DISTRIBUTION OF HEAVY METALS IN THE AGRICULTURAL SOIL OF THE FERRARA ALLUVIAL PLAIN

The knowledge on the chemical composition of terrains and its regional variability is essential to understand the origin (natural vs. anthropogenic) of potentially harmful elements; moreover, it is very important to assess the human impact and to fix guide values and quality standards. In particular, in alluvial areas the geochemistry of sediments records complex tectonic, climatic and hydrological processes occurring within a river basin. The varying contributions of confluents which drain geologically different sub-basins lead to various geochemical signatures on the sedimentary deposits, reflecting the geochemistry of the mother rocks and the weathering mechanisms. Moreover, in urbanized areas, anthropogenic contributions can overprint the pristine (geogenic) geochemical signatures of the alluvial sediments. This study investigates the easternmost part of the Po River Plain in northern Italy, i.e. a sedimentary basin bordered by the Alps and Apennines that hosts about 30-40% of the Italian population and most of Italy’s total productive activities. The outcropping sedimentary facies reflect climatic changes and human impacts that deeply modified the configuration of the local drainage system, represented by the evolving Po River (containing significant part of the Alpine belt in his catchment) and minor rivers, such the Reno River, flowing down from the Apennines (Amorosi et al., 2002; Bianchini et al., 2002; Stefani & Vincenzi, 2005; Simeoni & Corbau, 2009). In the easternmost and terminal part of the basin, in historical times, high lateral mobility of the active channel belts also permitted the development of fens and swamps (probably developed in few decades) characterized by peat deposition. When the high-energy alluvial deposition outranged the organic deposition, the peat level was buried and incorporated into the stratigraphic record (Miola et al., 2006). In this paper we focus the attention on the geochemistry of sediments collected in the surrounding of the city of Ferrara, around the towns of Argenta and Vigarano, where alluvial sediments, consisting of sands, silts and clays related to both the Po River and the Reno River, have been recognised. A fourth sampling zone has been focused close to the Town of Ostellato (Mezzano Zone) where the organic-rich fine sediments prevail. The data, presented as GIS-based geochemical maps, intend to define the geochemistry of the main facies of the area, highlighting the local backgrounds of potentially harmful elements, such as the heavy metals, and nutrients (such as nitrogen), which are progressively affecting the interacting waters causing eutrophication problems (Mastrocicco et al., 2009). The results should be taken in consideration by the local authorities to provide guidelines for the agricultural activities