Another significant adverse effect of algal blooms is their propensity to cause de-oxygenation. During the daytime, algae use carbon dioxide and transfer oxygen into the water. At night, this process is reversed, with the carbon dioxide respiration causing localised oxygen depletion and, consequently, fish mortality.

Cyanobacteria as well as algae contain pigments to capture light for their photosynthesis. It is these pigments which can be used to quantify the algae and monitor the development of algal blooms. As different classes of algae contain unique combinations of pigments, monitoring of separate algal classes on the basis of their pigment fingerprint is also possible.

There are two main ways to determine the pigment composition of a water sample, to derive its algal composition. The first is by detecting the wavelengths at which light absorption reaches peak values using a light intensity and spectrum sensor, a hyperspectral radiometer. This method is often used in remote sensing applications. The second methods involves measuring the amount of fluorescence light around 680 nm as emitted by algae and cyanobacteria. Submersible field monitors often make use of this technique. Both methods have their advantages and drawbacks, as described in more detail in the Sensileau Sensor Database, under the parameters Algae and Chlorophyll-a.

Comparison: Fluorescence sensors to detect algae and cyanobacteria in surface water

Sensileau frequently compares existing sensor technologies for specific applications, such as in the table below, evaluating online fluorescence sensors for the detection of algae and cyanobacteria (blue-green algae) in surface water. The information in the PDF was provided by various technology suppliers and evaluated by Sensileau's experts, resulting in an overall score in the PDF.

The Algae & Cyanobacteria course focuses on the similarities of and differences between three laboratory methods and two field monitoring methods for the quantification of algae and cyanobacteria. The advanced course includes principles of quality assurance and quality control measures for these methods, the design and execution of a suitable monitoring strategy, and the evaluation of monitoring data.

During this webinar, Louise Vanysacker sheds light on how De Watergroep (Belgium) monitors blue-green algae in their intake reservoir. Arco Wagenvoort of AqWa Ecologisch Advies explains how to perform a valid fluorescence measurement. The third speaker, Ron van der Oost of Waternet Water Utility (Amsterdam, NL), discusses the guidelines for the Dutch Bathing Water Protocol. This webinar illustrates the various perspectives of different experts in this field with regard to the monitoring of blue-green algae.

This webinar is in Dutch.

In this podcast, Arco Wagenvoort of AqWa Ecologisch Advies and Corina Carpentier of Sensileau discuss how the quality of fluorescence measurements for determining the density of (blue) algae can be ensured. Topics covered during this conversation include the functioning of online fluorescence meters, tips for checking the quality of field meters, and the implications of using live algae for calibration. This podcast is in Dutch.

For the past years, Sensileau and its partner Aqualab Zuid, have organised a yearly Calibration Day for algal fluorescence sensors used in the national monitoring programme for natural bathing waters in the Netherlands. In the coming years, this service will be expanded to include a larger variety of field monitoring instruments to monitor algal densities. Sensileau also offers this service for contractors of the Dutch Ministry of Infrastructure and Water Management, who have been tasked with algal monitoring in large rivers and coastal zones under the direct responsibility of the Ministry.

Interested in participating in one of our calibration events? Let us know what type of field monitoring equipment you have to monitor algal densities, and we will contact you to discuss how we can include you in one of our annual calibration events.