An operational monitoring and alert system for cyanobacterial blooms: application to water bodies in the Landes

Abstract

The large lakes of the Landes have bathing areas regularly monitored for public health by the environmental services of the Community of Municipalities of the Great Lakes (in French CCGL) and the community of municipalities of Mimizan. Regulations impose biological monitoring, especially for cyanobacteria, as they are potentially toxic to humans (due to cyanotoxins production). However, analyses are carried out in the laboratory and have a response time of at least 36 hours, which is damaging to sanitary safety and leading to important financial costs. The work carried out jointly by Irstea and the CCGL makes it possible to propose the reduction in response time and to limit the costs by modifying the monitoring and alert decision tree with the use of a fluorimetric field probe. The adapted decision tree is based on thresholds of cyanobacteria quantities expressed in chlorophyll-a equivalent, instead of the number of counted cells usually practiced. It provides at least the same safety level and is, sometimes, more protective than the regulatory protocol. This work enables the CCGL to implement a monitoring and alert protocol for cyanobacteria based on the use of the fluorimetric probe during the summer seasons.