Ricerc@Sapienza

Effects of two chemical forms of Nitrogen (NH4
+ and NO3
?) on ?15N in Ulva lactuca were analysed separately and
in mixture at two concentrations.We assessedwhether the ?15Nvaluesof U. lactuca discriminate between Nitrogen
from synthetic fertilisers (inorganic) and from fresh cow manure (organic), and the isotopic ability of the
macroalga to reflect Nitrogen concentrations. Isotopic signature and N content of themacroalga reflected different
nitrogenous sources and their concentrations after 48 h. The inorganic Nitrogen source (NH4NO3) altered the
isotopic values of themacroalgaemore than Nitrogen fromfresh cowmanure (NO3
?). ?15N values observed in the
mixed solution did not differ from those displayed in NH4NO3 treatment alone.We conclude that stable isotope
analysis of U. lactuca collected in an unpolluted site and experimentally submerged in sites suspected of being affected
by disturbance is a useful tool for rapid monitoring of anthropogenic discharges of Nitrogen pollutants.