The project SIGNAL addresses the crucial question of the eutrophication sources and what impact additional nitrogen has on the productivity in remote regions. The investigation will be carried out in the Baltic sea where the impact of eutrophication is one of the main threats to the ecosystem due to the 80 million people living in its watershed. The nitrogen input from the rivers, the atmosphere and N2 fixing cyanobacteria will be qualitatively and quantitatively assessed. This task will be accomplished through regular measurements in the mouths of several rivers, and in the precipitation.
Stable isotope ratios of the most important elements are indicating eutrophication from various sources and have not been used simultaneously. However previous studies proved the utility of stable isotope ratios as indicators of external nitrogen inputs(.eg. fertilizer and soil runoff) and that they allow the identification of pathways through the ecosystem. Finally the role of the imported nitrogen for the productivity of the central Baltic Sea will be evaluated by means of budget calculations and box modelling.