engleski

Geochemical Mapping of Topsoil in Croatian Karst: Provenance Implications and Pollution Signatures

The results of geochemical baseline mapping performed in dominatly karst parts of the Croatia show that soil chemistry is influenced by diffrent geogene sources from which the soils were derived. As most of the underlying carbonate rocks contain low insoluble residua the chemistry of mineral dust from which the soils were formed originated from two sources during thr LGM the Po and the Neretva rivers floodplains which were submerged during the Holocene sea level rise. These two different provenances give the distinct geochemical patterns. The high concentrations of Al, As, Co, Cu, Fe, La, Pb, Ni, Mn, Th, V, Cr, and Zn have higher mean values in soils transported (by wind) on carbonate bedrock from the Neretva floodplain during the LGM than hose from the Po plain. An interesting association of elements in a geogene sense is Zr (Fig. 3)-K-Na-Ba association of elements with high concentrations associated with soils on the large Adriatic islands Mljet, Korčula, Hvar Brač and the Pelješac peninsula and central and southern Dalmatia. The geochemical mapping program whose goal is to determine geochemical baselines i.e., the distribution range and variation of chemical elements in soils of the Croatian karst region was used in this case to asses the extent of environmental change in a protected natural reserves due to human influence (acid rain) on the distribution of the Pb. Other elements attributed to atmospheric pollution show a less pronounced increase in concentration (Zn, Cd, As, Hg). With the application of the Pb/Sc ratio obtained during the geochemical baseline mapping of the topsoil cover in the Croatian at 1550 sampling sites, the spatial risk of acid deposition in areas of high geomorphic variability was evaluated. The use of normalization on Sc to evaluate probable anthropogenic inputs of Cu, Zn, and Pb, is based on calculation of enrichment factors (EF) for these elements. The EF is a concentration ratio of a given element (Cnsample) to the conservative element (Sc in this study) in the sample (Ccons.sample) with respect to same ratio in the standard material Cn ref./Ccons. ref. (Förstner & Wittmann, 1981 ; Li, 1981): EF = (Cnsample/Ccons.sample ) / (Cn ref./Ccons. ref.) This calculation method of enrichment factors in sediments is widely used in environmental studies and usually relies on the use of the average composition of shale which often is not necessarily representative of the local or regional sediments and soils in the study area (Van der Weijden, 2002). Therefore a calculation procedure which does not use an average referent material but rather concentrations of heavy metals and conservative elements from deeper layers (Ferguson, 1990 ; Ridgway & Shimmield, 2002) as relative background geogenic ratios was used to asses possible anthropogenic inputs. Also an empirical model built on the neural networks related the amount of atmospherically introduced Pb (calculated from the Pb/Sc normalization variable which separates the anthropogenically introduced Pb from lithogenic lead), extent and type of forest cover, digital elevation model with its variations as well as the mean annual precipitation. The correlation model was very high (R>0.85). The presented model, which links soil geochemistry with precipitation and degree of forest damage, was found to be a suitable tool for evaluation of the spatial acidification risk. Although the central and southern Dalmatian karst soil have higher mean concentrations of Pb than most soils in the high mountain karsts (only soils at altitudes higher 1000 m have elevated Pb concentrations) these concentrations are of geogene origin related to source materials from the central Bosnian ore mountains.

geochemical baseline mapping; atmospheric pollution; karst soils; enrichment factors; provenance

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