Abstract
The last decades have recorded a growing interest in geochemical mapping, and refined statistical techniques have been used in order to define the pedogeochemical content of potentially toxic metals in soils, following definition by ISO/DIS 19258. Advances in sedimentological and soil research provide today the opportunity to examine distribution of pedogeochemical contents of selected elements within a mixed pedological and sedimentological framework, through integration of geochemical data with detailed soil characterization.
Pedological and geochemical analyses of 200 soil samples from 100 sites of Parma alluvial plain (Sheet 181 of Soil Map to 1:50,000 scale), collected within depths of 20-30 cm and 90-100 cm, respectively, enable precise identification of the pedogeochemical content of selected geochemical elements as a function of soil maturity and sediment provenance. Increasing soil evolution invariably results in Ti, Zr, V, Fe2O3 and Al2O3 enrichment. In contrast, Ca is strongly depleted in highly mature soils, in response to leaching processes.
Similarly to what recently documented from the Po Delta area, sediment supplied by Po River to Parma alluvial plain is characterized by remarkably high natural concentrations of Cr and Ni, reflecting erosion of ultramafic complexes cropping out in the Po drainage basin. A striking similar composition is recorded within sediments supplied by Taro River, which also hosts ultramafic rocks in its drainage basin. In contrast, a markedly different composition, with significantly lower Cr and Ni values, is recorded within sediments supplied from other Apenninic (Stirone, Parma and Ongina) rivers. Soil distribution of other metals, such as Cu, Zn and Pb, does not reflect important differences in sediment provenance.
In order to obtain a realistic view of the pollution status of the study area, the pedogeochemical content, measured at 90-100 cm depth, was matched against metal content recorded in topsoil units (20-30 cm). Despite their locally very high concentrations, nickel and chromium do not show enrichments due to anthropogenic disturbance. In contrast, a diffuse (although moderate) soil contamination is observed for copper, lead and zinc.
The Pedogeochemical map illustrated here, including a Map of Pedogeochemical Content and a Map of Geochemical Anomalies, represents a novel approach to geochemical mapping. This map constitutes a powerful tool to assess the anthropogenic impact on alluvial plains, which can be of use for legislative purposes and for planning strategies for environmental protection.
Keywords: Pedogeochemical map, Heavy metals, Sediment Provenance, Geochemical anomalies, Po Plain