Modelling the effects of atmospheric sulphur and nitrogen deposition on selected lakes and streams of the Central Alps (Italy)

The dynamic model MAGIC was calibrated and applied to selected sites in North-Western Italy (3 rivers, 10 alpine lakes) to predict the future response of surface water to different scenarios of atmospheric deposition of S and N compounds. Results at the study sites suggest that several factors other than atmospheric deposition may influence the long-term changes in surface water chemistry. At present the lumped approach of dynamic models such as MAGIC cannot represent all the processes occurring at the catchment scale. Climate warming in particular and its effects on surface water chemistry proved to be important in the study area. Furthermore the river catchments considered here showed clear signs of incoming N saturation. This condition and the increasing concentrations of NO3 in river water were simulated using N dynamics recently included in MAGIC. The modelling performed in this study represents the first application of MAGIC to Italian sites. The results showed how including other factors specific to the Mediterranean area, such as dust deposition and climate change, may improve the fit of experimental data and the reliability of the model forecast. Despite these limitations, the model captured well the main trends in chemical data both of rivers and lakes. The outputs clearly demonstrated the benefits of achieving the emission reductions in both S and N compounds agreed under the Gothenburg Protocol rather than making no further emission reductions. It was also clear that, besides the substantial reduction of SO4 deposition from the peak levels of the 80s, N deposition too must be reduced in the near future to protect freshwaters from further acidification.