discussion and conclusion
Due to the lack of fertile soil and surface water, karst areas have traditionally not been very densely populated and were considered to be less suitable for human settlement owing to unfavorable natural conditions, at least in the temperate zone, arid and semi-arid areas (variegated relief, shallow soil, absence of watercourses on karst plateaus and flood risk in karst poljes or in contact karst).
However, in recent years even karst areas worldwide are facing the expansion of different
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