The effects of nitrogen pollutants on the isotopic signal (δ15N) of Ulva lactuca: Microcosm experiments.

Effects of two chemical forms of Nitrogen (NH4+ and NO3-) on δ15N in Ulva lactuca were analysed separately and in mixture at two concentrations. We assessed whether the δ15N values of 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 the macroalga reflected different nitrogenous sources and their concentrations after 48h. The inorganic Nitrogen source (NH4NO3) altered the isotopic values of the macroalgae more than Nitrogen from fresh cow manure (NO3-). δ15N 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.