Evaluation of terra rossa geochemical baselines from Croatian karst regions

Abstract

In karst regions of Croatia, regolith is the only favourable medium for geochemical mapping. Mediterranean climate and good drainage due to hard, fissured, permeable limestones and dolomites result in a spacious distribution of terra rossa (FAO-luvisols and cambisols) — a polygenetic type of soil. Samples of terra rossa from coastal and inland Croatian Dinaric karst terrains were collected during the initial studies for the Geochemical Map of Croatia at a density of 1 site/25 km 2. A total of 87 terra rossa soil samples taken from a depth of 5–25 cm together with 27 samples from deeper profiles (down to 850 cm) were analysed for total Al, Ba, Ca, Co, Cr, Cu, Fe, Ga, La, Mg, Mn, Ni, Pb, Na, Sr, Ti, V and Zn concentrations. A stoichiometric approach was applied by modeling of terra rossa baselines on the basis of linear regressions of metals on Al and the calculation of enrichment factors (EF and CEFs) on the basis of soil standards. A noticeable enrichment of Pb was found in surface samples compared to the terra rossa deeper in the soil profile. Using these baseline relationships, an attempt is made to partition terra rossa metal concentrations into natural and anthropogenic fractions. Also, the models from both polluted and less polluted (uninhabited) karstic terrains improve the comparability of element contents through correction of variable background concentrations. A comparison of elemental concentrations revealed that due to contributions of bauxite debris, a number of studied samples is enriched in Cr and Ni (also with variable amounts of boehmite). The corrections will serve to reduce data variability and to increase the detection of spatial and temporal differences presented on the geochemical maps.