The general aim of the thesis is testing the potential of the nitrate MIF (massindependent
fractionation) signature as a tracer of biogeochemical processes.
Nitrate δ15N, δ17O and δ18O of water samples collected at the Marano lagoon (Italy)
have been analysed, by combining the denitrifier method with the N2O thermal
decomposition in a gold furnace. No clear correlation between the magnitude of the
capital delta (Δ17O=δ17O+0.5*δ18O) and the local atmospheric deposition has been
found. Moreover, sewage treatments with ozone might be responsible for some high
Δ17O values associated to sampling points close to populated areas. Overall, the signal
is low (0.6‰ on average, which would correspond to roughly 2% of atmospheric
nitrate in sample water) and the error associated to the measure is no less than 75%.
To test the assumption that the atmosphere is the only source of a MIF signature, a set
of nitrate minerals of different origin was analysed. The capital delta in a specimen of
buttgenbachite (with formula Cu36(NO3)2Cl8(OH)62*4−10H2O) from Likasi mine
(Congo, 4‰±1) and in a sample of nitromagnesite (Mg(NO3)2*6H2O) collected at
Pozalagua Cave (Spain, 10.3‰±0.4) would indicate the possibility that a significant
isotope anomaly could be generated due to geochemical processes.
So far the MIF in atmospheric nitrate has been interpreted as the result of chemical
reactions only, but it could be demonstrated that a series of mass dependent processes
might generate an apparent Δ17O.
The study of the MIF is a relatively new field and the present work underlined some
limits of this novel tracer. Further work should be focused on identifying the systems
and the conditions for what the nitrate MIF can be considered as a conservative tracer.
Particularly, attention should be paid to the effects of biological processes involved in
the nitrogen cycle, such as nitrification and denitrification, and transport processes
