Nitrogen and oxygen isotopes as indicators of pollution sources in the Faxinal Dam watershed, Southern Brazil

  • Tiago De Vargas
  • Ari Roisenberg
Original Article


Isotopic signatures of δD-H2O, δ18O-H2O, δ15N-NO3, δ18O-NO3 and δ15NFertilizer isotopes were used in order to evaluate the impact of agricultural inputs (fertilizers and calcium nitrate) and sewage effluents on the water of tributaries of the Faxinal Dam, which supply the city of Caxias do Sul in Southern Brazil. δ2H and δ18O were identified by spectroscopy laser absorption tunable diode-type cavity ring-down spectroscopy, while the isotopic ratios of 15N and 18O in nitrate were determined by isotopic ratio mass spectrometry, applying the chemical denitrification method. The results showed that most of the analyzed samples are compatible with the Global Meteoric Water Line, Local Meteoric Water Line and Carlos Barbosa Wells and Fountains Tendency Line, except for the Fx-07 sample that presented greater similarity to δ18O values for groundwater. The isotopic signatures of δ15N-NO3 versus δ18O-NO3, in the great majority of the samples, pointed out the influence and the contribution of the fertilizers. In a monitored affluent, the results show the impact of the direct discharge of domestic sewage, while in the sewage treatment plant there is clear evidence of denitrification. This study demonstrated that isotope application of δ15N-NO3 and δ18O-NO3 is efficient tools for identification of N-NO3 of synthetic fertilizers and domestic sewage.


Nitrate Stable isotopes Nitrate source Fertilizers Domestic sewage 



The authors thank the Municipal Autonomous Service of Water and Sewage of the city of Caxias do Sul for the great support for this research.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Institute of Geosciences of the Federal University of Rio Grande do Sul (UFRGS)Porto AlegreBrazil
  2. 2.Service Autonomous Municipal of Water and Sewage (SAMAE)Caxias do SulBrazil

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