engleski

Impacts of past mining and present aggregate quarrying on Dalmatian karst environment, Croatia

The carbonate (karst) terrains, which have the attributes of carbonate platforms consist of the karstic Dinarides, the Adriatic belt and the Adriatic Islands. This unit covers approximately 50% of Croatian territory. The Dalmatian karst located within the Mediterranean region lacking any significat soil cover (bare karst) due to the open hydrological system reacts very fast to anthropogenic activity. Within the karst of the Dalmatian region more than 1000 deposits of bauxite located within a belt 150 km long were mined during the second half of the 20th century. The Dalmatian region is also an area that has a high production of primary and secondary aggregates (debris from dimension stone production). In the four Dalmatian counties aggregates and natural stone are quarried at 155 sites and there are 73 abandoned sites (Fig. 1.). Most aggregate producers in the study area are sited in counties with high population densities. Negligible aggregate producing operations are sited in municipalities with low population densities, reflecting the lack of a sufficient market demand for aggregate in most rural areas. The bauxite production was terminated during the early 1990-ties due to unfavourable market prices and the expensive underground mining. The past bauxite mining practices have resulted in two types of environmental impacts ; dispersion of bauxite dust by wind (more) and surface water (less) which has changed the topsoil chemistry and numerous open pits (more than 800) of which some are deeper than 400 m. The bauxite pits are a constant threat to the water resources since they have been used as illegal and uncontrolled waste disposal sites. The bauxites are enriched in Cr, V, As, Cd, Ni and Pb. During a geochemical topsoil mapping program which covered the whole Croatian karst region with almost 1700 sampling sites it was determined that the soils from the Dalmatian region had 30 to 50 % higher concentrations of these metals than other karst regions (Fig. 2.). Using normalization on conservative elements, mineralogical and GIS methods an attempt was made to determine whether the elevated concentrations of metals in soils are a consequence of bauxite mining or is the bauxite signature in the soils inherited as a geogene imprint of bauxite dust debris from outcrops on soil formation during the Pleistocene and Holocene. The carbonate aggregate quarries are visually, in landscape terms, the most dramatic anthropogenic impact on Dalmatian karst terrain. And as in the case of bauxite pits, abandoned aggregate quarries are frequently used as illegal disposal sites threatening groundwater. In order to minimize future impacts of aggregate quarrying on the karst landscapes, GIS modeling has been proposed as a tool for optimal site selection of new quarries. The modeling is based on map- correlation and map-integration processes, in order to define relationships between spatial layers (e.g. GIS layers containing environmental variables) and combine predictor factors in supporting a hypothesis. In this study, the response variable is the set of point locations of current aggregate and natural stone quarries (termed training sites), and the predictor variables (termed evidence themes), are thematic map layers (scale 1:100, 000) showing transportation network patterns, population density distribution, maps of geological mineral potential, and areas of mineral exploitation restrictions defined by Master plans of the counties (protected areas and landscapes, distance to the coast) and visual exposure based on DEM analysis. The evidence themes have categorical values (e.g., aggregate production status), or ordered values (e.g., distance to an object such as a highway). The aims of this study are to raise awareness of various mining problems and impacts on karst, to help manage better the use of mineral resources in Dalmatia, based on identification of more suitable areas for stone production by taking into account both environmental and marketplace restrictions and to help local environmental policy makers to correctly manage the fragile karst environment and to preserve the natural landscape.

Bauxite ; Karst ; Geochemistry ; Mineral resources ; Soil ; GIS-modelling

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