Environmental geochemistry of Peat-rich sediments in the Po river Delta area (Mezzano lowland, Ferrara)

This study is focused on the easternmost part of the Po river alluvial Plain in northern Italy, i.e. a sedimentary basin bordered by the Alps and the Apennines, which hosts about 30–40% of the Italian population and most of the Nation’s agricultural activities. In particular we investigated a specific sector of the Province of Ferrara known as “Valle del Mezzano” (45° 50’ 33’’ N and 12°05’40’’ E) hereafter reported as Mezzano low-land (MLL) that is included in the Regional natural park of the River Po Delta. The outcropping sedimentary facies (and the related soils) reflect climatic changes and human impacts that profoundly modified the configuration of the local drainage system, which is represented by the evolving Po river (Amorosi et al. 2002; Bianchini et al. 2002; Stefani and Vincenzi 2005; Simeoni and Corbau 2009). In the easternmost terminal part of the basin the delta environment developed high lateral mobility of the active channel belts, permitting in historical times the development of fens and swamps characterised by peat deposition. When the high-energy alluvial deposition outranged the organic deposition, the peat levels were buried and incorporated into the stratigraphic record (Miola et al. 2006). Therefore it has to be noted that the MLL outcropping soils are significantly different from those recorded in the surrounding part of the plain (Amorosi et al. 2002; Bianchini et al. 2002), as they evolve from saline sedimentary deposits peculiarly rich in peat material. This site specificity is also related to the geomorphological history of the area deeply influenced by anthropogenic activities: MLL was a marsh wetland since fifty years ago (see the 1944 geographic map of the area) and has been drained and reclamated in several stages mainly during the years fifties and sixties. Nowadays MLL is mainly 3-4 m below sea level and drained by hydraulic pumping and a system of artificial channels. The geochemical characterization of these deposits is very important taking into consideration that the local backgrounds of elements potentially toxic exceed those recorded in other sectors of the Padanian plain (Amorosi et al., 2002; Bianchini et al., 2002). This is possibly related to a remarkable role of the organic fraction in the metal complexation. The aim of this study is to evaluate possible geochemical risks of former wetland converted in agricultural areas, taking into consideration the nitrate pollution problem, as well as the potential bioaccumulation processes of heavy metals. The analyses reported in this contribution include a) nutrient evaluation (TOC, and nitrogen measured as extracted nitrates); b) XRF data carried out on bulk soils; c) tests of metal extraction with both aqua regia and EDTA that highlight the distinct elemental mobility; d) tests of bioavailability realized analyzing lattuce (lactuca sativa acephala) grown on the studied soils. This approach is useful provide guidelines for agricultural activities (i.e. mode and style of soil amendment and fertilization) and to evaluate possible geochemical risks, i.e. contamination of the local agricultural products by harmful elements in the food chain.