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

作者：De Vargas Tiago^*; Roisenberg Ari

来源：Environmental Earth Sciences, 2018, 77(6): 229.

DOI：10.1007/s12665-018-7395-5

• Nitrate
• Stable isotopes
• Nitrate source
• Fertilizers
• Domestic sewage

Isotopic signatures of delta D-H2O, delta O-18-H2O, delta N-15-NO3-, delta O-18-NO3- and delta N-15(Fertilizer) 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. delta H-2 and delta O-18 were identified by spectroscopy laser absorption tunable diode-type cavity ring-down spectroscopy, while the isotopic ratios of N-15 and O-18 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 delta O-18 values for groundwater. The isotopic signatures of delta N-15-NO3- versus delta O-18-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 delta N-15-NO3- and delta O-18-NO3- is efficient tools for identification of N-NO3- of synthetic fertilizers and domestic sewage.

• 出版日期2018-3