Biodiversity of the Lake

The lower water body of Lake Cadagno is rich in minerals and reduced compounds leaking from subaquatic springs; in contrast the upper layer which is rich in oxygen and low in salts.  At the interface of the two layers, ideal environmental conditions are present for a massive growth of anaerobic phototrophic bacteria. Between 10 and 13 m depth they form during the year a purple red layer of a thickness of 70 to 150 cm. The low light intensity at this depth satisfies these organisms to convert with anaerobic metabolism the toxic hydrogen sulfide into sulfate. These purple bacteria act as biological filter, inhibiting that hydrogen sulphide and other reduced compounds as well as nutrients such as phosphate leading to eutrophication enter the upper layer.

Investigations at Lake Cadagno enable to clarify the relationship between the natural meromixis in Lake Cadagno and the man-made meromixis in eutrophic lakes. Lake Cadagno provides the possibility to study in a small stable system (maximum depth of the lake is 21 m) the metabolism of the microbes following the process of eutrophication. With continuing pollution load, mainly triggered by the activity of men, the biomass produced in the surface water of some lakes in the Swiss midland is not fully degraded in the bottom water layers anymore. This leads to a permanent anoxic lower water body (biogenic meromixis).