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Researchers at the University of Amsterdam (UvA) and the Netherlands Institute of Ecology (NIOO) have discovered that this increase in carbon dioxide can reduce the impact of toxic blue-green algae, a bacteria especially common in the water at Dutch beaches in summertime.

Global warming is caused by the increasing atmospheric concentration of carbon dioxide. Researchers at the University of Amsterdam (UvA) and the Netherlands Institute of Ecology (NIOO) have discovered that this increase in carbon dioxide can reduce the impact of toxic blue-green algae, a bacteria especially common in the water at Dutch beaches in summertime. Blue-green algae thrive when temperatures are high, but an increasing concentrations of carbon dioxide are causing the non-toxic strain of blue-green algae to oust its toxic sibling. The research was conducted by UvA researchers Prof. Jef Huisman, Dr Jolanda Verspagen and Dr Dedmer van de Waal and NIOO researcher Prof. Ellen van Donk, and was funded by the Netherlands Organisation for Scientific Research (NWO).

The researchers have good and bad news. The bad news is that blue-green algae do indeed thrive under high temperatures compared to other types of algae. But the good news is that increasing concentrations of CO2 are causing the non-toxic strain of blue-green algae to supplant the toxic strain. The research findings will be published in the ISME Journal in September and will also feature in the News & Views section of Nature Climate Change magazine.

Toxic blue-green algae can cause stomach and bowel complaints, nausea, headaches and skin and eye irritation, while higher concentrations can also seriously damage the liver and the nervous system.

Rising temperatures

Researchers performed a field experiment at Nieuwe Meer in Amsterdam in summer 2003 aimed at controlling blue-green algae. The experiment failed: the growth of blue-green algae proved better than expected. This may have been caused by the extreme heat wave that prevailed at that time. In order to understand why, the researchers developed a model linking the growth of algae to the climate. The model shows that blue-green algae grow faster than other types of algae under high temperatures. In addition, high temperatures make water more stable, reducing its ability to mix. Blue-green algae contain tiny gas bubbles, causing them to float in stable water to the surface where there is abundant light. This enables them to grow even faster.

The predictive model and the explosive growth of blue-green algae in 2003 match seamlessly. Initially, this led the researchers to suppose that the impact of blue-green algae would be more adverse in the future as a result of climate change, particularly during warmer weather. But more factors come into play.

Rising concentrations of carbon dioxide

By man’s own doing, the atmospheric concentration of carbon dioxide is rising sharply. Blue-green algae need carbon dioxide for photosynthesis and thus benefit from higher concentrations of carbon dioxide. But do all blue-green algae benefit equally from the increase in carbon dioxide? To answer that question, researchers developed a model that predicts the rivalry between toxic and non-toxic blue-green algae. In fact, the results of the experiment revealed that the toxic agent aids the intake of carbon dioxide for photosynthesis. Toxic blue-green algae thrive under low concentrations of carbon dioxide while non-toxic blue-green algae benefit from high concentrations of carbon dioxide. This was confirmed by comparative laboratory experiments performed with various toxic and non-toxic blue-green algae. As expected, the toxic blue-green algae won when concentrations of carbon dioxide were low, while the non-toxic blue-green algae reigned supreme when concentrations of carbon dioxide were high.

It would seem to be a blessing in disguise: while global warming does indeed stimulate the growth of blue-green algae, the increasing concentrations of carbon dioxide will reduce their toxicity. Continued researched should show whether the laboratory research can also be translated to the field situation.

The research was funded by the Netherlands Organisation for Scientific Research (NWO).