In May 2016, scientists observed an intense algal bloom very close to the Belgian coast. They managed this by using the European satellite Sentinel-2. This satellite can help monitor areas that are unreachable for a research vessel. In 2017, the same phenomenon was confirmed on the satellite images.
All European member states are required to regularly report on the quality of their coastal waters. Since the 80's, scientists collect these data from research vessels and, for over a decade, supplement them with satellite data. But the satellite images were not yet sufficiently detailed and complete to monitor the coastal areas. Areas within two kilometers of the coast remained a ‘blind spot’ because the water is too shallow for most research ships. The Sentinel-2 satellite of the European Space Agency ESA, carrying high resolution cameras on board, now offers a solution.
‘The satellite images of the algal bloom along the Belgian coast were a complete surprise to me’, says Kevin Ruddick of our Institute. ‘Over the last 20 years, I have done measurements on board of the research vessel Belgica every year, but we could not sample the coastal zone because the water is too shallow. On several occasions we must have sailed quite close near the algal bloom however, but we did not realize what was going on.’
Algal Blooms vs Water Quality
Algal growth is a completely normal phenomenon, supplying food for marine organisms. When large amounts of algae develop, we speak of algal blooms. Sometimes adverse effects may also occur. Certain blooming algal species produce toxins that may be harmful to humans and animals. Or, if the bloom lasts, they reduce the oxygen concentration in the water. Then the algal bloom significantly reduces water quality. Therefore, rapid detection is important. Especially in coastal waters, as these are important for coastal tourism, water sports, coastal fishing and shellfish culturing.
Sentinel-2
Sentinel-2 is a high resolution satellite (up to 10 meters accurate) that captures different wavelengths within the electromagnetic spectrum. Due to the presence of different bands in the red part of the spectrum (specifically 665 nm and 705 nm), chlorophyll concentration can be derived from the images. Also turbidity, together with chlorophyll one of the determining aspects of water quality, can be observed separately.
Testing Methods
The intense algal bloom from the coast of Nieuwpoort to Ostend was unlikely to be problematic. Most probably it concerned the non-toxic algae Phaeocystis globosa.
The Royal Belgian Institute of Natural Sciences develops and tests methods for the use of Sentinel-2 data, and receives European support from the FP7 research program HIGHROC for this purpose. ‘In this context, RBINS developed the software ACOLITE, which is freely available through the website,’ notes developer and administrator Quinten Vanhellemont, also affiliated with our Institute.
