Marta Čović

Distribution of Iron and Manganese in Terra Rossa from Istria and its Genetic Implications

Haematite and goethite are the predominant pedogenic mineral phases in terra rossa from Istria. Limited variation of selected Fe oxide characteristics in analysed samples indicates the specific pedogenic environment in which terra rossa is formed. The mean value of the Fed/Fet ratio, taken as an index of weathering is 0.7 and reflects quite a high degree of weathering of Fe-containing primary silicates. Relatively uniform Fed/clay ratios clearly indicate a predominance of co-illuviation of clay and Fe oxides. Low values of Feo point to the low content of poorly crystalline Fe oxides in analysed terra rossa. Feo/Fed ratios in the analysed profiles vary. In the upper part of the Pomer, Porec and Novigrad profiles Feo/Fed ratios are higher than in the lower part of those profiles which may be explained as a result of different pedogenic environments and/or additions of external materials in the upper part of those profiles. The lack of positive correlation between Mnd and clay and Mnd and Fed is a consequence of remobilization of manganese due to hydromorphic processes which post-dated co-illuviation of clay and Fe oxides. During the Late Tertiary and Quaternary the pedogenic environment on hard carbonate rocks of the Jurassic-Cretaceous-Palaeogene carbonate plain of southern and western Istria generally remained suitable for rubification. However, (Neo)tectonic activity and the input of external material, as well as various climatic fluctuations might have significantly effected terra rossa through the processes of erosion, colluviation, yellowing and secondary hydromorphy.

Partitioning of Heavy Metals in Sequential Extraction Fractions in Soils Developed over the Historical “Sv. Jakob” Silver Mine, Mount Medvednica, Croatia.

Phase-selective sequential extraction techniques have been used to identify the residence sites of metals in soils developed over a historical silver-mining site. The operationally defined phases selected for extraction have been assigned to the following five fractions: adsorbed, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The following reagents had been used: NH4-aceate, Na-acetate, hydroxylamine hydrochloride, hydrogen peroxide + nitric acid, mixed acids (HCI-HNO3-HF), respectively. The solutions were analysed by atomic absorption flame photometry (Pb and Cd) and inductively coupled plasma atomic absorption photometry (other analysed elements). Mineralogical analysis was performed to detect Zn-Pb-bearing phases and cerussite was the only phase detected. Other mineral phases detected by XRD in the soil samples were as follows: quartz, dolomite, micas, plagioclase, K-feldspar, goethite, hydrargillite, kaolinite, chlorite, and organic matter. Assuming that mobility and biological availability are related to the solubility of the geochemical forms of the metals and the latter decreases in the order of extraction, the apparent mobility and potential metal bio-availability for these highly contaminated soils is: Cd> Pb> Zn> Cu> Ni. The distribution of Pb, Zn and Mn in mineral phases is similar in samples with both high and baseline trace-metal values. Cu, Fe, and Ni exhibit different distribution patterns in the two types of samples.