engleski

Environmental baseline geochemistry of sediments and percolating waters in the Modrič Cave, Croatia

A comprehensive study of Modrič cave, which included mapping, analysis of waters, and cave sediments, as well as age determinations was undertaken to evaluate the baseline conditions within the cave before its utilization for tourism. Silty loams with guano contain abundant quartz, illite and taranakite and minor vivianite and high concentrations of Cu (2869 mg/kg), Zn (951 mg/kg) and Cd (28 mg/kg). Also sediments mixed with guano are enriched with light REE as well as elevated concentrations of U, Th, Rb and Hg in comparison with local topsoil. Sediments with bone fragments contain abundant quartz, illite, calcite and hydroxylapatite and minor carndallite and lower contents of heavy metals. All sediments analyzed showed various degrees of contamination by Cu and Zn from dispersed guano. Most of the Zn and Cu in cave sediments and the hydroxyl-apatite crusts are mainly controlled by the iron and manganese hydroxide and the organic fractions, the organic fraction plays an important role in sediment samples with direct influence of guano and in hydroxylapatite crusts while in samples with bone fragments the hydroxide control is dominant. Guano influenced sediments contain 5 to 10 % of Zn and Cu in the adsorbed and carbonate fractions. Guano influence on the percolating waters was observed in two cases in the left channel where due to the higher content of orthophosphates saturation in respect to hydroxyl- apatite is present. These waters also contain elevated concentrations of Cu, Al, Mn, Cd, Zn, K, nitrates and ammonia. The contents of d18O and d2H in the percolating water are similar to those of infiltrated coastal precipitation water of the region.

speleology ; cave sediment ; cave mineral ; gauno ; Modrić cave ; Croatia

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