Study sites and context

The spatio-temporal survey was performed on three French lakes: a natural alpine lake, Lake Aiguebelette (45°33’30.24”N, 5°48’3.6”E), a large dam reservoir, Lake Serre-Ponçon (44°30’52.92”N, 6°20’31.2”E), and a small lowland lake, Etang des Aulnes (43°35’30.84”N, 4°47’33”E) (Fig 1).

Locations of the lakes: (a) Aiguebelette, (b) Serre-Ponçon, (c) and Etang des Aulnes (IGN, 2019–2021).

Lake Aiguebelette is a natural, deep peri-alpine lake, located at an altitude of 374 m. This oligotrophic lake has a perimeter of 16.7 km, an area of 5.24 km², a volume of 166 million m³ and a maximal depth of 71 m. During the year, the natural range of shoreline variation is about 2 m. This monomictic lake exhibited thermal stratification from April to November in 2019 [50].

Lake Serre-Ponçon is a hydroelectric dam reservoir, built on the Durance, a few metres after the Ubaye confluence, at an altitude of 779 m. This oligotrophic dimictic lake has a maximal volume of 1.27 billion m³, a perimeter of 103.2 km, an area of 27.9 km² and a maximal depth of 129 m. It exhibits an annual water-level variation of about 23 m and thermal stratification from April to October.

Lake Etang des Aulnes is a natural, shallow freshwater lake surrounded by wetlands, at an altitude of 11 m. This eutrophic lake has a perimeter of 5 km, an area of 1 km², a volume of 3.34 million m³ and a maximal depth of 5.5 m. The annual variation of the shoreline is about 0.6 m, without stratification over the year.

Field site access was approved by the water managers of each lake: Communauté de Communes du Lac d’Aiguebelette (CCLA) for lake Aiguebelette, Syndicat Mixte d’Aménagement et de Développement de Serre-Ponçon (SMADESEP) and by Conseil Départemental des Bouches-du-Rhône for lake Etang des Aulnes. No specific authorization were necessary to filter water.