Distribuzione e origine dei nitrati in falda nella pianura Pontina (Lazio meridionale)

The nitrogen and oxygen isotope ratios of dissolved nitrate were used to study nitrate contamination in the groundwater from the Pontina alluvial plain. The present study is based on the water sampling carried out during 2007 from 19 weIls, uniformly distributed throughout the plain. The chemical data show that nitrate concentrations vary greatly with some values being as high as 270 mg/l, often depending on agricultural activities. Isotopic nitrate values range from +3.13 to + 14.85 ? for ?15N, and from + 3.11 to + 11.17 ? for ?18O. These results indicate that the main nitrate source is represented by nitrified soil organic nitrogen and /or fertilizers with subordinate contribution of animal/ human waste. No evident denitrification process was observed, probably owing to a scarce water self-softening capability of the soil. Key terms: Groundwater, Nitrate, Origin, Isotopes, Denitrification