At the start of august 2012, a dangerously high concentration of the dinoflagellate Alexandrium Ostenfeldii was found within a creek near Ouwerkerk, Zeeland. This species is known to produce very toxic substances (saxitoxine among others), and with concentrations of millions of cells per liter this could pose a threat to humans and wildlife. Luckily these algae could be isolated in time. But how to get rid of them?
In a cooperative effort between Rijkswaterstaat, Arcadis, the University of Amsterdam and the local authorities a newly developed method was tested. By adding low concentrations of hydrogen peroxide the bloom could be destroyed. The CytoSense instrument owned by Rijkswaterstaat was used for analyzing the effects of the treatment. By closely monitoring the concentrations and activity of the species using the Cytosense, the effects of the treatment could be tracked in real time. The results of this analysis were used to tune the exact amounts of H2O2 to be added. Within two hours after the addition of the peroxide the photosynthetic capacity was dimished by 97%, and after two days the concentrations of Alexandrium Ostenfeldii was brought back to only 1% of its original value, making the water fit for mixing with other surface waters again. Since peroxide breaks down into water and oxygen, it poses no long-term threats to the ecosystem.
In september 2011 a 36 hour measurement was done in the Berre Lagoon, Marseille, France. Using a CytoSense instrument every half hour approximately 4ml of water was analysed, and images of particles were made. Several clusters of particles could be identified and their dynamics through the day could be studied. The video to the right (courtesy of Dr. Gérald Grégori Ph.D.) shows further information about project.
A Cytosense equipped specially for long-term monitoring applications has been mounted on the EOL buoy, close to Villefranche sur Mer, property of the OVLFR. By means of a wireless connection the instrument can be controlled, data can be acquired and results processed - over a distance of multiple kilometers. The project serves as a pilot for a larger scale deployment, in collaboration with M. Dénis, G. Grégori and L. Thyssen of the University of Marseille and CNRS.