Algal blooms: A summer nuisance and a future resource in the Baltic Sea
Summer is here, bringing sun, sea and long days on the coast. But for many people living around the Baltic Sea, summer also means something less welcome: the return of algal blooms. How can you tell whether the water is safe for swimming? What causes algal blooms? And how can algae help solve some of our environmental challenges? Algae researcher Elin Lindehoff has the answers.
“During algal blooms, the water may become cloudy, with yellowish-green or bluish particles suspended in it, and sometimes thick mats form on the surface and drift towards the shore. What are commonly referred to as ‘algae’ in the Baltic Sea’s summer blooms are not, in fact, algae at all, but cyanobacteria – an ancient group of microscopic organisms”, explains Elin Lindehoff, associate professor of marine ecology.
Are algal blooms dangerous?
Cyanobacteria have been present in the Baltic Sea for thousands of years, making summer algal blooms a natural phenomenon. However, some species can produce toxins that affect the liver, so it is important to be careful during severe blooms. Young children and pets are particularly vulnerable, as they are more likely to swallow water while swimming or playing at the water’s edge.
“If the water contains tiny yellowish-green or greenish-blue particles during the summer, it could be an algal bloom. If you’re unsure, I recommend filling a bottle with water and letting it stand for a while. If the particles float to the surface, they are probably cyanobacteria. In that case, it’s best to wait until the water has cleared again before going for a swim – and to keep your dog out of the water”, says Elin Lindehoff.
Why are algal blooms becoming more common?
Algal blooms are a natural phenomenon, but they have become more widespread and frequent over recent decades. One of the main reasons is eutrophication – the enrichment of water with nutrients such as nitrogen and phosphorus, which enter the sea through, for example, agricultural runoff, sewage and industrial discharges. Nutrients from decades of past emissions also remain in the sea, continuing to fuel the blooms.
“Cyanobacteria use the excess phosphorus in the Baltic Sea. They flourish in warm, stable summer weather and can multiply rapidly, forming extensive blooms”, says Elin Lindehoff.
More than just a summer nuisance
It is easy to think of algal blooms as nothing but a problem. But algae and cyanobacteria are more than that. They are cornerstones of marine ecosystems. They produce around half of the oxygen on Earth. Through photosynthesis, they convert carbon dioxide and nutrients into new algae that form the foundation of the marine food web, supporting life from tiny zooplankton to large fish.
“This very ability also makes algae a promising resource in tackling some of the major environmental challenges of our time. By absorbing both carbon dioxide and nutrients, they can help reduce climate impact while at the same time combating eutrophication”, explains Elin Lindehoff.
Algal blooms as an asset
At Linnaeus University, researchers are exploring ways to harness the potential of algae. As part of the ALGOLAND projects, microalgae are grown under controlled conditions and used to remove carbon dioxide from flue gases and absorb nutrients directly from industrial process water. In this way, natural processes are replicated in a controlled environment, where their environmental benefits can be maximised.
“The biomass produced can be used in a number of ways: as animal feed, biofuel, soil improver, biochar or even bioplastics. This means that something that’s sometimes seen as a problem in the natural environment could instead become part of the solution in a sustainable, circular society – an asset rather than a problem”, says Elin Lindehoff.
