Applicazione di un modello dinamico ad alcuni corsi d'acqua nell'Italia nord-occidentale per valutare la risposta alle variazioni negli apporti atmosferici di zolfo e azoto

The chemistry of three rivers in northern-western Italy (River Cannobino, a tributary of Lake Maggiore, and Rivers Pellino and Pellesino, tributaries of Lake Orta) has been investigated since the 1980s. Deposition of nitrogen compounds in the study area is remarkably high (25-30 kg ha-1 y-1 as sum of ammonium and nitrate) and has been approximately constant in the last 15-20 years. As a consequence of atmospheric load, nitrate concentrations in river water sharply increased in the same period, showing signs of nitrogen saturation of soils in the catchments. The dynamic model MAGIC has been applied to the study sites to detect the response of surface water to different scenarios of atmospheric deposition. Results show how the status of nitrogen saturation will lead in the next future to a further increase of nitrate concentrations in rivers. Only a sharp reduction of the atmospheric emission of nitrogen compounds, and consequently of ammonium and nitrate deposition in the next years, could allow a reversing of nitrate trend in surface waters