CyanoClim: Changing water quality in Swiss Lakes
CyanoClim: Health implications of changes in cyanobacterial outbreaks in Swiss surface waters under warmer climatic conditions
Cyanobacteria, which are oxygenic photosynthetic prokaryotes, can be found in all aquatic ecosystems within particular “bandwidths” of temperature, light intensity and nutrient levels. Under certain conditions, in particular as a direct or indirect consequence of water temperature increase, these micro-organisms can proliferate in what is known as cyanobacterial blooms. This may lead to some water quality problems that are detrimental to human health, either because contaminated water may enter into drinking-water supply systems or by direct contact through recreational activities. According to the level of contamination, pathologies may range from mild skin allergies to severe problems of the liver and digestive tracts, respiratory ailments, muscular paralysis and even death. Cyanobacterial blooms generally occur towards the end of summer, when slow-moving waters such as encountered in lakes have warmed during the season, and exceed the temperature threshold beyond which growth explodes. While summer is often the privileged period for bloom outbreaks, they can occur at other times of the year and even be perennial.
This project is based on the hypothesis that a warmer climate may lead to more frequent episodes of algal bloom outbreaks in many parts of Switzerland, resulting in enhanced health risks, particularly when water withdrawal facilities are located in shallow waters or in rivers that flow out of contaminated lakes and thereby transport the cyanobacteria downstream, a situation that has been documented several times in the recent past, notably in France to give an example of a neighboring country. The project proposes to investigate the possible changes in algal bloom outbreaks in a future climate under enhanced atmospheric greenhouse-gas concentrations. The focus will primarily be on the physical aspects of surface water warming through the coupling of a simple lake model (that will include motion in the vertical plane, advection of temperature and changes in the depth of the thermocline) with a Regional Climate Model that will provide the appropriate atmospheric boundary conditions for driving the lake model. Cyanobacteria growth will be modeled through empirical relationships based on water temperature, daylight duration and intensity, as well as different levels of dissolved nutrients. In this manner, the bacterial concentrations will be determined as a function of time during the summer season, in order to determine the depths to which they may proliferate and whether the projected levels of bacteria may significantly enhance health-related risks. Health hazards will be assessed on the basis of current knowledge of the exposure of human populations to various levels of cyanobacterial contamination.
The coupled model system will first be tested against observed data, where cases of cyanobacteria contamination have been documented in the recent past, prior to applying the methodology to future climatic conditions. These will be based on Scenario A-2 (a high-emissions scenario leading to strong global warming by the end of the 21st century) developed by the IPCC (Intergovernmental Panel on Climate Change), for different geographical locations, ranging from deep water bodies such as the Lake of Geneva, to shallow lakes at different elevations that feed into rivers whose waters are used for drinking water. This will enable an assessment of the depths at which cyanobacteria may proliferate in the future, and the altitudes of mountain lakes above which the risk of contamination becomes small. Throughout the project, contacts will be maintained with water quality specialists and the medical community in order to jointly develop an appropriate set of adaptation options aimed at reducing the risk of infection.
Scientists involved in the project:
Ms Marjorie Perroud, PhD Student
Ms Diana Forster, PhD Student