Soil chemistry of heavy metals under contrasting vegetation covers
The site of study (Pollok Park, Glasgow) features soil under both a coniferous canopy (predominantly Corsican Pine) and a deciduous canopy (predominantly Beech). There is a clear segregation between the two vegetation types which enables a direct comparison into the contribution of canopy type to the heavy metal distribution in soil. Average total metal contents of cores extracted from the two soil types indicated that the deciduous cores have a greater total content of Cr, Cu, Fe, and Mn, and that the two core types contain approximately the same Pb and Zn content. Concentration profiles for Cr, Cu, Fe, Mn, Pb and Zn were established for the two soil types. They showed enrichment of Cr, Cu, Pb and Zn at the surface. Correlation graphs [LOI vs. metal (Cr, Cu, Pb and Zn)] showed there to be a correlation between organic matter content and concentrations of these metals. Molar ratios (carbon : metal [Cr, Cu, Pb and Zn]) were estimated from the correlation graphs. In each case, these were found to be of considerable value, indicating that perhaps these metals are complexed by large organic molecules. Mn and Fe showed no enrichment to the surface and no correlation with organic matter. Speciation studies (Modified BCR sequential extraction procedure and cupric ISE investigations) were conducted on the surface soil (top 5cm), litter and leaves taken from below both vegetation types (deciduous and coniferous) in order to gain an understanding of soil-metal associations. The deciduous and coniferous soils were found to have virtually identical fractionation patterns of Cr, Cu, Pb and Zn (Modified BCR sequential extraction).