Long-term changes in the chemistry of high altitude lakes in the Alps over 30 years

The subalpine and alpine areas in North-Western Italy and Southern Switzerland (Ticino region) are subject to high deposition of atmospheric pollutants transported with the air masses from source region located in the lowland. Starting in the 1980s, some these lakes were recognised to be affected by acidification, due to the long-range transport of acidifying compounds, mainly sulphate and nitrate. In response to decreasing acid deposition, lakes in the Western Alps showed signs of recovery from acidification since the mid 1990s. Nevertheless pH and alkalinity remained low in several lakes, and just a few examples of biological recolonization by acid-sensitive species were found in the lakes. Climate change, especially temperature increase, has proved to be an important driver of change for high altitude lakes in the Alps. Lakes lying in catchments containing also basic, soluble rocks, showed a tendency to increasing solute concentrations, primarily as a response to reduced snow cover and more exposed soils and rocks to weathering processes.