engleski

Human and climatic impacts on karstic phenomena - examples from Croatia and Hungary

A Hungarian-Croatian joint project is dedicated to environmental changes on karstic sites with special attention to recent processes. In the framework of this ongoing project we investigate impacts of human activities and effects of recent climate change on karstic sites. Four case studies are to present giving an impression about environmental hazards threatening karstic phenomena of our countries. 1. Ice cave study Ledena Pit in Lomska duliba (Ledena jama u Lomskoj dulibi) and Vukušić Ice Cave (Vukušić snježnica) are located in the northern part of the Velebit Mts both of them host significant perennial ice body. Ledena Pit (1235 m asl) is a knee-shaped, 536 m deep karst pit. A part of the entrance pit preserves a vast ice block. It spreads from 50 m depth to 90 m depth, and takes 20 30 m in diameter. Vukušić Ice Cave (1490 m asl) is located near the Zavižan Peak. Thickness of its ice deposit is estimated to be more than 10 m. On the basis of historical cave maps and recent monitoring data ice level subsidence were estimated to 9.2 m and 0.25 m between 1962 and 2008 in Ledena Pit and Vukušić Ice Cave, respectively. The ice loss trend in Ledena Pit has seemed to slow down since the mid 1990s. High amount of snow and low winter temperatures are regarded as favouring climatic factors to maintain cave glaciation. Climate scenarios predict milder winters for the Velebit Mts so continuing ice loss can be predicted for this special icy speleothems in the near future. 2. Monitoring environmental changes by investigation of stalagmites and drip waters The detailed study of speleothems and modern cave dripping waters are essential to interpret paleoclimate records. However the monitoring of recent formation processes may contribute significantly to our knowledge of the behaviour of the cave deposits and the environmental factors. 2.1. Comparison of the recent and palaeoclimate records from the continental and coastal caves In order to compare past and present environmental conditions in continental and coastal parts of Croatia, two caves, Baraćeve and Modrič Cave, were chosen for the stalagmite and dripwater isotopic studies. Modrič Cave is located on the eastern Adriatic coast at the altitude of 32 m asl some 120 m from the coastline at the SW slope of Velebit Mt. It is generally horizontal cave and consists of two channels with total length of 829 m. The cave was formed in Upper Cretaceous limestone and current thickness of the overlaying bedrock varies from 1 to 27 m. Vegetation cover above the cave is maquis and the region is under Mediterranean climatic influence with mean annual temperature of 15.9 °C, and mean total precipitation of 1199 mm/a. Barač’ s caves are located in the middle part of the Slunj karst plateau, which is mainly built of limestone and has typical characteristics of karst relief. On the fault contact of the permeable and impermeable rocks springs and ponors are situated. There are three dry caves: Gornja Baračeva (520 m long), Donja Baračeva (565 m long) and Nova Baračeva (94.5 m long). The active cave in the Baračevac spring is ~450 m long and channels are mainly full of water. The Barač's caves have been formed by work of the undergrond water stream which now flow trought Baračevac spring cave. Obtained results of Croatian case studies will be compared with Hungarian sites in order to reconstruct (palaeo)environmental settings further to the north 2.2. Isotope hydrology and chemical investigation of dripping waters in urban environment The Szemlohegy Cave is one of the well-known show caves of the Buda thermal karst region, situated underneath of the densely populated Budapest. The studied 9 drip sites revealed significant differences in term of the studied parameters according to the mapped coverage of the surface, the contribution of the anthropogenic pollution and the type of vadose flow towards the dripping site. Temperature, pH and specific electric conductivity measurements were carried out weekly within the cave beside the quantity readings, along the collection of water samples for chemical analyses (Mg2+ ; Na+ ; K+ ; HCO3- ; Cl- ; SO42- ; NO3-). According to our results „ natural” and „ polluted” sites were distinguished. “ Polluted” sites represents important anthropogenic effect in the chemical composition of drip waters (elevated Na+, Cl-, NO3- and co-variation with precipitation amount). The leakage of water-conduit and wastewater can be demonstrated, as this was also confirmed by the study of d18Owater. 3. Detection of U ore mining effects in speleothems Our objective was to determine the possible effect of the uranium (U) ore mining activity on the environment, as recorded by a cave deposit. The investigated Trio Cave is located in S-Hungary 1.5 km east of the nearest air shaft of the Mecsek uranium mine. The uppermost ca. 3 cm of a stalagmite core were selected for this study, which represents the last few hundred years. With increased detrital input in the uppermost ca. 3 mm, the U concentration also increased radically (especially in the topmost 1.3 mm), starting from a background value of 0.2-0.3 ppm, to about 2 ppm, followed by constant values for about 0.5 mm, and then declining to about 1.5 ppm The relationship between changes in the U content and d234U values of the speleothem, and the history of U ore production and pollution strongly suggest a causal link. Our study therefore demonstrates that speleothems can reliably record environmental pollution signals, a hitherto largely unexplored source of information.

speleothem; isotope hydrology; geomorphological mapping; Croatia; Hungary

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