Thirty Years of Chemical Changes in Alpine Acid-Sensitive Lakes in the Alps
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The subalpine and alpine areas in North-Western Italy and Southern Switzerland (Canton Ticino) receive high deposition of atmospheric pollutants transported from emission sources in the Po Valley. Long-term studies on high-altitude lakes in these areas indicate widespread recovery from acidification, even though most of them are still substantially affected, especially by deposition of nitrogen compounds. We analysed long-term trends of the major chemical compounds in a sample (n = 41) of high-altitude lakes, both at the site and regional levels, with the aim to assess the response of water chemistry to changes in atmospheric deposition and climate. These lakes have been studied since the early 1980s in the context of research programmes on acidification and atmospheric pollution. The significant decrease of sulfate and acidity in atmospheric deposition led to acidification recovery in the majority of the lakes. However, some lakes are still acidic or show a high sensitivity to acidification. This sensitivity is particularly evident at the snowmelt, when alkalinity is still fully depleted in some lakes. At present, nitrate is the dominant acidifying agent in the studied lakes, due to the high input of nitrogen compounds from atmospheric deposition. Our study also demonstrated that climatic factors interact with atmospheric deposition affecting the long-term changes in lake water.
KeywordsMountain lakes Atmospheric deposition Recovery Nitrogen Climate change
This study was supported by the Italian Ministry of the Environment and the Swiss Federal Office for the Environment through the ICP Waters Programme. We are indebted to Dr. Luca Paro (Regional Centre for Territorial and Geological Research, ARPA Piemonte) for providing us with information on the rock glaciers distribution in the Piedmont Alps. Special thanks are given to the staff of the chemical laboratories at CNR Institute of Ecosystem Study and at the Section of air, water and soil protection of Canton Ticino and to all the students and friends participating in the sampling and in the field work.
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