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Rising CO2 concentrations in the atmosphere will stimulate harmful algal blooms at a global level. This warning is issued by UvA scientists Jolanda Verspagen and Jef Huisman on the basis of new mathematical models, laboratory experiments and field research. Their results will be published open access in the scientific journal PLOS ONE.

Volkerakmeer algengroei
Dense algal blooms in the Volkerak dam. Photo: Zeeland Province

Harmful algal blooms are a threat to the water quality of nutrient-rich ponds, lakes and reservoirs. Dense blooms may smother water plants and can even destroy fish populations. Several harmful algal species can produce toxins causing serious and sometimes fatal liver, digestive and neurological diseases in birds, mammals and humans. Harmful algal blooms are therefore a major concern in  water quality management, and often lead to the closure of recreational waters.

Dutch scientists Verspagen and Huisman provide both theoretical and experimental evidence  –  based on research with toxic cyanobacteria – that algal blooms will intensify with rising CO2 levels. Algae require CO2 for photosynthesis and growth, and during bloom development they can deplete the CO2 concentration dissolved in water. Rising CO2 concentrations in the atmosphere enhance the influx of CO2 in lakes, which delays depletion of the dissolved CO2 in water, enabling algae to develop much higher population densities.

A global issue

Jolanda Verspagen: ‘The novelty of our work is the tight combination of mathematical models and experiments. This approach allows detailed quantitative prediction of the complex feedbacks between algal growth and the availability of CO2 in water. Algae are responsible for about 50% of the global primary production of our planet. Such quantitative approaches are therefore highly needed.’

The model results show that algal blooms will intensify particularly in nutrient-rich waters. If all  nutrients (such as nitrate and phosphate) are in sufficient supply, thenCO2 availability is the major controlling factor for the development of dense algal blooms.

Jef Huisman: ‘In essence, the rise in atmospheric CO2 concentrations is one big fertilisation experiment at an unprecedented large scale. An enhanced CO2 influx into aquatic ecosystems is not only a problem for a few local lakes, but will also intensify algal blooms in nutrient-rich waters across the globe. Water managers and policymakers will have to prepare for a deterioration of the water quality due to climate change.'

Nutrient-rich versus nutrient-poor waters

In a recent publication in Ecology Letters, Verspagen and Huisman already demonstrated that rising CO2 levels  will specifically intensify algal blooms in lakes and reservoirs with high nutrient loads. The response to rising CO2 is completely different in low-productive waters, where a lack of nutrients prevents the development of dense algal blooms. In nutrient-poor water, the carbon-to-nutrient ratio of algal biomass will increase with rising CO2 levels, which reduces the nutritional quality of algae as food for other organisms in the food chain.


The research was carried out at the Department of Aquatic Microbiology of the University of Amsterdam, the Netherlands, in collaboration with the Netherlands Institute of Ecology (NIOO-KNAW) in Wageningen. It was financed by the Netherlands Organisation for Scientific Research (NWO).

Publication details

Jolanda Verspagen, Dedmer van de Waal, Jan Finke, Petra Visser, Ellen van Donk, Jef Huisman (2014): Rising CO2 levels will intensify phytoplankton blooms in eutrophic and hypertrophic lakes. PLOS ONE 9(8): e104325.