LEON-BLOOM project - Origin, spatial and temporal dynamics of cyanobacteria blooms in lake Léon, France

International audience

إنجليزي. Lake Léon (Landes) has recently experienced important cyanobacteria blooms, leading to severe restrictions on recreational activities of this popular tourist waterbody of the Atlantic coast in France. To investigate the origins of these algal blooms, the dynamics of biological patterns, and to provide management strategies for mitigation, the "Léon-Bloom" research project established a collaboration between environmental watershed managers and research scientists. The project aims to identify the potential sources of algal growth and gain a better understanding of their spatial and temporal dynamics. The project is structured in several workpackages, each investigating a potential mechanism. (1) Firstly, nutrient fluxes from the watershed are analyzed, including the use of passive phosphorus samplers. We also set up an experimental design to investigate the role temperature, light and phosphorus on the development of phytoplankton biomass. (2) Secondly, a chemical analysis of the lake’s sediments is carried out resorting to sediment coring and experimentation to measure the potential of phosphorus release under anoxic conditions. (3) Thirdly, the role of temperature and oxygen on phytoplankton composition will be assessed using a statistical modeling approach. We measured temperature and oxygen in several stations of the lake to calibrate these models using autonomous high-frequency sensors. (4) The phytoplankton community is studied both spatially and temporally, at the taxonomic and algal group level. Cyanotoxins are also regularly monitored. Finally, two modeling-based workpackages will focus on (5) analyzing the role of wind in the spatial distribution of the plankton community and physical parameters and (6) developing remote sensing methods for monitoring algal concentrations in this lake. Ultimately, we aim to decipher the relative contribution of wind, nutrients (fluxes and internal release), and environmental variables, to understand the conditions of cyanobacterial blooms emergence.