Hydrogeological and multi-isotopic approach to define nitrate pollution and denitrification processes in a coastal aquifer (Sardinia,Italy) |
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| Authors: | Daniele Pittalis Raul Carrey Stefania Da Pelo Alberto Carletti Riccardo Biddau Rosa Cidu Fulvio Celico Albert Soler Giorgio Ghiglieri |
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| Institution: | 1.Mineralogia Aplicada i Geoquímica de Fluids (MAG-UB) research group, Dept. De Cristal·lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia,Universitat de Barcelona,Barcelona,Spain;2.Unità di Scienze della Terra - Dipartimento di Scienze Chimiche, della Vita e della Sostenibilità Ambientale,Università di Parma,Parma,Italy;3.Dipartimento di Scienze Chimiche e Geologiche,Università di Cagliari,Cagliari,Italy;4.Nucleo Ricerca Desertificazione (NRD),Università di Sassari,Sassari,Italy |
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| Abstract: | Agricultural coastal areas are frequently affected by the superimposition of various processes, with a combination of anthropogenic and natural sources, which degrade groundwater quality. In the coastal multi-aquifer system of Arborea (Italy)—a reclaimed morass area identified as a nitrate vulnerable zone, according to Nitrate Directive 91/676/EEC—intensive agricultural and livestock activities contribute to substantial nitrate contamination. For this reason, the area can be considered a bench test for tuning an appropriate methodology aiming to trace the nitrate contamination in different conditions. An approach combining environmental isotopes, water quality and hydrogeological indicators was therefore used to understand the origins and attenuation mechanisms of nitrate pollution and to define the relationship between contaminant and groundwater flow dynamics through the multi-aquifer characterized by sandy (SHU), alluvial (AHU), and volcanic hydrogeological (VHU) units. Various groundwater chemical pathways were consistent with both different nitrogen sources and groundwater dynamics. Isotope composition suggests a mixed source for nitrate (organic and synthetic fertilizer), especially for the AHU and SHU groundwater. Moreover, marked heterotrophic denitrification and sulfate reduction processes were detected; although, for the contamination related to synthetic fertilizer, the attenuation was inefficient at removing NO3? to less than the human consumption threshold of 50 mg/L. Various factors contributed to control the distribution of the redox processes, such as the availability of carbon sources (organic fertilizer and the presence of lagoon-deposited aquitards), well depth, and groundwater flow paths. The characterization of these processes supports water-resource management plans, future actions, and regulations, particularly in nitrate vulnerable zones. |
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