The large lakes south of the Alps: current limnological status, with a special focus on Lake Garda

The large lakes south of the Alps (DSL: Garda, Maggiore, Como, Iseo and Lugano) are one of the most important lake districts in Europe. In the last decades, the DSL showed a tendency to oligotrophication, warming of the water column, decrease in the frequency of full mixing episodes followed by a lower supply of nutrients to the upper layers. In Lake Garda, the decrease of nutrients caused a decline of the mesotrophic cyanobacterium Planktothrix rubescens (microcystin producer), which was partially replaced by Tychonema bourrellyi (anatoxin-a producer), a “new” species identified in 2014. The discovery of Tychonema can be considered a paradigmatic example of the unknown biodiversity in the DSL. To solve this gap, high throughput sequencing has been recently used to analyze bacteria, cyanobacteria, protists and fish. The new approach has been extended to the whole Alpine region within the EU Alpine Space project Eco-AlpsWate