Influence of ultramafic rocks and hot springs with travertine depositions on geochemical composition and baseline of soils. Application to eastern central Greece

摘要

Ultramafic rocks and hot springs, which occur on almost every continent of our planet, lead to enriching concentration to several elements, including some potentially toxic ones, to the soil, groundwater, fauna and flora, and subsequently are posing potential risks to human health. A geochemical and mineralogical soil survey was undertaken in eastern central Greece, an area characterised by the presence of ultramafic rocks of ophiolite complexes and hot springs, with thermogenic travertine depositions. The research aimed to investigate their influence on soil mineralogy and geochemistry and to establish the soil geochemical baseline values. One hundred four soil samples were collected from 74 sites at depths of 0-25 cm and 25-50 cm. They were found to be enriched in Ca (5.17%), Fe (3.72%), Mg (2.08%), Co (28 mg/kg), Cr (252 mg/kg), Cu (32 mg/kg) and Ni (267 mg/kg) relative to the median values of both Greek and European soil and upper continental crust. Factor analysis revealed three main factors controlling the soil chemical composition reflecting the influence of ultramafic rocks (Ni, Co, Cr and Fe), pedogenesis processes (Ba, Al and K) and thermogenic travertine deposits (Ca and Sr). All the factors showed a significant spatial correlation, with the geological features within the study area. Geochemical baselines were estimated for three sub-areas, based on the three controlling factors, revealed by the multivariance statistical analysis and spatial data. Calculating only one baseline value, based on the total dataset, would lead to incorrect baseline values for several elements. The outcome of the present research could be used in future studies at regions with similar geological features, i.e. serpentine soils and hot springs depositions, providing a comparative example concerning the concentrations of several elements, including some potentially toxic ones to the soil, their host mineral phases and a scientific approach for setting pragmatic geochemical baseline values for pollution assessment.