Potentially toxic elements biogeochemical and isotopical markers as indicators of environmental quality in a complex territorial system (Ravenna, Italy)

This proceedings is focused on the multicomponent exchange processes and elemental cycling in the subsurface and superficial environments which constitute the area of the Pineta di San Vitale and nearby farmlands. The coastal aquifers in the area of the Pineta underwent severe seawater intrusion due to subsidence and over-pumping, yielding a decline in the water quality and driving a number of processes in aquifers and soils. These include cation-exchange reactions by clay minerals, even if the cation exchange capacity of the aquifer is probably low; iron oxy-hydroxides extensive precipitation due to oxic seawater recirculation; adsorption processes of both essential micronutrient and potentially toxic elements on the sur-face of Fe and Al hydroxides. The development of local anoxic conditions due to respiration and decomposition of organic matter allows the reductive dissolution of the iron oxy-hydroxides, which liberate the sorbed elements to porewaters. This re-dox cycling appears to be important in the bioavailability and geochemical cycling of a number of trace metals in the subterranean environment of the Pineta. CO2 charged waters in soils account for the high alkalinity observed in most water sam-ples, through the role of carbonates and the control of pH and the Ca2+ content. The active processes in the surface ecosystem of the plain bordering the Pineta di San Vitale, exploited for agricultural uses, include dry and wet atmospheric deposi-tion from marine and anthropogenic sources, leaching processes during runoff and retention and transport of trace elements by Fe and Mn oxides colloidal particles, through the network of canals and ditches towards the coastland. These processes are sensitive to flow fluctuations, and are deeply influenced by the management of water resources during summer, when a high water supply in irrigated crops is re-quired. Using geochemical simulation codes it is highlighted that the reverse phe-nomenon to salinization, leading to groundwater freshening, is a long process, also depending on the low cation exchange capacity of the site. Even if a detailed study concerning the recharge rate of the aquifers would be necessary, these preliminary observation indicate that attenuation planning for salinization is urgent.