Lake Cadagno

Lake Cadagno (Italian: Lago di Cadagno) is a meromictic lake in the Piora valley (canton of Ticino), Switzerland. As one of a few meromictic lakes in Europe, it is the object of numerous scientific studies. The Piora valley - located in the Saint-Gotthard Massif (central Swiss Alps) in the Southern part of Switzerland near Airolo at an altitude of 1921 m above sea level - is a landlocked alpine valley whose scientific value has been recognized for more than two centuries. In the past, the lake was used as a reservoir. Lake Cadagno is a rare example of crenogenic meromixis. Its waters show a permanent stratification due to a natural geological phenomenon. The lower abounds with dissolved mineral salts (sulphate, magnesium, calcium, carbonate) originating from sublacustrine springs, whereas the separate upper layer is permanently oxygenated. Anaerobic phototrophic bacteria – among them Chromatium okenii—thrive between the two layers where they find the ideal conditions for their development. Such an ecosystem provides a good opportunity to study the metabolisms connected with eutrophication on a stable model, as it is well known that one of the advanced stages of eutrophication is biogenic meromixis.