Closing the carbon budget on Lake Geneva Inland waters are extremely reactive and they are known to both transport a lot of carbon and also emit and sequester it, yet research has historically focused on boreal rather than clearwater lakes. We spoke to Professor Marie-Elodie Perga about her research into the carbon cycle on Lake Geneva, in which she aims to find out more about the processes responsible for this reactivity and transport. There are typically two types of lakes
Lake Geneva
in mountainous areas like Switzerland. There are the smaller lakes that are found at high altitudes and which are usually relatively unproductive, then there are very large lakes at lower altitudes. “Lake Geneva for example is only about 370 metres above sea level,” says Marie-Elodie Perga, an Associate Professor in the Institute of Earth Surface Dynamics at the University of Lausanne in Switzerland. These lakes tend to have quite ‘hard’ waters, with a higher dissolved mineral content (especially in calcium and bicarbonates) – related to the presence of chalk deposits – than ‘soft’ waters, and the lakes themselves tend to be very clear. “We have a very limited understanding of carbon cycling in these clear, hardwater lakes,” continues Professor Perga. “A lot of work has been done on boreal lakes, for example in Canada or Sweden. However, those lakes are completely different – they usually have very soft waters, and there is a lot of organic carbon that gives the waters a brown-ish appearance.”
The majority of the studies on carbon cycling in lakes so far have been conducted on boreal lakes, while the clearwater lakes are relatively under-represented. This issue is at the heart of Professor Perga’s work as the Principal Investigator of a research
interface between two environments, two chemistries. “Remote sensing images show a point where the lake turns a blue, chalky colour, which is caused by an in-lake calcite precipitation event that we call whiting,” outlines Professor Perga. “This whiting is created where the Rhone comes into the
The metabolism of a lake is certainly important, but it’s not the full picture. There are many other processes that may be responsible for the overall CO2 concentration in lakes, for example all the processes involving inorganic carbon. project in which she is investigating carbon cycling in Lake Geneva, looking to close the carbon budget and account for the complexities of the lake. “We are working on the pelagic area of the lake, the off-shore area, where the water is quite deep. We are also looking at the interaction between the Rhone river, which is the main tributary, and the lake,” she explains. This represents the
lake. It’s an interface that introduces a lot of spatial variability.” A further point of variability is between the littoral area of the lake, which is relatively shallow and has more concentrated chemistry, and the off-shore area. Professor Perga and her colleagues take full account of the varying nature of these different environments. “We look at the lake not
The Lexplore platform on Lake Geneva. © Pascal perolo
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