Identification of the nitrate contamination sources of the Brusselian sands groundwater body (Belgium) using a dual-isotope approach

Abstract

Isotopic fingerprinting is an advanced technique allowing the classification of the nitrate source pollution of groundwater, but needs further development and validation. In this study, we performed measurements of natural stable isotopic composition of nitrate (¹⁵N and ¹⁸O) in the groundwater body of the Brussels sands (Belgium) and studied the spatial and temporal dynamics of the isotope signature of this aquifer. Potential nitrogen sources sampled in the region had isotopic signatures that fell within the corresponding typical ranges found in the literature. For a few monitoring stations, the isotopic data strongly suggest that the sources of nitrate are from mineral fertiliser origin, as used in agriculture and golf courses. Other stations suggest that manure leaching from unprotected stockpiles in farms, domestic gardening practices, septic tanks and probably cemeteries contribute to the nitrate pollution of this groundwater body. For most monitoring stations, nitrate originates from a mixing of several nitrogen sources. The isotopic signature of the groundwater body was poorly structured in space, but exhibited a clear temporal structure. This temporal structure could be explained by groundwater recharge dynamics and cycling process of nitrogen in the soil-nitrogen pool.

Keywords:

• contamination
• groundwater
• isotope geochemistry
• nitrogen-15
• nitrate
• oxygen-18
• stable isotope tracer technique

Acknowledgements

The reported work was funded by the ‘Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture’ (FRIA, Belgium). The sampling campaign and the water analyses were funded by the ‘Fonds de la Recherche Scientifique’ (FNRS, Belgium). The authors are grateful to the SPW – Service public de Wallonie, Vivaqua, Société wallonne des eaux, IECBW, Commune de Perwez, UCL and VMW for delivering permission to sample the groundwater and to Luk Peeters (K.U.Leuven, Belgium) for providing them with data about chloride concentrations.