In partnership with their counterparts at IMBE in Marseille, researchers from the MIO laboratory at the University of Toulon are studying the role of dissolved organic carbon in the ecology of Lac des cordes. Classified as a 'sentinel' lake, this ecosystem is sensitive to climate change and could be a harbinger of future oceanic changes.
Having arrived in Cervières (Hautes-Alpes), a small mountain village on the heights of Briançon, the researchers from Aix-Marseille University's Institut Méditerranéen de Biodiversité et d'Écologie (IMBE) and those from Toulon University's Institut Méditerranéen d'Océanologie (MIO) still had to get the 150 kg of instrumentation and measuring equipment out of the lorry, some of it on their shoulders, and the rest on the back of the horse hired for the occasion, before covering the rugged track that separates them from the Lac des cordes, at an altitude of 2446 m, for two hours.
Changes due to climate are exacerbated and perceived first by sentinel lakes, an ecosystem whose balance is fragile. They react more quickly than seas or meadows.
CARAmBoLe project
The CARAmBoLe project aims to characterise inputs of dissolved organic carbon (DOC) - compounds derived from the degradation of animals and plants in water - and their effects on biological communities in a high-altitude lake.
Led mainly by the IMBE in Marseille, one of whose major areas of research is understanding how lakes function, this study is a first: it is the first time in France that scientists have analysed the entire life cycle of a lake. Specialists in applied fish ecology and the study of phytoplankton and zooplankton, the ten or so researchers from Marseille wanted to combine their skills with those 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 spectrofluorimeter, the MIO is able to characterise the DOC and understand what compounds it contains, their quantities and whether these change between the thawing and refreezing of Lac des cordes.
The Toulon-based scientists also invested in sampling and measurement equipment to carry out in situ measurements during the campaign, which ran from June to October 2020.
n situ, the researchers will be taking advantage of the opportunity to extract soil in order to identify nutrient inputs through rainwater run-off, the consequences of pastoralism.
Having a more detailed understanding of how the Lac des cordes system works will enable us to act more quickly and effectively when an imbalance is detected. This will not be against nature, as lakes are naturally destined to change 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 is due to start in June and run until October 2021.
"We also wanted to carry out in situ monitoring to understand the impact of photodegradation, which is particularly strong in a high-altitude lake. The proximity of the lake to the sun, the lesser atmosphere with fewer particles blocking the sun's rays and the transparency of the water mean that photochemistry plays almost as important a role as nutrients," explains Stéphane Mounier, a geochemist at the MIO laboratory and lecturer at the Science and Technology Department of the University of Toulon. The sun's rays will prevent phytoplankton from living at the surface. We need to see the variability between day and night, the bottom and the surface, to understand the dynamics of the lake.
Contacts
MIO Laboratory
Stéphane Mounier
Research teacher
Email : mounier@univ-tln.fr
Benjamin Oursel
Teacher Researcher
Email : benjamin.oursel@univ-tln.fr
Christian Martino
Technical Manager
Email : christian.martino@univ-tln.fr