Multi-isotope approach for the identification and characterisation of nitrate pollution sources in the Marano lagoon (Italy) and parts of its catchment area

A multi-isotope approach has been used in the Marano lagoon (NE Italy) and parts of its catchment area to identify causes of increased NO3- pollution. The hydrogeochemical features of different water types and potential sources of NO3- were characterized using the isotopic composition of NO3- (δ15N, δ18O, and Δ17O) and other source-related species such as B (δ11B), water (δ2H and δ18O) and SO42- (δ34S and δ18O). Water samples from the lagoon, its tributary rivers, the groundwater up-welling line, groundwater, sewer pipes, and open sea water have been collected at quarterly intervals in the years 2009–2010. The results indicate that the NO3- load in the lagoon was not only derived from agricultural activities but also from other sources such as urban waste water, in situ nitrification and atmospheric deposition. The δ34S signature in the lagoon clearly denotes the largely prevailing origin of aqueous SO42- from seawater, and practically points to the absence of any appreciable redox process involving S species in the lagoon. It also supports the existence of a connection between the lagoon and the nearby Tagliamento river.

• Multi-tracer approach for the identification and characterisation of nitrate sources in a lagoon environment was used. • Different nitrate pollution sources in the lagoon were identified. • Isotopes in nitrate and boron were applied to distinguish different anthropogenic pollution sources. • Atmospheric depositions (based on Δ17O analyses of nitrate) were recognized as additional nitrate source.