Luca Colombo

Thirty Years of Chemical Changes in Alpine Acid-Sensitive Lakes in the Alps

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.

Effect of Acid Deposition on Chemistry and Biology of High-Altitude Alpine Lakes

Trend analyses of the key parameters involved in acidification processes measured in 20 Alpine lakes during the period 1980–2004 revealed significant decreasing sulphate (15 out of 20) and increasing alkalinity trends (14 out of 20) in most studied lakes, while trends for base cations and nitrate were small and mostly insignificant. The average increase in alkalinity between 1980 and 2004 was 0.012 meq l−1. Today two lakes out of 20 are still acidic (alkalinity < 0 meq l−1), 13 are sensitive to acidification (0 meq l−1 < alkalinity < 0.05 meq l−1) and five have low alkalinities but are not at risk (0.05 meq l−1 < alkalinity < 0.2 meq l−1). Differently, in the 1980s four lakes were acidic, 14 were sensitive to acidification and two had low alkalinities. During the same time period the pH increased on average by 0.3 units.

Oligochaete assemblages of Swiss Alpine lakes

Abstract The present paper describes the oligochaete assemblages of 12 Swiss Alpine lakes (1700–2500 m above sea level) in Canton Ticino. The lake catchment geology is dominated by gneiss. The scarcity of carbonate rocks leads to a low buffering capacity, increasing the lakes’ sensitivity to acidification. Because of their very low phosphorus concentrations, they are defined as ultraoligotrophic. Oligochaetes were identified from kick-samples taken from the outflow and littoral zone of the lakes one to three times per year in 1991–1994, 2003 and 2007, when the lake water chemistry was also characterized. Oligochaete assemblages consisted of 19 species in total, 18 of which were found in the littoral zone, and 10 in the outlets. Amongst them, Cernosvitoviella goodhui Healy, 1975 was recorded in Switzerland for the first time. Principal component analysis (PCA), performed excluding the highly alkaline Lake Bianco (pH = 7.8 and alkalinity = 566 µeq L−1) due to its atypical chemical composition, divided the remaining lakes into two groups with different sensitivity to acidity: the first group of four lakes was characterized by a higher average pH (6.4) and alkalinity (32 µeq L−1), whilst the second group of seven lakes was characterized by a lower average pH (5.7) and alkalinity (5 µeq L−1). Multivariate analysis performed on data collated from the littoral zone highlighted geo-lithology as a key driver in determining the species distribution among lakes. When applied to the lake outlet data, a similar distinction between acidic and calcareous waters was implied. Precipitation influenced the oligochaete assemblage in the littoral zone. During years with higher annual rainfall, the relative abundance of Enchytraeidae increased, probably because their semi-aquatic nature allows them to colonize the littoral zones that dry out periodically.

Are swiss alpine lakes recovering from acidification

What are the effects on acid-sensitive ecosystems? Drawing from long-term monitoring data, we evaluated trends in the chemistry of 20 high-elevation lakes in Canton Ticino, Switzerland, an Alpine region that was severely impacted by acid deposition in the past. We report on the trends of the main acid anions (sulfate and nitrate), alkalinity, and pH in the lakes from 1986 to 2011, and compare these trends to changes in regional atmospheric deposition during the same period.