Temperature and stratification of the artificial lake and the proliferation of cyanobacteria, case of the lake of the Eguzon dam, France

International audienceLocated 200m above sea level on the first foothills of the Massif Central, Lake Chambon (or Lac d’Eguzon), created in 1926, partially flooded the Quaternary valley of the Creuse between Fresselines and Cuzion to form the highest dam d’Europe of the time. Soon a century old, this reservoir shares with the natural lakes the contemporary problematic that is the proliferation of the cyanobacteria, question all the more crucial since the political authorities have founded the tourist attraction of the territory on the lake and they have been forced in recent years to manage various prohibitions (bathing, fishing...). Inprevious work (Qsair et al. 2014), we were led to conduct a study in which 69% of those questioned on site complained about these proliferations and accused the dam of being responsible for this illness. As the limnic scientific literature emphasizes the thermal functioning of lakes in cyanobacterial proliferation analyzes (Jennifer et al., 2008) (Robarts and Zohary,1987) (Reynolds and Walsby 1975), we wanted to explore this path by applying a scientific approach that takes into account both the periodicity and the extent (Sournia and Frontier, 1967), but also the spatial variation of the measurements. This study is based on 40,100 thermal measurements collected from 2014 to 2016, measures associated with cyanobacterial analyzes (partly carried out in the laboratory and others in situ with the Fluoroprobe probe). Correlations of temperature and cyanobacterial monitoring results helped to verify the link between the two criteria and to highlight some elements: (i) the effect of the dam is only a catalyst and can not be the determining factor of the phenomenon; (Ii) cyanobacteria affect stagnant lake water, but they also adapt to waters with varying hydrody-namics