Assessing nitrate origin in a volcanic aquifer using a dual isotope approach
Mongelli, G. | Paternoster, M. | Sinisi, R.
Identifying the origin of nitrate is important for the control and management of groundwater quality in aquifer systems. In the southern Apennines (Italy), the Mount Vulture volcanic aquifer is a large and valuable resource of potable and mineral water supply. Unfortu- nately, signs of anthropogenic impact, especially nitrogen contamination, have recently become evident. In this study, and for the first time, stable isotope ratios ( δ 15 N and δ 18 O) of NO 3 - were determined in groundwater to identify their origins and evaluate the presence of transformation pro- cesses. The Mount Vulture groundwaters are meteoric in origin, as demonstrated by measurements of δ D and δ 18 O, and can be divided into two distinct areas based on their NO 3 - content. In the southeastern area, characterized by active agricultural land use, the high NO 3 - content and the δ 15 N-NO 3 isotopic values are due to anthropogenic con- tamination (inorganic fertilizer). In groundwaters from the western area, the NO 3 - contents below 4 mg/L and the δ 15 N-NO 3 values can be associated at organic soil N. Evidence for local denitrification may be assumed in a few groundwater samples of the western area showing rela- tively heavy δ 15 N values and low concentrations of nitrate. Finally, the low measured δ 18 O values indicate that nitri- fication occurred in both investigated areas.
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