Mission of studies in high mountains with the MIO and the IMBE
In partnership with their Marseille counterparts at IMBE, researchers from the MIO laboratory at the University of Toulon are studying the role of dissolved organic carbon on the ecology of the rope lake. Classified as a "sentinel", this ecosystem sensitive to climate change could foreshadow future ocean changes.
Arriving in Cervières (Hautes-Alpes), a small mountain village on the heights of Briançon, researchers from the Mediterranean Institute of Biodiversity and Ecology (IMBE) of Aix-Marseille University and those from the Mediterranean Institute of Oceanology (MIO) of the University of Toulon have yet to remove the 150 kg of instrumentation and measuring devices from the truck, of samples, carrying one part on their shoulders, the other on the back of the horse rented for the occasion, before covering for two hours the uneven track that separates them from the Rope Lake, located at 2446 m.
The changes due to the climate are exacerbated and perceived first by the sentinel lakes, an ecosystem whose balance is fragile. They react more quickly than seas or meadows.
The CARAmBoLe project aims to characterize dissolved organic carbon (DOC) inputs - compounds resulting from the degradation of animals and plants in water - and their effects on biological communities in a high-altitude lake.
Mainly conducted by the IMBE in Marseille, one of the major research axes of which is the understanding of the functioning of lakes, this study is unprecedented: it is the first time in France that scientists have analyzed the global life cycle of a lake. Specialists in ecology applied to fish, the study of phytoplankton and zooplankton, the ten or so researchers from Marseille wanted to combine the skills of environmental chemists from the University of Toulon to study the role of nutrients (carbon, phosphate, nitrogen, etc.) in the food chain. Equipped with a spectrofluorometer, the MIO can characterize the COD, understand what the compounds are, their quantities, if they evolve between the thaw and the refreeze of the string lake.
Scientists from Toulon have also invested in sampling and measurement equipment in order to carry out in situ measurements during the campaign which lasted between June and October 2020.
On site, the researchers will take advantage of this to make soil extractions in order to identify its nutrient contributions by rainwater runoff, the consequences of pastoralism.
Having a better understanding of the functioning of the Cordilleran Lake system will allow them to act more quickly and efficiently when an imbalance is observed. Without going against nature, lakes are naturally destined to transform themselves on a geological scale. The results obtained could be extrapolated and applied to other ecosystems or even prevent systemic changes in the oceans.
A second sampling campaign should begin in June and last until October 2021.
"We wanted to monitor in situ as well to understand the impact of photodegradation, which is particularly strong in a high-altitude lake. The proximity of the lake to the sun, the lower atmosphere and therefore fewer particles that can block the sun's rays, the transparency of the lake water... mean that photochemistry plays a role almost as important as that of the nutrients," emphasizes Stéphane Mounier, geochemist at the MIO laboratory and lecturer at the UFR Sciences et Techniques of the University of Toulon. The sun's rays will prevent phytoplankton from living on the surface. We need to see the variability between day and night, bottom and surface, to understand the dynamics of the lake. »