New methodological and modeling approaches for the environmental monitoring through the nitrogen isotopic signatures of algal primary producers

Aquatic ecosystems represent unreplaceable sources of ecosystem services. On the other hand, the exploitation of water resources and the influx of human activity-related pollutants in the water bodies undermine the structure and function of these ecosystems, until the inability of all their use. Despite the efforts in environmental monitoring and inputs management, around the 28% of the European water bodies is nowadays affected by nutrient pollution. Among the anthropic nutrient inputs, Nitrogen loadings are spreading with human-related loads. The expected increase of climate change can exacerbate the negative effects of these inputs on the aquatic environment. Unfortunately, the environmental monitoring of the anthropic Nitrogen inputs is constrained by three main factors: the dilution process in the aquatic medium, the assimilation by different compartments and the identifiability of their organic/inorganic origins. To overcome all the previously cited constrains, the Nitrogen isotopic signature of macroalgae and epilithic association is nowadays widely used. Firstly, the Nitrogen signature of a macroalgal/epilithic sample is the result of the assimilation process of Nitrogen from the surrounding water, solving both assimilation and dilution issues. Lastly, the value of the macroalgal/epilithic Nitrogen signature is highly dependent by the origin of the uptaken Nitrogen, solving the third issue. However, while for marine ecosystems a wide scientific Nitrogen isotopic signature literature is available, for freshwater and land locked ecosystems there is a large lack of information about method applicability for the environmental monitoring. This dissertation investigates the changes of the epilithic association and macroalgae Nitrogen signatures to different Nitrogen inputs affecting, three rivers (Itri, Capodacqua Santa Croce and Garigliano) and one lake (Lake Bracciano), in Central Italy, and the Iranian Caspian Sea littoral zones. The results confirm the applicability of the method in land locked and fluvial ecosystems regardless the several differences between the aquatic ecosystems considered. Both epilithic association and macroalgae Nitrogen signatures discriminate the origin of the various Nitrogen inputs, changing according to the spatial and temporal variability of the anthropic activities, and provide a robust determination of four well separated Nitrogen impact classes.