Problems with cyanobacteria will get worse if CO2 concentrations keep rising

Problems caused by toxic cyanobacteria are likely to become worse in the future. In an article in the journal Science Advances, scientists from the University of Amsterdam, together with NIOO-researcher Dedmer van de Waal, demonstrate that one common cyanobacterium in particular adapts exceptionally well to rising CO₂ concentrations. Its CO₂ uptake rate can even reach record-breaking levels.

Each summer, the water quality of lakes and ponds is threatened by the growth of cyanobacteria, also known as blue-green algae. Cyanobacteria can produce a variety of toxins that are harmful to humans, other mammals and birds. In humans, these toxins may cause nausea, dizziness and even liver damage.

Intense cyanobacterial growth increases the amount of toxins in the water, which can negatively affect the use of lakes for recreation, drinking water or fisheries. Cyanobacterial growth already affects water quality across the globe, for example in Lake Erie (USA), Lake Taihu (China), Lake Victoria (Africa) and many European lakes.

Fertilising water

CO₂ (carbon dioxide) is an essential nutrient for algal growth. Just like plants, algae acquire CO₂ through photosynthesis. The rising concentrations of CO₂ in the atmosphere also lead to more CO₂ in surface waters. "We're basically fertilising waters with CO₂ on a global scale", says UvA researcher Jolanda Verspagen.

A team of scientists from the UvA, the East China Normal University in Shanghai, NIOO-KNAW and Germany's Alfred Wegener Institute have studied what happens when one of the most common toxic cyanobacteria, Microcystis, is cultured at low and high CO₂ concentrations.

"The study shows that cyanobacteria increase their photosynthesis when there is more CO₂", says NIOO-researcher Dedmer van de Waal. "This could give them an advantage in the future if CO₂ concentrations in the atmosphere continue to be high."

Dire warning

When the CO₂ uptake rate of Microcystis was measured with an advanced laboratory instrument known as a Membrane Inlet Mass Spectrometer, explains PhD student Jason Ji (UvA), it turned out to have increased "by a factor 5" at high CO₂ concentrations.

"To our knowledge, this is the strongest CO2 response ever recorded!", says Ji. Other non-toxic algae, including green algae and diatoms, adapt less well. "In some cases, their growth actually slows down at high CO₂ concentrations."

Model predictions by the research team show that this exceptional ability to adapt could have far-reaching consequences for water quality, particularly in nutrient-rich waters. The researchers warn that, if atmospheric CO2 concentrations continue to rise, problems with cyanobacteria in the future will continue to get worse.
 

Photograph: cyanobacteria in Edinburgh's Holyrood Park (Wikimedia Commons)

• Study: 'Phenotypic Plasticity of Carbon Fixation stimulates Cyanobacterial Blooms at elevated CO₂', Science Advances 19 February 2020
• More about Dedmer van de Waal's cyanobacteria research:
  • Dedmer Van de Waal wins 2020 Yentsch-Schindler Early Career Award
  • Extreme weather of 2018 challenged ecologists 'to think along broader lines'
  • Concern over 'red tide' in Dutch coastal waters