Soil baseline geochemistry and plant response in areas of complex geology. Application to NW Euboea, Greece

A soil and vegetation survey was undertaken in NW Euboea Island, Greece. The objectives of the study were to establish the geochemical baseline of soil and identify the impact of local geology on threshold values of potentially harmful elements. The studied area is characterized by complex geology comprising metamorphic and ultramafic rocks as well as active hot springs. A total of 117 soil samples were collected from 89 sites at depths of 0–25 cm and 25–50 cm. Eighteen vegetation samples were also collected representing prevalent indigenous perennial species in the region. Soil samples from the present study were enriched in As, Ca, Cu, Mg, Ni with concentrations reaching 233 mg/kg, 38%, 336 mg/kg, 10.8%, 1560 mg/kg respectively. Factor analysis revealed three main factors controlling the chemical composition of soil reflecting the influence of ultramafic rocks (Cr, Ca, Mg, Ni), hot spring deposits (Ca, S, Sr, As) and paedogenesis processes (Fe, Co, V, Mn, Al). The first two of these factors showed significant spatial correlation with the geological features within the study area. Subsequently, baseline concentrations based on statistical and spatial data were estimated within sub-areas reflecting the influence of local geology in soil composition. Concentrations of potentially harmful elements in the plant tissues of indigenous perennial vegetation species showed a wide range of variation from below the detection limit up to 1700 mg/kg for Ni in the hyperaccumulator Alyssum chalcidicum demonstrating that plant species have adapted to the stressful conditions caused by high elemental concentrations in soil. The results of this study can be utilized in future studies at areas of similar geology by providing an objective basis for setting realistic threshold values for pollution assessment and remediation.